351Lab4

# 351Lab4 - Laboratory 4 TEMPERATURE MEASUREMENT Time Aigbe...

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Laboratory 4 TEMPERATURE MEASUREMENT Time Aigbe Partners: Andrew Collins Ugonna Madueke Amandeep Chhabra ENME 351 Section 0102 Date of Experiment: 10/2/07

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Time Aigbe ENME 351 – Sec 0102 Lab 4 – Page 2 INTRODUCTION: In this lab, we are introduced to thermocouples and how we can use them to turn an input voltage signal into a temperature reading. The thermocouple works by experiencing a voltage difference between the reference junction and measurement junction, whenever a temperature difference between these two junctions is observed (see Figure 1 for a thermocouple). This induced voltage (the Seebeck voltage) is directly proportional to the temperature change. Figure 1: Schematic of a Thermocouple showing junctions Because the K type thermocouple that we’re using has a sensitivity (K) of 41 μV/ o C, we must amplify the -10 to 80 mV output readings of the thermocouple. All this can be done only after filtering out the noise produced by the thermocouple first with a 2 Hz cutoff frequency low pass filter. To achieve amplification and filtering, a signal conditioner will be used (see Figure 2). Figure 2: Signal Conditioner To avoid measurement error, Cold Junction Compensation (CJC) will be used to give the temperature of the reference junction so that the output of the thermocouple will be an absolute temperature. It is built into the signal conditioner shown above. Thermistors are thermally resistive sensors that have a negative (NTC) or positive (PTC) temperature coefficient. NTCs are made out of transition metals and are considered to be temperature dependant semi-conductor resistors. They are able to measure temperatures as low as -200 o C and as high as +1000 o C. NTCs are most useful when a continuous change in resistance is occurring over a wide temperature range. PTCs can operate in three modes. First of all, they can act as temperature sensors at a range of 60 – 180 o C. Secondly, they can act as a fuse to deter too high a current from ruining a circuit. Lastly, they can act as a liquid level sensor. Relative to the thermocouple, thermistors are more accurate, and operate over a large
Time Aigbe ENME 351 – Sec 0102 Lab 4 – Page 3 range of temperatures (as mentioned earlier). The downside to thermistors is that the more sensitive the temperature measurement, the less linear the thermistor. Resistive temperature detectors (RTDs) are similar to thermistors in that they rely on a

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## This homework help was uploaded on 04/17/2008 for the course ENME 000 taught by Professor Staff during the Spring '08 term at Maryland.

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351Lab4 - Laboratory 4 TEMPERATURE MEASUREMENT Time Aigbe...

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