Analog Input as Pulse

[EliWaldner]

I think I read somewhere (if my memory is correct) that an analog input, on BRx PLCs can be used as digital input. With that in mind, would it be possible to use an analog input on a BX-DM1E-36AR3 as a pulse input, at a rate of about 15 pulses per second? Or would this be asking for poor performance?

[Bolt]

What would you do with the pulsed input? You can't map an AI into a high speed instruction, so you would be better off using one of your existing high speed inputs for such? And then re-purpose the AI as a regular, slow speed input? I'm not sure how to do wire the AI as a DI, it is possible, but I'll let someone else chime on on that.

[EliWaldner]

The pulse input would be coming from a flow meter and the plan is to use the input to count liters of water. The model of PLC we have, has AC volt inputs and the pulse coming from the flow meter would be DC volts. That is the reason for wanting to use the analog input, which would be DC volts, as the pulse input.......

[BobO]

The onboard AI is pretty fast, conversions are a touch over 1ms. At 15Hz you would likely be fine, but it's a scan based update so your scan time needs to be stable enough and short enough to see all transitions.

[EliWaldner]

@BobO thanks for sharing your opinion. We used a relay to convert the signal from DC to AC. It seems to work okay but if we run into issues we may try the analog input. Thanks again for your help and for sharing your thoughts.

[Garyhlucas]

A few years ago I needed Just One More high speed counter for a flow meter. The rate was too high for a standard digital input. So I built a high speed input using the Interrupt function. Not as fast as the normal high speed inputs but way faster than a standard input.