National Instruments NI PCI-6110 - Manual (Page 38)

Chapter 4 Connecting Signals
NI PCI-6110/6111 User Manual 4-8 ni.com
Connecting Analog Input Signals
The NI PCI-6110/6111 channels are configured as pseudodifferential
inputs. The input signal of each channel, ACH<0..3>+, is tied to the
positive input of the PGIA, and each reference signal ACH<0..3>–, is tied
to the negative input of the PGIA. The inputs are differential only in the
sense that ground loops are broken. The reference signal, ACH<0..3>–, is
not intended to carry signals of interest but only to provide a DC reference
point for ACH<0..3>+ that may be different from ground.
Pseudodifferential signal connections reduce noise pickup and increase
common-mode noise rejection. This connection type also allows input
signals to float within the common-mode limits of the PGIA.
Caution Exceeding the differential and common-mode input ranges distorts the input
signals. Exceeding the maximum input voltage rating can damage the device and the
computer. NI is not liable for any damage resulting from such signal connections.
The maximum input voltage ratings are listed in the Protection column of Table 4-3.
You can use the PGIA in different ways when using different input
configurations. Figure 4-3 shows a diagram of the PGIA.
Figure 4-3. NI PCI-6110/6111 PGIA
V
m
= [V
in+
– V
in–
] × Gain
+
+
PGIA
V
in+
V
in–
–
–
Measured
Voltage
V
m
Instrumentation
Amplifier