Exceeding Maximum Switching Voltage

[JWanklin]

Hi, I've got a (hopefully) quick question about electrical safety and a PXI-2536 switch.

In a suite of tests that I'm performing I've got one that requires connecting an output channel from my device, an input to a DMM, and the positive power from my power supply (through a pull-up resistor) through the switch. The device can run from 12V-24V and the switch datasheet lists it's maximum switching voltage as +/-12VDC, so I'm thinking I should be fine as long as I run at 12V.

However, I've got another test which doesn't require anything that's connected through the switch, but it does set the power supply output to 28V to check the shutoff circuit of the device. I can disconnect the channels of the switch and close it (programmatically) during this test but I don't know if that actually affords it any protection.

Can anyone tell me if I'm in danger of damaging my switch if I've got one of the channels (a column in this case if it makes any difference) connected to a 28V source, even if it's not open and connecting?

Thanks,
Jon

[Frank-L · Accepted solution]

JWanklin,

However, I've got another test which doesn't require anything that's connected through the switch, but it does set the power supply output to 28V to check the shutoff circuit of the device. I can disconnect the channels of the switch and close it (programmatically) during this test but I don't know if that actually affords it any protection.

That is expected. (The relay will remain open despite software telling you that it is closed).

The Overvoltage protection is in the hardware, and does not give any feedback to the software state. If you attempt to close the switch, the software and hardware will still attempt to drive the FET to be closed, and will still report the relay as closed. The FET used on this specific switch has the specific feature where it will open the circuit if it detects the voltage across the switch is above 12 volts from chassis ground. 

Can anyone tell me if I'm in danger of damaging my switch if I've got one of the channels (a column in this case if it makes any difference) connected to a 28V source, even if it's not open and connecting?

Given the overvoltage protection, you are technically safe from damaging the switch, but given that the Maximum switching voltage is 12 VDC, I would not recommend keeping the 28V on the column if it is not being used. Ideally, you should never have anything connected to the switch that is purposfully above the Maximum switching voltage.

[JWanklin]

Thank you Frank, that's just what I needed - 'Technically safe, but not recommended'.

Hopefully I'll be able to use a different solution that doesn't involve putting 28V into the switch, but it's nice to know I won't immediately damage it if I need to persue it short-term.

Thanks,

Jonathan