Thermocouples are two wire products made up from different steel welded collectively which when warmed generate a tiny millivolt prospective. The productivity is dependent upon materials of design having a complete variety of diverse resources for varying applications and temperature ranges, which can be way beyond the scope on this post. Such as a basic affordable thermocouple would be a variety K which happens to be created from Nickel and Chromium and produces an production of 41µV/oC being a magnet material might cause some issues with linearity at conditions over 350ºC this is again outside the scale on this article. For higher temp programs Type B, R or S can be utilized as much as 1600ºC these thermocouples are considerably more costly getting manufactured from Platinum / Rhodium with the output of 10µVºC.
The disadvantage of thermocouples is that they cannot be linked to normal copper cable tv as yet another junction of different materials could be created in the linking head which would also generate a millivolt transmission thus an error. So a cable tv using the same qualities as being the thermocouple must be used to connect returning to the k type temperature sensor this is called compensating cable television. The connection on the instrument terminals using the comp cable tv can certainly produce a tiny millivolt possible which must be paid for this is often referred to as the cold junction temp.
The temp device or transmitter supplies the lowest voltage towards the platinum level of resistance sensing unit which then causes a current to circulate; creating an electric circuit.
By ohms regulation the voltage decrease in the circuit and hence the actual flow is proportional on the amount of resistance within the circuit. Because the temperatures increases the amount of resistance of your PT100 raises:- this is a optimistic thr0k coefficient. The situation together with the two cable settings may be the musical instrument says the level of resistance in the linking cable television as well as the temp sensor.
There are many simple ways to circumnavigate this issue has listed below in the link particulars to the 3 And 4 wire methods.