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presented by: Bill Griffith

presented by: Bill Griffith. Product Characterization Through Data Logging. April 3, 2002. DAC Back to Basics. And, how to make better measurements!. Product characterization through data logging. Why perform product characterization Data logging system overview Sensors

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presented by: Bill Griffith

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  1. presented by:Bill Griffith Product Characterization Through Data Logging April 3, 2002

  2. DAC Back to Basics And, how to make better measurements! Product characterization through data logging • 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

  3. What is Product Characterization Automated test can collect more data and will have more repeatable results The use of measurements on a product or design to verify proper operation • 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?

  4. Product Characterization Temperature is the most common measurement- typically changes slowly Some examples • 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

  5. Product Characterization Some more examples • 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

  6. Why Product Characterization Temperature can affect reliability • 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 • Hot spots can be caused by: • Components • Dead air spots

  7. Why Product Characterization Temperature can affect performance • Performance • A change in temperature can cause frequency drift • In addition, voltage can change with temperature • Temperature can affect energy efficiency • 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.

  8. Why Product Characterization An example of product characterization • 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

  9. Why Product Characterization Product characterization is the process of using electrical and physical measurements to gain insight and improve a design • 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

  10. Data Logger System Architecture Consider PC connectivity - Cables - Adapters - SW Digital Multimeter (DMM) Signal Conditioning Transducer Multiplexer 28.32 C SCAN A/D MON VIEW Overview Display Analysis & Reporting

  11. Temperature Flow Pressure Strain Position Weight Speed Data Logger System - Transducers Choose the correct sensor Mount it correctly Position it correctly Physical parameter to electrical signal Physical Parameters Electrical Signals • dc Volts • ac Volts • dc current • ac current • Resistance • Frequency Transducer

  12. Data Logger System - Transducers Dewar Sensor Temperature background • How is heat transferred • 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 Glass is a poor conductor Gap reduces conduction Metallization reflects radiation Vacuum reduces convection

  13. Data Logger System - Transducers 97.6 98.6 99.6 36.5 37 37.5 Making temperature measurements • What is your normal temperature? • Thermometer resolution, accuracy • Contact time • Thermal mass of tongue, thermometer • Human error in reading

  14. Data Logger System - Transducers Good junction Thermal shunting Noise and leakage current Thermocouple specs Calibration of TC Metal A + VAB - Metal B Thermocouples • Need accurate, sensitive measurements-- • J-type thermocouple at room temp = < 1 mV • A 1C change at 0C = 50.38 V • To see a 0.1C change in a J-type TC at 0C, your instrument must be able to resolve down to 5 V.

  15. Data Logger System - Transducers VAX - + + Tx Tb + VAB   eAdT eBdT - VAB = Ta Tx Thermocouples - Gradient Theory • 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 TA Metal A TX Metal B TB

  16. Data Logger System - Transducers VAX - + Ta Tx Metal A Tb + VAB - Thermocouples - Gradient Theory • 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 Metal A

  17. Data Logger System - Transducers A modern data logger will make it easy to make measurements • 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

  18. Data Logger System - Transducers Having a good understanding of transducers will allow us to make better measurements In order to make good measurements - care has to be taken More information is available • For more details on making temperature measurements - see application note 290.

  19. Data Logger System - Transducers VAX - Ta + Tx Metal B Tb + + V Metal C VAB - Metal A - Tx Metal B Metal C Thermocouples - Gradient Theory • 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? Metal A

  20. Data Logger System - Transducers Metal A Metal C Tx VX Metal B Metal C + Tref V - Thermocouples - How to measure a TC • Create a reference junction • Measure Tref using thermistor • Lookup Vref for TC at reference junction • Compute Vx = V+Vref • Solve for Tx using Vx Compute Vx=V+Vref Vx V Vref Tx Tref 0 o

  21. Data Logger System - Transducers mV E E E 60 K J N 40 20 R T S deg C 0 500 1000 2000 Thermocouples - Common Types Platinum T/Cs Base Metal T/Cs

  22. Data Logger System - Transducers Often physically small mass • Won’t cause thermal loading • A large measurement current will cause self heating + Rmeas - Thermistor Rlead • Better accuracy and more expensive • Absolute temperature • A common thermistor type has 5000  at 25C with 4%/ C • 1C = 200  • 10  of lead resistance would cause a .05 C error Rtemp Rlead

  23. Data Logger System - Transducers 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 i + V - RTD - Resistance Temperature Detector DMM + Vlead - • RTDs • Absolute measurement • Accurate measurement • A common RTD has 100  at 0C with .385 / C • 10  of lead resistance would cause a 26 C error Rlead RTD Rtemp Rlead + Vlead - R=V/i

  24. Data Logger System - Transducers For more information on 4-wire ohm measurements see application note 1389-2 i RTD Rtemp + V - RTD - Four wire ohm measurement DMM Rlead I=0 V=Vtemp=i*Rtemp Rtemp=V/i Rlead Rlead R=V/i I=0 Rlead

