Troubleshooting Thermocouple Wiring
Date Published: June 14, 2012
Thermocouple Basics for Your Temperature Monitoring Application
When it comes to temperature probes, users have many sensor types to choose from, including thermistors, RTDs and thermocouples. Thermocouples come in many different types and tend to be the most commonly used probe due to their low cost, high durability, and wide temperature range. A thermocouple works by using 2 different metals to create a reaction producing a small voltage which alters depending on the temperature. The many types of thermocouples are distinguished by the color of the insulation on the individual wires within the outer sheath. For a list of the types of thermocouples, including what metals are used and what the insulation color codes are, see: http://en.wikipedia.org/wiki/Thermocouple. The applications specialists at CAS DataLoggers have put this quick article together to guide you through thermocouple basics and also enable you to troubleshoot simple but common wiring issues.
Users in many fields including supply cold chain management, equipment monitoring, life science monitoring, and many more use temperature measurements as their most common data logging application. When selecting temperature sensors, workers and staff most commonly use thermocouples as one of their most affordable solutions where the highest accuracy is not needed, as they’re very easy to use and can measure across a wide operating range. Consisting of 2 metal wires of different alloys which have been fused together at a single point, a thermocouple produces an output voltage (usually at the millivolt level) related to the temperature. A temperature data logger is used to measure this voltage and utilize a calibration equation to convert the voltage into temperature. These data loggers also feature a cold junction reference to compensate for offset voltage that may occur at the connections between the thermocouple wires and the data logger.
You will notice when you look at the thermocouple color codes that all the pairs are made up of a red wire and a different colored wire depending on its type. The red wire in the pair is always the negative or ground wire. An easy way to tell if the wires are reversed is to place the end of the thermocouple into something warmer than the surrounding air and see what your temperature reading does--if the reading drops, it means that the thermocouple has been wired backwards, and all you need to do is reverse the wiring to fix the problem.
As one of the largest datalogger distributors in North America, CAS DataLoggers has sold automated monitoring solutions and real-time systems to customers since 2001 and has been in business for over 20 years. Customers can select from hundreds of different models from over 16 trusted manufacturers to tackle all manner of data recording applications. Users can select from many models of temperature dataloggers which can read the signals from thermocouple sensors including wired and wireless models, lightweight and compact units, power over Ethernet loggers, etc.
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