How to connect PT100 wires to a transmitter
Suitable connections for all three types of sensors (2-wire, 3-wire and 4-wire) to the user-adjustable transmitter are shown in the following images
It is very important to note that the common connections shown for the 3 and 4 wire sensors show the connection points in this sensor. Neither the terminals that were jumped by the technician during installation nor the internal jumpers of the transmitter. The whole purpose of having 3 -wire RTD and 4-wire circuits is to eliminate errors due to voltage drops along the current-carrying wires, and this can only be achieved if the sensor wire (s) extend to the RTD itself. And connect there
Jumpers located in the transmitter terminals reduce the purpose of the 3-wire or 4-wire capabilities of the transmitter and reduce its performance compared to the 2-wire system. A similar problem occurs when someone tries to connect a 3-wire RTD to a 3-wire transmitter using a suitable available 4-wire cable
The 3-wire RTD measurement is based on the assumption that both current-carrying wires have exactly the same electrical resistance. By paralleling two of the four wires in a 4-wire cable, you will create unequal resistance in the current path, thus leading to measurement errors in the transmitter (note).
A picture of a modern temperature transmitter capable of receiving input from 2-wire, 3-wire or 4-wire RTDs (as well as thermocouples, another type of temperature sensor in its entirety) describes the connection and labeling points of the sensor. . To connect to suitable terminals
The rectangular symbol shown on the label indicates the RTD resistance element. The symbol with “+“ and “–“ symbols indicates the connection of the thermocouple and may be ignored for the purposes of this discussion. As shown in the diagram, a two–wire RTD is connected between terminals 2 and 3. Similarly, a three–wire RTD is connected to terminals 1, 2, and 3 (using terminals 1 and 2, connecting the two. Common RTD wires). Finally, the four–wire RTD is connected to terminals 1, 2, 3, and 4 (terminals 1 and 2 are common, and terminals 3 and 4 are common in RTD). After connecting the RTD to the appropriate terminals of the temperature transmitter, the transmitter for that type of RTD must be configured electronically. In the case of this particular temperature transmitter, the configuration is performed using a “smart“ communication device using the HART digital protocol to access settings based on the transmitter microprocessor.RTD configures 2 wires, 3 wires or 4 wires.
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