Problems with sinusoidal offset signal on analog input on PXI-6281

[andreas_p]

Hi,

I'm trying to read an analog ~5 V signal on one of the analog input ports (ai3) on PXI-6281 (with a CB-68LPR). The signal seems to be read fine when i'm monitoring the input with Measurement & Automation Explorer but when the signal is turned off there is a horrible sinusoidal ~ -4 V offset. This effect is also seen on the other analog inputs and with no cables attached (could not be any problems with the external electronic equipment). I have created a task in Measurement & Automation Explorer with the options "aquire signal" --> "analog input" --> "voltage" --> "ai3" and connected signal + on pin 30 and zero on pin 64 (assuming the CB-68LPR maps to the same pins on PXI-6281). Would be very glad for some help on this issue.

Andreas

[PelleS]

Hi Andreas,

If you are connecting two poles, i.e. + and 0, then you should connect the 0-signal to channel AI_x+8 and select the differential terminal configuration. If you connect the +-signal to AI_3, the 0-signal must be connected to AI_11. If you have chosen to measure RSE instead, you have connected the signals correctly. But RSE is big no-no if the 0-signal is grounded. To get rid of ghost signals on channels not connected, you should connect all to AIGND. For more information please have a look at the following link. Data Acquisition: Troubleshooting Bad Readings

Hope it helps

[andreas_p]

Ok. Thanks. Not so clear though which pins to connect to on the terminal block. I thought that i was supposed to connect the ground to AI GND, e.g. pin 64. But thanks again anyway!

//Andreas

Message Edited by andreas_p on 06-19-2008 04:09 AM