A thermocouple is probably the most popular thermal protective device used for temperature measurement. They are constructed using two different metals with different properties that are welded together at one end. The sensor produces a voltage output from the open end of both metals for a temperature reading. As the temperature continues to rise, the output voltage rises as well.
The device is used a lot in industrial products and applications. They are known for being very rugged and accurate with a broad temperature range. Many manufacturers still prefer to use a sensor in their heating, ventilation, and air conditioning products.
Thermocouples are a popular choice because of their flexibility. They can be easily constructed from almost any material that best fits the application they are used for. They are very rugged and responsive devices. There is no need to use an excitation source when using them. The most appreciated feature about a sensor is the fact that they have the widest temperature range of any all contact-type sensor.
A Type Thermocouple has an alloy f copper and nickel. These are the most commonly used control devices for calibration. Other popular versions are sensor types B, E, K R, S, T and N. The standard ISA calibration table was developed by the Instrument Society of America.
When you need to find the best thermocouple for a specific application, follow this criteria:
A thermocouple is known to measure temperatures at a small point of reference. The current output is also nonlinear. What this means is that they need an external linearization performed through a cold-junction compensation. Performing a cold-junction compensation is very important if you need very accurate readings.
Incidentally, the output voltage tends to be quite low as well. The voltage usually falls somewhere within the tens to hundreds when measuring microvolts. This requires a careful wiring layout technique to help eliminate excess noise and drift. You can also reduce the noise by placing resistors with the thermocouple along with a capacitor across the connection to device.
A common mistake is using the copper wire from a thermocouple connection and running it directly to the measurement device. This will only introduce another thermocouple into the measurement process which is not what you want. The wire used to create it is only one of the components that can cause accuracy results to vary. Still, a it is one of the easiest temperature sensors to operate. They are simple to use, inexpensive, adaptable and measure a broad range. A thermocouple is not foolproof, but its popularity in different industries makes it a top choice amount temperature measuring instruments.
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