A thermocouple wire is a wire used in a thermocouple between the induction point and the cold end compensation point where the signal is measured. A thermocouple is a sensor for measuring temperature, which is connected by two different metals at the induction end. Different types of thermocouples (such as J, K, T, E, etc.) use different metal wire combinations. At the cold end compensation end, the millivolt value provided by the thermocouple represents the temperature difference between the inductive end and the cold end compensation end (also known as the reference end).
How to mark insulated thermocouple wires
The insulation layer of thermocouple wire is identified by color coding. The common criteria include red for negative wire in insulated thermocouple compensation conductor, and the color of positive wire is consistent with that of compensation conductor. The coat of thermocouple wire is usually brown, while high temperature wire is usually white.
The difference between standard error limits and special error limits
Standard and special error limits relate to the wire accuracy. Special error limiting wires are the same as standard error limiting wires, but with higher accuracy. The precision of the thermocouple varies with its type. For example, T-shaped with the lower-temperature range, consisting of positive copper wire and negative constantan (copper-nickel mixture), has good precision specifications.
The difference between thermocouple wire and compensation wire
The thermocouple wire is used to make the thermocouple induction point, while the compensation wire is only used to extend the thermocouple signal to the instrument reading this signal. The compensation wire usually has a lower ambient temperature limit, that is, it can transmit signals of higher temperatures obtained from the probe, but it is not itself exposed to higher temperatures. Thermocouple wires can be used as compensation wires, but compensation wires cannot be used to make the induction point (or probe part) of the thermocouple.
The maximum length of a thermocouple wire
There are many factors that can affect the available length of the thermocouple. The two factors that determine the available length of the thermocouple are the total circuit resistance and the prevention of electrical noise into the signal. Since the thermocouple wire is made of different materials, the resistance will vary with different materials and different diameters and lengths. The permissible loop resistance is affected by the input resistance of the amplifying circuit connected by the thermocouple. But as a rule, the usual goal is to keep the total loop resistance below 100 ohms. The second major factor in running thermocouple wires is the distance from any electromagnetic field. Thermocouple wire will generate a low voltage signal, so it is not suitable to run near the power line, motor, etc. In order to minimize noise pickup, wire braided or shielded strands are commonly used.
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