Hi,

I'm new to working with PLCs and with Step 7/Siemens so every help would be arrpeciated.

I'm using a s7-1200 CPU 1214 DC/DC/DC and a Relay Changeover Output Module (Sm 1222, 8 DO), and I'm trying to power up a pump (which has two wires - 24Vdc and 0Vdc).

However, the Relay Changeover has 3 contacts for each input and I don't have any clue about how to wire this. I saw the schematics given by Siemens and I still don't understand how to do it and where to put each of the pump's wires.

Can someone help me? I would appreciate it a lot.

Thanks in advance

Hi!

It works like a relay with  a normal open, NO and a normal closed, NC contact which have a common point.

First you will have to connect the feed to the module: 24V DC from your power source to L+ on the module, and 0V from your source to M on the module.

If you use the first output on the module for your pump, you have to connect 24V DC to 0L which is the common point of the NO and NC contacts.

Then you sould connect the 24V wire of your pump to .0 on the module. The 0V wire of the pump goes to the 0V of your power source.

Thus you use the NO contact of the output, and when you turn on this output in your program, you turn on the pump. E.g. if the address of the module is QB3, then you can turn on the pump with Q3.0.

After reading the manual (https://support.industry.siemens.com/cs/ww/en/view/107623221, Chapters A.7.2 and A.7.3, I say:

The suffix "L" is the common contact, "X" the normally closed contact and "" the normally opened contact.

So you have to use "L" and "" as switch. Your pump will run when the DQ is set to true.

The "a" is the byte address of your output. It is defined when in TIA Portal in "Devices & Networks" and 0 to 7 are the bit address of your output.

Of you are using DQa.0 you should connect your 24C from the power supply to Pin 5 and your pump to Pin 7 and 0V from the power supply.