The four most common temperature transducers are thermocouples, resistance-temperature detector’s (RTD’s), thermistors, and integrated circuit sensors.
Here we are discussing about advantages and disadvantages of each devices
Thermocouple:
A thermocouple is an active transducer which directly converts thermal energy into electrical energy. It is a simple device made by joining to dissimilar metals or semiconductor forming a junction. It produces a voltage when the temperature at the junction changes. Have a temperature range in different types -300 to 3200°F
Chara & symbol:
Advantages:
- Self-powered
- Simple
- Rugged
- Inexpensive
- Wide variety of physical forms
- Wide temperature range
Disadvantages:
- Non-linear
- Low voltage
- Reference required
- Least stable
- Least sensitive
- Complicated conversion from emf to temperature
RTD:
RTD (Resistance Temperature Detectors) uses metals that change their resistance when exposed to temperature, which has a positive temperature coefficient. For PT100 RTD it has a temperature range from -400 to 1200F.
Chara & symbol:
Advantages:
- Most stable
- Most accurate
- More linear than thermocouple.
- Interchangeability over wide range
- Works in wide temperature ranges
Disadvantages:
- Bulky in size and fragile
- Expensive
- Slow
- Current source required
- Small resistance change
- Four-wire measurement
- Self-heating problems
Thermistor:
Thermistors are semiconductor devices which have a negative temperature coefficient, this means that the resistance decreases with an increase in temperature.
Thermistors are available that perform temperature measurement from -73 to 316°C (-100 to 600°F). It should be noted that many have limited ranges and cannot be used above 120°C (250°F).
Chara & symbol:
Advantages:
- High output
- Fast
- Two-wire ohmic measurement
- Very high sensitivity (Select range)
- Inexpensive
- No cold junction compensation
Disadvantages:
- Not easily interchangeable
- Limited temperature range
- Fragile
- Current source required
- Self-heating
- Narrow span
- Unstable due to drift and decalibration (especially at high temperatures)
I.C sensor:
They are semiconductor devices. These are available in both voltage and current-output configurations, Some integrated sensors even represent temperature in a digital output format that can be read directly by a microprocessor.
Chara & symbol:
Advantages:
- Most linear
- Highest output
- Inexpensive
Disadvantages:
- T < 250°C
- Power supply required
- Self-heating
- Limited configurations