Time Constant of a Thermometer Project

Keywords – Time Constant (tau or t), Step Response, First Order System, Wheatstone Bridge, Dynamic Characteristics

 

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1. Explain what is meant by the ‘time constant’ of an instrument and describe a simple experiment to measure the time constant of a mercury-in-glass thermometer

 

2. A thermometer has a time constant of 6 seconds and is suddenly moved from ice to boiling water.  How long will it take before it will read 100 ºC?

 

3. Sketch the output from a Pt100 RTD that is suddenly moved from ice to boiling water.  Assume it has a time constant of 8 seconds.

 

4. Rank the following in order of increasing time constant:

 

Thermocouple, mounted in stainless steel

Thermocouple, bare wire

Pt 100 RTD, mounted in stainless steel and installed inside a thermowell in a pipe

Thermistor, bead type, unprotected

Pt100 RTD, mounted in stainless steel