Can shutting down a PXI 4110 cause damage?

[janaf]

I have a PXI 4110 and I see a potential problem. When the outputs are disabled, they short to Common floating Ground, i.e. pin D,E. 

When outputs are disabled, outputs A-L-K, will be grounded and any connected capacitance would discharge through the terminals of the PXI-4110. The resistance of disabled outputs seems to be around half an ohm. An abrupt shutdown discharging a cap from the maximum 20V over 0.5 ohm would cause a significant current spike, worst scenario a 40A peak

Is there some protection against damage on shutdown or does one need to ramp down down the voltage before disabling outputs?

(I have one dead 4110 on the shelf, trying to asses how to prevent it from happening again ). 

[DGuest]

Hi Janaf,

Please could you give some more detail on the resistance you are measuring for when the device is turned on and turned off between:

A - COM

L - COM

K - COM

This way we can understand whether it is an intentional design choice or manufacturing issue. 

From everything I have seen there are 2 isolated channels and 1 non-isolated channel with no path between them. It is odd that this has happened before.

[janaf]

I use this as a generic power supply on a workbench for all sorts of circuit testing.

I can say is that there's virtually always some small or larger capacitance connected, typically without any series resistance ignoring some milli-ohms in the hookup cable.

[DGuest]

Hi Janaf,

Having another look at the Device specification (http://www.ni.com/pdf/manuals/371635h.pdf) the output protection is shown as:

Channel 0  = 20V 

Channel 1/2 = 34V

Here, the outputs are connected to the common ground. 

The isolation voltage for Channels 1 and 2 (Pins C and F) connected to earth ground is 60VDC, CAT 1, verified by dielectric withstand test, 5s, continuous. This should be ample protection for your application.

I hope this answers your question,

David