Micrologix 1000 DC COM

mavrick · Nov 20, 2019

I have searched every where but cant seem to find the answer. Is the DC COM terminal on a Micrologix 1000 controller internally connected to the inputs?

I'm wanting to install a pnp sensor and the manual request you take a jumper from the 0vdc(-24) from the 24 volt power supply and land it on the DC COM terminal.

I'm trying to understand why and what is it doing? Thank you

duckman · Nov 21, 2019

Very basic concept as to how the PLC inputs are configured, so it's entirely how the DCCOM terminal is powered
https://www.youtube.com/watch?v=6sQt1N0nBeE

Ken Moore · Nov 21, 2019

With the 1000 you can use your own external power supply OR use the on board supply as long as your needs are within it's power limit.
The DC Com is for a group of inputs, on larger units there may be more than one group so more than one DC com.

mavrick · Nov 21, 2019

I may have missed spoke. I'm trying to understand how the DC COM terminal operates. Is it internally connected to the related input group or is it just there to be utilized as a isolated jumper terminal to supply 24 volts. to my sensor.

mavrick · Nov 21, 2019

I miss spoke on my original post . The manual request you terminate the 24vdc+ on the DC COM. for pnp. That is where I'm confused is why does the DC COM need 24+? Couldn't I just supply my fiber senor the 24+ and 24- from the dc power source and the take my switch leg to input I/4? Thank you for the help.

OkiePC · Nov 21, 2019

The DC COM terminal is a point of reference for its associate group of inputs. If you take the DC COM terminal low, then a high signal at an input point will be "true". If you take the DC COM terminal high (+24vdc) then a low signal at any of its input points will be true. There must be a difference in potential between the DC COM and its associated input points in order for it to detect a "true" signal and place a "1" in its memory location. If there is no difference, you will get a "0".

parky · Nov 21, 2019

See this from Rockwell page 2.3 it shows you the connections for sink & source

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1761-um003_-en-p.pdf

mavrick · Nov 21, 2019

Thank you OKIE PC. That's what I was looking for. That makes sense as to why the DC COM is needed. Thank you all for the help!

Geospark · Nov 21, 2019

Spot the difference?...

parky said:
See this from Rockwell page 2.3 it shows you the connections for sink & source

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1761-um003_-en-p.pdf

Hi,

Just be careful with that sample reference for a 1761-L32BWA controller. The wiring diagram is correct but the wire descriptions are a bit mixed up for the lower diagram on Page 2-3.

If we use Publication 1761-IN001 - MicroLogix 1000 Programmable Controllers Installation Instructions, and refer to the same 1761-L32BWA example wiring diagram on Page 19, we will see the correct descriptions for the wires. This is with respect to VDC +/- and Sinking/Sourcing.

I just wouldn't want anyone to find that the above "Sourcing" leaves them with a "Sinking" feeling.

Regards,
George

parky · Nov 21, 2019

Well spotted Geospark I must admit I never took a real close look

mavrick · Nov 21, 2019

Thank you for the help. Great catch!

geniusintraining · Nov 21, 2019

mavrick said:
Great catch!

We would not expect anything less from George

Micrologix 1000 DC COM

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