1959 Enslein: Twvo Economical Circuits for High-Speed Checking of Contact Closures 51

emission may be anticipated. If such emission is prob-G A S able, then its effect upon the instrument readings must

be evaluated for the unique case involved.MULTI-CHANNEL ACKNOWLEDGEMENTNOZZLE

The authors wish to acknowledge the support andencouragement offered by Dr. Orville Harris, Director

PROBE i/ --- of the Engineering Experiment Station of the Univer-sity of Virginia.

ELECTROMETEF / \--<ELEC/.\TRO COSINE DENSITYTUBE COIEDNIYBIBLIOGRAPHYTUBEJGRDLEAD DISTRIBUTION

[1] J. A. Victoreen, "Electrometer tubes for measurement of smallFig. 8-Probe arrangement. currents," PROC. IRE, Vol. 37, Pp. 432-441; April, 1949.

[2] D. L. Collins, "Electrometer tubes," Instruments, vol. 26, p.1708; November, 1953.

[31 J. R. Keithley, "Vacuum-tube electrometer applications," Instru.It was nientioned at the beginning of this paper that ments, vol. 25, p. 458; April, 1952.probe surface emission can become an important factor. [41 G. F. Metcalf and B. T. Thompson, "A low grid current vacuum

tube," Phys. Rev., vol. 36, p. 1489; 1930.If ions or metastable atoms possessing a combination of [51 L. B. Loeb, Basic Processes of Gaseous Electronics, University ofkinetic or potential energv, or both, equal to twice the California Press, Berkeley; 1955.

[61 G. R. Partridge, Principles of Electronic Instruments, Prentice-probe surface work function are present, then surface Hall Inc., New York, N. Y.; 1958.

Two Economical Circuits for Hhh-SpeedChecking 0f Contact Closures*

KURT ENSLEINt

I. INTRODUCTION I I. DESCRIPTION OF METHOD

N many circuits utilizing relays in definite arrays, There are basically two ways of performing a paritythe need exists for checking that the contacts have or one-out-of-N check. The first method described inproperly operated. For example, in the perforated Keister, Ritchie and Washburn' is essentially a parallel

tape reader, it is often necessary to parity-check the checking operation. The second, embodied in this pa-contact closures resulting from the code just read. per, consists of looking at the contacts one at a timeAnother example is that of an electromechanical stor- and counting the contact closures. While this method isage device in which one and only one of N relays must generally included in many digital computers for paritybe picked up to signify the storage of one and only one or biquinary checking purposes, the embodiment of thedigit. logic is generally suited to microsecond operation. The

Keister, Ritchie and Washburn' describe several result is that the logic is generally more complicatedtypes of relay circuits that can perform the types of and expensive than that which is justified for operationchecks to be detailed here. However, these relay circuits in the millisecond range. This latter range is compatibleare necessarily slow, since they operate at relay speeds. with the operation time of the relay contacts to beThis speed restriction proves to be cumbersome in some checked.applications. The method described in the present paper Referring now to Fig. 1, we have the block diagramcircumvents the speed restrictions inherent in relay- of one method of implementing the counting ideas withtype contact checking circuitry, and still accomplishes economical components. The system basically consiststhis function at moderate cost. of a vacuum tube, bistable circuits, a glow-tube dis-

tributor, and two thyratrons, coupled through invertersManuscript ~~~~~~~~anddrivers. A 2,000-pps clock drives the entire system.* Mnucrptreceived by the PGJ, March 20, 1959. Le'snwaayeteoerto fti ytm s

t Brooks Research, Inc., Rochester, N. Y. Ltu o nlz h prto ft1 ytm s1 W. Keister, A. E. Ritchie and S. H. Washburn, "The Design of sume that the system is in the condition shown in Fig. 1Switching Circuits," D. Van Nostrand Co., Inc., New York, N. Y. ihtego,f h itiuo nvse nis1tpp. 298-299, 427-443; 1951. thtego oftedsrbt nvtdonlS1h

52 IRE TRANSACTIONS ON INSTRUMENTATION September

VIIST, IFLUTORINVERTtR R GLOW-TUBE c,S z2 i)I/Z ILAl7 FD 0 Z 3 4E 5 6 1 8 9 '0 110 ~~~~12-AX7 1

GATE P.abE-4GAS56RE6

START CONTACTS TO .i _bECQEcC0;_F - T_r -r Tr T T

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Fig. 1-One and only one out of ten checking logic.

