adjustable DI threshold

[YellowDart003]

Hello,

I have a 9402 DI card I'm using in a 9139 cDAQ. I'd like to take some PWM voltage measurements and do some sort of counter scheme to back out RMS values, harmonics, etc. However, the voltage is (nominally) 220 V (on), and all I have are 100x attenuation probes, knocking my "on" voltage to ~2.2V (well below the "on" level for traditional 5V TTL). Does anyone know if there's a way to adjust the on/off threshold voltage for a 9402 card (or just general LabVIEW tricks with DI/DO)?

Thanks!

[fblerg]

Hi YellowDart,

The NI 9402 is LVTTL device with a minimum input high voltage of 2 V.  Using a 2.2 V high is not a recommended setup because it is very close to the minimum high input. However, it should work for the most part. You also could construct a voltage divider as suggested in the other post instead.

http://forums.ni.com/t5/Digital-I-O/adjustable-digital-input-voltage/td-p/3068146

As for general DAQmx tricks, you can use property nodes to access and set device properties. The properties you can set are device dependent, and allow you to tweak your acquisition settings. The 9402 doesn’t have the Digital Input Logic Level Select property because it is defaults to LVTTLs.

Basics of NI-DAQmx Property Nodes

http://www.ni.com/white-paper/5338/en/