Temperature Detectors
Resistance Temperature Detectors (RTDs)
RTD resistance is proportional to temperature.
RTDs output a measurable voltage proportional to the resistance of the RTD and temperature of the process (fluid) being measured.
By Voltage = I (Current) x Resistance
If we apply a constant current through the resistance of an RTD, then we should be able to measure the temperature as a voltage.
Thermocouples
- Constructed of two dissimilar metal wires joined at one end and encased in a metal sheath.
- The other end of each wire is connected to a meter or measuring circuit.
- heating th emeasuring junction of the thermocouple produces a voltage that is greater than the voltage across the reference junction.
- The difference between the two voltages is proportional to the difference in temperature and can be measured on a voltmeter.
Functional Uses of Temperature Detectors
Temperature detectors are used for:
- Indication
- Alarm functions
- Control functions
If a temperature detector becomes inoperative:
- A spare detector may be used (if installed)
- A contact pyrometer can be used
Environmental concerns:
- Ambient temperature
- Humidity
Temperature Detection Circuitry