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W A T L O W

Sensor catalog - 7347 GeneralInformation

Application Hints

XACTPAK
® and MI InsulatedThermocouple
SERV-RITE ® Insulated Wire andGeneral Application Thermocouples General Information

How does Watlow check forthermocouple accuracy?

CalibrationStandard Calibration Points°F* CalibrationStandard Calibration Points°F* Application Hints Watlow uses a verification process at selected temperature points toassure wire and XACTPAK
® productsconform to ASTM error limits. Samples are taken to our calibration laboratory and verified for accuracy against NIST traceable standards. Conformance to error limits is required at all test temperatures. When test temperature exceeds the rating of wire insulation or sheath, Watlow will perform calibration to the highest test point below materialsrating. Calibration at intermediatetemperatures can be performed on aper order basis. The following charts provide the standard testtemperatures by thermocouple type.
* Calibration not made when temperatureexceeds sheath rating.E200, 600, 1000, 1600J200, 600, 1000, 1400 K600, 1000, 1600, 2000N600, 1000, 1600, 2000T200, 400 * Calibration not made when temperatureexceeds wire insulation rating. E300, 500, 1000, 1600J200, 500, 1000, 1400 K300, 500, 1000, 1600, 2000N300, 500, 1000, 1600, 2000T200, 500 BX212, 400 CX200, 300, 400, 500EX200, 400JX200, 400 KX200, 300, 400NX200, 300, 400RX400 SX400 TX200, 400

Is there a maximum lengthfor thermocouples and thermocouple wiring?

The length of a thermocouple has noeffect on its measurement accuracyor its ability to transfer the signal to the instrument. In other words,thermocouples do not experience "voltage drops" or power loss along its length as a high current powerline might possess. The reason for this is due to the very low current andvoltages associated with temperaturemeasurements and that the thermo- couple wire becomes the voltagesource. In reality the sensor can be inches or thousands of feet long and the accuracy will not be affected. In practical applications where thethermocouple is a substantial distance from the instrument,electrical noise can be induced andthe sensor selected should be shielded and grounded at one end. In severe environments, or when the distance is in excess of 150 feet, a 4-20mA signal conditioner is suggested.Additional information is available inthe ASTM Manual on the Use ofThermocouples in TemperatureMeasurement. 19