Converting a Binary Output to an Analog Output Using PWM (Pulse Width Modulation)

I recently ran into a situation where I needed an additional analog output on a Schneider Electric IA Series BACnet (MNB300) Controller.

I was able to accomplish this by providing a pulse width modulated output from one of the triac outputs. Essential, a pulse width output communicates an analog number between 0 and 100% by keeping the binary output on for a percentage of some given time base. For example, if your time base is 10 seconds and your binary output is on for 5 seconds, then you would be communicating that you wanted to analog output at 50%.

In this case, I wanted a 2 - 10 volt signal for an actuator. I used a PWA-1A from Kele.com to convert the pulse width modulated binary output from my MNB300 into a 4-20ma signal. Then I simply installed a 500 ohm resistor accross the output to make convert the 4-20ma signal into a 2-10 volt signal.

Schneider's Workplace Tech software makes configuring a binary output as a pulse width modulated output easy by providing a PWM software block that can be used to configure the binary output.

Here is my wiring diagram.

If you know of a better method, please let me know!