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8/6/2019 astsyshansatlauvehsec5_073007090028

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A s t r i o n i c s S y s t1

S e c t i o n

CHAPTER 5MEASURING AND TELEMETRY

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1MEASURING SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .2 .15 . 2 . 1 G e n e r a l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 . 2 - 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2 . 2 T r a n s d u c e r s 5 . 2 - 35 . 2 . 3 Signa l Condi t ion ing . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 1 1. . . . . . . . . . . . . . . . . . . . . .. 2 . 4 M e a s u r i n g D i s t r i b u t o r 5.2.1 3REM OTE AUTOMATIC CALIBRATION SYSTEM . . . . . . . . . . . . 5.3.1T E L E M E T R Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .1

. . . . . . . . . . . . . . . . . . . .. 4 . 1 S a t ur n T e l e m e t r y S y s t em 5 .4 .15 . 4 . 2 F M / F M T e l e m e t r y S y s t em . . . . . . . . . . . . . . . . . . . 5 .4 .3. . . . . . . . . . . . . . . . . . . .. 4 . 3 S S/FM T e l e m e t r y S y s t e m 5 .4 .10. . . . . . . . . . . . . . . . .. 4 . 4 P CM /D DA S T e l e m e t r y S y s t e m 5 .4 - 1 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .U L T I P L E X E R S 5 . 5 - 1

5. . 1 M od 270 M u l t i p l e x e r . . . . . . . . . . . . . . . . . . . . . . . . . -15. . Re m o te D ig i t al S u b mu l t i p l e x e r. . . . . . . . . . . . . . . . . . . . . . . . . . .M O ~DSM-ID) 5 .5 .4. . . . . . . . . . . . .. 5. Re mo te D ig i t a l M u l t i p l e x e r ( M od 410) 5 5-4.. . . . . . . . . . . . . . . . . . . . . .5 . 4 V ib r a t i o n M u l t i p l e x e r 5 5-4T E L E M E T R Y CA L IBRA T IO N S U BS Y ST E M . . . . . . . . . . . . . . . . 5 .6 .1DIGITAL DATA ACQUISITION SYSTEM . . . . . . . . . . . . . . . . . . 5 .7 .15 . 7 . 1 DDAS/Compute r In te r fac e Uni t . . . . . . . . . . . . . . . . . 5 . 7 - 2TELEVISION SYSTEM (SATURN V) . . . . . . . . . . . . . . . . . . . . . .8 .1


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Astrionics System, Section 5. 1

SECTION 5.1INTRODUCTION

The combined measuring and telemetry systemis essentia lly an independent operating subsystemwithin the overall Astrionics System.

The combined measuring and telemetry sys-tems of the Saturn Launch Vehicles measure physicalquantities and signals onboard the vehicle and tra ns-mit the data to ground stations . The complexity of thelaunch vehicle and its missions dictate a larg e numberof measurements. The data transmitted by the meas-uring and telemetry syst ems supply information forthe following operations:

Automatic prefli ght checkout of the vehicle.Monitoring of vehicle performance duringpowered flight.

Postflight evaluation of vehic le performanceMonitoring and checkout of the veh icle dur-ing orbital flight.Verification of commands r ece ived in thevehicle fr om ground stations.

Figure 5. 1-1 illu stra tes the signal flow througthe system. The tran sdu cers convert the physicalquantities to be mea sured (e. g . , pressure, tempera-ture, etc. ) into electrical signals. These transducersignals are modified by signal conditioning devicesinto voltages suitable as inputs to the telemet ry systemThe measuring di stributo r feeds the conditioned transducer signals to the telemetr y system. In the tele -metry system the signals are modulated on RF

Figure 5.1-1 Measuring and Telemet ry System5.1-1

Transducers SignalConditioning(Measuring Racks)b

I- - - - - - l - l - - - L I I ~ I - l I I - - - - - - I

VEHICLE

----I----+ Measuring

Distributor i. MEASURING SYSTEM

vTelemetry

r-RFTransmitter

SystemsPCM/FM

VEHICLETELEMETRY SYSTEMFM/FMSS/FM

DDAS Outpu t(Coax Cable)

VEHICLEGROUND

*Ground

VehicleCheckoutFaci l i ty

IBM B4 6


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Astrionics SystemSection 5. 1ca rr ie rs and transmitted during flight to the tele-met ry ground stations. Before launch, the meas uringand telemet ry syst ems send digital data by coaxialcabl e from ea ch stag e of th e vehicle to the checkoutfacility. The digital information is used for automaticcheckout of the vehicle on the launch pad. In thi s modeof operation the tele metry s yste m is called the digitaldata acquisition system. Figure 5. 1-1 also indicatesthe division between the measuring syste m and thetelemetry system.

Each st age of the launch vehicle has a n inde-pendent measuring and telemetry system, DDAS

output, and RF transmission. The telemetry syst emof the S-IVB Stage is als o connected to the teleme trysys tem in the IU for the purpose of digital data acqui-sition and alternate mode transmission. Fo r moni-toring of digital data, the IU tel eme try sys te m has a ninterface with the LVDC through the LVDA.

To simplify vehicle checkout, data handling,etc. , standardization is practiced wherever feasible.A remote automatic checkout system is standardizedon each st age to provide automatic checkout ofmeasurements from ground equipment. This syste mgreatly minimizes checkout time.


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Astrionics System1 Section 5.2

SECTION 5.2

5.2.1 GENERALThe measuring system includes transducers,

measur ing rac ks (which contain the signal conditioningmodules), measuring distributors, measuring racksele cto rs, and measuring voltage supplies. Themeasuring sy stem converts the signal o r quantity tobe measu red into an electrical signal that is accept-able to the telemetry system. According to this defi-

nition, the measuring sys tem ends a t the input to thetelemetry system (at the subc arri er oscillator, mulplexer, etc. ). Figure 5. 2 - 1 illustrates typical compnents of the measur ing system. The measurementsin the launch vehicle cover the areas of:

Propulsion Guidance andStructure controlFlight mechanics Environment

Figure 5 .2-1 Typical Saturn Measuring System5.2-1

FromMeasuring Rack

SelectorUmbilical Remote Automatic

Cable Calibration System

1 ( R A W

ReferenceThermocouple - unctionImpedanceMatching

-Strain Gauge -+

+w

*

MeasuringRacks

) Measuring ToControl Computer +

ACAmplifier

DCAmplifier

Distributor- elemetrySystemsPower

(Lift-Off, Etc. )IBM B47

Carrier

'

Amplifier


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Astrionics SystemSection 5.2 . 1

Physical quantities to be measured, such as, measured in the S-IC Stage, the S-IVB Stage, and thepres sur e, temper ature, and vibrations must be tran s- Instrument Unit of the Saturn V Researc h andformed by transducers into electrical signals for Development and Operation Vehicles.transmis sion by telemetry. Measurements of elec-tric al signals (voltages, current s, and frequencies) Certain meas uremen ts will be used as inputsoriginating in onboard equipment ar e used fo r moni- to the emergency detection syste m (se e Chapter 4).tori ng the perfor mance of this equipment and the Operational measurements a re those measuremen tssequence of flight events (e. g. , stage separation, used for flight (mission) control. Operational meas-engine cutoff, and others ). The signals to be measuremen ts indicate the sta te of the vehicle and itsur ed exist in analog and digital form. Measurements systems and also provide trend information (beginningof el ectr ica l signals do not req uire transd ucers. with the orbita l flight phase). All operat ional meas-

urements a re transmitted over the PCM telemetrylinks of the S-IVB Stage and the IU. Typical oper -The number of me asureme nts made in the ational measurements for the Saturn V Vehicles arevar ious st ages of Satu rn IB and V Launch Vehicles given in Table 5.2-3.ar e listed in Table 5. 2-1. A la rg er number of meas-

urements is necessary for performance evaluationand tes ting of r es ea rc h and development vehicles, The number and type of measuremen ts givenwhile for operational vehicles, this number is reduced in the tables ar e best estimates and a r e subject toconsiderably. Because of the la rg e number of differ- changes a s the development of vehicl es proceeds.ent measu rements , no detailed lis t of measuremen ts is This applies particularly to the figures f or oper-given. Tab le 5. 2-2 indicates so me of the quantities ational vehicles.

Table 5.2-1 Number of Measurements, T ra ns du ce qa nd Measuring RacksSATURN IB

StageS-IBS-IV B

IUTotalVehicle

Transducerseasurements

SATURN V366 1

R & D305298

9269 5

R & D542432

2781252

Measuring Racks

StageS-I CS-I I

S-IV B- --

IUTotalVehicle

Oper106115

45

Oper263218

134615

R & D1917*

945

Oper -57*

517

* Signal conditioning panels

MeasurementsR & D901913432278

2524-

Oper297446218134

1077-

Transd ucers Measuring RacksR & D72358929892

1702-

R & D273517*9

88

Oper15718011545

497- A

Oper587*5

25-


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Astrionics System, Section 5.2

5.2.2 TRANSDUCERSTransducers ar e electromechanical measuring

instr ument s which contain sens itive devices for con-verting mechanical quantities into electrical signals.Evaluation of vehicle performance and in-flight moni-toring re qui res the meas ureme nt of a larg e varie ty ofphysical quantitie s onboard the vehicle. Therefore,many different types of trans duc ers ar e used. Sometypical transducers and the corresponding measure-ments a r e iste d in Table 5.2-2. Because of the manytypes of tra nsd uce rs and mea surem ents used i n launchvehicles, no atte mpt is made to give a complete de-

scri ption of all t ransd ucer s on each stage. Thefollowing measurement descriptions generally applto the S-IB and S-IC Stages. The number of tra ns -duc ers used in each s tage may be found in Table 5.2-Figure 5. 2-2 ill ustra tes s evera l typical transducersBENDING MODE VIBRATION MEASUREMENTS(ALL STAGES)

Bending mea surements a r e made using forcebalance accelerometers. The principle of operatio nof the force-balance a ccel erom eter i s shown inFigure 5.2-3. These instruments operate a s a sub-

Table 5.2-2 Typical Saturn V Measurement s

Quantity Measured

Acoustic energyTemperature

P ressu re

Vibration

Propellant flowrateLiquid levelStrainRPM (turbopump)Acceleration

Voltage, current,and frequency

SignalsGuidance andControl SignalsR F & telemetrysignalsAngular velocity

Typical Tra nsducer

MicrophoneResistance thermo-meter thermocoupleVibration pres sur etransducer & othertypesPiezoelectricaccelerometer

