General Information

Thermocouple Insulation, provides electrical insulation for thermocouple and thermocouple extension wire. If the insulation breaks down for any reason, the indicated temperature may be in error. When selecting insulation moisture, abrasion, flexing, chemical attack, temperature extremes and any other adverse environmental considerations must be evaluated. Insulations are rated for a maximum continuous use temperature and also a maximum single exposure temperature because after excessive temperatures have been encountered the insulation may become conductive or conductive residues may form even though the insulation remains physically intact. Also do not assume the temperature rating as the temperature at the sensing junction of the thermocouple without evaluating the thermocouple system.

Fibrous Insulation, is either braided or wrapped on the conductors. In general, fibrous insulations are used for applications where extreme moisture and abrasion resistance requirements are not prevalent. Available at moderate cost for upper utilization temperatures of 900°F (482°C) for fiberglass, 1600°F (780°C) for high temperature silica fiber, and 2400°F (1315°C) for ceramic fiber.
Plastic Insulation, is used on comparatively lower temperature applications and provides good moisture and abrasion resistance. Available at low to moderate cost for typical upper utilization temperatures of 220°F (104°C) for PVC and 500°F (260°C) for teflon and silicon rubber.

WIRING ELECTRONIC INSTRUMENTS to conform to national and local codes does not address the “noise” problems of electronic instruments. Shielding of thermocouple and thermocouple extension wire may be necessary but not the only requirement of reducing noise. Ever since the introduction of electronics into instruments, noise generated by external relays, switches, motors, phase fired thyristors, etc., have caused problems that interfere with the instrument’s operation. Now that microprocessors are being increasingly incorporated into many more varied instruments, external sources that generate noise pulses that, in some cases, may render the instrument completely inoperative, have become crucial to instrument applications. While much can be done within the instrument to reduce its sensitivity to external noise, the solution in many cases can only be resolved by supressing the noise generation at its source.