Pulse width modulation PWM example

angela133155 · Dec 13, 2013

Hi, I am trying to write a ladder logic using PWM and INI instructions to actuate a fast switching solenoid valve at a range of frequencies. I have tried looking around for examples but just can't find any except for the very basic example from the manual.
Wonder if anyone has any examples to show the application or would care to draw one simple ladder logic using PWM and INI?
Just more information: I am using CP1E PLC from Omron.
Thanks!

Lare · Dec 13, 2013

Here is couple examples:

http://www.plctalk.net/qanda/showthread.php?t=21112&highlight=valve

http://www.plctalk.net/qanda/showthread.php?t=83509

shooter · Dec 15, 2013

with plc impossible to make PWM unless you have special output.

daba · Dec 15, 2013

shooter said:
with plc impossible to make PWM unless you have special output.

How do you come by that statement shooter ?

You most certainly can, with the correct programming, make an output turn on and off with a variable pulse width, and fixed cycle time : a.k.a. "Pulse Width Modulation"

Highland Controls · Dec 16, 2013

You can make a PWM output in ladder, but the performance will be limited. Special output cards allow PWM frequencies starting at about 5kHz and going on up. You will never get that by turning on and off outputs in ladder. So the answer depends on what you need.

Peter Nachtwey · Dec 16, 2013

Shooter is right. The best thing to do is to buy the right amplifier card for the valve. It will convert an analog value from the PLC to a PWM current signal.

daba · Dec 16, 2013

angela133155 said:
..... to actuate a fast switching solenoid valve at a range of frequencies.....

I doubt you'll be able to go above 15 to 20 Hz - obviously depending on the vale used.

What frequency do you want to go up to ?

And since you'll be operating a mechanical device, I don't think your PWM output needs to be super accurate.

angela133155 · Dec 18, 2013

I will be seeking help from Omron, so perhaps I can get some questions answered.
My solenoid valve has a max switching frequency of 500hz so I guess it should be able to give me the range of frequencies that I need (yup Daba, it doesnt need to be super accurate). I will ask about the amplifier card too.

Will update here when I get the issue resolved

milldrone · Dec 19, 2013

angela133155,

Eurotherm makes a signal conditioner that converts analog dc volts in to frequency out. It's old legacy equipment. Download the full line product catalog here.http://www.actionio.com/ and search the PDF for AP7500.

angela133155 · Jan 3, 2014

I found a solution to achieve on off actuation via the use of two timers. Actually this is similar to flip flop if I am not wrong. Basically, I have one timer (TMHH(540)) acting as OFF timer and another timer acting as ON timer, which will be run when the OFF timer runs out. I can adjust the on off frequency through the Set Value of the timers.

Pulse width modulation PWM example

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