FlowmeterLevel probeStrain gaugeTachometerForce balanceaccelerometer

-

-

-

-

Rate gyro

R&D4

257

235

80

1051768

5

3

11

97

-

-

-

NumberS-IC

Oper0

61

82

10

0805

1

11

97

-

-

-

ofR&D

6

163

72

38

4

6

122

1

38

53

-

-

-

MeasurementsS -N B

Oper0

50

4 6

6

4

6

02

1

30

53

-

-

-

R&D1

56

13

29

11

-

-

-

6

15

6

58

2835

IUOper

0

30

6

6

1

-

-

-

6

12

6

45

6

3


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Astrionics SystemSection 5.2

Table 5.2-3Typical Saturn V Operational Measurements

S-IVB Auxiliary Propulsion SystemPropellant levelHelium supply pr es su rePropellant temper ature

S-IVB Main Propulsion SystemGas supply pre ssu rePropellant valve positionsPropellant massesEngine sequencing signalsTank press urePropellant flowThrust chamber pre ssu reHydraulic system pr ess ure and fluid tempe ratur e

S-WB/IU Electrical SvstemBattery voltages and curren tsBus voltages and cur ren tsInverter voltages

S-IVB Attitude Control and Stabiliza tion SystemAttitude contr ol sig nal s (pitch, yaw, rol l)Angular velocity (pitch, yaw, roll)Engine a ctuat ors positionControl computer temperatureServo amplifier s ignalsSpacial amplifier signalsValve po sit ions

Navigation, Guidance, and Digital SignalStee ring commands (pitch, yaw, ro ll)Space fixed velocity (3 components)Space fixed displace ment (3 components)Computer tim eTim e to S-IVB second ignition and cutoffAccelerometer output (X, Y, Z)Gyro servo output (X, Y, Z)Gimbal angles (pitch, yaw, roll)Launch Vehicle Digital Computer signalsTem per atu res of computer and platformcomponentsAir bearing supply pr es su reSwitch Sele ctor output

Environmental Control SystemPr es su re and tem per atu re of coolant atsever al placesCold plate te mpera tureGas supply pre ss ur e

Inst rumen tation and .Communication SvstemPower output of the PCM tr an sm it te r (S-IVB & IU)

miniature servosystem, which i s responsive to linea racceleration along its sensitive axis. Due to inert ia,the accelerati on sensitive mass, commonly calledthe paddle wheel, moves relative to the position de-tector when accele ration is applied. The position-error detector and servoamplifier generate afeedback signal to the rest oring mechanism. Theelectromechanical servoaction r esult s in a balancebetween the input force proportional to the accelerationand the feedback force proportional to the cu rr en t inthe restoring coil. The restoring current, or thevoltage it develops across a ser ies resistor, providesthe output of the accelerometer, and is a precisemeas urement of acce lera tion.

The advantage of the force-balance acc ele r-ometer over ea rli er potentiometer type accele r-omete rs is that friction is almost negligible. Theforce-balance accelerometer will sense both ex-tremely slow vibrations and continuous accelerationin a s ingle direction. Their measuring range is 0. 5g.The s ame instruments ar e employed to sense la teralacceleration along the pitch and yaw axes in the IU.Similar measurements a re also made to determinethe bending or flapping act ions of the vehicle fins.The instrum ents used to sen se this movement havea ran ge of *O. lg .

FLIGHT MECHANICS MEASUREMENTSLongitudinal a cceleration measurements a r e

made to mea sur e the thr ust decay of engines. Thesemeasurement s a r e made with the s am e type of ac ce le r-ometers that ar e used for s tra in and vibration meas -urements. Longitudinal acce lera tion meas urem entsto determine thr ust and thru st decay of the S-IVB Stagea r e made in the IU.

Angular velocity measurem ents a re madeusing Rate Gyros (s ee Chapter 3). The instrumentis acc ura te within a range of *10 degrees pe r second.In case of a catast rophic situation, the vehicle als oca rr ie s Rate Gyros to measure angular movement inexces s of 100 degre es pe r second along the pitch andyaw axis.

Propulsion system measurements a r e made bypre ssu re transducers, flowmeters, tachometers, andliquid level sensors. A brief functional descriptionfor each i s given in the following paragr aphs.PRESSURE MEASUREMENTS

Pre ssu re measurements ar e made by twodifferent methods: potentiometric and str ai n gage.


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Astrionics SystemSection 5.

The potentiometric transd ucer is basically awirewound potentiometer with the wiper mechanicallyconnected to a pressure controlled diaphragm asillustrated in Figure 5.2-4. The output voltage isobtained by applying 5 volt s to the potentio meter.The magnitude of the output will vary fr om 0 to 5 volts,depending upon the position of the wiper. Since theoutput voltage is within the limit required by the sub-ca rr ie r oscillator, no signal conditioning is required.Approximately 70 per cent of the total pre ssu remeasurements a r e made with the potentiometric typetransducer.

On th e S-IB Stage most of th e pote ntio metr ictype pre ssu re transducers may be calibrated whileon board the vehicle by using the calibration valve thatis associated with each transducer. The calibrationvalve, connected between the transduc er and the sour ceof pr es su re being measu red, may be coupled to a cali-bration line that is connected through a quick discon-nect coupling to a controlled pr es su re source. Whenthe calibration line is connected to the valve, thetransducer sensor is mechanically positioned to sensethe controlled pressu re. The transducer automaticallyretur ns to sense the system pressu re when the calibra-tion line is removed. All other type pr es su re tran s-ducers ar e calibrated electrically.

SensitiveAxis Mass Position+ - - - - - - -, Detector

R-

-IB M B4

Figure 5.2-3 Force-balance AccelerometerBlock Diagram

In addition to the potentiometric pre ssu retransducer, press ure measuremen ts are made withunbonded str ain gages (Figure 5.2-5). Each st ra ingage transducer consists of four individual straingages mechanically connected to a pr es su re s ensitivdiaphragm and arran ged in such a manner that compres sion on two of the gages r esu lts in tension on th

PiezoelectricVibrationAccelerometer

F

Pressure Gage

IBM B4

Thermistor

Figure 5.2-2 Typical Tran sduce rs5.2


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MeasuredI B M B50

Figure 5.2-4 Bourdon- tube Potentiometer TypePres sure Transducer

othe r two. Thi s action, in effect, res ult s in an out-put when the s tra in gage transducer is excited by anexterna l voltage. The output voltage of the str ai n gagetransducer is approximately 40 millivolts a t full pres-sur e; therefore , the signal must be fed into a signalconditioner (dc amplif ier) before it can be applied tothe sub carr ier oscillator. In some cases, the signalconditioning is incorporated in the transduce r package.RPM MEASUREMENTS (S-IB STAGE ONLY)

This measurement utilizes a variable reluc-tance type of tachometer mounted on the turbine. Asthe turbine turn s, the varying reluctance of a magne-tic path genera tes an ac voltage. The frequency of

the output voltage is proportional to the rp m of the tu r-bine. Thi s frequency is too high for the bandwidth ofthe available telemetry channels; therefor e, signalconditioning is requ ired to divide the frequen cy by 32to make the output signal compatible with availabletelemetry channels.

The signal conditioner is a magnetic frequencydivider which uses the rectangular hysteresis charac-teri stic s of a saturab le core.LIQUID LEVEL MEASUREMENTS (S-IB STAGE ONLY)

The liquid level of the propellant is measuredby two different methods: the disc re te and the con-tinuous method. The dis cret e method (Figu re 5.2-6)utilizes a photo-electric cell to obtain signal output.The sens or con sists of a light source, photo-electriccell, and a prism. Because the liquid diffuses thelight rays, no output i s obtained until the level of theliquid drops below the pr ism s. As the level of theliquid drops below the prism, light rays f rom thelight source a re reflected back to the photo-electriccell by the pris m faces, which ar e at 45-degree ang lesto the light rays. Fifteen sensors a re located alongthe length of the tank. When the output fr om one sen-sor is detected, it is possible to determine the amountof propellant (fuel or lox) that was consumed in thetime interval that lapsed between outputs from thissensor and one that was previously initiated.

Figure 5.2-5 Strain-gage Type Pr es su re Transd ucer5.2-6

r----- 1I Calibrate I1 5 0 0 I Circuit I

-

10 VPowerSupplyT i n mp-- --I

-IIIIIII

----qi 5 o n !I 20k- I A A

IL "Bal" I,,--A-

IDC Amplifier Input

IBM B51


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Photo-Electric Cell 50ms Pulse& ---+ dzF TO

Meas Distr-- * - - - -uiquid LevelLight

Prism Light SourceIBM B 5 2

Figure 5.2-6 Liquid Level, Discr ete,Functional Diagram

The continuous method of measu rin g liquidlevel i s used in the lower portion of the propellanttank to determi ne the amount of prope llants r emai n-ing af te r engine cutoff. Pri nci ple s of operation ofthe continuous method ar e illu stra ted in Figure 5.2-7.The se nso r cons ists of two tandem capac itors with thediele ctri c being the propellant. The top capacitor(Cs) is approximately 40 inches in length and exhibitsa capaci tance proportional t o the height of th e liquidI 1

ExcitationA9-Bit Digital Word

toI PCM Telemetry

L - - - - - counter II IBM B53

Figure 5.2-7 Liquid Level Sensor

Astrionics System, Section 5. 2

and the diel ect ric constant of the liquid. The bottomcapacitor (C,) i s approximately 3 inches i n length andis submerged in propellant when a measurement ismade. The capacitance of Cr is proportional to thedie lec tri c constant of the liquid.

Each capacitor is connected in a bridge circuiThe outputs of the two bridge c irc uit s ar e connected athe excitation to a thir d bridge cir cuit which is alwaykept in balance by an electronic se rvosy stem . Thefeedback elements of the s ervos yste m a r e nine binaryweighted capa cito rs controlled by a counter. Thecounter provides a par alle l binary output fo r tele metr

FLOW RATE MEASUREMENTS

Flowmeters ar e used to determine the rat e ofpropellant flow to a n engine. Basic princi ples of op eation of the flowmeter a r e illustr ated in Fig ure 5.2-8The flowmeter is inserted directly in the liquid line adeter mines the volumetric fluid flow. Turbine bladesa r e mounted on a hub which is imbedded with twopermanent magnets. The blades ar e set so that theforce of liquid flow causes the b lades and the hub containing the magnets to rotate. On the periphery of thdevice is an E-core pickup with a number of wire turAs the permanent magnets rotate, a sinusoida l voltagis generated in the core and its frequency is directlyproportional to the flow rate.TEMPERATURE AND RADIATION MEASUREMENTS

The principal temperature and radiation measurements a r e in the following are as:

IBM B54

Figure 5.2-8 Basic Principl es of a FlowmeterElectrical Schematic


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Cryogenic temperature measurementsHeat flux (radiation and convective)Temperature measurementsFi re detection temperature measurementsGeneral environmental temperaturemeasurements

Cryogenic Measurements. An important fact orin engine operating efficiency is the densi ty of the oxi-dizer and the fuel. Temperature measurements ar eperformed at cr itica l points in these s ystem s duringflight. The oper ating efficiency of the engines can bedetermined from thes e and other measurements.

