Problems with integrated thermoresistors
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The integrated thermoresistor includes a load resistance of 250 and a transmission wire resistance of 100. Does the resistance of a transmission wire refer to a resistance of no more than 100 ohms? Does the load resistance refer to the condition that the resistance from its output signal to the cabinet (DCS) is no more than 250 ohms? If that’s the case, then there must be requirements regarding the transmission distance.
An integrated thermoresistor uses a PT100 sensor; its resistance output is 100Ω at a temperature of 0℃； The integrated thermistor temperature transmitter has an output current of 4~20mA and a load resistance of 250Ω; it converts the current of 4~20mA into 1~5V.
A load resistance of 250Ω refers to the load-carrying capacity of the integrated temperature-sensitive device; in other words, the load resistance must not exceed 250Ω.
The so-called integration refers to the combination of the temperature element and the temperature transmitter into one unit; therefore, its load capacity refers to the load capacity of the temperature transmitter.
The original poster has a confused understanding of the concept. For thermoresistors used to measure temperature, there is a table that provides reference values for resistance at different temperatures. The cable resistance of 100Ω mentioned by you is something that we generally need to eliminate in order to ensure accurate measurements; therefore, for thermoresistors, a three-core cable should be used, with two of its wires connected together, in order to eliminate the cable’s resistance. Another approach is to use a temperature transmitter, which corresponds to the 250Ω loop resistance you mentioned. In measurement circuits that typically use 4–20mA signals, a 250Ω measurement resistor is placed at the measurement point to convert the current signal into a 1–5V voltage signal. This makes it possible to distribute a single measurement signal to multiple points. In the measurement circuits of instruments, a constant current source is used for the 4–20mA current, so changes in the circuit resistance do not affect the current level, thereby ensuring accurate measurements. From what you said, an integrated thermal resistor should refer to one with a temperature transmitter, so the output is a 4~20mA measurement circuit. :L