The most significant difference between the thermocouple and the thermistor is that in thermocouple the sensing parameter is the voltage that induces between the two dissimilar metals. Whereas in thermistor the resistance is the temperature sensing parameter. The other differences between the thermistor and the thermocouple are shown below in the comparison chart.
The thermocouple and thermistor both are the temperature sensing devices, but they have different working principle. In thermistor, the variation in temperature changes the resistance of their material. While in thermocouples the change in temperature induces the voltage between the wires of different metals.
Content: Thermocouple Vs Thermistor
Comparison Chart
| Basis For Comparison | Thermocouple | Thermistor |
|---|---|---|
| Definition | The thermocouple is a type of device used for measuring the temperature | Thermistor is the thermal resistor whose resistance changes with the temperature. |
| Symbol |  |  |
| Sensing Parameter | Voltage generate at the junction. | Resistance |
| Material | Copper, iron, Constantan, Chromel, Alloys of metals like Chrome, chromium and nickel, platinum and rhodium, tungsten and rhenium, rhodium and iridium. | Manganese, nickel or cobalt oxides, semiconductor material. |
| Accuracy | High | Very Low |
| Temperature Range | -50°C to 250°C | -200°C to 1250°C |
| Response Time (Depends on size and packing) | 0.12 – 10 Seconds | 0.2 – 10 seconds |
| Characteristic Curve | Non-linear for negative temperature coefficient. | Linear |
| Cost | Expensive (because of external power source and devices on circuit.) | Cheap |
| Uses | In home appliances like ovens, refrigerators, fire alarm etc. | In Industries. |
| Applications | For controlling temperature, Measurement of temperature, thermal conductivity, temperature compensation etc. | Measuring and controlling temperature. |
Definition of Thermistor
The thermistor is the type of thermal resistor whose resistance changes with the temperature. It is made of semiconductor material. The thermistor has two types of temperature coefficient, i.e., the positive and the negative. In thermistor, the temperature coefficient shows the relation between the variations in the value of resistance and the temperature.
In positive temperature coefficient, the resistance increases with the increase in temperature while in negative temperature coefficient the resistance decreases with the increases in temperature.
The thermistor is used for measuring the small temperature. Thermistor has lead whose resistance reduces their accuracy. It has high sensitivity, i.e., it can detect even small variation in temperature.
Definition of Thermocouple
The thermocouple is used for sensing and measuring the temperature. The thermocouple is a temperature measuring device. In the thermocouple, the two wires of different metals are connected at one point. The two dissimilar metals induce a voltage because of the variation in temperatures of the metals.
The thermocouples are used for measuring the temperature of large industries. It is less costly and more accurate.
Key Differences between Thermocouple and Thermistor
- The thermocouple is the temperature measuring devices and thermistor is a type of thermal resistor.
- The thermocouples are made from metal or alloys of metals. While the thermistor is made by the semiconductor or by the oxides of magnesium, nickel or cobalt.
- The thermocouple has high accuracy as compared to the thermistor. The thermistor has lead whose resistance reduces their accuracy.
- The temperature measuring ranges of the thermistor is -50°C to 250°C whereas that of the thermocouple is -200°C to 1250°C.
- The thermistor gives the quick response as compared to the thermocouples. The response time of both the sensors depends on their size.
- In thermocouples, the variation in temperature is determined by the voltage induces at their junction. The resistance of the thermistor changes when their surrounding temperature varies.
- The characteristic curve of the thermocouple between voltage and current is linear. The curve shows that the voltage of the thermocouple increases concerning the temperature. While in the thermistor, the characteristic curve between the resistance and temperature is non-linear when the thermistor has a negative temperature coefficient. The non-linear curve of thermistor shows that their resistance decreases with the increases in temperature.
- The thermocouple is less expensive as compared to the thermistor because the thermistor requires the external power source.
- The thermistor and thermocouple both are used for controlling and measuring temperature.
- The thermocouples are used in large industries, while the thermistors are used in home appliances.
Conclusion
The thermistor and the thermocouple both are the types of the temperature sensor. The thermistor is used in small appliances for sensing the temperature, and the thermocouple is used for detecting the high temperature.