6

Connecting AI Signals on the

USB-6215/6218 Devices

You can connect the USB-6215/6218 directly to a variety of devices and other signal sources. Make sure the devices you connect to the USB-6215/6218 are compatible with the input specifications of the module.

When connecting various sources to the USB-6215/6218, you can use differential, single-ended, or a combination of single-ended and differential connections. Refer to Figures 6-1,6-2,and 6-3for diagrams of each connection type.

Note You must always connect AI GND to a local ground signal in your system using a low impedance connection. If you leave AI GND unconnected, you cannot ensure that AI <0..31> are within 10 V of AI GND, and your measurement may be unreliable.

Differential Measurements

To attain more accurate measurements and less noise, use a differential measurement configuration. A differential measurement configuration requires two inputs for each measurement.

Differential Pairs

Table 6-1the signal pairs that are valid for differential connection configurations with the USB-6215/6218.

 

Table 6-1.

I/O Connector Signals

 

 

 

 

 

 

 

Channel

 

Signal +

 

Signal –

 

 

 

 

 

 

 

 

 

 

 

 

0

 

AI 0

 

AI 8

 

 

 

 

 

 

 

1

 

AI 1

 

AI 9

 

 

 

 

 

 

 

2

 

AI 2

 

AI 10

 

 

 

 

 

 

 

© National Instruments Corporation

6-1

NI USB-621x User Manual