presented by: Bill Griffith

presented by:

Bill Griffith

Product Characterization Through Data Logging

Product Characterization Through Data Logging

April 3, 2002

Click to edit Master subtitle style

Page 2

• Why perform product characterization

• Data logging system overview

• Sensors

• Signal Conditioning

• Multiplexing / Switching

• Analog to Digital Converter

• PC Connectivity

• An example of characterizing a power supply

• Questions and answers

Product characterization through data loggingDAC Back to BasicsDAC Back to Basics

And, how to make better

measurements!


Page 3

• Does it meet design goals?

• Does it meet standards (UL,CUL,CSA, GS/TUV,CE, etc.)?

• Is it reliable?

• Can it be manufactured ?

• Is it energy efficient?

• Is the product safe?

The use of measurements on a product or design to verify proper operation

What is Product CharacterizationWhat is Product Characterization

Automated test can collect more data

and will have more repeatable results


Page 4

Product CharacterizationProduct Characterization

• PC board / Components

• Life / Durability tests

• Operation vs. temp and humidity

• Noise, accuracy, gain checks

• Incoming value screening

• Battery Tests

• Charge / Discharge rates

• Life test

• Temperature Rise

Some examples

Temperature is the most common

measurement- typically changes

slowly


Page 5

Product CharacterizationProduct Characterization

• Mechanical Enclosures• Heat rise, hot spots

• Cooling effectiveness

• Air flow

• Whole Product• Environmental tests (extreme

temp and humidity)

• Standards (UL, CE, etc.)

• Specification development - through margin analysis

• Reliability - Vibration, Stress Tests

Some more examples


Page 6

• Reliability

• Changes in temperature create mechanical stress

• Strain will lead to failure

• Possible safety issues

• Temperature changes can occur during power up or thermal gradients caused by hot spots

Temperature can affect reliabilityWhy Product CharacterizationWhy Product Characterization

• Hot spots can be caused by:

• Components

• Dead air spots


Page 7

• Performance

• A change in temperature can cause frequency drift

• In addition, voltage can change with temperature

• Temperature can affect energy efficiency

Temperature can affect performanceWhy Product CharacterizationWhy Product Characterization

• Solutions - reduce differences in temperature

• Add vents

• Add fan - optimize design (size, cost, quiet operation, power consumption, magnetic flux)

Hitachi has developed what it says is the first water cooled laptop. The machine has no fan to cool its CPU.


Page 8

• Power Supply - unique challenges• Smaller transformer often more desirable

• drawbacks include less efficiency and more heat

• Transformers create more heat at lower frequencies

• Measurement challenges• Magnetic flux and RF energy can interfere with

temperature measurements • Parts maybe grounded creating potential ground

loops with instruments used to measure temperature

An example of product characterizationWhy Product CharacterizationWhy Product Characterization


Page 9

• Most common measurements include:• Temp, DCV, Current, ACV, Frequency, and Events

• Measurement characteristics include:• Multiple inputs: typically < 20 channels

• Relatively slow reading rates: ~ 1 channel/sec

• Standalone or PC-connected: Most analysis done in a PC

• Data storage: Electronic memory or documented on paper

Product characterization is the process of using electrical and physical measurements to gain insight and improve a design

Why Product CharacterizationWhy Product Characterization


Page 10

OverviewData Logger System ArchitectureData Logger System Architecture

TransducerSignal

ConditioningMultiplexer

Digital Multimeter

(DMM)

Display Analysis & Reporting

A/D 28.32 C

MON

VIEW

SCAN

Consider PC connectivity - Cables - Adapters - SW


Page 11

Data Logger System - TransducersData Logger System - Transducers

• Temperature

• Flow

• Pressure

• Strain

• Position

• Weight

• Speed

TransducerTransducer

• dc Volts

• ac Volts

• dc current

• ac current

• Resistance

• Frequency

Physical Parameters Electrical Signals

Physical parameter to electrical signal

Choose the correct sensorMount it correctlyPosition it correctly


Page 12


• Thermal mass• Don’t let the measuring device

change the temperature of what you are measuring

• Response time is a function of the mass of the sensor and the mass of object being measured

Temperature background

Dewar• Glass is a poor conductor• Gap reduces conduction• Metallization reflects radiation• Vacuum reduces convection

• How is heat transferred

Sensor


Page 13


• What is your normal temperature?

