PWM to ANALOG Signal Conditioning ??

milmat1

Member
Join Date
Aug 2005
Location
North Carolina
Posts
209
Hey Folks.

I have a project where I will have have to control a VFD speed via analog voltage (0-10V) with the PLC, From an signal coming from my radio receiver. That signal will be PWM. So I will need to convert the PWM to a Analog for the PLC analog input.

This signal will be used to control a VFD speed via a Micrologix 1400 PLC . PLC has AC inputs and 2 Analog available on the brick, and 16 DC inputs on a IQ16 expansion module.

My Question is how can I convert the PWM signal to an analog signal that the PLC will accept ?

One suggestion was to build a low pass filter, which would give me a varying DC voltage output....

Anyone found a method to do this conversion ?



With all that said, I ask this, Could I use the speed increase / decrease with digital inputs then use them to count UP/DOWN with a counter. Then scale my analog output from the ACC value of that counter.

Any other suggestions ???
 
What is the speed of the pwm signal? If it is slow enough, you could potentially just feed it into the DI. The on-time of the DI would be the "command percent".
 
I may just breadboard something. I think I can just use a Low Pass Filter (R/C) To get a dc voltage, This should vary the dc voltage as the pulse width is varied. It may even need a follower ( Op Amp), don't yet know the frequency of the PWM signal. This unit is still a couple of weeks from delivery to me.

I also thought about the idea of using the HSC input depending on the freq of the PWM. Guess I'll wait until its here on my bench and play with it....
 

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