Sink/Source NPN/PNP Delima

I have existing equipment that uses both Sinking and Sourcing Sensors. The new control hardware I'm putting in is Sinking only. Is there a circuit that I can use to allow me to use both input devices? I know I can use a pull up resister, but 1. I have to only install it on the devices that need it and 2. It inverts the signal which is not good for photo eye logic.

I know that at one time AB had a circuit inside their I/O that would accept either type of input automatically.

Does anyone either have a schematic of that circuit or a similar one?

Thanks!!!!!


Dave

See link below if I read your question correctly.

http://www.plctalk.net/qanda/showpost.php?p=437331&postcount=4

Mickey,

Thanks for the prompt reply.

What I'm doing is designing an interface board between the old field wiring and the new I/O. I want to incorporate this circuit on all inputs. So I can't use the part you forwarded to me. Instead, I would like to build the circuit directly on my PCB.

Do you happen to have the schematic of the circuit?

Go back to the link Mickey posted. There are two links in the post. Follow the first to find out what kind of circuit you need. Then google for hardware.

Why won't that hardware work for you? The one module performs for both NPN/PNP in to both NPN/PNP outs, giving you universal conversion.


(edit: Its weird how some questions seem to come in twos or threes)

Instead, I would like to build the circuit directly on my PCB.

Click to expand...

Is this a contest to see who can build the best PCB? Otherwise why do this? Most likely you will eventually either replace the "control hardware" with the proper sinking or sourcing, or replace the field devices to match your control hardware.

The reason is failures. When something goes ka-pooey, the question is going to be "Is it the field device, or is it the PCB circuit"? After 3 or 4 times wrestling with this, you will fix it like you should have the first time.

I like the smart plug from Turck:

http://www.turck-usa.com/illustrations/B0313_07-08.pdf

I've used these in the past with great sucess. It might not fit your exact need, but for many, it is very easy to use - especially if you use all QD devices in the field.

Also, an interface board for old field wiring and new I/O? Sounds like this should really be a terminal strip.