PWM with CompactLogix L32E AB

Hello all!

I'm sorry for so basic questions. I'm newbie with PLC.

I'd like to know if is possible to implement a pulse-width modulation (PWM) using CompactLogix L32E? (without signal conditioning)

Are there enough timers to implement 6 different PWMs?

Should I use a board such the 1769-OB32?

The frequency needs to be around 50Hz with duty cycle between 5% and 10%.

Most PWM outputs require a much faster frequency, and the CompactLogix has no hardware-based PWM outputs.

When you say 5% at 50 Hz, your ON-pulse will be 5 % of 50/1000 = 2.5 milliseconds.

That's close to the physical limit of the hardware (0.1 ms ON delay, 1.0 ms OFF delay) and the logical limit of the software (minimum RPI and Scantime considerations) for the controller.

What are you driving with the PWM signal ?

Ken,

you mixed. When I say 5% of duty cycle with 50Hz it means 5% of 20ms = 1ms ON-pulse.

As you said it's the physical limit of the hardware. So seems to be not viable to implement this PWM with CompactLogix, right?

I want to drive a small servomotor but the controller will be used to control other final elements as well (MIMO plant)

You can get PWM outputs if you use a 3rd party IO module, such as this Turck BL20 module with appropriate gatewway:

http://pdb.turck.de/media/_en/Anlagen/Datei_EDB/edb_6827341_gbr_en.pdf

Tks for replying!

Ken Roach said:

"That's close to the physical limit of the hardware (0.1 ms ON delay, 1.0 ms OFF delay) and the logical limit of the software (minimum RPI and Scantime considerations) for the controller."

Click to expand...

What would be 0.1 ms ON delay and 1.0 ms OFF delay? Commutation delay?
What's RPI?

Any reference also would be very usefull

Just to be more clear: I need to vary the duty cycle (on-pulse/high level) between 1.5 - 2 milliseconds therefore between 18.5 - 18 milliseconds of off-pulse/low level.



Tks again!

The 0.1 and 1msec times Ken mentioned are the switching times for the OB32 ( the outputs have some protection components which limit the switching speeds ) . The RPI is the backplane comms speed . If you have several cards on your rack , then the speed you require could be very hard to achieve . Also be aware that the OB32 , like most output cards , generates transient pulses of 1 msec if the output current is less than 1mA on start up . See the installation PDF for the 1769-OB32 .
Another alternative is the ML1100 ( Version 1763-L16BBB ) .This micro PLC has 2 high speed FET outputs ( 2 & 3 ) . It has an instruction for PWM . It also has Enet Comms to talk to your L32E . If you need them , it also has a couple of high speed inputs for feed-back .
Paul

Try this PWM module for the 1734 series Point IO distributed IO.

https://www.amci.com/plc-automation...se-width-modulation-plc-module-allen-bradley/