NI 6062E DAQ long measurement decay

[davidmcc]

hello

Using the NI-6062E DAQ board I have input the +'ve from an audio signal from a headphone jack of a battery powered device into the input channel 1, reading the manual it looks like I should then place the -'ve from the headphone jack into one of the gnd sockets, but when I do this no matter what settings I seem to put into the properties and test panel of NI MAX the output diagram and measured values show a value that goes up to the Max 10 V as soon as a noise is produced then the value slowly decays in a logarithmic function back down to 0v. When placing the +'ve and -'ve straight onto an oscilloscope it produces a signal as expected, high frequency voltage change with a lower frequency envelope as rather rubbishly shown in attached image.

I know a bit about labview but next to nothing about electronics or DAQ boards so any help appreciated.

Thanks

david

[Stefo]

Hi David,

What configuration of Analog Inputs did you choose? Could you try to perform measurement in MAX, and double check if you have connected signals to proper pins. If you see the kind of signal you posted here, it might be that you actually don't have any signal connected to the input - which means it is floating, and you would see exactly what you have posted here. Therefore, if you have problems with measurement, please post here information like what is the input configuration, what AI are you using and what are the physical pins on the board you have connected signals to.

regards,

Stefo

[davidmcc]

the signal is definetly connected, +'ve to AI0 -'ve to AIGND, as the signal goes high as soon as the sound starts, also tried it with a 5v signal. reading goes straight to 5 v when connected and switched on but slow decays when disconnected.

measurement and output seen in both Labview scope example and in NI-MAX test panel

Guess i have connected it wrong some how but not sure how.

thanks

[Stefo]

I think I see now!

When you connect signal source with finite impedance, you can measure properly. Then when you disconncet signal source, then it starts floating, because signal source impedance is practically infinity (as it is disconnected). It means, that the charge in AI circuity is not dissipated, or discharged, as it doesn't have really path to ground.

Some explanation of this behavior can be found here.

Regards,

Stefo

[John_P1]

Hi David,

You said you're connecting to ai0 and AIGND, but did you explicitly set the channel to RSE?

       

The default for ai0 on the 6062e is differential, which would require you to connect your reference to ai8 rather than AIGND.  Leaving the (-) terminal of the ADC disconnected would very likely result in the behavior you are seeing.

For an explanation of the different connection types, you can refer to this link.

Best Regards,