"preload" NI USB-6251 Input Channels

[me1ody]

Hi,

I have a number of different measurements happening on the 6251 device. The analogue input voltage varies from 0.2V to 4V in the worst case.

When I configure the instrument to take the low voltage measurement just before the low voltage measurement, I can see the reading frequency on the low signal. To get a better result, I use a second channel to measure the same low signal.

At the moment it looks like this

Ch1: 4V

Ch2: 0.2V

Ch3: 0.2V

In this case the internal voltage is already close to the input voltage I expect on Ch3.

Is there a way to solve this in the code? Some set the internal voltage to value I expect at the input before making the measurement?

[Kevin_Price · Accepted solution]

Have you included the recommended bias resistors (generally 10k-100k) between your signal terminals and AI Gnd?   See this article for details (plus a lot more good info).

-Kevin P

[ZYOng]

How did you measure the "internal voltage"? Did you connect it to a 0V signal? Or did you leave the channel open? Please noted that an unconnected channel does not return 0V in NI-DAQ. See Incorrect Readings on Unconnected or Open Channels of DAQ Device

[me1ody]

I didn't measure it, sorry. I just thought that's the case.