would you please explain to me the interaction between PLC and contactors

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Jul 2018
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Hello,

I started my new job at a factory and I found that when I opened the PLC cabinet there are "ABB contactors" that are connected to the PLC. would you please explain to me how does the PLC interact with the contactors ? explain to me how they interact with the input and output of the PLC.

I will appreciate your time explaining that to me.
 
Without any further information, all I can say is that based on the state of various inputs in the field (switches, transmitters etc), the PLC will energize the coil of the contactors when a certain condition has been met. The contactors then power whatever loads they're attached to.

A simple example would be a water tank with a pump on the outlet. When the water rises to a certain point, it triggers a level switch, which is an input to the PLC. When this input goes true, an output will energize the coil of the contactor, which switches power to the pump motor, draining the tank to a certain level or for a certain number of seconds.
 
I have a generic AOI for Logix that handles my contractors.


For inputs, I have:
Overload Status
Breaker Status
Contactor Aux Status
Disconnect Status


For outputs I have:
Contactor Run
Contactor Pulled in
Overload Okay
Disconnect Okay
Breaker Okay.


Internally, the AOI determines, and exposes the following faults:
Overload Trip
Breaker Trip
Disconnect Open
Contactor Didn't pick up (failed to pull in in 500 mSec)


Those are the basics, you can do a lot more, but a simple contactor has a lot of information to give to an HMI to make maintenance easier. There is more to my contactor AOI, but those are the most important. Some other things I do is have a control bit to enable it to stay on for some period after the run command is lost (think motor blowers, keep cooling for a couple minutes), or the ability to toggle it on and off from a single input.


In this day and age, it is good to expose as much information about potential failures on an HMI alarm as possible, to enable maintenance techs to quickly determine and rectify the problem.
 
I have a generic AOI for Logix that handles my contractors.


For inputs, I have:
Overload Status
Breaker Status
Contactor Aux Status
Disconnect Status


For outputs I have:
Contactor Run
Contactor Pulled in
Overload Okay
Disconnect Okay
Breaker Okay.


Internally, the AOI determines, and exposes the following faults:
Overload Trip
Breaker Trip
Disconnect Open
Contactor Didn't pick up (failed to pull in in 500 mSec)


Those are the basics, you can do a lot more, but a simple contactor has a lot of information to give to an HMI to make maintenance easier. There is more to my contactor AOI, but those are the most important. Some other things I do is have a control bit to enable it to stay on for some period after the run command is lost (think motor blowers, keep cooling for a couple minutes), or the ability to toggle it on and off from a single input.


In this day and age, it is good to expose as much information about potential failures on an HMI alarm as possible, to enable maintenance techs to quickly determine and rectify the problem.
Does it bring up a list for each contactor like in our boxes we have up to 30 contactors.
 
Hello,

I started my new job at a factory and I found that when I opened the PLC cabinet there are "ABB contactors" that are connected to the PLC. would you please explain to me how does the PLC interact with the contactors ? explain to me how they interact with the input and output of the PLC.

I will appreciate your time explaining that to me.




Not sure if this helps but all our PLC's do with our contactors is send the low voltage to the contactor when it is time for the motor to turn on.
 

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