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NI 5734 Low Input Impedance
MBoyd
Member
03-21-2014 02:56 PM
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I recently got a NI 5734 along with a FlexRIO card and am running into an issue when I connect the ADC up to one of my sources. I noticed on the specifications sheet that the input impedance of the 5734 is 50Ohms. This seems relatively small causing a higher current than one would expect at higher voltage (i.e. 10V input). Knowing that, I couldn't find any current limits on the card. I am guessing it is in the specification sheet, but those sheets have a lot of values with which I don't fully comprehend.
With the above established and knowing that 50Ohms isn't a lot of input impedance. Is there a way that I can increase the input impedance to decrease the current draw from a source? Also, I know that LabVIEW sometimes has functionality selectable (hidden) with Property Nodes. Is there something I can leverage with Property Nodes to aid in my issue?
A preemptive thank you for the assistance.
-You can never have too much power...
Matt_L
NI Employee (retired)
03-24-2014 03:47 PM
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Hi MBoyd,
While you don't have to worry about the 5734 being within current limits (we spec it at +/-10V with the 50Ohm impedance), I can understand your concerns about drawing more power from your device. There isn't a way to do this on the card unfortunately; it is set at 50Ohms. I believe this is due to the fact that we typically see this sort of Scope adapter module at higher acquisition rates and smaller voltages, where impedance matching is more of a concern than power draw.
So to decrease current draw from the source, I would look at lowering the voltage of the signal you're acquiring, if possible, and if not then using some additional BNC attenuators in line with the cable from your device to the 5734. There is a wide assortment on sites such as DigiKey here (http://www.digikey.com/product-search/en?FV=fff40036,fffc01f5), so I would explore that route as a workaround for your issue.
Best Regards,