• Thermometer resolution, accuracy

• Contact time

• Thermal mass of tongue, thermometer

• Human error in reading

Making temperature measurements

97.6 98.6 99.6 36.5 37 37.5


Page 14


• Need accurate, sensitive measurements--

• J-type thermocouple

at room temp = < 1 mV

• A 1C change at 0C =

50.38 V• To see a 0.1C change

in a J-type TC at 0C, your instrument must be able to resolve down to 5 V.

Thermocouples

VVABAB

++

--

Metal AMetal A

Metal BMetal B

• Good junction•Thermal shunting• Noise and leakage current•Thermocouple specs• Calibration of TC


Page 15


Thermocouples - Gradient Theory

Metal AMetal AVVAXAX++ --

Metal BMetal B

TXTA

TB

• The wire is the sensor, not the junction

• Heating one end of a wire creates a voltage Vax

• The voltage is a non-linear function dependent on wire type and the temperature difference from one end of the wire to the other

• The Seebeck coefficient (e) is used to quantify the voltage that is created

VVABAB

++

--

Ta

Tx

Tx

Tb

+eAdT eBdTVAB =


Page 16

• If a “thermocouple junction” is made with two wires of the same metal - what voltage would the TC produced (VAB)?

a) 2*VAX - twice the gradient voltage of metal A

b) No voltage

c) Can’t determined without knowing the temperature difference

d) Can’t determine without knowing the metal type



VVABAB

++

--Metal AMetal A

TxTa

Tb

Metal AMetal AVVAXAX++ --


Page 17


• We are taking a deeper look at how measurements are made - a lot of the details are handled by the data logger

• The architecture that we have presented makes it possible to connect any type of transducer to any channel.

• Simply setup the data logger with the type of transducer and channel information

• The data logger will make the necessary measurements, conversions and display the correct results in scientific units

A modern data logger will make it easy to make measurements


Page 18


• For more details on making temperature measurements - see application note 290.

More information is available

• Having a good understanding of transducers will allow us to make better measurements• In order to make good measurements - care has to be taken


Page 19



• If a thermocouple was made of a single metal Metal A the TC would produce zero volts

• Two different metals are combined to create a TC

• How do you measure a TC?

VVABAB

++

--Metal BMetal B

TxTa

Tb

VVAXAX++ --Metal AMetal A

VV++

--

Metal AMetal A

Metal BMetal B

Metal CMetal C

Metal CMetal C

Tx

Click to edit Master subtitle style• Create a reference

junction

• Measure Tref using thermistor

• Lookup Vref for TC at reference junction

• Compute Vx = V+Vref

• Solve for Tx using Vx 0 Tref

Vx

Vref

Tx

ComputeVx=V+Vref V

o

Data Logger System - TransducersData Logger System - TransducersThermocouples - How to measure a TC

Tref

VVXX

Metal AMetal A

Metal BMetal B

Metal CMetal C

Metal CMetal C

Tx VV++

--


Page 21

Data Logger System - TransducersData Logger System - TransducersThermocouples - Common Types

0 500 1000 2000

mV

deg C

20

40

60

EE

R

NKJ

E

ST

Platinum T/CsBase Metal T/Cs


Page 22


• Better accuracy and more expensive

• Absolute temperature

• A common thermistor

type has 5000 at

25C with 4%/ C

• 1C = 200 • 10 of lead resistance

would cause a .05 C error

Thermistor

RRmeasmeas

++

--

Rtemp

Often physically small mass• Won’t cause thermal loading • A large measurement current will cause self heating

