6210 mutil analog input

[Blinov]

I use VbA to read several analog inputs from the 6210. But the ai0 is greatly influenced by ai 1. I use NRSE mode to read 2 0-10 volts, ground the negative wire to the earth, they there is no singal coming into the DAQ, the analog values stay steady. Once the ai1 is increasing, the ai0 just follows ai0 to go up.

Does anyone here met the same situation? please give me some advice.

Many thanks!

[Christian Mergl]

This can happen if you use very high sample rates.

The daq card is using a multiplexer to connect the different channels to the ADC. So imagine when this mux is switching fast between channels it can take "some of the electrons" from the AI0 to the AI1....and this is what you see in wrong measurements then.

Use AI0 and AI2 for the measurement, and connect the AI1 to the GND, this should help.

In software you have to configure your task using all the three channels that the mux is also connecting to AI1.

Hope this helps,

Christian

[Blinov]

Thanks Christian, I took your advice and did the test again. the result turned out to be the same. i will attach two files, one is from the signal express, and the other one is from my vba program. The data reads from the signalexpress looks just fine, with the ai0 stays the same (though it's pretty vibrating), and the ai2 goes up. But in the excel file, the ai0 follows the pattern of ai2 goes up and down. i ground the ai0, and it reduces the noisy instead of eliminate it from changing.

do you have any idea about how this happened?

thanks,

Ben

[JohnDoe-]

I am having similar issues with the board except it is with the PFI input lines for counter/timer operations and not analog inputs.  Is there a way to turn off the multiplexing?  There must be a way around it, otherwise what is the point of having four inputs and only being able to use one?

[CWolf]

The 6210 is an M-series, multiplexed card.  This means that it does not have a separate analog-to-digital converter for each channel, and the voltages from the channels must be multiplexed to use one ADC for all of them.  Therefore, there is no way to turn of the multiplexing.  However, there are many strategies for reducing or eliminating the crosstalk you are seeing between the channels.  Here is a KnowledgeBase article that talks more about why you see this behavior and how to mitigate it.  Also, our S-series, or simultaneous sampling, cards are designed with one ADC for each channel, so these cards do not use multiplexing. 

-Christina

[Dennis_Knutson]

But he/she is talking about the counter and not the analog input. There are two separate 32 bit counters.

[CWolf]

Dennis,

Thanks for pointing that out.  The multiplexing refers specifically to the analog lines.  For the PFI lines, it may help to enable the digital filtering on the card, as mentioned here in the user manual. 

-Christina