EELX N302 Instrumentation & Control 1 Year 2011

EELX N302 Lab Assignment 1 RTD Temperature Sensor (Calibration)

Purpose : To investigate the suitability of a resistance-temperature-device (RTD) as a sensor for measuring temperature.

IntroductionIn this lab you will use the temperature sensor module (fig. 1) on the Digiac 1750 Transducer and Instrumentation Trainer module. The trainer is described in Appendix A at the end of this document.

The active transducers are mounted within a clear plastic enclosure, which contains a heater. The heated enclosure is provided to raise the temperature of the sensor transducer to allow measurements to be taken during the experiment.

Figure 1

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EELX N302 Instrumentation & Control 1 Year 2011

PLATINUM RTD TRANSDUCERPlatinum RTD (Resistance Temperature Detector) consists of a thin film of platinum deposited on a ceramic substrate having gold contact plates at each end that makes contact with the film as shown below:

The resistance of the film increases as the temperature increases. Thus it has a positive temperature coefficient p.t.c.

Rt = Ro + 0.385 t Where, Rt = resistance at temperature t °C Ro = resistance at 0 °C (=100Ω) The increase in resistance is linear, the relationship between resistance changes

and temperature rise being 0.385 Ω /°C

Set the slider of the 10 K Ω carbon resistor to mid-way and connect the circuit as shown below with the digital voltmeter set to its 200 mV or 2 V DC range.

Switch ON the power supply and adjust the slider control of the 10 K Ω resistor so that the voltage drop across the platinum RTD is 108 mV. This calibrates the platinum RTD for an assumed ambient temperature of 20 °C since the resistance of the RTD at 20°C will be 108 Ω . Note that the voltage reading across the RTD in mV is the same as the RTD resistance in Ω, since the current flowing must be

= 1mA.

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EELX N302 Instrumentation & Control 1 Year 2011

Connect the +12V supply to the heater element input and note the voltage across the RTD with the voltmeter set to its 200mV or 2V range (representing the RTD resistance) and the output voltage from the IC temperature sensor with the voltmeter set to its 20V range (representing the temperature of the RTD) every one minute

Convert the two voltage readings to RTD temperature (°K) and RTD resistance measured (Ω) and record the values in the table below

Convert the RTD temperature into °C (°K – 273) and record in the table below.

Calculate the RTD resistance (= 100 + 0.385 x °C) and record in the table below.

Time (minutes) 0 1 2 3 4 5 6 7 8 9 10

RTD °KTemperature °C

RTD Resistance

Plot the graph of RTD resistance (measured) against temperature °C .

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EELX N302 Instrumentation & Control 1 Year 2011

Report

You should complete a report for this lab and submit it by ____________

Assessment

Descriptor Grading Weight ScoreReport Layout 1 2 3 4 5 *2 /10Table /Results 1 2 3 4 5 *3 /15Graph 1 2 3 4 5 *3 /15Summary/Conclusion 1 2 3 4 5 *1 /5

Total /45For the grading, 1 represents the lowest score and 4 the highest score. No attempt will receive no score in that element.

Appendix A

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EELX N302 Instrumentation & Control 1 Year 2011

The layout diagram of the DIGIAC 1750 Transducer and Instrumentation trainer unit

PART A (IC TEMPERATURE SENSOR)

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EELX N302 Instrumentation & Control 1 Year 2011

The IC temperature sensor is an LM 335 providing an output of 10 mV/°K

The IC temperature sensor gives a voltage output of 10mV/ oK. That is 0.01 x oK. In other words,

V = 0.01oK, or oK = 100 x V.

Therefore, oC = 100V – 273, since oC = oK – 273.

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