Rlead

Rlead


Page 23


• RTDs • Absolute measurement• Accurate measurement• A common RTD has 100

at 0C with .385 / C • 10 of lead resistance

would cause a 26 C error

RTD - Resistance Temperature Detector

• Avoid self heating, a 5 mA current source would create 2.5 mW of power in our RTD. • At 1 mW/ºC, that is an error of 2.5/ºC

iRtemp

Rlead

Rlead

VV++

--

RTD

+ Vlead -

+ Vlead -

DMM

R=V/i


Page 24

Data Logger System - TransducersData Logger System - TransducersRTD - Four wire ohm measurement

I=0

I=0

iRlead

Rlead

Rlead

Rlead

R=V/i

V V

++

--Rtemp

RTD

• For more information on 4-wire ohm measurements see application note 1389-2

DMM

V=Vtemp=i*Rtemp

Rtemp=V/i


Page 25


• Linear change in voltage or current with change in temperature

• 10 mV/K (voltage IC)

• Room temp approx. 3V with

a 10mV/°C change

OR

• 1 A/K (current IC)• Need an external power

source• Absolute measurement

IC - Temperature sensor

VVtemptemp

++

--

• Have limited temperature range < 150 C• Fairly large mass

10mv/K v


Page 26


+ Most accurate

+ Most Stable

+ Fairly linear

- Expensive

- Slow

- Needs I source

-Self heating

-4-wire meas.

RTD Thermistor IC Thermocouple

Temperature sensors

+ High output

+ Fast

+ 2-wire meas.

- Very nonlinear

- Limited range

- Needs I source

- Self-heating

- Fragile

+ High output

+ Most linear

+ Inexpensive

- Limited variety

- Limited range

- Needs V source

- Self-heating

+ Wide variety

+ Cheap

+ Wide T. range

+ No self-heating

- Hard to measure

- Relative temperature only

- Nonlinear

- Special connectorsAbsolute temperature sensors


Page 27


• Your designing an electronic device and have included an IC temperature sensor in your design and want to verify the accuracy of the IC sensor - what type of sensor would you use with your data logger to make the measurement?

A) Thermocouple

B) RTD

C) Thermistor

D) IC Sensor

Polling Question


Page 28

OverviewData logger System ArchitectureData logger System Architecture

TransducerSignal


Digital Multimeter

(DMM)

Display Analysis & Reporting y

A/D 28.32 C

MON

VIEW

SCAN

V

V

Wiring errors


Page 29

Data Logger System - Wiring ErrorsData Logger System - Wiring Errors

• Extension wires are less expensive, more rugged, but have slightly different temperature curves than the thermocouple

Thermocouple extension wires

Long rugged extension wiresSmall diameter measurement wires Possible problem

• Keep the junction of the extension wire and the thermocouple wire near room temperature


Page 30

Data Logger System - Wiring ErrorsData Logger System - Wiring Errors

Metal AMetal A

Metal BMetal B

Common Mode Errors

DMMZL

ZH

Icom

•Make ZL as large as possible

•Avoid connections to grounds

• Common mode errors create a current into both the high and the low measurement paths

• Typically caused by a difference in grounds

H

L


Page 31

Data Logger System - Wiring ErrorsData Logger System - Wiring ErrorsNormal Mode Errors

DMM

Inorm

magneticcoupling

• Normal mode noise introduces a current that is in the same direction as the measurement current

• Magnetic flux or RF energy are common sources of normal mode errors

Reduce the size of the measurement loop - twisted pair wire - move measurement hardware closer to the source - run measurement wiresperpendicular to high current wires

V


Page 32

Data Logger System - Wiring ErrorsData Logger System - Wiring ErrorsNormal Mode Errors

Electrostatic noise

• Large ZL is important to avoid capacitance coupling through tip of thermocouple

Shielding will provide an alternative path for electrostatic energy - Only ground one end

DMM

Inorm

ZL


Page 33


TransducerSignal


Digital Multimeter

(DMM)


A/D 28.32 C

MON

VIEW

SCAN

V

V


Page 34

Data Logger - Signal ConditioningData Logger - Signal Conditioning

• Convert signal to be compatible with system• Thermocouple

reference junction

• Filter• Strain gauge bridge

completion circuit• Shunt resistor for

indirect current meas.

