Справочник Пользователя для National Instruments NI PCI-6111

Figure 4-5 shows how to connect a floating signal source to a channel on 
the NI PCI-6110/6111.

Figure 4-5.  Differential Input Connections for Nonreferenced Signals

Figure 4-5 shows a bias resistor connected between ACH0– and the 
floating signal source ground. If you do not use the resistor and the source 
is truly floating, the source often floats outside the common-mode signal 
range of the PGIA, and the PGIA saturates, causing erroneous readings. 
You must reference the source to the respective channel ground. 

Figure 4-4 shows connections for signal sources that are already referenced 
to some ground point with respect to the NI PCI-6110/6111. In theory, 
the PGIA can reject any voltage caused by ground-potential differences 
between the signal source and the device. In addition, with 
pseudodifferential input connections, the PGIA can reject common-mode 
noise pickup in the leads connecting the signal sources to the device.

+

+

Floating

Signal

Source

Instrumentation

Amplifier

V

m

Measured

Voltage

I/O Connector

ACH0GND

Bias

Current

Return

Paths

ACH0–

ACH0+

ACH0 Connections Shown

PGIA

1M

Ω 

100pf

10nf

Bias
Resistor 
(see text)

V

s

–

+

–

–