Wednesday 28 November 2012

It Is Vital To Know How Use A Type J Thermocouple Correctly

By Lenore Bolton


The different variations of thermocouples available today are distinguished with the help of charts and color coding. The four most common calibrations are J, K, T and E. Each calibration has a different temperature range in order to suit specific requirements. Type J thermocouple are ideally used for legacy temperature recording and control equipment.

Usages range from immersion in liquid to exposure to gas and air as well as general purpose. This product can also be customized for usage in soft solid infiltration as well as air and exterior temperature extent. As this specific thermometer can be adjusted for a miniature or standard connection.

Characteristically the J model is fabricated using copper-nickel alloy and iron, the negative copper-nickel alloy wire and the positive iron wire. The positive aspect being that it is cheap and readily available. But is considered as less popular as the K type as a result of its rigid temperature scope measuring from -40 to 750 C and due to the iron fabrication which can lead to possible rust, giving a shorter life span.

Needless to say, it is very important to use the right wiring for the right junction and the right purpose. In other words, do not mix J & K wires. Use of any wire other than the same design wire will result in serious errors, as these wires are polarity sensitive. Therefore is vital to ensure to match wire colors when splicing wires together, bearing in mind that for both J and K wires, the red wire is negative.

Careful attention should be paid to the possible points of error that may effect the overall accuracy of the measurement, as a result of the output signals, which are usually in the mill volt range and in general have a very small voltage to temperature sensitivity. Therefore the principal sources of errors for precise measurement that should be taken into account are thermocouple malfunctions, cold-junction return, accuracy balance and gain errors, as well as noise errors.

These small temperature gauges are manufactured using two different metals which are welded together at one end. Electromotive forces are generated as a result of the variation in temperature between its cold and hot point of fusion, generally known as the thermoelectric or Seebeck effect, thus igniting the theory behind thermocouple instrumentation. This way of measuring miniscule temperatures is the most extensively used method and remains to this day.

Manufacturers have a ready to use configuration table or code guide for every possible application in their catalogs, as well as and technical support of expert engineers should there be a need. This can ultimately eliminate errors. Guidelines tend to be uniform but may differ slightly from one manufacturer to the next.

Specific thermocouples need to have exclusively designed control programs to ensure truthful reading. Recalibration can occur as a result of the thermocouple makeup material altering, due to the severe magnetic sway, and exposure to soaring operating temperatures, making the type J thermocouple unsuitable for use in applications higher than 760 C. In the event that you are unsure of how to correctly utilize the equipment or the code guide, go to the manufacturer's website and seek expert advice.




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