The Industrial Raspberry Pi Forum

I have a project that will require me logging an analog signal (4-20ma) when a valve is open (Digital signal).
I was thinking of using Revpi Core with MIO or Revpi Compact for this job.
I would like to use Node Red to capture and send to data to DB on the Revpi itself.

My main concern is that the Valve will only be open for 200ms and I would like the sample rate for the analog to be at 20ms. or quicker.
I know that the sample rate for the analog on the MIO is rated at 8ms. Just wondering has anyone done something like use using nodered at this sort of speed before I go down this route.

Thank you.

MIO is analogue voltage input only! if you need 4-20 mA you would need an AIO or a converter. Using just a shunt resistor reduces the overall precision. To get 10 V from 20 mA you would need a 500 Ohm shunt. But keep in mind that the analogue input is single-ended and one terminal of the shunt must be GND level! So you cannot use current transceivers which are referencing to any other level. Calculate the precision you need first and then decide which method would fulfil your needs. The PiBridge is able to allow 20 ms sampling to the process image of the RevPi. But this depends on the overall system configuration (e.g. number of other IO modules).

Thank you for your reply. Wasn't aware the MIO was voltage only. Might be that a dedicated datalogger is what I would need for this project.

Thank you.

Hi,

as for the cycle time, 8ms are possible with AIO for 4-20ms.
But this is depending on the number of inputs you re reading.

Kind regards,
Boris

Thank you. It should just be one 4-20 input and 1 digital.