Conveyor Belts & Timers

ruby.n · Mar 1, 2010

How do I know if the conveyor belt is moving or not? How do I use timers to detect this? And if the conveyor has stopped, I need to send an alarm to the SCADA system!

Im working on an SLC500, but guess the logics the same?

I have never coded before! I only understand pretty basic logic...

jstolaruk · Mar 1, 2010

I usually put a prox switch monitoring a moving part of the conveyor that has a periodic change (like a shaft with a gear that can be turned into pulses). I then set up 2 timers that are:

#1 enabled when the motor is running and the prox sw is ON, and

#2 enabled when the motor is running and the prox sw is off.

Set the presets so that during a normal pulse of the prox while the motor is running, the timers will not timeout. If something happens mechanically, like a jam, one of the timers will timeout and I use the done bits to flag a fault. Hope that helps.

(note: if the conveyor starts & stops often, I'll use retentive timers (RTO))

ruby.n · Mar 1, 2010

Thanks jstolaruk!

But how will I know if the motor is running? Do I need to check the phase current? I think there is an Intelligent overload device...

PeterW · Mar 1, 2010

I ususally use 1 off delay timer and a 1 shot. Keeping the input on when not running, when running, create a 1 shot on the proxy rising and/or falling edge.

PeterW · Mar 1, 2010

ruby.n said:
Thanks jstolaruk!

But how will I know if the motor is running? Do I need to check the phase current? I think there is an Intelligent overload device...

Contactor feedback.

jstolaruk · Mar 1, 2010

PeterW said:
Contactor feedback.

Or your output that energizes the contactor is you don't have a monitoring contact. Of course, then the list of things that could be wrong is longer but at least you are detecting some kind of fault.

ruby.n · Mar 1, 2010

What is a one-shot?

What does its ladder form look like?

OZEE · Mar 1, 2010

Sounds like you need to start here

Then we can talk about the rest...

As far as how you detect if a conveyor is running, the aux contact on the starter will tell you if the starter is engaged. You don't need anything as fancy as current monitoring, though you could certainly do that.

However, monitoring the aux contact will only tell you whether or not the starter is engaged. It won't tell you if something between the motor and the conveyor drive has broken. That's why it has been suggested to use a prox to monitor a moving part on a driven shaft of the conveyor.

Which class are you in?

ruby.n · Mar 1, 2010

I am a Graduate...I have been asked to do some SLC 500 coding to see if the DCV is running, and if so to make the Conveyor belt run. And to check that they both are running fine. And to alarm anything to iFIX.

Sorry I have never worked with PLC's before. So findging it a bit tough, as I have a deadline to meet.

texasbirds · Mar 1, 2010

I wonder if he isn't using an Encoder to control / monitor the speed of the conveyor. If he is, he could simply compare the pulse count to zero, then make a decision.

ojz0r · Mar 1, 2010

ruby.n said:
Sorry I have never worked with PLC's before. So findging it a bit tough, as I have a deadline to meet.

Are you sure you should be doing this as first project ever on plcs?

PLCMentor · Mar 1, 2010

ruby.n said:
I am a Graduate...I have been asked to do some SLC 500 coding to see if the DCV is running, and if so to make the Conveyor belt run. And to check that they both are running fine. And to alarm anything to iFIX.

Sorry I have never worked with PLC's before. So findging it a bit tough, as I have a deadline to meet.

You are really being put in a poor position unless you have someone over you that knows what they are doing. It doesnt sound like that is the case. This sounds like a great first programming task - as long as there is someone to help you through it. Otherwise you are risking making a mistake that could do harm. Using the Aux contact off of the motor starter is a standard way to determine motor run/stop status. You might want to look up seal in circuits. This type of circuit will allow you as a programmer to drop your output if the starter contactor drops out if there is a problem. This way your PLC program will not immediately try to start the motor back up when the problem is cleared. This could injure someone that was not expecting the system to start without the operator restarting the system.

ruby.n · Mar 1, 2010

Ya I guess. But I am only trying it on test kit for now.
Once I feel confident, I will definitely take it to a Senior person for verification.
But its just that I really don't even know where to start!
Ive never seen an Electrical drawing before! So its definitely going to be a great learning experience.

Thanks to all your inputs, I am actually on the right path now...!

PLCMentor · Mar 1, 2010

ruby.n said:
Ya I guess. But I am only trying it on test kit for now.
Once I feel confident, I will definitely take it to a Senior person for verification.

Oh ok. I think we all thought you were flying solo on this. I can agree with your initiative on this to be able to bring back a solution to your senior person without bugging them. It is always hard to find that balance between taking initiative and tapping that knowledge. Tap the senior person too much and you get known as the guy that has no initiative. Tap too little and you end up wasting time and possibly doing something very wrong.

ruby.n · Mar 1, 2010

Yes I know what you mean

But thank you all so much. I feel much better,and a lot clearer about things...

Cheers!

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