sinking/sourcing input wiring

Good morning all.

I have never seen this done but I want to ask if it is possible. On an AB 1766-L32BWA, can you have some of the inputs wired as sinking and some wired as sourcing, depending on whether you connect the 24 VDC or the 0 VDC to the "DC COM". See attached screenshot of the manual.

Example: So if I connected the 24 VDC to the DC COM 0, 1, & 2, inputs 0 through 11 would be sourcing and I connect the 0 VDC to DC COM 3, inputs 12 through 19 would be sinking inputs? I am not sure if all of the DC COMs are electrically isolated from each other.

It seems like this can be done, and there is a small blurb about it in the manual but I wanted to make sure I read it correctly.

I have done that in the past and it works fine. All inputs in each group have to be the same but the groups can be different.

https://literature.rockwellautomati.../documents/um/1766-um001_-en-p.pdf#G7.1065072


That also says yes.

since you have multiple commons, you can have both types of inputs.
i have never done this and to me it is a bad practice.
a sensor goes bad and maintenance sees the part number for a sourcing input,
gets the sensor, and wires it into a sinking input. then things really go wrong.
regards,
james

James Mcquade said:

since you have multiple commons, you can have both types of inputs.
i have never done this and to me it is a bad practice.
a sensor goes bad and maintenance sees the part number for a sourcing input,
gets the sensor, and wires it into a sinking input. then things really go wrong.
regards,
james

Click to expand...

OT: Congrats on post #3k!

a sensor goes bad and maintenance sees the part number for a sourcing input,
gets the sensor, and wires it into a sinking input. then things really go wrong.

Click to expand...

Not sure about what "really goes wrong" in that scenario. Replacing the sensor that failed with the the wrong type of sensor results in a sensor that still doesn't work. It doesn't take anything else down with it.

wilkerson29847 said:

Good morning all.

I have never seen this done but I want to ask if it is possible. On an AB 1766-L32BWA, can you have some of the inputs wired as sinking and some wired as sourcing, depending on whether you connect the 24 VDC or the 0 VDC to the "DC COM". See attached screenshot of the manual.

Example: So if I connected the 24 VDC to the DC COM 0, 1, & 2, inputs 0 through 11 would be sourcing and I connect the 0 VDC to DC COM 3, inputs 12 through 19 would be sinking inputs? I am not sure if all of the DC COMs are electrically isolated from each other.

It seems like this can be done, and there is a small blurb about it in the manual but I wanted to make sure I read it correctly.

Click to expand...

You have read the manual correctly.

"Sinking and Sourcing - Any of the MicroLogix 1400 DC embedded input groups can be configured as sinking or sourcing depending on how the DC COM is wired on the group."

Your uncertainty seems more focused on the isolation between the DCOM for each group and how they might be somehow linked and could be damaged if you tried this?

Just to further reassure you that they are definitely electrically isolated...

"Input Group to Backplane Isolation and Input Group to Input Group Isolation

Verified by one of the following dielectric tests: 1100V AC for 1 second or 1697V DC for 1 second
75V DC Working Voltage (IEC Class 2 reinforced insulation)"

Also see here for further confirmation...

ID: QA33300 | Access Levels: TechConnect
MicroLogix 1400 DC COM information

(It simply states they are not internally connected).

Regards,
George

Steve Bailey,

you just had to be there to see what happened.
a sensor went bad, they replaced it with a sinking not sourcing one.
well joe went to break and jeff steps in and says there's the problem. he also replaces a different sensor with the incorrect part. long story short, all sensore were switched with the wrong type. it took several hours to fix the real issue, 1 prox switch went bad.

PreLC, thanks, i never thought i would get this far. i hope that i have helped as many of you as those of you have helped me with issues. if i have offended anyone on this site, i do apologize and ask for forgiveness.

james

James Mcquade said:

If i have offended anyone on this site, i do apologize and ask for forgiveness.

james

Click to expand...

You do say that a lot. Maybe Catholicism is a good choice for you? My understanding is that it's reasonably easy to avoid eternal damnation. Those two maintenance guys might want to go with on Sunday as well, it sounds like they have many sins to repent.

Now I've probably offended a bunch of people too... bugger.