I am using an NI9266 4-20mA output card to drive pneumatic positioners (I2P) via intrinsically safe galvanic isolation barriers (the actuators are located in a hazardous area).
My controller is a cRIO 9035 and I’m running labVIEW 2019 ( I don’t have the VI’s to show right now, but I think this is a hardware issue anyway ….
the I2P positioners are powered from the 4-20mA current loop.
I set a minimum 4mA so the positioners are always powered however some positioners don’t power up and I’ve noticed the 9266 output channels are not driving a current despite my request to drive 4mA. The only way around this I’ve found so far is to manually disconnect and reconnect the current loop to my load which kick starts the 9266 card to turn its output on/ the positioners then power up
the NI datasheet says … “The NI-9266 provides channel-based indicators for open current loop condition or if the loop is out of regulation. This could be the result of a wire disconnect or a violation of the maximum load or maximum compliance voltage”.
and is a safety feature designed to prevent actuators operating on first power up.
I think this is the problem but I don’t understand what the root cause is (my intrinsically safe barrier maybe??) and how to get around it without manually disconnecting/reconnecting the loop wires every time!
has anyone had a similar issue and know what I need to do?
many thanks