Thermocouple
A thermocouple is a sensor consisting of two conductive conductors with different properties, soldered together. The measurement occurs due to the formation of a thermal electromotive force (voltage) generated between the conductors. Depending on the cold or hot source, the current at the sensor will change direction between a positive or negative value. The sensor does not require any special settings; you just need to check the readings with a reference device.
The measuring range of the sensor varies from -270 to 2500 degrees and depends on the conductors used inside the alloys. For example, the tungsten-rhenium alloy in a thermocouple is capable of measuring temperatures up to 2500 degrees Celsius.
The disadvantage of the sensor is the small output signal, which requires the presence of an electronic amplifier and signal converter. The measurement accuracy depends on the size of the device; if chosen incorrectly, the temperature error reaches 2.5-4 degrees Celsius.
Thermocouple is widely used in the following industries:
- in scientific research and medicine;
- in industry (production of metal products);
- in automated control systems (CNC machines).
Thermistor
A thermistor is a semiconductor device that operates on the principle of variable resistance.
As the temperature changes, its internal resistance changes depending on the type of sensor selected. There are two varieties of this electrical semiconductor:
- NTC thermistor (resistance drops as temperature increases);
- PTC thermistor (resistance increases with temperature).
Among the features of the sensor, one can highlight its accuracy to the measured temperature. The thermistor error is only 0.05 degrees Celsius.
Measuring range: from -50° to +300 degrees at any measured interval.
Sensor disadvantages:
- As the temperature increases, the service life decreases. The manufacturer provides a guarantee of up to 1000 hours of operation;
- Calibration with a reference meter is required for accurate readings.
Summarizing
The accuracy of temperature readings is certainly higher with thermistor sensors, but thermocouples can boast a larger measurement range. The material from which a thermistor is made degrades over time, while thermocouples last much longer.
Sensors have different methods for determining temperatures. Each type requires its own device or controller that allows you to control the readings.
The main selection criterion can be considered the measurement range. If the temperature exceeds the threshold of 300 degrees, a thermocouple should be used. Otherwise, there is no point in overpaying; you can get by with inexpensive thermal resistances, since a thermocouple costs an order of magnitude more.
