Should I connect to chasis ground?

[Rafi2003]

HI,

I'm testing a device through an Interface Box which include a 5V and 12 V power supplies.  The power supplies are used to power the UUT which has no ground reference.  I'm using NI 6520 to measure several inputs both single ended (with reference to ground) and differential.

All my grounds, digital and analog are connected together to the 5V & 12V RET lines of the 2 power supplies.

The only problem is with the RS232 link to the PC.  The   COM ground is also connected to my 5V ground, but in the PC it is connected to the chassis ground.

Therefore, by using this com link, I connect my ground to the chassis as well.

The question is:  Should I connect the 5V & 12V RETs to the chassis ground or not?

Thanks

Rafi

[JustinP]

Hello Rafi,

A schematic would be helpful in determining the correct connections.  The NI-6520 is connected to chassis ground and the RS232 is connected to chassis ground so connecting the 5 V and 12 V RET lines could possibly introduce ground loops depending on the setup.  This document is a good resource in determining a suitable wiring configuration.

Regards,

Justin

[Rafi2003]

Hi justin,

The schematic is pretty straight forward, however, I made a drawing, just to make it clearer.

The question again is whether to connect my Power supplies RET line to the chassis ground in the JIG or not.

We know that the RET get a connection to chasis ground via the RS232 GND line.

I assume that in the PC they connect the power supply RET to chassis ground.

Please advice

Thanks

Rafi

[JustinP]

Hello,

Both the PC and the power supplies are grounded to the wall outlet, therefore the power supplies do not need to be grounded to the PC chassis. 

Regards,

Justin