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Below, I have included a link to the user manual for the NI 6013. Chapter 4 details the procedures for connecting signals to this device. If you are using the NI 6013 in differential mode, you will connect ACH0 and ACH8 to the circuit from which you want to acquire analog input data. These correspond to terminals 68 and 34 on the CB-68LPR connector block, respectively. ACH0 should be connected to the positive signal, and ACH8 should be connected to the negative signal. After you have made this connection, you should be able to acquire a signal from your circuit with analog input channel 0 in the MAX Test Panel.
NI 6013/6014
User ManualSpencer S.