Wiring method for platinum resistors and temperature transmitters

For a four-wire thermal resistor, it is first necessary to know where the wires come from: two wires are led out from each side of the resistor, labeled as +1, +2, -1, and -2. In other words, +1 and +2 represent one wire, and -1 and -2 represent another wire. The following explains how to connect to a temperature transmitter. Most transmitters these days are of the 3-wire or 4-wire type. For 3-wire transmitters, connect +1 or +2 along with two negative wires (or two positive wires and one negative wire; the principle is the same). For 4-wire transmitters, follow the wiring instructions on the transmitter and connect all the wires; if one wire is missing, no reading will be displayed. It is connected to the flow computer you mentioned; assuming this device requires only 2 wires, then one + wire and one – wire are sufficient. Resistors don’t have a positive or negative side, so it’s enough to connect the two wires that lead from either end of the resistor.

The method of connecting two wires to each end at the base of the thermoresistor is called the four-wire system; two of these wires supply a constant current I to the thermoresistor, converting R into a voltage signal U, which is then transmitted to the secondary instrument via the other two wires. This type of lead configuration can completely eliminate the influence of lead resistance, and is mainly used for high-precision temperature detection.

Reply to 2# a985658: Thank you, the explanation was very clear. I have another question: what is the difference between three-wire and four-wire systems for temperature measurement? Can these two systems be switched with each other? Can the wiring methods of three-wire and four-wire thermal resistors be swapped? I’ve seen some materials state that in a four-wire thermistor, two wires are used to provide a constant current source, while the other two wires are used to detect and output voltage changes in the resistance. However, our engineers say that all four wires are used to measure the resistance value. I’m not sure about this; who is correct?

Three-wire and four-wire transmitters operate on different principles: the three-wire type uses the balanced bridge principle, while the four-wire type relies on a constant current source. The main issue lies in the number of wires required for the transmitter’s signals; the wiring is determined by the type of transmitter. Since three-wire and four-wire transmitters operate on different principles and are both integrated modules, it’s not possible to convert a four-wire transmitter to a three-wire configuration. However, you can replace the three-wire thermistor with a four-wire thermistor; as already mentioned, there is no need to repeat that here. As for the second question, the two sets of connections are actually the same set; so it’s correct to say that they are all connected to resistors. It’s also right to say that one set is connected to a constant current source while the other set is used to detect voltage changes.

Currently, the RTD module accepts both three-wire and four-wire connections; the principle involved is that of a balanced bridge, with only slight differences in the wiring details. The three-wire system is converted into a four-wire system by using shorting wires before connecting to the module

I would like to ask, which one is more accurate, level 3 or level 4?

What was said on the 6th floor is correct – modern smart temperature transmitters can accept both 3-wire and 4-wire signals; they are generally operated in a 4-wire configuration. To switch to a 3-wire system, it’s necessary to use a Hart 375 to make the necessary adjustments, which is quite troublesome. It’s better to make changes to the wiring by using one fewer wire.