Fault In Proximity Sensor!

backendcode

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Good Morning Everyone,

I am working on conveyor project at my company. There are two indicator lights on the control panel, one is for motor overload fault and another one is a sensor fault.

I have completed my program to control the conveyor but I want to stop the conveyor if there will be a motor fault or proximity sensor fault.

my question is
How can I find the proximity and motor fault?

Please help me with that if possible.

My assumption

1. I was thinking to find the motor fault, I will check the state of my auxiliary contact of my three phase motor which is going to my input card of PLC( Found from control panel electrical wiring diagram) and this will give me my motor fault. Am I thinking correct?

2. I have no idea how can I find the proximity fault? and turn on the indicator on the control panel and stop the conveyor line.

Please give me an idea how can I do that

Note: I am not asking you to write a ladder logic for me but I just want somebody help me to find a black cat in the dark room! ;)


Thank you,
 
the auxiliary contacts from the motor contactor will give you a fault indication. You will need to know the orientation of those contacts, though... either NO or NC, to write the logic.

for the proximity, it also depends on the orientation of the contacts.
 
This is what I got so far,

My motor overload is NO
My motor run is NC

I have 6 motors in total and I am checking the state of the individual motor and putting them in internal memory bit and then all 6 memory bits are in parallel and indicate the light if anyone goes to 1 or fault. Please check the link below.

https://ibb.co/gPb9gv

Conveyor motor control is motor run state of each conveyor
motor run is state of my auxiliary contact
motor overload is state of my motor overload

Proximity sensor

for the proximity, it also depends on the orientation of the contacts.

I didn't get any idea from what you just said. I have 6 prox sensors and they are going to input card of my PLC and they are NO and when they will detect the part they will write 1 in the memory bit and this will turn on the motor.

How would I find the fault from this?

Situation:- Let's say part come on top of my prox and It detects and become 1 and when part moves forward and prox become zero again but assume, proxy didn't go back to zero and stay 1 even though there is no part on it. this is a fault and how can I stop the conveyor system?

Thanks again
 
1. I was thinking to find the motor fault, I will check the state of my auxiliary contact of my three phase motor which is going to my input card of PLC( Found from control panel electrical wiring diagram) and this will give me my motor fault. Am I thinking correct?
Click to expand...
This assumes that the starter coil is controlled by the PLC. The fault condition will be when the state of the auxiliary contact does not agree with the state of the coil.
The best you can do with the proximity switch is to define conditions where the failure of the prox is a possible cause. For example, too much time between a change in state of the prox could be because the prox has failed or it could be because it has been bumped out of alignment with its target. It could also be because there aren't any boxes on the conveyor or because something prevented the pneumatic cylinder from fully extending.
 
1.) what type method driving you ac motor? VFD or DOL system?
2.) where point you tap for your motor feedback? AC or DC?
3.) Are the feedback NO or NC contact or you using analog feedback?
4.) if the motor fault if using VFD what terminal to use? if using DOL system what aux contact to be use?
5.) the signal fault using AC or DC source? what contac to use NO or NC ?
6) proximity sensor what contact to be use NO or NC ? which more better?
7.) if proximity fault are there any secondary sensor to work or it will act as are fault signal?
 
Use a double throw prox, by which I mean one with N.O. and N.C. contacts. Monitoring them both will give you a reasonably good status for both the sensor and wiring. Or you could use an IOLink prox, but then you need IOLink hardware...
 
Are your prox sensors set up in a series for a single product run? Or are they parallel for six different runs of product?

Usually the only way to detect a fault in a prox sensor is by using a timer based on some other measurable signal from the process (like another prox, a motor starting, a gate opening, etc.). For example, if you have something you can use to indicate a piece of product being released, you can get a fairly good idea of how long it will take for the product to move from the release point to when it's SUPPOSED to hit the prox. When it's released, start the timer. Say it normally takes 5 seconds for the product to hit the prox after being released. Set the timer to 10 seconds. If the timer completes without seeing the prox, you likely have a faulted prox or a product was misplaced. You can also use a timer to detect if a prox is stuck on. Once the prox writes a 1, start timing. If product is NORMALLY in front of the prox for .5 seconds after the motor starts, start count when the prox is 1 and the motor is started, count to 2 and initiate a fault if the timer completes.

