9476 on a cRIO 9068 pulsing on and off after turning on too many channels.

[dest2ko]

I am having an issue with the ON/OFF transitioning of my relays. I am currently operating 18 channels with one NI 9476 32ch module, but have disconnected the last 6 when I had been isolating the issue. On channels 1-12, if I flip a toggle switch to subsequently activate my channels, everything works fine until I get to the 9th or 10th one. If I activate the 11th switch, one of the relays, typically channel 1, will start flickering on and off. I have measured the current going through each DO channel to be 9.1mA through the "coil" circuit of each solid state relay, well below the 250mA limit (I am using a 24VDC PS-17 power supply). The period between the two is very systematic, which led me to think it was a result of this:

Per pg. 15 of the NI 9476 Startup Guide: 

"Excessive current through a DO pin causes the channel to go into an overcurrent state. In an overcurrent state, the channel cycles off and on until the short circuit is removed or the current returns to an acceptably low level. Each channel has a status line that indicates in software whether the channel is in an overcurrent state."

Does anyone know how to access this module information in the software? Is it via the error terminal? Some kind of property node? I dug up a thread from 2010 but there was nothing relevant to my application: the cRIO 9068 using FPGA.

Thanks

[dest2ko]

Update: I have tried it with a (new) 9476 module as well as deployed the software to another chassis with the same result. Still the same issue. 

[Miro_T]

It does sound like you might be running into overcurrent state. Double check your wiring, make sure there is no short anytime during relay operations.

You should also consider adding flyback diode as shown in the figure 4.

You should be able to check overcurrent using “Check Output Status” FPGA I/O method as described in this help document.

"Check Output Status" method is also shown in the 9476 shipping example  "NI 9476 Digital Port Output.lvproj"

[RH2]

I have flybacks installed on each channel. Also, I can toggle channels 1 through 12 in any order and it will still pose a problem despite the combination used. I am compiling my fpga to now indicate this feature. Will update asap. Thank you 

[dest2ko]

Also, this overcurrent would seem to only apply to the "coil" circuit side of the relay and not so much the main channel (protected with flyback) that is operating the solenoid valve. The coil side only has 9.1mA current nominal. 

[testingHotAir]

I'm having the same issue.  Did you ever solve the problem?

[dest2ko]

Yes, it ended up being a faulty power supply. We swapped it with another and the problem went away.

Hope this helps.