Needless to say, I am not happy with the boss right now. Here is the problem. We have a small motor, DC, 0 to 10 volts that has its speed controlled by a old electronic (Home made) PID controller. Speed is 0 to 1950 rpm and it uses a small encoder as the feed back to the controller. The system works very well, but, if it works, this is not good enough for the powers that be. Ron gave me some real good help with PID in the past, but now I have this question. How do I incorporate the feedback loop from the encoder. We currently use a PC with a D/A converter connected to the motor and another A/D converter connected to the PC for the feedback. Please don't ask me about the program used by the PC. Thats top secret!!!
The PLC is a SLC 5/02 using a 1746-NIO4V analog input/output card residing in slot 5. I put it there. The PLC is configured correctly and I have connected another motor to the output for the time being so I can play some. But how do I wire the encoder feedback and use it in the PID control?

You may be able to bring the encoder pulses to a 1746-HSCE card and get an internal analog value from that...

Yes connect the encoder to a high speed counter card and convert the pulses to speed, properly scaled for your pid. You should be able to tune that in. I have done it with a control logix platform successful and it worked fine. I have not tried it on a SLC tho.

You may want to consider using a signal converter instead the pulse input module, should be cheaper.
If you know the expected freq. range, you can get a freq./4-20 converter.

I'll try the HSC module and go from there. Should work just fine, but then again, it's a SLC 5/02, but should work. Thanks for the help folks.

OK, now that you have your problem somewhat addressed........


What's so secret about the SLC Program?

The only secrets I've ever seen in a SLC program was out of a group in NJ that just didn't want anyone to see how an RTO worked. I'm not sure if he realized that an RTO just gets really hot an destroys whatever you put in it.

The bottom line came out later, he didn't know how to make his system work and didn't want anyone to find that out. (I don't think that is what you are saying here)

Anyone else ever classify their programs? I've locked (passworded) the processors from time to time because I had gremlins that seemed to be helping me program when I wasnt' around.

He said the PC code was secret, not the PLC code.

NOTE TO SELF: Try reading what is written before you consider what was said. Don't be a skimmer!


Thanks Ken, now I really feel dumb!! Hope I'm not related to Wild Bill's boss!!

No Problem, we stick our feet in our mouths on occassion.

In another direction
So, they have a system that already works, and your happy with that system...Now they want you to spend heaps of money on the appropriate IO cards.... heaps of time trying to firgure out what you need to do, design, implement and test which equals more money... If the company has so much money to throw around it's time for a decent payrise for your self don;t you think... at least then it will be goning to a good cause...

I like your login. I used Wombat for a time on one of my BB's.

Bullitin Boards... now your taking me back to dial up with 9,600 bps connections and DOS with ASCII text based graphics etc....