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Semiconductor Temperature Sensors:
Semiconductors have a number of parameters that vary linearly with temperature and they form the core of today’s electronic temperature sensors. Normally the reference voltage of a zener diode or the junction voltage variations are used for temperature sensing. Transistors or diodes can also be used for temperature measurement. The outputs of these semiconductor devices are very linear and are good for
temperature sensing within a narrow range. Semiconductor temperature sensors have a limited operating range from –50°C to 150°C.
Advantages:
- They are very linear with accuracies of ±1°C or better.
- Their electronics can be integrated onto the same die as the sensor giving high sensitivit
- They can be easily interfaced with control systems, making different digital output configurations possible.
- They have a good thermal time constants which varies from 1 to 5 s.
- Semiconductor devices are rugged with good longevity
- They are inexpensive.
For the above reasons the semiconductor sensor is used extensively in many applications including the replacement of the mercury in glass thermometer in industrial applications.
Disadvantages:
- Internal dissipation can cause up to 0.5°C offset resulting in errors in temperature measurement
- Limited range of operation
- Limited range of operation
Comparison of Temperature Sensors
Whether it is a thermocouple, an RTD, a semiconductor temperature sensor, filled bulb sensor or a thermistor, they all have their place in industrial temperature measurement. The choice of any given temperature sensor depends on the following factors and many more:
- Range of operation in the particular application
- Application environment
- Degree of accuracy of the temperature measurement required
- Thermal time constant of the sensor
- Linearity of the sensor
- Cost of sensor
- Remote indication capability
- Error correction capability
- Ease of calibration
- Vibration sensitivity
- Size of sensor
- Longevity
- Maintenance requirements
- Sensitivity /response of sensor etc.
The comparison between some of the common temperature sensors is now given below based on some of the factors enumerated above :
| Type of Sensor | Linearity | Advantages | Disadvantages |
| Bi-metallic | Good |
Low cost, rugged,
wide range |
Local measurement,
or for On/Off
switching only |
| Resistance Temperature Detector (RTD) | Very good | Stable, wide range, accurate |
Slow response, low sensitivity, expensive,
self-heating, wide range |
| Thermistor | Poor |
Low cost, small,
high sensitivity,
fast response | Nonlinear, narrow range, self heating |
| Thermocouple | Good | Low cost, rugged,very wide range |
Low sensitivity,
reference needed |
| Pressure | Medium | Accurate and wide range |
Needs temperature
compensation and
vapor is nonlinear |
| Semiconductor | Excellent |
Low cost, sensitive,
easy to interface |
Low sensitivity,
reference needed,
slow response, narrow range, power source |
