S7-1200 120VAC Inputs

Does anyone know of a supplier for a 120VAC input adaptor board for the new S7-1200 PLCs yet? I have to retrofit an existing PLC that is using all 120VAC inputs. Usually by now (in the new product life cycle), someone will have designed and is making a little comb board to stab into the Input terminal blocks and allow connection of 120VAC circuits to the 24VDC inputs, I just can't find it yet.

PS, I don't want this to be a debate on the benefits of 120VAC vs 24VDC, that's not an issue for me, I'm already standardized on 24VDC for anything new. The issue is when I have to retrofit an existing PLC like this and the end user is reluctant to rewire everything. And yes, I know the S7-200 has 120VAC input versions, I need the 1200.

Iono, couldn't you just use a stepdown transformer with a bridge rectifier?

Even easier than that you could get some 120VAC switching relays and run 24V through the contacts?

Complete amateur here!

I agree with Honga. Why not use one 6.2mm 24Vdc interface relay for each output.

Use opto isolators for the inputs - relay switch contacts bounce and the relay lifespan with frequenty operating inputs will be dtamatically reduced. Also the more coils that are operated, the more noise is generated and hence surpression is required to avoid false input signals.

Relays can be used for outputs if they handle heavy loads, or operate infrequently. Otherwise use opto's to drive the loads

nonuke said:

I agree with Honga. Why not use one 6.2mm 24Vdc interface relay for each output.

Click to expand...

That's what I proposed, but consumes too much panel space. Even though the S7-1200 is smaller than the old PLC being removed, they were counting on using the extra space for some new instruments. I may end up having to set up a stand off for the DIN rail and put the interface units above the PLC. Funky, but functional.

Funkytional?

If the PLC Outputs are wired to terminal blocks, you can replace the terminal with the interface relais. Just an idea.

have you check for din rail slim relay using the space of a terminel ? or board relay (micro etc)
It would be the solution i would choose because it won't really make bouncing on the 24vdc signal as the load is only 0.004 mA on each input.
If you need high speed reaction, you may look for a solid state relay or opto...

On the other side you may try to modify the electronic of the module for 120vac
input impedance is 6000 ohm for 24vdc so if you put a diode rectifier and a 24 000 ohm resistance is serie on each input with a small capacitor in paralele it should work but you would need a place to hide the electronics parts....

Youre still screwed up to use a product not really completly ready.....If you are lucky, the project will take time and 120 vac module will be released on time of completion...