Hi, I use the U6 as part of an in-house ATE system. I've been able to get everything working and reading correctly (agree with a DMM). The only way I was able to do this though, is using a GND isolator on the USB cable. This limits the U6 supply to 100mA.
What I'd like to do, is interrupt the PWR/GND to the U6 from my PC and supply that power from a wall adapter. That allows the GND to float with my system. Our systems measure about 8K to Mains GND, so you can see the problem of hooking the USB up direct. I end up with too much difference and it causes a power fault in our system. Interrupt the GND, using a B&B USB Isolator and it all seems to work. I just don't want to limit the U6 to 100mA. I might need that in the future.
Can you recommend doing this?
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... using a GND isolator on the USB cable. This limits the U6 supply to 100mA.
Here is an isolator we have used. The spec is not clear, but the description leads me to believe that this isolator can provide up to 500mA to the device if the host is capable of 500mA.
http://microcontrollershop.com/product_info.php?currency=USD&products_id...
What I'd like to do, is interrupt the PWR/GND to the U6 from my PC and supply that power from a wall adapter.
There is information about powering from an alternative power supply (something other than the USB connector) in the OEM section:
https://labjack.com/support/datasheets/u6/hardware-description/oem
... but U6-GND is the same as USB-GND, so you will still need a USB isolator.
Perhaps you can break the ground connection between your laptop and the wall, rather than between the U6 and laptop. If the laptop is running off battery it is obviously isolated from the wall, and if the laptop uses an external AC/DC power supply those are almost always isolated from the AC side to the DC side.
Hi, I decided I didn't want to do anything with the U6 itself. I've designed an isolator using an ADUM4160 (actually this design is available online!). It isolates all four lines and I can power it from my ATE on that side.
I've been able to test and I get the same readings from the U6 as from a DMM directly. Since I also have a Picoscope in the system, we needed to deal with it also. This design allows me to run both of them at the UUT ground, and still connect to the laptop.
I read the part about isolating power.
Thanks.