Introduction to Thermocouple Extension Leads and Compensating Cable
It’s usually desired for connecting thermocouples’ probes as parts of some very long circuits to a remotely operated unit of reference and/or some measuring instruments further away from the sensor itself. However, the expense is generally avoided of high-quality thermocouples’ cables in the longer run. It can be fine if some cheaper cable is connected, but this has to be done without worrying too much that the connection temperature is known & taken well into consideration. When thermocouples are connected to instruments, it’s necessary to use a cable with the same EMF-output as that of the thermocouple; else spurious EMFs will occur at those junctions. The finest solution hence comes with the utilization of the same material as that of the thermocouple (extension-cable). A cost-effective option is to utilize compensating cables with alloys different from those of the thermocouples, which have the same power in a limited range of temperature.
More about Thermocouple Extension Cable
Compensating & extension grades of wires tend to be provided in the bright-annealed form. To make this happen, the extra conductor’s thermoelectric properties mustn’t vary much from that of the thermocouples. Extension & compensating cable offers a highly-convenient & quite-economical solution; with its own advantages as well as disadvantages. The extension cable nominally utilizes a similar conductor as that of the thermocouples, so that it has similar thermal characteristics and no such problems appearing with the connection. The mismatching error appearing from high temperature of the connecting-box tends to be comparatively small.
About the Costs
Such cables tend to be less expensive than thermocouples’ wires, though not quite cheap; they tend to be produced in a form suitable for long-distance transport, usually as multi-core cable or flexible wiring. These are advisable for the highest level of accuracy. Compensating cables, alternatively, tend to be less accurate but less expensive even. They use quite a variety of relatively cheaper alloy conductors’ material. Therefore, combining these would harness the same power as a particular thermocouple, but the range of operating temperature must be limited to keep the mismatch error acceptably diminutive.
Insulation is known as the layer of polymer, plastic, or high-temp compound applied directly over the conductor. Generally, various insulations are offered along with a vast temperature range from -260 degree Celsius to 1200 degree Celsius. Most insulating materials are also being utilized for sheathing. Insulating material is selected as per their mechanical, electrical, and high-temp properties. Sheath means the outer layer of polymer, plastic, or high-temp compound applied to the cables. The outermost sheath (or better known as the jacket) is intended for mechanical protection of the insulated cores and other cable’s components.
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