THERMOCOUPLEDue to their simplicity, reliability, and relatively low cost, thermocouples are widely used. They are self-powered, eliminating the need for a separate power supply to the sensor. Thermocouples are fairly durable when they are appropriately chosen for a given application. Thermocouples also can be used in high-temperature applications.
Thermocouple Advantages:
- Self-powered
- Simple
- Rugged
- Inexpensive
- Many applications
- Wide temperature range
- Fast response
- Nonlinear output signal
- Low voltage
- Reference required
- Accuracy is function of two separate measurements
- Least sensitive
- Sensor cannot be recalibrated
- Least stable
Resistance temperature detectors are attractive alternatives to thermocouples when high accuracy, stability, and linearity (i.e., how closely the calibration curve resembles a straight line) of output are desired. The superior linearity of relative resistance response to temperature allows simpler signal processing devices to be used with RTD’s than with thermocouples. Resistance Temperature Detector’s can withstand temperatures up to approximately 800 C (~1500 F).
RTD Advantages:
- More stable at moderate temperatures
- High levels of accuracy
- Relatively linear output signal
- Expensive
- Self-heating
- Lower temperature range
Thermistors work similarly to RTD’s in that they are a resistance measuring device, but instead of using pure metal, thermistors use a very inexpensive polymer or ceramic material as the element.
Thermistor Advantages:
- High output
- Fast
- Two-wire ohms measurement
- Nonlinear
- Limited temperature range
- Fragile
- Current source required
- Self-heating
