Answers to Sample Problem Set 4

From Time Constant Project

1. Time constant is a measure of how quickly a device responds to a dynamic or changing input. If there is a step change in input it takes five time constants to reach steady state or 1 time constant to reach about two thirds of the total change.

Experiment – hold thermometer in ice/water at 0 ºC, Suddenly move to boiling water and start a timer. Stop timer after two thirds of the change has happened to get time constant OR stop timer when new steady state is reached and divide time by 5

2. 5 TC to reach steady state, TC = 6 sec, so answer is 30 seconds

3.

4.

1. Thermocouple, bare wire

2. Thermistor, bead type, unprotected

3. Pt100 RTD, mounted in stainless steel and Thermocouple, mounted in stainless steel

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