Worksheet

Instrumentation and Control

WS02/03

ECM 1

Prof. Dr. Michael Wlker

Subject: Signal conditioning

Team F: Survey and Summary

Give a synopsis of the more important methods for the measurement of electrical parameters (dc, ac, 3-phase ac) and survey the categories of I/O module types for signal conditioning.
What should a specification for a signal conditioning module state?

Team A: Demonstrations and Experiments

5B signal conditioning modules (thermocouple transducer with and without linearization), shunt resistor measurement, electric metering (S0 pulses), I/O modules for LON bus coupler

handle the signal conditioning available, record measurements and document experimental set-ups and results

Team B: Exercises and Worked-through Examples

Prepare a complete documentation of the exercise (Word, formula editor, plots)

Exercise 1: The specification of a signal conditioning module gives the following values
Range:
100 mV
Gain: 100
Absolute accuracy (15 to 35 C) in % of reading: 0.015% typical
0.02% max.
Offset: 25 V
System noise (peak, 3s) 20 V (single point)
5 V (average over 100 pts))
Temperature drift in % of reading/C 0.0005%
Offset temperature drift 1 V/C
Calculate the absolute accuracy for a 14 mV input signal assuming room temperature conditions (20 C). What is the value of the absolute accuracy for a measurement at 40 C? What is the system noise if 1000 measurement samples are taken?

Exercise 2: The performance of a temperature channel with a linearising signal conditioning module for a type K thermocouple needs to be checked. This signal conditioning module amplifies the thermocouple voltage in a way that a signal of 0 V to 5 V results for a temperature range of 0 C to 1000 C. The output voltage is digitised by a 16 bit A/D-converter with an input range of 0 V to 10 V. Therefore a digitisation step is ULSB = 10 V/216.
For the check a second type K thermocouple, which was fabricated the same way and can be held at the same temperature as the first one, is directly connected to a 16 bit A/D-converter with an input range of 0 V to 10 V and a programmable input amplifier with gains of 1, 2, 10 and 100.
Compare the temperature resolution of the normal measurement channel with that of the reference channel. To how many digitisation steps does the difference between the true signal and one assuming perfect linearity for the reference channel correspond at 300 C? Which problems could spoil the intended check? IEC 584 values for a type K thermocouple:

J/C

-200

-100

0

100

200

300

400

500

600

700

800

900

1000

U/mV

-5.891

-3,553

0

4.095

8.137

12.207

16.395

20.640

24.902

29.128

33.277

37.325

41.269


 

Team C: Relevance to RAPS at Offenburg

existing and planned signal conditioning on RAPS, web sites of suppliers

 

Team D: Internet Documentation and Resources

Find web sites of bigger suppliers and comment their value; just a few hints:

Team E: Research and Development

Discuss the problems of proper signal grounding and shielding (refer to High Performance Data Acquisition and Control by KineticSystems Cooperation, Lockport). Investigate the option to use National Instruments SCXI signal conditioning modules for RAPS (http://www.ni.com and catalogue in the lab).