some wire connection problem for SCB-68 usage in measuring voltage

[shuishen1983]

I am using FPGA 7831R along with SCB-68 to measure some voltage from my monitor terminal from my motor. When I measure the voltage between the monotor output and GND using a multi-meter the measurement is very reasonable and it can be changed when motor speed is changed. However, When I use FPGA input function to measure the monitor output(corresponding AI0 on SCB-68), the number displayed on the scope is always 10. The displayed value from GND is also 10(corresponding AI1 on SCB-68), so when I substract  AI0 from AI1 the value is zero. Did I do something wrong in wire connection.

Should I connect the AIGND terminal to somewhere or leaving it floating.

[jareds]

Hi shuishen1983,

What are the connections that you have made for this measurement?  What kind of signal is it?  Are you trying to do a differential or single-ended measurement?  In either case, you should have a look at this wiring guide.