PT100 three-wire connection
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As shown in Figures A, B, and C, there are three terminals, among which B and C are connected. . If I want to connect a PLC analog module, how should I do it? How should the compensation wire be connected? ?
I’m not quite sure what you mean, but I’ve just come across a PLC for a circulation machine; it uses a 3-wire system on-site, but inside the control cabinet it becomes a 2-wire system. You can simply connect wires B and C together
Analog modules cannot be connected directly to thermocouples; a temperature transmitter is required for conversion, or a PLC thermoresistance module can be used. It is recommended to add a transmitter, as the latter is not very convenient!
If connecting a thermal resistor directly, an analog module capable of handling thermocouples must be used; many PLC and DCS manufacturers now offer such modules. However, I have never heard of compensation wires being used for thermal resistors; they are only used for thermocouples. Since the materials used for thermocouples are generally quite expensive (especially when noble metals are used), and the distance from the temperature measurement point to the instrument is often large, in order to save on thermocouple material and reduce costs, compensation wires are typically used to extend the cold end (the free end) of the thermocouple into a control room where the temperature is more stable, thereby connecting it to the instrument terminals. It must be noted that the function of a thermocouple compensation wire is merely to extend the thermal electrode and move the cold end of the thermocouple to the instrument terminals in the control room; it cannot eliminate the impact of changes in the cold end temperature on temperature measurement, and thus it does not serve a compensating role. Therefore, other correction methods must also be employed to compensate for the effect of the cold-end temperature t0≠0℃ on temperature measurement. This post was last edited by smallcat007 on 2009-4-17 15:28.]
A PLC usually has four input terminals: two U+ and U- for measurement, and I+ and I- for applying a constant current. On the PLC side, there is a terminal that needs to be short-circuited with that separate wire. ———————————————————— U+ | —————————————— I+ | | | | | ———————————— U-/I-
What era is this? Are there still people who don’t know about PT100 systems in modules?