use of a grounded channel?

[david_jenkinson]

Hi,
I am inheriting another persons DAQ acquistion labview routine, and I see a DAQ configuration I have a question about.  In the code, I see 3 channels being initialized, but only 2 of them being used to graph data.  The 3rd channel whose data is not being used, is actually wired to ground (ai1).  ai0 and ai2 are  both measuring voltage, and all 3 channels are being initialized as "differential" in the daq setup task.  I've attached a diagram of the configuration.
My question is, is there any advantage to setting up in the daq task, and acquiring a channels data that is wired to ground, whose data is essentially being thrown away in the routine?  In other words, is there any internal hardware configuration on the daq side, which would more accurately measure data on the ai0 and ai2, merely because another channel is being scanned which is wired to ground?  I would normally chalk this up to old code that hasn't been deleted, but there are comments eluding to using this grounded channel in the code, implying it was intentional for some reason. 

Thanks

[CharlesD]

In General it does not help at all to tie a differential channel directly to ground and measuring that in LabVIEW and then throwing out that data afterwards.  The only thing that I can think of is that they were maybe trying to alter the time in between reading each channel.  Because your device is likely a multiplexed DAQ device it will read ai0, then will switch and read ai1, then switch and read ai2, then switch read ai0 again and so on. This increases the delay between the reads of each analog channel but it would be very small.  The switch time on the multiplexer is pretty insignificant, granted for some high speed (or correlated) applications it does become significant.  Come to think of it even if you were to read that channel in the scan list therewould be no point of tying it to graound as it would be thrown out anyways.  

What does the program state the reasoning is for reading channel 1?   What DAQ device are you using? The only other thing I could thing up is that it wants to verify the accuracy of the code by shorting ai1 to ground therfore you should read 0V no matter what this could be a check for accuracy/verification fof some sort... but you are saying that you are throwing out the data and not using it so I'm not sure this is the reasoning. 

Those are my thoughts with the information you have provided.  Please provide som more information on the code/application if you want more insight. 

Thank you