cathode. A START pulse sets flip-flop 1 to its ON state TABLE Iand enables gate 1. The first clock pulse is then allowed OUTPUT INDICATION FOR FIG. 1to come through gate 1 to the glown-tube driver. The0Ofglow-tube driver steps the glow-tube from the no. 11 1=On(reset) position to the zero position. The cathodes ofthe glow-tube are connected through resistors to the Number of |Lightsground. To each cathode is connected one of the con- Closed Contacts "0" ">1"tacts to be checked. Thus, if the contact connected to 0 1 0the zero cathode is closed, a signal will be propagated 1 0 0through gateS5 to inverter 3 and thus through gate 4 to 2 1 1FF2. We will analyze this action later. Five hundred mi- 4croseconds later another clock pulse is produced and fed 6c 1 1through gate 1, driving the glow-tube driver, which, in 7 o 1turn, steps the distributor by one position. This action 0 1continues through distributor position 10. The output 10 1 1from position 10 is used to sample gate 2. This functionwill be described below. Finally the glow comes to rest case none, or an even number of contacts, were closed,again on cathode 11 of the distributor. At this time a gate 2 will be enabled at the sampling time and thyra-RESET pulse is produced which drives inverter 1, and tron 1 will fire, thus indicating that none, or an eventhus resets FF1 to its original state. This, in turn, turns number of closed contacts, were encountered.off gate 1 and no further clock pulses are allowed to When FF2 reverts from its SET state to the RESETpass through this gate. The distributor thus rests on its state, which would happen for the first time on the sec-11th cathode ti next START pulse is fed to FF1. ond contact closure, a positive pulse is sent from FF2Thus we see how the sampling of the contacts, one at a to gate 3. The other input lead of this gate has beentime, is accomplished, enabled by FF1 after the start of the testing cycle. Thus,Now we proceed to the interpretation of the informa- thyratron 2 will firevhen the second closed contact in a

tion. From the explanation of the sampling, it has been sequence is detected.seen that a pulse is fed to the binary FF2 every time One more function is that of resettingFFt2 at the endthat a closed contact is encountered. Thus, FF2 will of a checking cycle. This is accomplished by sending achange state for every closed contact encountered. If positive pulse from FF1 to inverter 2 to reset FF2. Thisonly one contact is encountered during the entire se- positive pulse is derived from the resetting of FF1.quence, at the time that the distributor steps to cathode Table I shows the type of indication that will be ob-11, gate 2 will be disabled and the occurrence of the tamed from this system for the various types of errors.sampling pulse will not result in any further action. In The speed of this system is fundamentally limited by

1959 Enslein: Two Economical Circuits for High-Speed Checking of Contact Closures s3

- DELAY X D\EA

GATE 1I/ 1 3 bISrPBUTOR

____ -______ l r

THY-ATRc_N ERROR"TESTCOMPLETE MANUAL RESET

5TAR- _RCONTACTS TO T

13E CHECKED/

REUSET CoNPAcTI

Fig. 2-One and only one out of ten checking logic (alternate logic).

the speed of the glow-tube distributor. The particular 10, at which time the state of the counter is sampled as-tube used here has a maximum counting capability of explained below. The next step of the distributor en-4,000 pps, thus permitting the entire one-out-of-10 se- ables cathode 11 and a TEST COMPLETE signal isquence together with the setting and resetting to be produced from this cathode. The distributor then stopscompleted in approximately 3 milliseconds. Other tubes at this cathode, thus completing the cycle.are available which permit counting speeds up to 20,000 Every time that the distributor reached one of thepps. With these, total checking times on the order of zero- through-9 cathodes to which a closed contact is700 microseconds can easily be achieved. connected, a pulse was sent through gate 3 which fed

driver 2 which, in turn, caused stepping of the counter.III. ALTERNATE APPROACH Thus counter 2 contains a record of the number of closed

Fig. 2 shows a different logic which accomplishes the contacts that were encountered during the distributorsame function. In this case, the indicator lights have cycle. Thus, by connecting the cathodes of the counterbeen replaced and augmented by a counter which can as shown, if the state of the counter is anything but theindicate how many contact closures were sensed during no. 1 position at the time of sampling (that is when-any one testing sequence. This logic has the decided ad- the distributor reaches its position 10), gate 2 will pro-vantage of permitting ready identification of the source duce a pulse and the thyratron will fire, lighting the er-of difficulty as well as permitting, by proper connection, ror light. At the same time, it will be possible to readthe print-out of the error information in more detail off the number of closed contacts that had been encoun--than possible with the circuit of Fig. 1. tered from the position of the glow-tube counter.The logic of Fig. 2 operates as follows. Assume that It can be seen that the advantage of the logic of Fig.