Cryogenic measure ments a re performed bymeans of r esi sta nce the rmo met ers located in the fueland lox tanks and in the plumbing fo r both of t hesesyste ms. These positive temperature-coeffi cientre si st or s ar e fabricat ed of high purity platinum andrequire precise calibration techniques.

The maximum temperat ure range of thes edevices is f ro m - 2 0 0 " ~o +300c ( - 3 2 8 " ~o +572"F).Data reduction is accomplished through a straight-forwa rd temperature versus resistance method. Asin the other tempe ratur e measurements, dc amplif iersa r e employed to inc rea se the output signal level to therequir ed 0 to 5-volt telem etry input level.Heat Flux (Therm al Radiation) Measurements. Calori-met ers a r e located a t strategic points on the engineheat shield to mea sure thermal radiation and thus per-mit a pre ci se calculation of the minimum insulationweight allowable at these points.

One type of cal ori met er me asu res both thermalradiation and convective heat transfer. The heatingrate is determined from the temperature vers us timecha rac ter ist ics of the copper slug.

Another type of cal ori met er utilized in somemeas ureme nts on the Saturn Vehicle i s the "thin film"or "membrane" calorimeter. This calorimeter em-ploys a thin disc of constantan welded to a copper heatsink. An insulated copper lead is attached to thecente r of t he disc and another insulated copper lead isattached to the copper heat sink. The tempe ratur ediffe renti al between the cen ter of the disc and the ci r-cumference of the di sc produces the emf output whichi s tel eme ter ed to the ground. The emf output of themembrane calorimeter is a l inear function of the inci-

dent heating ra te with the slope of the output curvebeing determin ed by the physical si ze of the constantandisc.Fire Detection Measurements (S-IB and S-IC StagesOnly). The prelaunch fir e detection system i s ope r--tive during the period prior to vehicle lift-off. Whenthe ai r temperature, measured at critical points, ri se sat a ra te beyond a specified value, an ala rm signal isinitiated in the blockhouse and an automatic engine cut-off occurs.

A se ri es of thermocouples, arr ange d in loopswith se ver al thermocouples in each loop, a r e used.The thermocouples a r e located in back of the heatshield and in the engine compartment. The ra te ofri se of the temperatu re of the ai r is measure d in theimmed iate vicinity of the thermocouple, ra the r thanthe radiated heat from som e point re mote fr om themeasu ring device. The sys tem does not define theexact location because of the se ri es loop configuration.General Tempe ratur e Measurements. Surface tempe ra-ture measurements are made with thermocouples,thermistors, and resistance thermometers. Thermo-couples ar e normally used when the measuri ng rangeis 1 5 0 " ~302OF ) or greater, and resistance ther-mometers and thermist ors a re used for ranges of l es sthan 1 5 0 " ~ .The resistance thermometers a re ex-tremely accurate positive temperature coefficientre si st ors of which the resistan ce therm omete r typei s typical. Thermi stors ar e semiconducting deviceswhich exhibit a high-negative-temperature coefficientof resis tivity. Ambient a i r measurements down to1 0 c ( 5 0 " ~ )re also performed with thermistors.Thermocouples and Zone Boxes. Three types of ther-mocouples a r e used on the vehicles. In the circuitconsisting of 2 metals, an emf will be produced at themeasuring junction if a temperature difference exis tsbetween the measuring and the reference junctions.The 3 types in use a re : chromel/alumel, iron/constan-tan, and platinum/platinum 10 perce nt rhodium.

Thermocouples provide mea sureme nts of su r-face heat, fuel temperature, ambient ai r temperatures,and a r e used as fi re detection gages.

In a laboratory, the refere nce junction i s usuallymaintained at 0C (32 "I?). For vehicular purposes,such a temperature limitation is impractical; therefore,an alter nate method has been selected. Changes inreference junction temperature during flight are com-pensated for ele ctr ica lly by means of a bridge cir cui twith a resi stanc e thermome ter in one leg. A typical


12/55

Astr ionics Sys tem,Section 5.2

bridge cir cu i t with zone box is shown in Figu re 5 .2-9.The r e fe r enc e junct ion is contained within the zone box.The zone box is the junction between the vehicle net-wo rk wi r ing and the thermocouple leads . A r e s i s t a nc et h e r m o m e t e r is in therma l contac t with the re fe rencejunc tion. The res i s tanc e therm om eter has a knownposi t ive tem per a tur e coeff ic ient . S ince the res i s tanc ether mo me ter con t rol s the re s i s tan ce of one leg of thebridg e, the output emf of the brid ge cir cu it will followthe tem pe rat ur e induced emf output of the thermocouple(re f e ren ce junc tion) . The br idge c i rcui t is s o c a li -bra ted tha t it will canc el any emf pro duced by therefe ren ce junc tion as a r e su l t of a n i nc re a se o r de c re a sei n t e mpe ra t u re . The dc a mpl i f i e r i nc re a se s t he out -put s igna l l eve l to the requ i red te lemet ry input l eve lof 0 o 5 volts .

VIBRATION MEASUREMENTSVi bra ti on me a sure me nt s a r e ma de t o det e rminethe s t r uc tur a l s t rength and s tabi li ty of the Sa turnVe hic le . V i bra t ion a nd s t r e s s s e n sor s a r e mounte don the propel lant tanks, turbopum ps, engine mount-ings and engine combust ion chamber , and a t s t ruc-tu ra l junction points of the vehicle. Two typ es ofa c c e l e r o m e t e r s a r e u s e d a s v ib r a ti o n s e n s o r s o nboard the vehic les ; the piezoe lec t ric and the s t ra ingage types.

Piezoe lec t r ic Acce le rometer . Because of its s m a l lsize, l ight weight, and frequency response, thepiezoe lec t r ic acce le rometer is extensive ly used fo rfl ight vibrat io n instrumentat ion. The frequency re-spon se of a typica l piezoe lec t r ic acce le ro meter rangefrom about 5 her tz to sev era l kiloher tz . Fo r f l ightmeasurem ents , the useful f requency response islimited to the bandwidth of the telemetering channel.Th is type of acc elero me ter wil l not respo nd to stat icaccelerat io n. The effects of vehicular accelerat ionar e thus e l imina ted f rom the onboard measu reme nts ,and only loca l vibrat ion is detected by the sensor.

The piezoe lec t r ic acce le ro meter (Figu re 5 .2 -1consists of a se i sm ic ma ss which appl ies a fo rc e t o apiezoe lec t r ic c rys ta l , caus ing it to genera te an e lec-t r ica l s igna l. The e lec t r ica l output is proport ional tothe force appl ied to the c ry s ta l and is a t rue indica t ionof dynam ic acce lerat i on or vibrat ion. The high-impedance output of the device is coupled to a high-input-impedance em it ter-fol low er sta ge to maintainadequate low-frequency response.

The emi t te r- fol lower can be integra l to theacce le rom eter case , o r i t can be phys ica l ly removedbut joined elect rical l y through a coaxial cable. Typi-ca l sens i t ivi ty is in the ord er of 10 mv/g. Tempera-ture envi ronment is the de te rmining fac tor in thechoice of c ry sta l mater ial to be used. A sufficient ly

I

- +

Bridge O - n MeasuringSupply

I I E W I Junction0 +

ToTelemetry

IBM B5 5Figu re 5 .2-9 Typica l Bridge Ci rcu i t

5.2-9


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Astrionics SystemSection 5 . 2

< Power

4 k I < Calibrate]-( OutputTransducer (Crystal )

< Commonwith Emitter Follower

IBM ~ 5 6Figure 5. 2-10 Piezoelectric Acce lerometer and Emitter Follower

broad range of sensor types is available to permi tvibration measurements to be made in almost anytempera ture environment. The acceler ometers ar ecapable of operating up to an accelera tion level ofseve ral hundred g's and to a lower limit determinedby the associated electronic circuits. In flight appli-cations, the range is normally fro m Gg to *Tog.Tests have indicated that the acoustic environmentencountered on the vehicle will have negligible effect

on accelerometer output. This is the sensor mostfrequently used for vibration measurements.Strain Gage Accelerometer. The accele rometer(Figure 5 .2 - 11 ) consis ts of a mass suspended fromstrain- sensiti ve wire s connected to a Wheatstonebridge. When a force is applied to the mass, theresi stan ces of the supporting wir es change, thusunbalancing the bridge and causing an output voltage.

Figure 5 . 2 - 1 1 Strain-gage Accelerometer Block Diagram5 .2 - 10

4 Axis of Motion -bu0

Powe r

Bridge8

IBM B57


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Astrionics SystemSection 5. 2

The heavy arrows show the lower resistance circuitof an unbalanced bri dge. The ext ent of the unbal anceis indicated by the incr ease in voltage at the meter.In practice , a bias voltage is used to produce a2. 5-volt potential a t the output of the amp lifi er whenthe mass is a t r e s t. The bias prevent s the outputfr om going negative a s the movements of the ma ssis in both directions. Furthermore, the bias confinesthe output voltage to the 0 to 15-volt range.ACOUSTIC MEASUREMENTSMicrophone. A piezoele ctric type microphone is usedfor flight acoustic measurements. One of the adva n-tages of this microphone is that no shock mount isrequired. The microphone has a useful range of from110 db to 190 db.

5.2.3 S I G N A L C O N D I T I O N I N GThe following discus sion on signal conditioning

applies primar ily to the Instrument Unit.The signal conditioning syst em takes the signal

to be m easured and converts it to an analog signalthat is acceptable to telemetry. The signal may be an

electri cal signal from the vehicle o r it may be theoutput from a transduc er. Certain transducer s haveoutput signal s which do not r equ ire signal conditioninThese signals a re fed directly to the MeasuringDistributor.

A modular concept is used in the IU signalconditioning system. Thi s cons ists of a numb er ofmeasur ing racks , each having 20 measur ing channelsplus 2 calibra tion channels. The modules which pluginto the Measurin g Rack consi st of dc ampl ifie rs, a camplifi ers, channel sele cto rs (for calibration) andspecial modules. The amplifi ers have the provisionsfor plug-in signal conditioning cards to obtain a veryflexibl e measuri ng s ys tem with a minimum number ofcomponents.

