Good afternoon, I am Pablo, from Ecuador, do you know if it is possible to connect RTD with 3 wires directly to analog inputs in PLC S7 1200 AC / DC / RLY? I know analog inputs suport 10 VDC, but I have 24 VDC source, what can I do to get only 10 VDC? I gonna to use a voltage divider, but I'm not sure if it's a good idea.

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Split from PT100 - 4AI X RTD & S7-1200 1214.

Hello Pablo;

A RTD measures temperature by measuring the resistance of the sensor as it varies with temperature.

A voltage AI module expects a signal that varies between 0-10 V

They are not compatible.

To connect a RTD and an analog input module on a PLC, you have 2 choices, as far as I know:

1. purchase a RTD module such as the S7-1231 4AI-RTD, it is designed to handle the measurement of the varying resistance of the sensor directly and scale the value so the PLC can understand it.

2. purchase a signal transmitter/conditionner that you will place between the RTD and the voltage analog module, It is designed to produce either a current or a voltage signal that follows the resistance value produced by the RTD, so the PLC can read and interpret the signal.

For example, look at these products from Acromag. There are many other manufacturers you might want to look at, such as Omega, Laurels, Intempco... different configurations, different price ranges.

https://www.acromag.com/catalog/117/signal-conditioners-converters/temperature-transmitters/rtd-input

Hope this helps,

Daniel Chartier