Initializing NI-9478 with FPGA

[rolfk · Accepted solution]

Well, this is not really about normally open switch or not. What is "normal" when activated through a logic state?

Basically when you set the digital output value to 0, the switch will be closed and there is a low impedance current path from the output to ground through this switch. When you set the digital output value in the FPGA to 1, the switch is open and there is NO current through anything (well technically you will probably have a minimal leakage current to ground through the solid state relay substrate in the range of a few nano amps. Without an external pull-up resistor, the output is simply floating and can logically look like anything.

This module is meant to switch on a load that is connected to VSUP on one side and the relay module output on the other side. If the switch is on there is a low impedance path that provides a path for the current through the load. If it is off there is no current path and the load is not energized. If you just connect a high impedance voltage meter to that output to measure the voltage on the output in respect to ground, you measure about 0V when it is activated and about the same when it is open since there is nowhere where another voltage could come from.

[eli.barber · Accepted solution]

Thank you,

that makes sense.

For anyone else, my over current protection was not set correctly. You need to set the adjust the overcurrent settings before you do PWM. This is what was causing the card to constantly reset itself. instead of old open or closed