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Entry type: FAQ Entry ID: 23671451, Entry date: 04/25/2016

How do you connect a PT100 sensor to the LOGO! analog expansion module AM2 PT100 or AM2 RTD?

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To the LOGO! analog expansion module AM2 PT100 or AM2 RTD you can connect sensors with 2-conductor, 3-conductor or 4-conductor connections.

2-conductor connection
In the case of the 2-conductor connection (Fig. 1) there is no correction of the error caused by the ohmic resistance of the measuring circuits. You must build in a jumper between the U1- and IC1 connections:

Fig. 1
3-conductor connection
In the case of the 3-conductor connection (Fig. 2) the measuring circuits' resistance is compensated and does not enter the measuring result. For correct measuring results all the conductors must have the same resistance. You achieve this by making sure that the conductors all have the same length and the same cross-section.

Fig. 2
4-conductor connection
In the case of the 4-conductor connection (Fig. 3) you connect the PT100 in the same way as the 3-conductor connection. The fourth conductor of the PT100 remains open.

Fig. 3
You can use a multimeter to determine the various connections of a PT100 or take them from the data sheet. In order to determine the connections with the multimeter you have to measure the resistance between the connections (Fig. 4). If the resistance is 100 Ω, this indicates an input and an output of the PT100. If there is no resistance measured between the connections, this indicates 2 inputs or 2 outputs.

Fig. 4
Further Information
  • More information about the analog expansion module AM2 RTD is available in the LOGO! manual. 100761780
  • Information about how the PT100 Sensor can be read in the LOGO! program and how a digital output can be switched as a function of temperature threshold value is available in Entry15398450

Additional Keywords
PT100, PT1000, Expansion module, Connection technology, 4-wire conductor

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