How to protect EUT from a NI module failure?

[question_from_allen]

I have a system consisting of NI 9403, ni9217, ni9201, ni9221 modules in a mainframe powered by 24 volts.  In a fault condition, is it possible that 24 volts appears on the output or inputs to the NI modules?  Is there an internal 5 volt regulator in the modules that limit the output voltage?  If I were to add zener diodes to the input/outputs of the NI modules what would the maximum voltage and current I would need to worry about?

[ColdenR]

What chassis are you mounting those cDAQ modules in?

You can find all the information about maximum current and voltage inputs and outputs as well as overvoltage protection from the product pages of those devices:

https://www.ni.com/en-us/shop/model/ni-9201.html

https://www.ni.com/en-us/shop/model/ni-9221.html

https://www.ni.com/en-us/shop/model/ni-9403.html

https://www.ni.com/en-us/shop/model/ni-9217.html

Check out the data sheet and specifications document for each component.

[question_from_allen]

The chassis is NI 9114.  The power supply for the chassis is a PS-15.

I looked at the links you provided and I did not find the information I needed.  What I am looking for is not normal operation but when there is a failure inside the NI chassis or module.

Assume that the NI 9114 is powered by the PS-15.

Assurme that there is a failure in the chassis, PS-15, or other NI module.

I assume that a fault voltage is generated from NI module outputs and inputs connected to my EUT.

What is the worst case output voltage from the NI module going to my EUT?  What is the maximum current.  I would like to add a zener to protect my EUT.

Do you have a regulator within your modules to take the 24V and step down to 5V?  If so my zener could be smaller.

   Thanks.

[ColdenR]

The chassis converts the 24V power down to 5V, and all the modules are powered off of that 5V supply. 

The 9403 has over-current protection (see page 9 of the NI 9403 "Operating Instructions and Specifications" (https://www.ni.com/docs/en-US/bundle/sbrio-9403-seri/resource/372617a.pdf). It will essentially shut off its outputs in the case of an overcurrent situation. Page 11 of that document lists the maximum output current of the module to be 64mA.

The other modules are analog input modules, and they basically just leading directly into buffers into ADCs. They have some overvoltage protection (specific to each card, as noted in the datasheet), but there shouldn't an issue with them outputting voltage or current.