Contrologix Ramp instruction?

Does Contrologix have a single instruction that can be used to ramp an analog output? I could build a ramp out of multiple instructions, but if a single instruction was available it would be easier. I am currently using a Moog ramp card to provide the ramp for my servoamplifier, and was wondering if their was a way to do it easier in the PLC.

RLIM oughta do it...

Yeah, that would work but the rest of the program is in ladder and don't want to add just one function block. I guess I'll just stick to the Moog module.

Do you have the SCP AOI? Put a timer .acc in for input, 0 for input min, timer .pre for input max, ramp starting point for output min and ramp ending point for output max. (see an example here)

You can also use a timer and a CPT instruction. The equation for a ramp is
Y = Starting_Point + ((Ending_Point - Starting_Point)*Elapsed_Time/Total_Time)

1756 Analog output modules can also do the ramping for you. Ramping is configured in the module setup.

TConnolly said:

Do you have the SCP AOI? Put a timer .acc in for input, 0 for input min, timer .pre for input max, ramp starting point for output min and ramp ending point for output max. (see an example here)

Click to expand...

Nice, I'll have to remember that one Then bundle it all up in an AOI, and you have your "ramp" instruction.

One thing to watch out for on the ControlLogix platform is that a timer .ACC can overrun the preset. So you need to range check the result if overrun is a problem for the application.

SLCs and PLC-5s can overrun too. Just put a rung or branch to move the preset to the accumulator when the timer is done (after the timer, before the scaling math) so the ramp doesn't end with an unexpected jerk at the end. I learned this working on a tire inflation valve with analog pressure control, with one particular tiny tire they were developing, the inflation was too fast with no mechanical means to restrict it. The designers thought the balance problems were because it was inflating too fast on the assembly drum where the raw rubber inner components blow up from a lamp shade shape into what kinda looks like a tire.

To make a short story long, I added a ramp time and ramped the pressure signal just like TConnolly shows. It did solve the uniformity problem with the tire after a couple of egg shaped ones I made when I discovered the oversight and the nice round ramp up ended with a flat... Just glad it was a pressure valve and not some big mechanical drive I was fiddling with.