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