Hope that makes sense!
 
Steve Bailey said:
This assumes that the starter coil is controlled by the PLC. The fault condition will be when the state of the auxiliary contact does not agree with the state of the coil.
The best you can do with the proximity switch is to define conditions where the failure of the prox is a possible cause. For example, too much time between a change in state of the prox could be because the prox has failed or it could be because it has been bumped out of alignment with its target. It could also be because there aren't any boxes on the conveyor or because something prevented the pneumatic cylinder from fully extending.
Click to expand...

Thank you steve,

I get an idea of motor fault, I am going to check the state of auxiliary contact to find the state of my motor and turn on the fault light if there will be any fault.

The problem to tracking the time of change in state of my prox is the onload and offload of conveyor system is manual so the part can stay conveyor for whole shift without moving untill someone put the part on conveyor and take off from the conveyor and I don't think I can keep track of time in this situation.

what do you think?

Thanks
 
osmanmom said:
1.) what type method driving you ac motor? VFD or DOL system?
We are not using VFD and I am not aware of DOL system. but There are contactors in the control panel with motor overload. Contactors are internally wired to my PLC output card and my Motor is wired to those motor starter or contactors.
2.) where point you tap for your motor feedback? AC or DC?

Auxiliary contact of contactors is giving feedback to input card of PLC and I think it tells the state of motor
3.) Are the feedback NO or NC contact or you using analog feedback?

Motor feedback is NC

4.) if the motor fault if using VFD what terminal to use? if using DOL system what aux contact to be use?
Have no idea :/
5.) the signal fault using AC or DC source? what contac to use NO or NC ?
What signal fault are you addressing here?
6) proximity sensor what contact to be use NO or NC ? which more better?
No contact
7.) if proximity fault are there any secondary sensor to work or it will act as are fault signal?
Click to expand...

No secondary sensor, Once I find out the fault, I want to stop the line for safety issue!
 
LoganB said:
Are your prox sensors set up in a series for a single product run? Or are they parallel for six different runs of product?

Usually the only way to detect a fault in a prox sensor is by using a timer based on some other measurable signal from the process (like another prox, a motor starting, a gate opening, etc.). For example, if you have something you can use to indicate a piece of product being released, you can get a fairly good idea of how long it will take for the product to move from the release point to when it's SUPPOSED to hit the prox. When it's released, start the timer. Say it normally takes 5 seconds for the product to hit the prox after being released. Set the timer to 10 seconds. If the timer completes without seeing the prox, you likely have a faulted prox or a product was misplaced. You can also use a timer to detect if a prox is stuck on. Once the prox writes a 1, start timing. If product is NORMALLY in front of the prox for .5 seconds after the motor starts, start count when the prox is 1 and the motor is started, count to 2 and initiate a fault if the timer completes.

Hope that makes sense!
Click to expand...

Thank you Logan,

Worker from one end of conveyor puts the part of it and it moves to another end of conveyor and there will be another worker who will take off the part from conveyor So the change state of my prox is not consistence and it depends upon the speed of workers who are loading and offloading the parts. I think it would be hard to use timer i guess or may be I am wrong.

What do you think?

Thanks
 
AutoMax said:
Use a double throw prox, by which I mean one with N.O. and N.C. contacts. Monitoring them both will give you a reasonably good status for both the sensor and wiring. Or you could use an IOLink prox, but then you need IOLink hardware...
Click to expand...

we already ordered prox and I don't think my manager wants to order IOLink Hardware and double throw prox but I really appreciate your suggestion and I would definitely make a note of it so I can use in a future application!

Best,
 
Take care when creating fault definitions that you don't generate false positives. When your logic generates too many faults that aren't true, you are training your operators to ignore your warnings and to find ways to bypass real faults.
 
I cant work out what the proxes is for?

If its a manual conveyor and someone presses the the start and stop button, is the prox just checking boxes are moving?

If the conveyor runs but no boxes could be present for a shift, why bother with it?

If you have output to the contactors and the aux contacts confirm the correct state and the feedback from the overloads are ok, then safe to assume everything is healthy.
 

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