PWM to voltage


Thread Starter

Sepi Sopo


My goal is to measure the control signal used to control a proportional valve.I need to plot it into the same chart with pressure. (x=DC,y=bar).

We use 100Hz/12V PWM to control solenoidvalves.
Our x-y recorder can only deal with voltage.

How is this PWM-voltage conversion usually done? Filterig? What kind?
Commercial products?
(There are abrubt changes in the closed loop control signal)

Thank you for Your attention.
Sepi Sopo.

Johan Bengtsson

If you put in a low pass filter you will get what you want. If you do it directly on the 12V signal you will get 12V as 100%, if you want something else you should either use the same signals to switch another voltage source (with the voltage you want as 100%) before the filter or you can convert the smothed voltage using a voltage divider (for smaller values) or an amplifier (for higher values)

If your filter have a time constant at least 10 times the PWM time-base you will get a relatively smooth voltage but with some varioations left
(probably useful enough), in your case that would be 0.1s. A higher value would give you a even smother signal but more delay. I would probably
have used an approximately 1s filter in your case.

The easiest filter to make is a simple resitor and capacitor

---| |-------*--------
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filter time constant = R*C be aware that your resistor have to be significaltly less than the input impedance of whatever you connect to this filter, otherwise you have to make some more calculations (both your filter time and your voltage will be decreased) Output impedance from where you get the signal need to be much lower than the resistor inthe filter, probably not a problem.

The above gives you a valid resistor range (keep at least a factor 10 in both directions), select a suitable capacitor to get whatever filtertime
you want.

The above is if you want to build it yourself, off the shelf alternatives do most surely exist and would probably work like this but include
amplifiers and similar to make sure there is the right impedance at the right places.

/Johan Bengtsson

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