-the glow-tube distributor is on its no. 11 cathode (re- 2 is to simplify considerably the flow of information,set position), and the glow-tube counter is on its no. 10 and thereby to mnake a more reliable system. In ad-cathode (also reset position). A START pulse is now fed dition, more data are available at the end of the checkinlgthrough gate 1 and a delay circuit. This pulse causes sequence than for the logic of Fig. 1. The disadvantagedriver 1 to generate a pulse which advances the distribu- of this alternate logic lies in the fact that an accidentallytor from its no. 11 to its no. zero position. The no. zero grounded contact will cause the system to stop on acathode signal is then fed into gate 1 which again emits particular distributor cathode. This problem can beia pulse to the delay circuit which in turn feeds driver 1, remedied by further complication of the logic, but ifcausing the distributor to advance by another position. the probability of this type of event is high, the circuitIn this way, we eventually arrive at distributor position of Fig. 1 is to be preferred to that of Fig. 2.

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1959 Otterman: Optimization of the Aperture Corrective Systems 55

IV. OTHER APPLICATIONS state device because of the level at which the inputIt is obvious from the description of the two systems resides.

of logic that it is possible to count in modulos other 2) The thyratrons (V722 and V723) are combinedthan 10 by simple reconnection of the distributor and/or with Gate 2 and Gate 3. In this way we have savedcounter cathodes. For example, parity checking is very a number of components and thereby enhance thesimply accomplished in the circuit of Fig. 1 by eliminat- reliability of the system to some extent.ing thyratron 2 and gate 3. One-out-of-five checking 3) Fig. 3 shows the system as it includes a steppingcould be accomplished by connecting the cathodes of switch distributor, as mentioned in Section IV ofthe distributor in pairs, and so on. In addition, it is pos- this paper, to share the checking circuitry amontgsible to check the operation of rather complex systems, several contact banks. This is evidenced by the ter-such as crossbar switches, by inserting an electro- minations called "to sample contacts" and by themechanical distributor, such as a stepping switch, be- wire going to the grid of V720B. If only one banktween the glow-tube distributor and the contacts to be of contacts is to be checked, then these contactschecked, to enable certain banks of contacts at certain appear between terminals 24-33 and the wire la-times. This means that a distributor checking system, beled 12K701,R.such as that described, can be shared among many The remaining circuitry in this system is quite con-banks of similar contact structures. ventional and will not be detailed here.

V. EMBODIMENT OF LOGIC OF FIG. 1 VI. CONCLUSION

Fig. 3 is an embodiment of the logic of Fig. 1. The de- We have described in this paper both the logic andscription of the functions of the various tubes of the sys- embodiment of a method that permits economical par-tem explain their use in terms of Fig. 1 and wAill not be ity, and, in general, contact closure checking in mediumdetailed here. However, the following points may be of speed data processing systems. The functions are ac-interest: complished by means of simple, reliable circuitry and

1) V717 is a vacuum-tube gate rather than a solid- should be usable in a variety of applications.

Optimization of the Aperture Corrective Systems*JOSEPH OTTERMANt

INTRODUCTION AND SUMMARY SYSTEMATIc DISTORTION AND RANDOM DISTORTION

I N a previous paper1 networks have been described A rectangular aperture has the transfer functionthat offset the averaging effect, inherent in many sin (ao/2)sensing devices, which is known as the aperture ef- f()= hI eI _iaco (1)

fect. In this paper comparison of a system with and co2without the corrective network is carried out and the where a is the aperture length in units of time and h isoptimization of the aperture length under different noise the sensitivity. This transfer function causes distortion,conditions and under different optimization criteria is the nature of which has been discussed in the previousdiscussed. paper1 and several of its references. The distortion canThe discussion will be concerned with rectangular be referred to as systematic distortion, since it always

apertures and with exponential apertures. Rectangular exists.shape will be implied unless an exponential aperture is In carrying out the analysis of possible improvementsspecifically indicated. in performance offered by the corrective networks, it

has to be remembered that arbitrarily small systematic* Mauscrptrceied b thePGI May8, 159.distortion can be achieved in a system consisting only

t VVTllow Run Laboratories, The University of Michigan, Ann of the sensing device, if the length a of the aperture isArbor, Mich. dcesdEe fi eetcnclyfail ordc1 Joseph Otterman, "Aperture corrective systems," IRE TRANS.derad.EniftwreecialyesbetoeueON INSTRUMENTATION, VOl. I-8, pp. 8-19; March, 1959. the length of the aperture indefinitely, the system would