• Amplifier / Attenuator• AC converter

VV++

--

Metal AMetal A

Metal BMetal B

Metal CMetal C

Metal CMetal CIsothermal Reference Junctions

Signal Conditioning - Examples

VV++

--

I


Page 35

Data Logger - Signal ConditioningData Logger - Signal Conditioning

• Reduce noise that has been coupled into the signal “normal mode error”

• Allow for filter settling time

Filtermagneticcoupling

Inoise

Include lead and switch resistance,

plus lead and switch capacitance

when calculating settling time

I < InoiseV


Page 36


TransducerSignal


Digital Multimeter

(DMM)


DMM 28.32 C

MON

VIEW

SCAN

V

V


Page 37

Data Logger System - MultiplexingData Logger System - Multiplexing

2-wire, 4:1 MUX

H

L

H

L

H

L

H

L

4-wire, 2:1 MUX

H

L

H

L

H

L

H

L

1-wire, 4:1 MUX

Multiplexing - Examples

H

L

H

L

H

L

H

L


Page 38

Data Logger System - MultiplexingData Logger System - Multiplexing

FET

SolidState

Reed 300 V50 mA

6 µV1

500 ch/s 10 M16 V1 mA

25 µV1 k 100k ch/s Infinite

300 V1 A

3 µV3 200 ch/s Infinite

Armature 300 V1 A

3 µV1 60 ch/s 10 M

Typical

MAXVoltage Offset Speed Life

Switch characteristics


Page 39


TransducerSignal


Digital Multimeter

(DMM)


DMM 28.32 C

MON

VIEW

SCAN

V

V


Page 40

Data Logger System - DMMData Logger System - DMM

• Reduce the complexity of signal condition

• May only need one RMS converter

• May not need additional attenuation and amplifiers in signal conditioning

DMM - Digital Multimeter

Control and reading memory

A/D Converter

Amplifier, attenuator and shunt resistors for current

AC RMS

Current Source for resistance

H

L

ZL


Page 41

Data Logger System - DMMData Logger System - DMMNormal Mode Errors

A/D Converter

Inorm

magneticcoupling

• Normal mode noise introduces a current that is in the same direction as the measurement current

•An integrating A/D can be used to reduce normal mode noise

When using an integrating A/D the integration period will be set to line frequency - Use at least 1 PLC to reject noise - Higher frequency noise will be integrated and reduced along with power line noise


Page 42

• Normal mode noise is typically generated by large currents that have the same frequency as line frequency - integrating over one Power Line Cycle will make Vnoise=0

• Can trade off reading rate (speed) for resolution

• 1 line cycle = 60 rdgs/s

• 10 line cycles = 6 rdgs/s

Data Logger System - DMMData Logger System - DMM

VTemp

Integrating A/D Converter

Vnoise

V

T

1 PLC

2 PLCNPLC


Page 43

Data Logger System - DMMData Logger System - DMMMeasurement Characteristics• Resolution - How many bits or digits the ADC/system produces

• Repeatability - How consistent results are reading-to-reading

• Accuracy

Relative accuracy - statistical determination of error (deviation from norm)

Absolute accuracy - statistical determination of error from a traceable source


Page 44


TransducerSignal


Digital Multimeter

(DMM)

Display Analysis & Reporting

DMM 28.32 C

MON

VIEW

SCAN

System error is a sum of the error from each component - avoid noise sources!


