National Instruments USB-621 Series - Taking Non-Referenced Single-Ended Measurements

Chapter 4 Analog Input
NI USB-621x User Manual 4-38 ni.com
Figure 4-25. Connecting to the USB-6215/6216/6218 in Referenced
Single-Ended Mode
In an referenced single-ended connection configuration, each input channel
is measured with respect to AI GND.
Taking Non-Referenced Single-Ended Measurements
To reach a compromise between referenced single-ended and differential
measurements, you can use an non-referenced single-ended measurement
configuration. This configuration allows for a remote sense for the negative
(–) input of the instrumentation amplifier (PGIA) that is shared among all
channels configured for non-referenced single-ended mode. The behavior
of this configuration is similar to that of referenced single-ended
connections, except it provides improved noise rejection. Figure 4-26
shows an non-referenced single-ended connection configuration.
Figure 4-26. Connecting to the USB-6215/6216/6218 in Non-Referenced
Single-Ended Mode
In non-referenced single-ended connection configuration, each input
channel is measured with respect to AI SENSE.
AI 1
AI 2
AI GND
USB-6215/6216/6218
Mux
ADCPGIA
AI 1
AI 0
AI GND
Mux
ADC
PGIA
AI SENSE
USB-6215/6216/6218