  25. Data Logger System - Transducers Have limited temperature range < 150 C Fairly large mass v + Vtemp - IC - Temperature sensor • 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 10mv/K

  26. Data Logger System - Transducers Temperature sensors IC Thermocouple RTD Thermistor • Most accurate • Most Stable • Fairly linear • Expensive • Slow • Needs I source • Self heating • 4-wire meas. • 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 connectors Absolute temperature sensors

  27. Data Logger System - Transducers Polling Question • 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

  28. Data logger System Architecture Digital Multimeter (DMM) Signal Conditioning Transducer Multiplexer 28.32 C SCAN MON V V VIEW Overview Display Analysis & Reporting y A/D Wiring errors

  29. Data Logger System - Wiring Errors Keep the junction of the extension wire and the thermocouple wire near room temperature Thermocouple extension wires • Extension wires are less expensive, more rugged, but have slightly different temperature curves than the thermocouple Long rugged extension wires Small diameter measurement wires Possible problem

  30. Data Logger System - Wiring Errors H L Common Mode Errors Metal A ZH Metal B DMM ZL Icom Common mode errors create a current into both the high and the low measurement paths Typically caused by a difference in grounds Make ZL as large as possible Avoid connections to grounds

  31. Data Logger System - Wiring Errors V Normal Mode Errors magnetic coupling Inorm DMM Reduce the size of the measurement loop - twisted pair wire - move measurement hardware closer to the source - run measurement wires perpendicular to high current wires 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

  32. Data Logger System - Wiring Errors Normal Mode Errors Electrostatic noise Inorm DMM ZL Shielding will provide an alternative path for electrostatic energy - Only ground one end Large ZL is important to avoid capacitance coupling through tip of thermocouple

  33. Data logger System Architecture Digital Multimeter (DMM) Signal Conditioning Transducer Multiplexer 28.32 C SCAN MON V V VIEW Overview Display Analysis & Reporting y A/D

  34. Data Logger - Signal Conditioning I Signal Conditioning - Examples • 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 Metal A Metal C + V - Metal B Metal C Isothermal Reference Junctions + V -

  35. Data Logger - Signal Conditioning Include lead and switch resistance, plus lead and switch capacitance when calculating settling time V Filter magnetic coupling • Reduce noise that has been coupled into the signal “normal mode error” • Allow for filter settling time Inoise I < Inoise

  36. Data logger System Architecture Digital Multimeter (DMM) Signal Conditioning Transducer Multiplexer 28.32 C SCAN MON V V VIEW Overview Display Analysis & Reporting y DMM

  37. Data Logger System - Multiplexing H L H L H L H L H L H L H L H L H L H L H L H L 1-wire, 4:1 MUX 4-wire, 2:1 MUX 2-wire, 4:1 MUX Multiplexing - Examples

  38. Data Logger System - Multiplexing Typical MAX Voltage Speed Life Offset 3 µV 300 V Armature 60 ch/s 10 M 1 W 1 A 6 µV 300 V Reed 500 ch/s 10 M 50 mA W 1 16 V 25 µV Infinite FET 100k ch/s 1 mA 1 kW 3 µV Solid 300 V ch/s Infinite 200 W State 1 A 3 Switch characteristics

  39. Data logger System Architecture Digital Multimeter (DMM) Signal Conditioning Transducer Multiplexer 28.32 C SCAN MON V V VIEW Overview Display Analysis & Reporting y DMM

  40. Data Logger System - DMM DMM - Digital Multimeter H • Reduce the complexity of signal condition • May only need one RMS converter • May not need additional attenuation and amplifiers in signal conditioning AC RMS Amplifier, attenuator and shunt resistors for current A/D Converter Current Source for resistance L ZL Control and reading memory

  41. Data Logger System - DMM Normal Mode Errors magnetic coupling Inorm A/D Converter 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

  42. Data Logger System - DMM Integrating A/D Converter V • 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 Vnoise VTemp 1 PLC 2 PLC NPLC T

  43. Data Logger System - DMM Measurement 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

  44. Data logger System Architecture System error is a sum of the error from each component - avoid noise sources! Digital Multimeter (DMM) Signal Conditioning Transducer Multiplexer 28.32 C SCAN MON VIEW Overview Display Analysis & Reporting DMM

  45. Data Logger System - Reporting Tasks Common reporting tasks • 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

  46. Data Logger System- Reporting Tasks PC Connectivity • Connecting to data logger • RS-232 • USB • LAN • GPIB • Software • Easy to use • Create documentation • Compatible with Microsoft Office Apps

  47. Data Logger System - Reporting Tasks Creating reports • 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

  48. Data Logger System - Reporting Tasks Using RS-232 / USB • 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 • 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

  49. Data Logger System - Reporting Tasks Using LAN connectivity • 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

  50. Data Logger System - Reporting Tasks Create Report Make 1st Reading Flexibility Cost Software Data logger SW Low - product specific Free to $300 Quick Quick Textual language Time intensive Time intensive $300 to $1,000 Great T&M graphical language $600 to $1,400 Medium Great Medium PC Software Summary

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