Page 45

• Quickly setup data logger• Self guiding menus

• Make sure that you are collecting valid data• Verify setup / possibly monitor a channel• Set limits and alarms

• Upload results to PC• Create final reports in Microsoft applications

• Use away from bench• Display viewing angle• Bright in multiple lighting conditions

• Save channel setups and easily modify

Data Logger System - Reporting TasksData Logger System - Reporting TasksCommon reporting tasks


Page 46

Data Logger System- Reporting TasksData Logger System- Reporting Tasks

• Connecting to data logger• RS-232

• USB

• LAN

• GPIB

• Software• Easy to use

• Create documentation

• Compatible with Microsoft Office Apps

PC Connectivity


Page 47

Data Logger System - Reporting TasksData Logger System - Reporting Tasks

• Typically report results in Microsoft Office applications; Excel, Word, or PowerPoint

• Need a way to cut and paste graphical data into these office applications easily

• Could create a program or use an off-the-shelf application designed for the task

Creating reports


Page 48


• Although a common interface RS-232 has a couple of drawbacks

• RS-232 can be slow

• Can be difficult to find the correct cable

• USB has become prevalent and addresses the common problems of RS-232

Using RS-232 / USB

• USB to GPIB converters have made it possible to take advantage of USB and create an opportunity to take advantage of portable computers away from the bench


Page 49


• LAN connectivity has several advantages

• Fast - although not tuned for measurement data like GPIB

• Can be used over long distances

• Allows resources to be shared

• LAN to GPIB converters can take advantage of LAN capability

Using LAN connectivity


Page 50

PC Software Summary

Textual language

T&M graphical language

Free to $300

Time intensive

Medium Medium

Great

Great $600 to $1,400

Data logger SW

Quick QuickLow - product specific

Software Create Report

Make 1st Reading

Flexibility Cost

Time intensive

$300 to $1,000



Page 51

PC Connectivity Summary

USB

$0 to Low

Yes

RS-232 Yes Yes Low

Interface Common to PC

Common to Instr.

Speed Cost

$500

Distance

Short

Need an adapter

Medium Short

LAN Yes $1100Need an adapter

Fast Long

GPIB Need an adapter

$400 to $600

Yes Fast Short



Page 52

• Specified an OEM power supply to speed product development. Requirements include:

• 100 Vac - 240 Vac +/- 10% line voltage

• Characterize temperature measurements in critical areas

• Voltage stability under full load

• Voltage regulation under low line voltage

Data Logger System DemoData Logger System DemoOEM Power Supply Characterization


Page 53

• Test setup

• Data acquisition / switch unit connected to:

• Four temperature measurements using T-type thermocouples

• Four dc voltage measurements

• A PC with USB/GPIB converter

• Data logger software

• Create a report, Temperatures vs. Time, Voltage vs. Time



Page 54

• Getting Started

• Use front panel of DAC system to quickly verify voltage and temperature setup

• The PC and SW is used to automate the measurements over time

• Varied line voltage manually

• The data logger screen images were then cut and pasted into a Microsoft Word document for the final report



Page 55

Power Supply TestData Logger System DemoData Logger System Demo

A/D 28.32 C

MON

VIEW

SCAN

Vab-

Vcd-

Vef-


Page 56

TransducerSignal


Analog-to- digital

converter

Display

28.32 C

MON

VIEW

SCAN

A/D

Summary - System AccuracySummary - System Accuracy

Transducer errors

Thermal gradient

Ref transducer accuracy

Thermal EMF / Offsets

DMM - offset, noise, linearity, resolution, accuracy

Data logger temperature conversion algorithm

System accuracy is the sum of the measurement errors for each component

Additional cable errors


Page 57

• Data logger may include PC cables and software

• Data logger will make thermocouple measurements easy - built-in conversion routines, reference junction, reading storage, monitor data from display

• Data logger may specify system accuracy - to determine complete error add transducer error

• For our example the data logger specifies the system error for a T-type TC as 1oC. The TC has an error of 1oC or .75% which ever is greater. So the total error is 2oC

SummarySummaryModern Data logger - Can help

Work to minimize external sources of error

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presented by: Bill Griffith

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