How can I ground voltage using myDAQ's DMM?

[Beeslo]

Not gonna lie. Don't have extensive electrical knowledge, so please excuse my ignorance in asking this question. I am trying to build a very simple VI in LabVIEW using the myDAQ. I am using the DMM probes to test the voltage of a single AA battery. The VI works as it does detect the voltage and displays the results but I notice that when in a neutral state (not testing the battery), the voltage shows -0.00424V.

Is there a way to ground the voltage so that it reads zero or is there a way in LabVIEW to make up for this difference?

Any assistance is appreciated.

[KyleTTU]

Hi Beeslo,

I hope you are enjoying the myDAQ!  You are definitely experiencing a floating ground on your signal when you disconnect the battery.  Basically, you have a circuit from the positive lead on the myDAQ through the battery to the negative leade which allows current to flow.  When you remove the battery you are essentially creating an open circuit that has no reference to ground and thus will have some sort of varying voltage being read in.  

One way to counteract this is to have a switch before the battery, so instead of removing the battery you switch to just shorting the two leads.  

[Beeslo]

Is there a way that I can simulate this through LabVIEW? So that it counters down to zero every time the leads aren't connected to the battery. Or is something like that not really possible?

[KyleTTU]

You could either set a case structure that checks to see if the voltage coming in is within a certain range and if so zero out the indicator.  Or you could constantly round the value such that it drops out your floating ground noise.  Those are two ways I can think of off the top of my head, but when dealing with software there are always countless methods! 

[Beeslo]

Yeah, I've noticed that it's always a constant -0.0044V...so I could also just place a simple math algorithm to add that difference. I'll probably just do that. Thanks for your help!

[KyleTTU]

Not a problem!