Using an Interposing Relay

[CodeMonkey01]

Hello, We have a 12v prximity senosor connected to an interposing relay. The interposing relay is giving a 5v input to the cRIO through the Digital IO sidecar for feedback of the loading arm position. Is this in violation of r65 and r66? We have attached a schematic of our setup. Thank you.
We have an image of the wiring diagram for this setup:

[Alan Anderson]

I don't see any reason for your relay to be against the rules.

The only problem I see is that the way you have it drawn, it won't do what you expect. If you leave a Digital Input pin unconnected, an internal pullup resistor will bring it to +5v and it will read True. Your relay will connect +5v to it, leaving the value unchanged. If you instead connect "ground" to it when the relay is activated, the input will read False and you can tell the difference. You'll want to remember that the signal is backwards from what you might expect -- or if the sensor has a white wire with the opposite sense from the black one, you could use that instead.

However, the relay might not be necessary. What is the part number of your sensor? If it is NPN output, it doesn't actually provide 12 volts on the output pin. All it can do is pull the pin to ground, and that is perfectly compatible with the DIO on the Digital Sidecar.

On the other hand, if it's a PNP or fully-driven output, then you do need to account for the higher voltage. But instead of the active relay, you could use a simple resistor divider, with 14k in series with the connection to the DIO signal pin and 10k from the DIO pin to ground. Depending on the exact part number, you might also need a 10k resistor directly from the sensor output to ground.

[CodeMonkey01]

Originally Posted by Alan Anderson

The only problem I see is that the way you have it drawn, it won't do what you expect. If you leave a Digital Input pin unconnected, an internal pullup resistor will bring it to +5v and it will read True. Your relay will connect +5v to it, leaving the value unchanged. If you instead connect "ground" to it when the relay is activated, the input will read False and you can tell the difference.

Sorry about the confusion. We are aware of this, and that is how this is setup. The 5v and 12v are just notes as to the line voltage and not the specific pin as the direction on that line is bidirectional. Thank you for mentioning that mistake.

Originally Posted by Alan Anderson

However, the relay might not be necessary. What is the part number of your sensor? If it is NPN output, it doesn't actually provide 12 volts on the output pin. All it can do is pull the pin to ground, and that is perfectly compatible with the DIO on the Digital Sidecar.

Our mentor, a 'Technical Consultant' from 'Rockwell Automation' who provided the part has told us that is is preferred to use this method. Now You may be right, but since we have this setup working right now, we will stick with it and prepare the solution you suggested in case we need to swap it for competition.

Thank you again for your quick reply.

[James Lightfoot]

I just want to make sure we have our photo switch (PE) connected properly. It is an A-B 42EF–D1MNAK–A2 (NPN Diffuse). Currently, we are feeding the photo switch from a dedicated circuit breaker (as it's a custom circuit per the rules). We currently have the white (it could be either the white or black) connected to pin 1 of GPIO5. Per the snap shoot of the wiring diagram from the A-B PE user manual:
Wiring Diagram Photoswitch (DO & LO) 42EF-D1KBAK-a.pdf
Brown - Connected to the +12VDC
Blue - Connected to the DC 12V common
White & Black are the photo switch's output signal.

From the picture of our hand drawn schematic ,
Schematic PE1 to GPIO5.pdf
I am bring the White wire into the signal pin (pin 1). I am not using the center pin (pin 2). Pin 3 is tied to the DC Common bus.

Now that I am looking at the A-B schematic and place it context w/ Alan Anderson's comments, I believe we wired the PE correctly. Being a sourcing input/output, I think we need to tie the White or Black Wire to a GPIO's pin 1. Please verify whether I am right or wrong. I would hate to waste time troubleshooting an easy fix that should have been caught at testing.

Thanks,

[Alan Anderson]

Originally Posted by James Lightfoot

...A-B 42EF–D1MNAK–A2 (NPN Diffuse)...

I am bring the White wire into the signal pin (pin 1). I am not using the center pin (pin 2). Pin 3 is tied to the DC Common bus.

There's no need to connect the (-) pin on the Digital I/O port. SIG alone will be sufficient. The sensor's blue wire going to a black Wago terminal on the Power Distribution Board is good enough to provide the path for the sensor's output to be pulled low. Having the extra connection to the Digital Sidecar isn't likely to break anything, but it's an unnecessary wire.

Being a sourcing input/output, I think we need to tie the White or Black Wire to a GPIO's pin 1. Please verify whether I am right or wrong.

The connection you describe is correct. However, the NPN part is a sinking output. It won't source current.

[James Lightfoot]

Originally Posted by Alan Anderson

The connection you describe is correct. However, the NPN part is a sinking output. It won't source current.

Thanks. So, the sinking output of the PE (it's providing to neg/common) needs the sourcing input of the GPIO; hence, connecting the PE's white or black wire to pin 1 (SIG) of a GPIO is correct. I get, and then when it comes up later my head gets twisted over it again.

Thanks, Alan.