Class Project - Drive Cabinet

Hello all,



I am currently working on a new trainer for our PLC/Motor controls lab. The drive is the first part of a conveyor system.

With this cabinet, I want to accomplish the following:



1. Develop typical circuits that are commonly used in large, say 300 hp drives (AC or DC) on a much smaller scale. 2 hp. What I have so far is the MCR, cooling blower/air pressure switch, thermal safety circuit, cabinet door switch, cabinet thermal switch and speed control. Enable, start, stop, jog, and reverse will be provided from the PLC through banana plugs. Feed back is optional for the drive, but will be used for both the drive and the PLC to provide location data on the conveyor.



2. The cabinet and conveyor will be separated with enough distance to make troubleshooting interesting.



3. The PLC's are SLC504's 505's hopefully soon. They have 0-10vdc analog cards with 2 input/2 output channels. Discreet IO is 120 VAC 8 in, 8 out. Each has its own programming station, ten in all. As mentioned before, the PLC's can be attached to the cabinet one at a time, and connected with banana plugs.





I would like to ask for suggestions with this project. I may want to add a watchdog circuit for example. While most students fresh out of a two year program still have a lot to learn, I'd like to get as many real world situations as possible. Hey I know, call them at three in the morning and ask what in the world they did to shut the mill down. Naw, but I thought the kind folks here would certainly have other common circuits that I didn't get to deal with during my run.



Thanks,



Robert Denton

One thing we do on the larger drives is to get an analog signal back from the drive for the current. Then if the current is below a threshold, we have an alarm . Low amps is an indication that the motor is not running or the coupling has failed.

I dislike cabinet door switches

At least for control cabinets under 600vac. I know they are used but I have never seen the justification for them, except some safety concept that wants a technician to be able to troubleshoot or repair a system with the power off. If I could work without the power on then, in my case, I would not need 1000's of dollars worth of test equipment i.e. scope, ampprobe, multimeter and more.

One thing is that a part of a process may run with another part having a problem, opening the cabinet requires all of the process to shut down.

Another aspect is if a drive etc has a fault then removal of power could remove that fault. This could mean that you could have an intermittent problem that is harder to locate, because of the loss, and allows the machine to be down more than it should.

I am not sure what the distance involved may be but with motors you have to provide a disconnet within 50 feet, not sure you should do that on the output side of the drive.

The rest of it sounds awesome, which I could attend a class or two.

Thanks guys,


Ken,

I plumb forgot about current feedback. Great catch.

Rsdoran,

Yeah, you are so right about cabinet switches. I agree, but it seems that every cabinet I have worked on had one. I've often wondered why. Still, it is a great bug to throw at the students for troubleshooting problems. The beauty is that I can disable it any time I want.

O'scopes will be an imoportant part of my troubleshooting class.

I'll let you know when I get this thing close to complete. You can visit any time you like. Fridays are best, as M-T I have students all day. Alabama Southern Community College, Thomasville Campus, I'm a little over a hundred miles South of B'ham. on Hwy 5.

I said which but meant wish, have to proofread my self. Thanks for the invite, I may take you up on it. I had already figured out where you had to be but it was not place to name it.

I also meant to say something along those lines of being able to disable it but offering it as a problem could be beneficial.

I have owned several scopes. I have a B&K dual channel 20MHz that is tried and true and usually within arms reach. There are so many issues in industrial applications that a tech needs to know how to use a scope.

Try and get a couple of bad scope probes. Ones that look perfectly good but are actually open.

I have a bit of a training background. Occasionally, students would break one of the probes and not realize it was bad. I found that it was a good exercise to give them 1 good one and 1 bad one to see if they would do the cal check to make sure they had "properly working" test equipment before they began to troubleshoot a problem.

I have a rewrite I did from the US Navy Electronics Technician course on Six Step Logical Troubleshooting. I pass it out at all of the maintenance courses I give at my work. I learned it once upon a time, or should I say while in ET school in the Navy they "POUNDED" it into me. If you train them right in school, they will use it always.

I have attempted to attach it for you and anybody else that wants it.

Leadfoot,

Where did you take A school? I was in Great Lakes for MM. That could be a complete thread. Lots of squids here.

The attachment is great. Using bad probes is a good idea. I also like to use a bad Output card and other devices. I have always taught people to destroy bad parts that would not be rebuilt, so its a bit hard to find bad parts around here. I had to rig some relays last semester. I try to teach guys to first use a pencil and paper/documentation, then test tools, and lastly replace/repair parts. I get some funny responses by charging points rather than dollars for replacing good parts. Replacing a blown fuse without checking for a short circuit will cost you fifteen points.

Hey Snipe,

I started BE/E school in Sept. 1969. I finished ET "A" school May 1971 and ET "C" school Aug. 1971. I crossed over to EW in 1975. That was fun being stationed at the "SPOOK" base.

We have a "nuke" show up here occasionally that is down the road from me. You are right about an ex-squid thread. It would be interesting.

Twiggit