The rack is a fabricated sheet metal structur ewith a tight fitting cover. I t is not pressurize d orhermeti cally sealed but has a ga sket sea l on the coveto protect the modules from foreign mat erial. Theinternal ele ctrical connections a re made through amultilayer printed c ircuit board with flexible integr alcable to the exter nal connectors. The multilayer boais als o the mechanical support for the measuringmodule connectors. A typical mea suri ng ra ck of thetype used in the IU is shown in Figure 5.2-12.

Figu re 5.2-12 Typical Measur ing Rack5.2-11


15/55

The re i s only one type of dc amplif ier used onthe IU. By making us e of a properly des igned signa lconditioning card, thi s one ampli fier is used for meas-uring temperatures, press ures, currents, voltages,er ro r signals, and other measurements.

The amplifier i s a high-gain chopper amplifierwith its input and output isolated fr om each ot her andground. The amp lif ier ha s a fixed gain of 100. Vari -ation in gain i s controll ed on the signal conditioningcard. It contains a dual frequency response amplifierranging from 0 to 20 hertz or 0 to 1000 hertz. Thefrequency response is dete rmine d by connectingjumper wire s on terminals. The amplifier has a ninternal dc-to-dc converter and operates directlyfrom the vehicle 28-volt supply.

The dc amplifier module contains a highlystable, isolated, and regulated power supply. Thissupply is used as a power source f or st rai n gagetransducers and temperature measurements and fora calibration voltage s ource in other meas urements.

A limiting ci rcuit i s included in the amplifierto prevent overdriving the sub car rie r oscilla tor ofthe telemet ry system.

Two relays a r e provided fo r checkout and cali-bration of the amplif ier and asso ciat ed measuringsystem. These relays ar e operated remotely throughthe remote automatic checkout system.AC AMPLIFIERS

Only one type of ac am plifi er i s used i n theIU . The ac amplifier has the s ame type of signalconditioning card a s the dc amplifier. It i s usedprima rily for vibration and acoustic me asurements.

The ampli fier ha s a gain of 240 and a frequencyrespo nse of 40 to 3000 hertz . Since pract ical ly allvibration and acoustic measurements a r e on SS/FMtelemetry, the lower frequency response lim it wasdesigned to be 40 hertz . The output i s tr an sf or me risolated f ro m the input and ground.

The amplifier contains an internal dc-to-dcconverter to supply an isolated power sourc e fo r theamplifier and to provide an isola ted power sourc efor use with the vibration transduce rs and emitt erfollowers.

The ac amplifier has the s ame type limitingcircu its and calibration rel ays a s the dc amplifier.Figure 5. 2-13 illustrates an ac amplifier used inthe IU.

Figure 5. 2-13 Ill ust rat ion of an AC Amplifier5.2-12


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Astr ionics Sys tem, Section 5. 2

SPECIAL MODULES 5.2.4 M E A S U R I N G D I S T R I B U T O RThe re a re s e v e ra l me a sure me nt s tha t r e qu i resignal condit ioning that a r e not compatible with the acor dc a mpl i f ie r . Special signal conditioning modulesa r e use d fo r the se me a sure me nt s . Examples of thesemodules a re : the dc conver te r used with f lowmeters ,the se r vo acce le rom eter uni t used with the force ba l -ance acce le rom eters , and the frequency measur inguni t used to acc ura te ly moni tor the 400-her tz vehic le

supply. Most of the special modules have re lay s fo rcal ibrat io n and checkout .SIGNAL CONDITIONING CARD

The sign al condit ioning ca rd is a pr inted c i rcui tcar d with a conn ector that mates with the signal con-di tioning card on the dc and ac ampl i f ie rs . The cardprovides the neces sary f lexibi l ity to obtain the meas-urem ents requ i red on the Sa turn Vehic le wi th a sm al lnum ber of differe nt type am plif iers . Thus, only onetype of dc amp lifier and one type of a c am plifi er ar eused on prac t ica lly a l l the measurements requi r ingsignal conditioning. The sign al condit ioning ca rdconta ins br idge comple t ion res i s tors , ca l ibra t ionres i s tor s , b ias ne tworks gain adjus tment , e tc .

A c i rcui t d iag ram of a typica l ca rd for t em-p e r a t u r e m e a s u r e m e n ts is shown in Fig ure 5.2-14.In thi s case , the t ransducer is a therm is tor . Smal lrange changes can be made by the span adjustmentpotent iometer. By changing res isto rs , the rang e canbe changed by a l a rg e amount and sev era l ranges oftem per atur e can be measu red by using one signalcondit ioning card. The system can be cal ibrate d byus ing the remo te automat ic checkout sys tem to op er-a t e t he r e l a ys a nd t hus shun t r e s i s t o r s R7 o r R8acr os s the bridge.

S i m i l ar c a r d s a r e u s e d f o r e r r o r s ig n al s,c u r re n t s , s t r a i n ga ge b r i dge t r a nsduc e r s , a ndother measurements .Signal conditioning in othe r vehicle stag esaccompl i shed i n a si m ila r way. Signal condit ioningmodules a r e mounted in measur ing r ack s conta ining20 mod ules each. In the S-IVB Stage, signa l con-di t ioning modules are mounted on panels distributedthroughout the stage. The num ber of measu ring racksin each s tage is given in Table 5.2-1.

The measur ing di s t r ibutors accept the 0 t o5-volt output of the s ignal conditioning mo dules androute them to the prop er t e leme t ry channel. Al lme a sure me nt s i n the me a sur i ng sys t e m a re c on-ne ct ed t o t he d i s t r ibu t o r a nd a re d i r e c t e d t o t he i rpreass igned channel . The di s t r ibu tors provide ve rsat i l i ty in changing channel assignments; changes aremade by physica lly rearrang ing jumper wi r es wi thinthe measur ing di s t r ibutors . The versa t i l i ty of thedis t r ibu tors e l imina tes extens ive cable changes andal lows channel changes to be made just pr ior to launcMore than one measur ing di s t r ibutor may be used depending on the number of m eas ure me nts to be madeand the physical locat ion within the IU of the m eas urements to be m ade.

Switching functions connect different se ts ofmeasurem ents to the sam e te leme t ry channels dur ingdifferent fl ight periods. Thes e switching funct ions,cont rolled by the Cont rol Dis t r ibutor , a re perfo rmedin the Measur ing Dis t r ibutor . Switching functions,control led fro m the ground via the umb il ical cable,connec t measuremen ts not requi red dur ing f light todigi ta l da ta acquis it ion sy s tem channels for groundcheckout and return the channels to fl ight measure-ments after checkout .

Transducer

IB M B6 0Figu re 5.2-14 Typical Signal Conditioning Car dfor Te m pe ra t u re Me a sure me nt s


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I

SECTION 5.3REMOTE AUTOMATIC CALIBRATION SYSTEM

The remote automatic calibration systempermits a remot e calibration of the measuring sys -tem pr io r to launch. During vehicle checkout, cali -brati on of meas ureme nts is accomplished through theRACS and various corrections can be made by ad-justing potentiometers on the modules. Pr io r tolaunch time, the RACS may be opera ted if the sy ste mdrifts o r deviates from the final adjustments. Thedata obtained is used to cor rec t the flight data formore ac curate measurements.

Each signal conditioning module contains 2relays and the necessary circuit to simulate the trans-ducer a s well a s the upper (HI) end and the lower (LO)end of the signal range fo r that parti cular meas ure-ment. The trans ducer is connected to the module inthe RUN mode.

A binary-coded signal is sent f rom the GSEthrough the umbilical cable to the Measuring RackSelector in the vehicle to selec t a particular meas-ureme nt for calibration. Figure 5. 3-1 shows theRACS of the IU. Each stag e has a sep ar at e RACS.The signals a r e generated in the GSE either by amanual keyboard o r fro m a computer program.These si gnals a r e decoded on the vehicle and dis-tributed to the various Measuring Racks to operatethe checkout relays.

The calibration signal cons ists of 13 bits inparallel. There ar e 6 bits for rac k selection, 5 bitsfo r channel selection, and 2 bits for mode sele ction.(One checkout r ela y is fo r the HI mode, or checkpoiand the other is fo r the LO mode, o r checkpoint. )The sa me code is used on all sta ges to provide a 31-ra ck capacity. The IU RACS is designed fo r 14 rack

G R O U N D I VEHICLEII MEASURING RACK (14 Maximum)IManua l Keyboard CH AN NE L SELECTOR

Channel Decode

LO HI

Relaysi n M o d u le

Measuring Rack Selector1. Rack Decode2. Mode Decode Recode3. Channel Buffered

II

IBM ~ 6

Figur e 5.3-1 Block Diagram of RACS fo r the IU5. 3 -1


18/55

5. 3

On the vehicle, the code is received in theng Rack Selector. The rack select code is

is addressed to the properRack. Buffer cir cuit s fo r mode codes

annel codes ar e provided in the Measuringich act s a s a distribution point to

The signa ls go to thek. Operation of the channel sele cto r requ ire s the

Rack select signal presentChannel select signal presentMode signal pres ent (HI or LO)Ther e a r e two channel sele ctor s in each Meas-

One decodes channels 1 through 10 andhe other decodes channels 11 through 20. The chan-el selector contains the necessary diode matri ces

and latch ci rcu its to complete the operation of theRACS.

The channel select modules contain 20 ANDgates. When the 3 conditions mentioned above a r efulfilled, the addr ess ed AND gate "latche s in" andenergi zes the corresponding calibration relay in thesignal conditioning module. This rel ay will rem ainenergi zed until another signal is sent to change themode.

In addition to HI and LO mode, th er e i s a th ir dmode of ope rat ion , cal led RUN mode, which is selectedwhen both calibration rel ays a r e in an unenergizedstate. The RUN mode is the no rmal mode of operat ionwith the transdu cer or input signal connected to the sig -nal conditioning module. During calibrat ion (followingHI or LO mode), the RUN mode is achieved by sendingthe proper code to the vehicle. Since the RACS is usedonly before launch, it is wired in such a way that thepower i s remov ed at launch. Removal of th e powercaus es al l rel ays to switch to RUN mode. This elimi -na te s the possib ility of l eaving any module in the check-out state (HI or LO).

Any number of channel s can be select ed indivi-dually, simultaneously, or in any sequence or combina-tion (with any combination of a HI, LO, o r RUN se le c-tion at the GSE keyboard). The GSE displa y panels a r eused to monitor the signal (code) sent to the vehicle(th ere is no code feedback fr om the vehicle). The cali-bration result s a r e observed through the teleme trysystem and connected ground-checkout system.

Each of th e sign al conditioning modules haspush buttons on the fron t of the module fo r manualoperat ion of the cal ibrat ion ins ide the vehicle.


