Does a usb-powered DAQ has "real" isolation in power source for analog part?

[fayx]

Dear Sir,

   Does a usb-powered DAQ has "real" isolation in power source for analog part?  According to the USB6216 user manual , the isolation is applied between analog block and bus block so that  the output of ADC 

   transmitted  to USB module will pass through some kind of coupler like optocoupler or transformer. Does the similar architecture or method exist and be used in power supply for analog block inside USB6216??

   Is the isolated DC-DC converter, like flyback converter, applied for isolating VDD_USB(DVDD) from VDD_ADC(AVDD)??

Thanks!

Regards

[Ting1224]

Hi,

According to your question, I think only NI's hardware R&D can answer your question.

However, that might be the knowhow of DAQ's curcuit design.

I am not sure if NI's R&D will release it in the forum.

Regards,

Ting

[fayx]

Thanks of your reply~~

It is not necessary to reveal the circuit design inside the black box. All I wanna know is  whether the usb-powered DAQ has some kind of isolation architecure applied to analog power source or not.

Because the measurement in  my experiment need isolatation from the earth ground and digital ground to achieve higher accuracy, I wanna make sure if USB6216 can handle it !!

Thanks!

Regards

[Ting1224]

According to the spec, USB-6216 utilizes Channel-to-Earth ground isolation.

Please check the following link and figure.

http://sine.ni.com/ds/app/doc/p/id/ds-9/lang/zht

There are three types of isolation in NI's DAQ hardware. Please check the detail in the following link.

http://digital.ni.com/public.nsf/allkb/CF71091043A6193B862573D70077138B

[Ting1224]

I double checked the spec of USB-6216.

Since it's utilizing the Channel-to-Earth isolation instead of Bank or Channel-to-Channel Isolation, the "power" circuit is not isolated.

Only the ground circuit is isolated.

I think in this case the digital power is not isolated from USB bus power.

[Process_Systems]

If you need good isolation, I would recommend that you use a 5B series signal conditioner on each AI channel. The 5B has 3-way total isolation (power to each channel, AI, and AO). I have used these where I have had severe ground loop problems, and for the ultimate in isolation, they are the cat's meow.

Good luck,

Dave