Analog-out isolation NI-USB 6009?

[Jeanius]

I'm a little fuzzy on the operation of the analog-out (and -in i suppose for that matter) on the NI USB-6009 DAQ unit as far as its individual isolation goes.  Our setup is as follows:  We are sending an analog-out signal through an opto-isolator (a series of AD8638 op amps and an IL300 to be exact) and then to a TEC controller powered by a seperate 12V power supply (not DAQ supply) that accepts a 0-5V signal for temp set point.  Question is whether or not the isolation is necessary, and if the analog-out ports (since they seem to have their own ground channel) have isolation associated with them, and could be directly connected to the ground and input pin of the TEC controller, despite the difference in grounds.  Is this possible?  Figured I'd ask before summoning the magic smoke!

Thanks!

[R Sandoval]

Hello There,

From my understanding, your question is regarding the isolation of two different grounded references.  If the TEC is powered by a floating voltage source, which I believe is not, then opto-isolators would not be neccessary.  However, assuming that the TEC is being powered by a supply that is connected to an outlet, the setup should include isolation.  Now, there is a good possibility that your setup will work perfectly fine without the opto-isolators (in consideration that you are using the same power outlet).  However, by taking the precaustion of isolating the devices, your DAC device will be protected.  Furthermore, the USB-6009 does not provide line isolation.  The USB-6009 is also rated for CAT I.  If the TEC is rated at CAT I, then you can connect the USB-6009 to the TEC controller directly and share the same GND without the opto-isolators.  Please reference the device specifications (http://www.ni.com/pdf/manuals/371303l.pdf).  I also included more information about CAT ratings (http://zone.ni.com/devzone/cda/tut/p/id/5019).  I hope this helps.