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I

SECTION 5.4TELEMETRY

5.4.1 SATURN TELEMETRY SYSTEM

Each stage of the Saturn Vehicle ca rr ie s anindependent tele metr y system. These syst ems modu-late the signals from the measuring system onto RFca rr ie rs f or transmission to ground stations. Threedifferent modulation techniques are applied in thetele metr y syst em of each stage:

a FM/FM tele metr y applies frequency modu-lation/frequency modulation with PulseAmplitude Modulation (PAM) and triple3Frequency Modulation (FM ) as auxiliarytechniques

a SS/FM telemetry uses single sidebandmodulation/f r equency modulation

Low-response/low and medium-accurac y datamay be sufficiently defined by sampling at a rate of10 hertz, or less. In te rm s of frequency respo nsethis would be 2 o r 3-hertz maximum variation. Thiscategory includes temperature, pres sure, and othermeasurements where dynamic variations a r e not verylikely or a r e not of particular interest.

Low-response/high-accuracy data requiresaccu raci es of 1 percent or better. Examples arelongitudinal acce lera tion and combustion chamberpress ure measurements.

Medium-response/medium-accuracy data re -quir es a 5 to 40-hertz re sponse. Data of this categocan be handled by sampling at 100 to 125 her tz pe rchannel or less, or by FM/FM channels below the3-kilohertz su bc ar ri er using the standar d deviationrat io of 5.

PCM/FM tele metr y use s pulse code modu-lation High-response/medium-accuracy data requir

a 50 to 1000-hertz channel response. Th is type of daThese different modulation techniques provide is readily handled by FM/FM subcarriers.

effic ient trans miss ion of the la rge number and vari etyof measuring data which has different req uirement s of Wide-band da ta has a bandwidth of roughly 50bandwidth and accuracy (Table 5.4- 1). to 3000 her tz and normally no dc component of int ere

Table 5.4- 1 Data Categories

Type

1. Low-response/low and medium-accur acy2. Low-response/high-accuracy3. Medium-response/medium-accuracy4. ~igh-response/medium-accuracy5. Wideband low-accurac y6. Event measurements7. Digital measurements

5.4-1

FrequencyResponse

(hertz)2-32-35-40

50-100050-3000

- - ----

AccuracyRequired(percent)

2-51225

---

- - -


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Astrionics SystemSection 5. 4Vibration data and sound intensity fall within this clas -sification.

Event measurements constitute a special cate-gory. Inter est in this data is limited to whether o r notan event has occured and, if so, the time of occur -rence with res pect to a specified time resolution.

In addition, much data origina tes in digitalform, e. g. , signa ls from the LVDC.

The wide-band data-carryi ng capability ofstandard FM/FM telemetry is very poor. The FM/FMsys tem ha s one channel with a frequency res ponse of0 to 1050 hertz at a s ub ca rr ie r deviation rati o of 5;the other channels have decreasing frequency responsesdown to 6 hert z. The sum of a ll the channel band-widths is only 4700 her tz. The bandwidth efficiencyof a standard FM/FM sy stem with subca rri ers operat-ing at a deviation ra ti o of 5 i s about 1.6 percent. Acorresponding figure for a PAM/FM syst em i s about3.5 percent; for a PCM/FM system, it is about 3.0percent.

The necessi ty to tra nsmit wide-band data(acoustic and vibration measure ments) led to theus e of SS/FM tel emetry. An R F ca r r i e r is frequencymodulated with single-sideband, amplitude-modulatedca rr ie rs . The bandwidth efficiency of such a systemis roughly 10 tim es gr ea te r than that of FM/FM. Itis capable of tra nsm itt ing 45 her tz of data ove r thesa me bandwidth used by the FM/FM link to tra nsm it4700 he rt z of data.

A theoreti cal comparison of the signal/noiseper for man ce of the SS/FM with a standard FM/FMsystem is useful. Since single-sideband subc arr ier sdo not po ss es s wide-band gain, one would logicallyexpect that SS/FM would perform le ss favorably inthi s resp ect than FM/FM, probably by a fact or equalto f i t i m e s the deviation ratio, which is the wide-band gain of the FM subc ar ri er . However, if th emodulating signa l of such a syst em is to be vibrationdata, other factors can more than compensate forthe lack of wide-band gain in the su bcar ri er .

These compensating fact ors result from apr io r knowledge of th e nature and cha rac ter ist ics ofvibration data. A Gaussian or normal curve is agood approximation of amplitude distribution cha r-act eri sti cs of such data. Since the summation ofGaussian functions is a Gaussian function itself, thecomposite signal modulating the transmitter (in anSS/FM sys tem c arry ing vibration data) could be ex-pected to res emb le a Gaussian function. The peak-

to-peak amplitude of the data applied to an FM sub-ca rr ie r must be limited to the band edges of thesub car rie r channels, the deviation being * 7. 5 percentof c ente r frequency, to prevent adjacent channelinterference . Thus, when data pos ses ses a highpeak- to-rm s ratio, the signal capacity of the channelis reduced below it s signal capacity for a sine wavemodulating signal (1. 41 peak-to-rms ratio). Cor re-spondingly, Gaussian data with a peak -to-r ms ra tioof 4. 0 reduces r ms data capability to 2. 83.

No such inherent peak data res trict ion exist sin the SS/FM system. The data peaks of the individualchannels add in a random manner, resulting in anamplitude distribution of the composit e signal simi la rto that of the data at the channel inputs and having apeak fac tor of approximately the sam e magnitude.Thus, with Gaussian-type cha rac ter ist ics and anidentical number of channels, the SS/FM s yst em willaccommodate two or more time s a s much peak c ar ri erdeviation per channel as an FM/FM system.

Data which originates in digital form and datarequiring high accuracy a re tra nsmit ted through thePCM/FM system . The digital data tran smis sion linkis relatively insensitive to imperfections in the trans-miss ion channel. Below a threshold noise level, theaccuracy is not appreciably affected by noise in thechannel. Nonlinearity in the tra nsm iss ion channel isof lit tle consequence. By a relatively simple andreliable operation, the se ri al digital data which con-tains noise and deteriorated rise time can be regener-ated into its original noise-free form.

Also, digital data trans miss ion i s compatiblewith real-ti me data processing by digital computersat ground stations. A sepa rat e digital data output ofthe PCM/FM s ystem is used for automatic preflightcheckout of the launch vehicle. This i s called thedigital data acquisition system. The Mod 301 PCM/DDAS Assembly i s a lso connected with the LVDC fo rcheckout of the S-IVB/IU Stage in orbit. During flight,all operational data is tran smit ted over the PCM/FMlink.

To incr eas e the data handling capacity of te -lemetry systems, seve ral data channels a r e multi-plexed. Two types of multiplexing ar e utilized: fr e-quency-division multiplexing and time-divisionmultiplexing.

Frequency-division multiplexing is the processof simultaneous frequency sharing of one RF car ri ertransmission link by dividing the available bandwidthinto a number of channels, each with a sepa ra te center


21/55


I

frequency. Spacing is provided between these channelsto allow each channel to be frequency modulated ordeviated about the center frequency. After modulationoccurs, the subc arri er signals ar e combined linearly,and the resul tant composite signal is used to frequencymodulate an RF ca rrie r. FM/FM and SS/FM areexamples of this frequency division multiplexing.

Time-division multiplexing i s the proc ess ofsequential sampling of two o r mor e data so urc es andapplying the data samples to a common output in afixed sequence. The samples may or may not besep ara ted by a "dead time" space. Usually some"marker" is made a pa rt of the output signal to desig-ate the beginning or end of a sampling cycle. Thisi s for identification and synchronization purpos es atthe data reduction point.

The Saturn tele met ry syst ems make use ofse ve ra l types of time-division multiplexers. TheMod 270 Multiplexer Assembly is a time-divisionmultiplexer for analog data. It is used in conjunctionwith the FM/FM teleme try system and the PCM/FMsys tem. The Mod 245 Multiplexer Assembly prov idestime-division multiplexing for wide-band data and isused for SS/FM telemetry and FM/FM telemetry.The rem ote digital submultiplexers and digital multi-pl exer s a r e used in connection with the Mod 301PCM/DDAS Assembly. Remote analog submu ltiplexersa r e used fo r analog data connected to the Mod 270Multiplexer Assembly.

The number of R F ca rr ie rs allotted to eachmodulation technique is chosen to provide an appro-pria te balance of data tran smi ssio n capability tohandle the quan tities and va rie tie s of d ata originatingon the stage. The teleme try equipment associatedwith each stage con sist s of a "building-block" ar ran ge -ment, which may be connected in numerous combina-tions to satisfy specific measuring re qu ir em ~~ it s. henumber of c ar ri er s allocated to FM/FM, SS/FM, orPCM/FM and also the specif ic combination of buildingblocks v ary fro m stage to stage and from vehicle tovehicle.

A typical R & D ver sion of the S-IVB/IU t elem-etry system is shown in Figure 5.4-1. Figure 5.4-2illustra tes the operational version. In operationalvehic les, the number of multiplexers and FM/FMsys tems will be reduced, and the SS/FM te lemetrywill be omitted. Flight (mission) contro l dat a willbe sent in para llel to the IU PCM/FM and S-IVBPCM/FM sys tems a s indicated in the figure. There-

fore , in the event of a fa ilu re in one of the PCMsystems (IU or S-IVB), the other PCM sys tem s canbe used to tran smit the flight control data.

Table 5.4-2 li st s the type and number of tel emetry s yste ms and multiplexers used in the s tag es ofSaturn Vehicles. Because of the smal le r quantity ofmeasu rement s requir ed in operational vehicles, thenumber of tele met ry sys tem s is also reduced. (Fi gurgiven for o perational vehicles a re "best guess" at thepresent time. )

Fro m one to six time-division multiplexers a rsynchronized fro m a cen tral timing sour ce located inthe PCM/DDAS Assembly. Each time-division multi-plexer provides an output to the PCM/DDAS Assemblywhich combines the outputs into a single s er ia l wave-train. The individual analog samples a re digitized ancombined into a digital for ma t which is transmitted vicoaxial cabl e to the ground checkout equipment. Thisdata is also transmitted via a PCM/FM ca rri er forin-flight monitoring.

Each of the time-division multip lexers has asecond data output which is identical to the outputprovided to the PCM/DDAS Assembly except that itis conditioned for PAM transm ission. These outputsmay modulate a 70-kilohertz, voltage-controlledoscillator in FM/FM telemeter assemblies. Thisarrang ement provides redundant tr ans mis sio n ofsome multiplexer outputs using both PAM and PCMtechniques.

