Motor controls

jtashaffer · Aug 22, 2010

Does any one have a example of a good motor start ladder rung, that uses a e-stop, pull cord e-stop, auto and man switch, and a holding contact for the motor. I have written some before but I wanted to get a new idea.

Tharon · Aug 22, 2010

Draw it up on paper as if you were wiring without a PLC. Then do that in your ladder. Ladder Logic is modelled after actual relay and contact wiring. It translates pretty much directly for simple stuff like this.

And remember that your Estops should be hardwired, not just PLC inputs.

sthompson · Aug 22, 2010

jtashaffer said:
Does any one have a example of a good motor start ladder rung, that uses a e-stop, pull cord e-stop, auto and man switch, and a holding contact for the motor. I have written some before but I wanted to get a new idea.

You weren't very specific about what you wanted the Auto/Manual to do. This is one possibility.

Stu....

jtashaffer · Aug 22, 2010

motor controls

That is pretty much what I had. The auto,man switch was to start the motor in either mode. I just didn't know if there was an ideal way or what I had was pretty much the norm.

PLCKeef · Aug 22, 2010

I'm not sure what safety requirements your country has but Standards usually dictate that all your Emergency stops have to be hard wired.

sthompson · Aug 22, 2010

PLCKeef said:
I'm not sure what safety requirements your country has but Standards usually dictate that all your Emergency stops have to be hard wired.

As pointed out by PLCKeef, we have only dealt with PLC Program side of things so it reacts to the E-Stop Button and Pull Cord correctly. There should also be a hard wired Master Control Relay (MCR) that breaks the power to all the Output Cards when the E-Stop is pushed, or the Pull Cord activated. Inputs from each device to the PLC allow the Program to react correctly, and allow for easy troubleshooting if the line stops, especially if you have an HMI.

Stu.....

sthompson · Aug 22, 2010

jtashaffer said:
That is pretty much what I had. The auto,man switch was to start the motor in either mode. I just didn't know if there was an ideal way or what I had was pretty much the norm.

I saw your posting in the second thread you started on the same subject. I would recommend you look at Ron Beaufort's video lesson located here.

http://www.ronbeaufort.com/sample_lessons.htm

Watch all eleven in order.

Stu.....

SMOKE · Aug 23, 2010

My E-Stops in logic are normally closed as well as the actual hard wired system. I am sure they have to be that way everywhere?

sthompson · Aug 23, 2010

SMOKE said:
My E-Stops in logic are normally closed as well as the actual hard wired system. I am sure they have to be that way everywhere?

E-Stops in the field are usually Normally Closed (N/C), this is the the most fail safe way of wiring them. So, as a result they are Normally Open N/O (AB XIC) in the PLC Program, because if the E-Stop is good, you will have a 1 in the Input Map. I normally use a Normally Closed (AB XIO) for an Alarm condition. I usually identify which E-Stop is pushed on the HMI to help the Operators out.

Stu....

Motor controls

jtashaffer

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jtashaffer

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