Ramp requirement in PID Block in AB Controllogix

There is a Ramp/soak function (RMPS) in Logix5000. I've never used it, so I don't know exactly what it's for. It would appear that you've already decided not to use it, too.

There is also a rate limit function (RLIM), which I think can do what you're asking.

Or, if you're using the PIDE instruction you can set the CVROCLimit parameter. Don't forget to look into CVManLimiting.

AK

Roll your own?

You could make your own function.

Desired SP - current SP = Amount of change
Ramp time divided by number intervals = interval time
Amount of change divided by number of intervals = step size

As an example:
current SP is 10, desired SP is 60, ramp time is 10 minutes, with 20 intervals
amount of change = 50
interval time = 30 sec
step size = 2.5

Then set up a simple rountine, move the interval time to a step timer, and the step size to an ADD function.

If SP is less than desired SP, and timer is done, then (SP=SP+2.5)



This just the basic idea, you will also need to account for negative step changes, and check for valid data entry from the operator.

sorry, slightly off subject

But sounds like someone here could help me

PID control on Cntrlgx 5561

RSView32(OPC) for HMI

When I try to assign address to tagname I get "Parent not found" error.

TIA

For Burnbomb: Are you using the PID faceplates? They require that the BASE PID tag be selected, the help files for the faceplates have some examples.

For the original poster: Yes, do as Ken Moore suggests, and 'roll your own' ramp. It's made easier if you just put the ramps in a timed task, so you know the update ahead of time, but in your case you will still need to play around with the interval, if that mode is selected...

MORE IMPORTANTLY: You might want to consider 'seeding' your ramp generator output with the actual PV of the process when it is in MANUAL mode. If you don't, you can run into a user-unfriendly situation (example follows):

Temperature Process is in AUTO, setpoint is 200, and PV is stable at 200.
Operator switches to MANUAL for a minute, and changes SP to 300.

Without seeding the ramp generator, the CV will attempt to cool the loop as the ramp goes from 0 to 250, only then will it start heating again.

With seeding, the CV will begin to rise immediately from 250, and track the SP as it ramps up.