Richards Thermocouple and Temperature Sensor Catalog 16

Thermocouple and Extension Wire - General Information

Thermocouple Wire - Thermocouple grade wire is typically used to make the actual thermocouple element. Note: thermocouple wire maybe used as extension wire but the outer jacket may have a different color code and in some cases it may be more expensive than using extension grade wire. Depending on the application service temperature range, envi- ronmental conditions, and physical constraints; a wire gauge, calibration type, and insulation material can be specified. Each of the calibration types have their own insulation standard color code for easy identification. See the thermocouple wire color codes in the index in this catalog. To aid in the installation of the thermocouple, the RED wire is always the NEGATIVE leg of the element. If the thermocouple wires are installed incorrectly the instrument in the circuit will give backwards or false readings. Thermocouple grade wire is offered with solid or stranded conductors and in a wide range of gauges. If he thermocouple wire will be in an application where it is subjected to repeated flexing stranded wire should be used to prevent conductor fatigue and failure. Thermocou- ple wire is available in AWG wire gauges from 40 (0.0031 inch - 0.079 mm) to 6 (0.1620 inch - 4.11 mm) in bare wire form or insulated with any of the common insulation materials. Insulation materials for thermocouple grade wire are available to cover temperature ranges from -190°F to 2000°F ( -123°C to 1093°C ). Extension Wire - Extension grade wire is used to complete the thermocouple circuit from the thermocouple element to the temperature instrument. Note: extension grade wire should not be used to make thermocouple elements. Extension wires can be divided into two categories. Category 1 extension wires are made with conductors which are the same as the thermocouple. Category 2 extension wires are made with conductors which are different from the thermocouple. The base metal thermocouples are used with Category 1 extension wires. Noble metal and a few non-standardized thermocouples are used with Category 2 extension wires. The extension wire and thermo- couple wire must both be of the same calibration type to maintain the accuracy of the thermocouple. The polarity of each set of wires must also be maintained during installation in order for the thermocouple circuit to function properly. The RED wire is always the NEGATIVE leg of the extension wire. Extension grade wire is also color coded to help with the identification and installation. See the extension grade wire color codes in the index in this catalog . If the extension wire will be subject to repeated flexing, a stranded wire should be used to prevent fatigue and failure. For typical, non-flexing, ambient temperature, indoor use, a 20 gauge ( .032 inch - 1.3 mm) solid con- ductor with PVC insulation is an excellent choice. Note: Never install extension wire in the same conduit as power lines. This will cause interference and errors in the temperature readings. It is good practice to keep the extension wire at least 1 foot away from power lines to maintain an accurate thermocouple circuit. Limits of Error for Thermocouple and Extension Wire - The limits of error for the calibration types listed in this catalog have been extracted from standards set by the American National Standards Institute, Inc. as shown in ASTM Standard E 230. All thermocouple grade and ex- tension grade wire are tested and calibrated in our own calibration laboratory to insure that they are within these standards or better.

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