5.4.2 FM/FM TELEMETRY SYSTEMThe FM/FM telemetry system frequency mul

plexes the input data. The conditioned signal s derivefro m pre ssur e, temperature, etc., modulate the fre -quency of the su bca rrie r osc illator s. The combinedoutput of s eve ral subc ar rie r oscilla tors is again f re-quency modulated on the RF car ri er . Standard IRIGfrequency channels a re assigned. The dat a bandwidthcapab ilities of th ese channels ar e shown in Table 5.4Slow-varying data is applied to the low-frequencychannels; data with higher frequency var iati ons , musbe applied to the higher frequency channels. FM/FMsys tems a re susceptible to variou s sou rce s of noiseand distortion (fluctuation noise, cro sst alk, harmonidistortion of the individual su bc ar rie r signals, sub-ca rr ie r data feed-through, and distor tion of individuasubcarrier signals due to band-limiting filters), whicaffect the acc uracy of the telemet ered data.


22/55


Table 5.4-2 Telem etry Systems in the Various Saturn Vehicle Stages

Each of the subc ar ri er osc illat ors of anFM/FM system may be preceded by another sub-ca rr ie r group. Each of these "sub-subcarriers"would, in thi s case, be modulated by the actualmeas ureme nt values. This technique is called3FM/FM/FM, or FM . The technique trades band-width for additional channels; therefore , the frequencyresponse of the channels is much lower. Since anothermodulation stage is used, the technique is les s accu-ra te than FM/FM.

Stage

IU

S-IVB

S 11

S-IC

S-IB

A time-multiplexed signal may be fed into asubc arr ier osc illator of an FM/FM system to increasethe channel capacity. Time multiplexing consists ofsequentially sampling a number of data signal s withan ele ctronic o r mechanical commutator. The com-mutator output ap pear s a s a tr ai n of pulses of varyingamplitude. This technique is known as Pulse-Amplitude Modulation (PAM/FM/FM).

The basic modulation scheme and principalcomponents used (subc arr ier oscillator s, mixer,power amplifier, and transm itter ) a r e essentiallythe same for each stage of the FM/FM system.Figure 5. 4-3 shows a typical Saturn stage FM/FMsystem. Each channel rece ives a signal fro m theMeasuring Distributor. This input signal modulatesa voltage-controlled su bc ar ri er oscillator. Thefrequency-modulated signal s from the vari ous sub-ca rr ie r osc illators a re combined in the mixer ampli-fier. The composite signal is frequency modulatedon a radio-frequency ca rr ie r in the VHF band (225 to260 megahertz) for t ransm ission to the ground stations.The trans mit ter provides a signal power level ofapproximately 20 watts.

Note: CIU = Computer Interface UnitRDSM = Remote Digital SubmultiplexerRASM = Remote Analog SubmultiplexerRDM = Remote Digital Multiplexer (Mod 410)

TelemetrySystem

FM/FMSS/FMPCM/FM

FM/FMSS/FMPCM/FMFM/FMSS/FM

PCM/FMFM/FMSS/FM

PCM/FMFM/FMSS/FM

PCM/FM

The available standard IRTG channels may beutilized in different ways. The sys tem shown in Fig-ur e 5.4-3 u se s 13 continuous data channels (channels2 through 14). The input signa ls fro m the Measuring

Number ofSystems

R&D

211

311

321

321

211

Number ofOper

1-1

1-12-11-1

1-1

TransmitterFrequency

Saturn IB:225-260 MHzSaturn V:22 5-260 MHz

and2200-2300 MHz

225-260 MHz

225-260 MHz

225-260 MHz

225-260MHz

MultiplexersR & D

l x CIU2x Mod 270lxMod245IxRDM

Mod 410IX RDSM4x Mod 270Ix Mod 245

5x Mod 270l x Mod 2457x RASM2x RDSM4~ M O ~702x Mod 245IX RDSM3x Mod 270lx Mod 2452x RDSM

Power

20 W

20 W-

20 W

20 W

20W

Operl x CIU2x Mod 2702x RDM

Mod 410

2x Mod 270

2x Mod 2702x RDSM2x RASMIX RDSM2x Mod 270

2x Mod 270lx RDSM


23/55

AstrionI

S-IU STAGE---------------S-IVB STAGE

AssemblyA M ul t icoup le r ---++-To F W F MAssemblies

APowerDivider -

LV DC

PCM/RF PCM/RFAssembly I TAssembly(UHF) W H F ) LV DA

Ground Sync toCheckout Ground 4 A l l M u x(DDAS) Checkout t(DDAS) Mod 301 Computer-CM/DDAS * InterfaceAssembly Un i tt t Assembly Assembly1L 'WT'ecordern tM ul t ip lexer M u l t ip lexer M u l t ip lexer Subm ul tip lexer M u l t ip lexerAssembly Assembly Assembly Assembly Assembly Assembly

From Programmer4 From ESE

h m p l e D a ta I

HighFrequency

M od 270

h m p l e D a ta7 -Analog Data

Sample Data

I Cont inuous Data I a n ti n w us e t a I Cont inuous Data

-- -

IHigh Frequency Data

&Sample Data

IFigure 5.4-1 Typical S-IVB/IU ~ e l k m e t r ~ystem ( R

Data \ JA ~ ~ I ~ ~ ~ D ~ ~ ~-_______------------------------------------------------------------------------------------------------------\I

RF PowerD iv ider - Div ider -

t t .-r=alibr ator From ESEM ul t icoup le r M u l t i coup le r

I JDig i t a l Dat a

RFAssembly

Assembly Assembly Assembly

RFAssembly

Cont inuous Data

A

F o m r d S k ir t t 'T Electr ical Tunnel )tt 4 8-

Assembly

Cont inuous Data

I I Ground Data Sample Data 1 , Ground*checkout v ) heckout- M ul t ip lexerAssembly

Mod 301 Mod 270 Mod 270- CM/DDAS Mult iplexer M ul t ip lexer F M / F M M od 245


24/55

AstrioniS

1

I Mission Engr I VHF

EngrAnalogs

From ESE

1

TM Calibmtor

7 v 7

Checkout EngrDiscretes Discretes @ Remote analog submultiplexer may be used at option ocontractor.

Figure 5.4-2 Typical S-IVB/IU Telemet ry System (Operatio

1-To LVDA Control Discretes

Mod 270 Mod 270 Mod 301

TM Assembly RF AssemblyDiscrete, @

A

Mod A3

wMultiplexer Multiplexer PCM/D DAS

A-

- Assembly

- 1 t , UHF1 V lComputer Mod 41 0Interface Multiplexer

Uni t Assembl y4

t Mod 41 0Multiplexer

Assembly

1 1 1 v

Assembly @ AU""b'yb4 AssemblyA 4 . UHF4 Sync & Data ) TransponderCS -

Prelaunch Engr Mi ssionCheckout Analogs Control Checkout DDAS Output ,T I U Umbilical

S-IU STAGE Analogs Analogs @.--I-----------------------------------S-IVB STAGE Sync & Data S-IVB S

1 ,T S-IVB U mb il ic alVHF

PCM/RF- ssembly L(UHF)

VHF

Mod 270Multiplexer

Assembly

JMod 270 Mod 301 .4 PCM/RFMultiplexer * PCWDDAS . Assembly NOTES:Assembly Assembly

A A 1

, @ Flight configuration shown with solid lines. Stagecheckout configuration shown wit h dashed lines.

@ Continuous channel inputs switched to time divisi onchannels for instrumentation checkout.@ Mission co ntrol measurements must appear i n sameformat location i n both S-IVB & 1U PCM/FM lin ks.

This connection used on Saturn V only.VHF @ Mounting provisions only for these assemblies.

SCO Assembly 0 Digital multiplexer per MSFC Dwg 50M67122 (estima(FM/FM) AssemblyCM/RF A release date August 1, 1965) may be utiliz ed in lieu

(VHF) RDSM at option of contractor for vehicles where scheare compatible wi th estimated released date.+

4 A A A41 t

0-Mission PrelaunchControl rAnalogs @ Checkout

-41Analogs

1-TM CalibratorFrom ESE

Mission Prelaunch

Remote Digita lSubmultiplexer0 +


25/55

Astrionics SysteSection 5

1

Table 5.4-3 IRIG Subcarrier Channels (* 7. 5% Channels)

Figure 5. 4-3 Block Diagram of Typical Saturn V FM/FM Teleme try System5.

r

Channel123456789

1011121314151 6171819

C270 Channels 1Analog Data II

UpperLimit( H z / s )

0.4300. 6020. 7851. 03 21. 3981.8282.4733.2254.1935.8057 . 9 0 1

11.28815. 58823. 65032.25043.00056. 43875.25099.975

CenterFrequencies

( H z / s )0. 400. 560. 730. 961. 301. 702. 303. 0 03. 905. 407. 35

10. 5014. 5022.0030.0040.0052. 5070.0093.00

Mod 270 Multiplexer3 0 x 120 Multiplexers10 x 12 Sub-multiplexers

on Selected MainMultiplexer Channels

LowerLimit

(kHz/s)0. 3700. 5180. 6750 .8881.2021.5722. 1272 . 7 7 53. 6074.9956.7999. 712

13.41220. 35027.75037.00048. 56264.75086.025

NominalFrequencyResponse

(Hz/s)68

1114202 535455981

11016022 033045 060 079 0

1,0501,400

, t t ,VCO+ 560 Hz i 7.5% *Subcarrier

NominalRiseTime(ms)58423224181410

7. 86. 04. 33. 22 .21. 61. 10. 780. 580. 440. 330. 25

-Mixer

Amplifier

Transmitter

VCO70 kHz * 30%Subcarrier

Channel 2Analog Signalsfrom ChannelsMeasuring System 3 through 13

III V CO22 kH z * 7.5%

SubcarrierNote: Channel 14

VC O =Volta ge -controlled Subcarrier OscillatorIBM ~

MaximumFrequencyResponse

(HZ/S)3042557298

12817322 529 340 555 178 8

1, 08 81, 65 02,2503,0003, 9385,2506,975

FM+

MinimumRiseTime(ms)

11. 78. 336. 404. 863. 602. 742. 031. 561. 2 00 .8640. 6350.4440. 3220.2120. 1560. 1170.0890. 0670 .050

Low PassFilter


26/55

Astrionics SystemSection 5. 4Distr ibutor a r e in the range of 0 to +5 volts dc (2 to 7volts peak-to-peak a c when a bandpass fil ter is usedin place of a channel or subchannel oscillator).

