USB-6009 Analog Input Reads Approximately 1.4V Offset with RSE Connections

[leishao87]

I plug the USB 6009 into the computer with all the ports unconnected. And I opened the MAE, and then the test panel to do an analog input test. If I use RSE input configuration, all the channels ai0-ai7 will show a 1.4 V offset. If I use differential input configuration, with channel ai0-ai3, then there is no offset. How can I get rid of the offset? Thanks in advance.

Lei

[_Bryan]

Wire the channel to ground and see if the offset goes away.  Channels can read an offset if nothing is wired to them.

[johnsold]

Lei,

Look at the User Guide. Figure 7. Analog input circuitry. It shows the input circuit of the USB-6009 as a resistive network which is terminated to approximately 1.4 V through an equivalent resistance of 144 kohms. This is not typical of most analog input devices but explains why it is important to drive the USB-6009 inputs from low impedance sources to avoid errors.

Lynn