Micro850 IPID function

Hi guys,

I'm using AB Micro850 PLC. I need a PID function: the one available in the function library doesn't work at all (At least to my understanding). A strange block diagram is shown in the manual (attached) that doesn't seem a PID control. Anybody with experience with IPIDCONTROLLER function?

Thanks

That doesn't look like a PID controller to me. There is an integrator time constant if that is what tau_i is but that is not how an integrator should be implemented.
Does a micro850 have floating point and what are you controlling?

There is no intergrator in PD

Peter, yes Micro850 has floating point and I’m controlling the synchronism between two rotating machines.

There is no integration function, the derivative action is done on the Process Value (and not on the error) and the proportional action is done on the error (seems the only correct thing).

I just do not understand why they have called this function IPIDCONTROLLER and actually, it's not a PID. I did some test with the PLC and the behavior matches with the block diagram (at least what I could test).

Anybody with experience with this function?

Gastone said:

Peter, yes Micro850 has floating point and I’m controlling the synchronism between two rotating machines.

Click to expand...

It is good to have floating point. If necessary you can write your own PID with feed forwards and ramps etc.
Synchronize how? Angular positions? Angular velocities. How fast? How precise?
You could be wasting your time using a cheap PLC or any PLC for a motion control task.

I need only to control the speed of these two machines, there is no motion control, no speed variation: I have only to guarantee the exact speed of the two machines (about 50rmp).
I’ll do the PID by myself if no other suggestions are coming.

I downloaded this add on from the sample code library I believe. It worked well for a vacuum pump application. If it's something you could use but can't find, I can probably email it to you to add into your program.

dginbuffalo said:

I downloaded this add on from the sample code library I believe. It worked well for a vacuum pump application. If it's something you could use but can't find, I can probably email it to you to add into your program.

Click to expand...

I already saw this block. The RA_PID uses as core the IPIDCONTROLLER. The only improvements of this block are:
. it manages manual value
. it limits the outputs with a maximum and a minimum value.
The other functions of the PID are managed by the same IPIDCONTROLLER function.

If you have experience with the RA_PID mode, can you explain me how the PID integrative function is working?

Unfortunately, I can't really give much feedback on this. We set it up and bench tested manually in the shop but I was not the one to tune out in the field once it was hooked up to the process.