3When used, tr ip le FM (FM ) is applied to thechannels above channel 13. A su bc ar ri er channel of70 kilohertz (130 percent) is used fo r time-multiplexedsig nal s fr om the Mod 270 Multiplexer Assembly. Whenthis PAM technique is applied, al l IRIG channels above30 kilohe rtz will not be used. The Mod 270 solid -sta te,time-division multiplexer oper ates a t a ra te of 3600sam ple s per second. It consists of 30 pri mar y chan-nels which ar e sampled 120 times pe r second. Inaddition, 10 submul tiplexers may be used on sel ect edmain channels; each sampled at a ra te of 12 per second.The multiplexer acce pts input signals in the range of0 to 5 volts dc and provides two PAM wave train out-puts. One wave tr ai n modulates the 70-kilohertz,voltage-controlled subc arr ier oscillator with a fre -quency deviat ion of *30 percent (i. e., 49 to 91 kilo-hertz for an input signal from 0 to 5 volts dc). Thesecond wave t rai n i s used for the PCM system.

The RF Assembly accepts single sideband FMand FM analog signals from the teleme try assembliesand provides the highly-stable, close-tolerance ca rr ie rfrequency (*O. 01 percent). It further provides thecapability of varying the ca rr ie r frequency in a manner( i 1 percent of the best straight line approximation for125-kilohertz deviation at modulation frequencie s fro m300 hertz to 100 kilohertz) proportional to the inputsignal amplitude, thereby providing an RF link fro mthe measurement systems in the flight vehicle to theground receiving station.5.4.3 SS/FM TELEMETRY SYSTEM

The Saturn SS/FM telem etry sy stem i s de-signed specifically for transm issio n of the la rge volumeof vibra tion data fr om the Sa turn Vehicle. This sys-tem c an tra nsm it 15 channels, each having a res ponseof 30 to 3000 her tz, fo r a total data bandwidth of ap-proximately 45 kilohertz within the standard telemetrycarrier bandwidth.

Each of the 15 data inputs i s fed to a balancedmodulator and heterodyned with a 455-kilohertzcarrier (Figure 5.4-4). The output of the modulatoris fed to a mechanical bandpass filter (455 to 458 kilo-hertz ) which passe s only the upper sideband. Theoutput of the fi lt er is fed to a second balanced modula-tor where it is translated t o the proper baseband fre-quency. The baseband position is determined by theca rr ie r supplied from the frequency synthesizer.The two balanced modulators and the mechanical

bandpass filter f or each data channel make up thechannel units. The channel units ar e identical forall channels.

The second modulator ca rr ie rs a r e suppliedto the channel unit from the frequency synthesiz erand comb filters. These 15 subc arr ier s transposethe data to an assigned frequency between 4. 74 and72 kilohertz. These a r e the lower sideband outputsof th e second modulators.

Both sidebands of the second modulators go tothe summing ampli fie r No. 1 and the 200-kilohertzlow-pass fil ter where all upper sidebands of thesecond modulator a r e fil ter ed out. Here a 75. 835-kilohertz pilot tone is summed into the channel unitoutputs. The pilot tone provides a signal at the re -ceiving stat ion for demodulation of the 15 channels.

After leaving the 200-kilohertz low-pass filter,the composite signal is passed through a signal regulator.From the signal regulator, the composite signal issumme d with the signal fro m the non-translated spec ialse rv ic e channel. The frequency respo nse of thischannel is 0 to 1200 hertz. Its normal use is to carrya 960-her tz signal provided by the Mod 245 MultiplexerAssembly for demultiplexing the signals a t the re ceive r.The output of the summing amp lif ier No. 2 i s used tofrequency modulate an RF transmitter.

All the carrier signals and the pilot tone aregenerated internally in the airbor ne SS/FM assem blyby a single 910. 025-kilohertz c ry st al oscil lator . Thissignal is used to drive a flip flop which provides the455.012-kilohertz ca rr ie r signal and a frequencysynthesizer provides all sub-carriers and the pilottone from the comb filte rs.

To provide a 3-kiloher tz information bandwidthand allow suffic ient guardband, a channel spacing of4. 74 kilohertz i s used. This spacing is convenient togenerate in the synthesizer and allows an adequateguardband of 1.74 kilohertz . The 75.83-kilohertzpilot tone falls just above the highest baseband fre-quency. It is used as a refer ence in the ground de-modulation equipment to regenerat e the basi c 455 and4. 74-kilohertz f reque ncies . Since the amplitude ofthe transmitted 75. 83-kilohertz pilot tone is regulated,i t is als o used a s an automatic gain control.

The SS/FM Assembly i s used in conjunctionwith a vibration multiplexer (Mod 245) to expand itsdata-handling capability by time-sharing specific datachannels. SS/FM telemetry is not carried in opera-tional vehicles.


27/55



28/55

5.4 .4 PCMIDDAS TELEMETRY SYSTEMThe PCM/DDAS telem etry syst em ser ves a

purpose in the Saturn Launch Vehicle. Thi sem functions a s a te lemet ry link for digital data

(PCM/FM) and a s a p ar t of t he DDAS. PCM/FMs required on the launch vehicle in order to obtainufficien t accu racy , with acce ptab le bandwidth effi-ciency, for digital data transmission fr om data

sourc es such a s the LVDC. The DDAS provideseces sary measurement data to the LVDC. Before

aunch, it als o provides mea surements to the launchcomputer in the ground checkout stations (via coaxialcable).

To provide flexibility, the syst em is "built" f rom s ev er al assem bli es which may be combinedrequired in a particular stage application. Th e

ollowing assemblies may be used to "build up" aPCM/DDAS te lem etr y system:

a Mod 301 PCM/DDAS Assemblya PCM R F Assemblya Mod RDSM-1D Remote Digital Sub-

multiplexera Mod 410 Remote Digital Multiplexera Mod 270 Multiplexer Assemblya A remote analog submultiplexer which

may be used with a Mod 270 MultiplexerAssembly

a Computer Interface UnitMOD 301 PCM/DDAS ASSEMBLY

The Mod 301 PCM/DDAS Assembly is th ecen tra l piece of equipment in both the teleme try linkand the DDAS link. It provides the output signals fo rtelemetry and automatic checkout.

The PCM/RF Assembly contains the signalconditioner, power amplifier, and RF transmit terfor the te leme try link.

The Mod RDSM-1D Remote Digital Submulti-plexer is used to connect digital data sourc es to theMod 301 PCM/DDAS Ass emb ly.

The Mod 410 Remote Digital Multiplexer isused in the IU to connect the LVDC to the Mod 301PCM/DDAS Assembly.

The Mod 270 Multiplexer Assembly is used toconnect analog data into the Mod 301 PCM/DDASAssembly.

The remote analog submultiplexer may be use dto submultiplex data being fed through the Mod 270Multiplexer Assembly.

The Computer Interface Unit allows the LVDC,operating through the LVDA, to re ad selec ted mea s-urem ent data which is being transmitted through theMod 301 PCM/DDAS Assembly.

A brief functional description of the Mod 301PCM/DDAS Ass embl y and the PCM/RF Asse mbly isgiven on the following pages. The multipl exer s andthe Computer Interface Unit a r e described in thefollowing paragraphs.

The Mod 301 PCM/DDAS As semb ly per fo rm ssix major functions a s follows:

a Scans the PAM wave trai ns of s ev er al(1 to 6) Mod 270 PAM Multip lexer As-sembles in a programmed sequence andcombines these wavetrains into a singlePAM wavetrain .Encodes the PAM samples in this wave-train into 10-bit digital form.

a Accepts data in digital form and pro-gra ms it into selected time slots in theoutput s er ia l format.Generates the required fra me and maste rfr am e identification codes, combinesthes e codes with the digital and encodedanalog data, and arran ges the desiredser ial f ormat for output.

a Pro vid es a 600-kilohertz FM modulatedcar r ie r as the DDAS output, and a n NRZmodulating output for the PCM RFAssembly.

a Provides the synchronization outputsnece ssary to synchronize the Mod 270Multiplexer Assemblies and remotedigital submultiplexers.

Figure 5.4-5 is a functional block dia gram ofthe Mod 301 PCM/DDAS Assembly . It compo sed ofthe si x functional sub syst ems lis ted below:

a PAM scanner (and associated p rogra mpatch).

a Analog-to-digital converter.


29/55

Astrionics SysteSection 5

8 Digital multiplexing and formati ng logic. Analog-to-Digital Conver ter. The analog-to- digitconverter encodes the PAM signals received throug8 Clock programming and timing logic. the PAM scanner by the su ccessiv e approximation

8 DDAS voltage contro lled oscillator .8 Power supplies.

PAM Scanner. The PAM scanne r connects one o rmore Mod 270 Multiplexer Assembly outputs in aprogram med sequence to the ADC input for digitizing.By means of the scanner progra m patch, any multi-plexer arrange ment compatible with the system ap-plication can be accomodated. Up to thre e multiplexerarrange ments (modes) may be programmed at th escan ner patch, and the automat ic switching betweenmodes is accomplished by applying external 28-voltdc commands.

The scanner gates a r e 4-transistor, back-to-back, balanced configurations which switch both legsof the PAM ci rc ui t of each PAM multiplexer. Thetra nsf orm er coupling of t he switching logic input ofthe gates provides a favorable impedance conditionfor the PAM signals.

method. The digital output is fed in parallel form ta parallel storage register according to commandsreceived fro m the programming and timing logic.Figure 5.4-6 shows a functional block diag ram ofthe ADC. It s operati on is non-synchronous (notsynchronized with other pa rts of the system) and a ta clock rat e of approximate ly 250 kilohe rtz which iprovided by a blocking oscillato r.

Encoder command pulses a t the sys tem worrate a r e provided by the programming logic. Whenan encode command is received by the ADC, it began encode cycle at its own clock rate; this requ iresapproximately 56 microseconds. At the end of thecycle, the ADC regi ste r swi tches have been se t to digital equivalent of the analog quantity present at tbuffer input during the encode cycle. The logic levfrom the regi ster switches provide a parallel digitaoutput until the next encode command ar riv es . Thereg iste r switches ar e then res et and a new encodecycle follows.

The PAM scann er and program patch ar e pack-aged on printed circ uit c ard s which plug into the Mod Digital Multiplexing and Formating Logic (See Fig u301 PCM/DDAS Assembly. 5.4-7). The function of the digita l multiplexing and

Digital Inputs

Parallel Outputto DDAS/CompInterface Unit

from RDSMand RDM

DDAS Outputto ESE

- erial PCMto RF Xmtr

DigitalMultiplexing&

FormatingPA MWavetrains I

(from up to six

Sync toPAM Comm

A DCPCl-10

Sync toRemote

Mod 270) 6 A

DigitalSub-Mux's

: ;:( I:, ;;,,

Mode 2Command b

Mode 3 +Command

Figure 5 . 4 - 5 General Block Diagram - PCM/DDAS ~ s s e m b l ~

Clock Timing & Programming Logic

4

ProgramPatch

PC MSerial

t600HzV C O -


30/55

Astrionics SystemSection 5.4formating logic is to combine the encoded data fromthe ADC, exte rnally generated digital data, and fr am e(and mast er fra me) identification words into the r e-quired output sequence. The specific time slo t intowhich data is inserted is controlled by commandpulses fr om the programming and timing logic. The10-bit output of the ADC is transf erred into the parallalstora ge regi ste r by each word rat e clock pulse (solong as the encoder inhibit bus is unenergized). Whenthe encoder inhibit bus in energized, the ten AND gatesa t the ADC output a r e disabled, and the ADC output isnot transferred into the parallel storage register.

Up to ten 10-bit groups of digital dat a fromexternal sou rce s can be programmed into selectedtime s lot s at any of the four syst em sampling rates.The data is accepted in parallel. A zero-volt levelrepresents a logical "0" and a positive level repr ese ntsa logical "1". Inputs ar e buffered and then shiftedinto a magnetic core r egi ste r before being transferr edinto the par all el stora ge reg ist er. The MCR providestem pora ry sto rag e and dc isolation of the data source.Each MCR, along with its ten associat ed buffers andother circ uits, i s powered by an individual supplywhich is dc isolated. This p erm its monitoring ofse ve ra l digital data s our ce s without interconnectingtheir dc commons.

A WRITE command to an MCR causes the 10bits of data to be stor ed in the magnetic core s. TheWRITE command is programmed (at the commandprogram patch) to occur before the time for transferof the data into the PSR. Typically, the commandocc urs during the previous word time, but it can beprogrammed to occur a t any word time aft er theprevious sample of the specific channel is read intothe PSR. For example, sever al 10-bit data set s canbe writte n into the ir MCRfs simultaneously and thenplaced into specific time slots in the output format.This mode of o perat ion is utilized in monitoring a40-bit s e t of data fr om the LVDC.

The READ command to the MCR is timed totra nsf er the data into the output reg is te r during theleas t significant bit tim e of the previous word time.READ commands a re als o ORfd together to providea function for inhibiting the transfer to ADC datathrough the encoder gate.

The digital input section has 10 channels. Eachchannel will accept a 10-bit input in parallel form.To inc rea se the data handling capacity, the inputsection may be fed from 10-channel remote digitalsubmultiplexers.

Figure 5.4-6 Analog-to-Digital Co nvert er Block Diagram5.4-14

>

Buffer) Comparator 4- LadderArnpl fi er Network

ReferenceVoltageRegulator

tPAM fromScanner Register ADC Output to

Switch Digita l Mux

EncodeCommand

from + Set-ResetProgramming LogicLogic

Encoder Block ing CounterCommand OsciI ator and

250 kHz Matrix

IBM ~ 1 8 1i


31/55

Astrionics SystemSection 5.

1

The fra me identification logic generates threeunique code groups and ins er ts the m consecutivelyduring the l as t thr ee word ti mes of the PCM/DDASfram e. Once each 30th fram e, the fra me ID logicreceives a signal from the frame ID reversa l flipflop. This signal cau ses the fr am e ID logic to com-plement (rev erse ) all bits i n the fram e ID code ofthe 30th frame. This forms the master frame identifi-cation code. The code group is as follows:

Word 29B 1 0 1 1 0 1 1 1 1 0Word 30A 1 0 1 0 0 0 1 0 0 1Word 30B 1 1 0 0 0 0 0 1 1 0

The seria lizin g logic shif ts the contents of thePSR bit-by-bit into the NRZ fl ip flop thus forming these ri al NRZ output. The st at es of the bits per wordcounter ar e decoded, combined with the PSR outputsand clocked to provide set-reset pulses to the NRZflip flop. The two complementa ry outpu ts of the NRZflip flop a r e buffered and provided at a n output con-nector f or use a s a modulating input to the PCM/RFAssembly. One sid e of the NRZ flip flop provides amodulating input to the DDAS/VCO.Clock, Programmi ng, and Timin g Logic. (See Figu5.4-8) The clock, programming, and timing logicprovides the timing signals nec essa ry for the Mod

B / W CounterStates fromPGMR OutputF/FADC Ou tpu t 10 Lines

Inh ibi t Bus ~~~~d~~b Gate

Word RateC lock --

Read -ommand

Figure 5.4-7 Digital Multiplexing and Formating Logic5 . 4 - 1


32/55

strionics SystemSection 5. 4

Figure 5.4-8 Clock Programmi ng and Timing Logic Block Diagram5.4-16

Clear PulseTo PSR

+ Read Clockto Encoder

Gate, MCR's,Frame ID

To Counter StatesSerializingLogic Bit Rate Clock Count No. 2D D - D . - Logic

EncodeCommandto ADC

A

72 kHzClock

7200 Hzv

Group Write Clock

+B PCounter(;lo)

-

Counteri

Synchronizing 3600 Hz 1) -Signals to +Counter States

-

-

Digital 2 1

ReadCommands

Submultiplexers r4 PPSSynchronizing 4

Signals to 3600 pps II

Multiplexers to MCR's120 Hz CommandCommSync

4 1 ProgramPatch

V (CPP)

\ L Pogic WriteCommandsto MCR's

To YFrame ID

Logic

IBM B183

Comm

Mode4 CommandsScanner Gating

L.) Counter+ 3 Program SignalsPatch to PAMSwitches


33/55


301 PCM/DDAS Assembly a s will as signa ls requ iredto synchronize logic in other telemetr y assemblies.

One phase of the 72-kilohertz clock providesbit r at e pulses t o the serializing logic while the otherphase ste ps the B/W counter. The outputs from eachtrigge r of the B/ W counter a r e decoded in the se ria l-izing logic and used to sele ct st age s of t he PSR to formthe s er ia l bit tra in which controls the NRZ flip flop.

Count "2" of the B/W counter is decoded andinitiates a se ri es of three suc cessive timing pulseswhich a r e 1. 75 microseconds apart. The fir st (clear)pulse occ urs approximately 2 microseconds a fter thelea st significant bit is tra nsf err ed to the NRZ flip flopand res et s al l 10 stage s of the PSR. The second pulse(READ clock) provides the correct timing phase for thetr an sf er of d ata into the PSR fr om the ADC, the fram eID logic, o r an MCR. The thi rd pulse (WRITE clock)provides the pr oper phasing for writing external digitalwords into the MCR's. This pulse als o signals theADC to proceed with digitizing the succeeding analogsignal.

The re se t pulse of the B/W counter ste ps thegroup counter. This pulse occ urs during the 2 bittime bec ause of offset in the seri aliz ing logic. Thisallows set tling time f or the analog data inputs, (whicha r e gated by the s canne r in synchronism with the groupcounter) before the ADC begins digitizing. The groupcounter is a divide-by-two counter (one fli p flop).

The re se t pulse of the group counter ste ps thechannel counter at a ra te of 3600 pps. This consis tsof a divide-by-five counter and a divide-by-six counterwhich together fo rm a divide-by-thirty counter.

The re se t of the channel counter steps thedivide-by-ten fr am e counter and the divide-by-threemultiplexer counter. Both of thes e counters a r estepped at the PCM/DDAS fra me repetition r at e of120 times per second.

Th e 4 counters define each time s lot in thePCM/DDAS format, The divide-by-two group counterprovid es the timing for the interlacing of two multiplexergroups. Each group is compr ised of up to thr ee Mod270 Multipl exers which a r e cont rolled by the divide-by-thr ee multiplexer counter, The divide-by-three multi-plexe r counter provides timing for the sharin g ofspecific mainframe time slots. The divide-by-thirtychannel counter st eps in syc hronis m with the samplingact ion of the 30 by 120-channel analog gate s (eachsampled 120 times per second) in the Mod 270 Multi-

plexer Assemblies. The divide-by-ten fr am e counterste ps in synchronis m with the 10 by 12 submultiplexe(10 gates sampled 12 times per second).

The counts of each of the 4 counters a r e decodand routed to the command pro gra m patch. A programing arr ang eme nt provides selection of READ andWRITE commands corresponding to specific time slotThese commands provide the timing signals to theMCR's nec ess ary to place ext ernal digital data inputsinto a spe cif ic format. Decoded outputs of the groupcounter and multi~lexer ounter are also routed tothe scanner progr am patch, which provides selectionof the multiplexer scanning sequence. Up to th re emultiplexer-scanning sequences may be programmedon the scan ner program patch. A specific sequenceis selectable by an externally generated mode com-mand. The mode commands a r e 28-volt dc signa lsfro m GSE, the vehicle command, or other sou rce sapp rop ria te to the application. (Note: Mode 1 doesnot re qui re application of a n externa l mode commandvoltage. )

The control logic als o genera tes 3 se ts of wavforms used for synchronizing logic in other asse mblieto the clock and fra me r at es of t he Mod 301 PCM/DDAAssembly. Two se ts of waveforms provide the cor rewaveform shape, frequency, and phase for synchroniing Mod 270 Tim e Division Mult iplexers. The twowaveform s et s a re identical except for the offset inphase nec essa ry for interlacing group A and group Bmultiplexers. Each se t con sis ts of a 3600-hertzsqu are wave and a 278-microsecond pulse with arepetition rat e of 4 time s per second.

The third waveform s et cons ists of an outputfro m each stage of the divide-by-ten fr am e counterand a 3600-hertz squ ar e wave. Thi s s e t of waveformis utilized to synchronize remote digital submulti-plexer assemblies.DDAS Voltage Controlled Oscillator. The DDAS/VCOprovides an FM modulated carrier (600 kilohertz)fo r tra nsm iss ion of the PCM/DDAS signal (vi a coax ialcable) to DDAS receiving equipment.

A 600-hertz tra nsi sto r multivibrator is biasmodulated by the serial NRZ data. An amplifierpreceding the multivibrator pr es ent s an impedanceof approximate ly 50 kilohms to the NRZ data inputand als o provides a non-linear modulating char act er-istic which makes the frequency deviation relativelyinsensitive to variations in the input data logic levels.A frequ ency deviation of a pproximate ly * 35 kilohertzis used.


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A common-collector buffer stage drives a filterwhich is designed to remove harmonics from the multi-vi bra tor output. This output stag e deli vers a nominal75 megawatts t o a 100-ohm load.Power Supplies. There a re six separate powersupp lies u sed in the Mod 301 PCM/DDAS Assembly.

A 28 Vdc-to-28 Vdc conver ter reg ulat es thepri mar y 28 Vdc power to the assembly and isolatesthe di gital r et ur n in the Mod 301 PCM/DDAS Assemblyfro m the vehicle 28 Vdc retur n line. It supplies 28 Vdc

1 percent a t a nominal 25 watts output to the remain-ing power supplies in the sy stem.

The 6 Vdc card accepts + 28

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