National Instruments PCI-1200 - Manual (Page 31)

Chapter 3 Signal Connections
© National Instruments Corporation 3-9 PCI-1200 User Manual
Differential Connection Considerations (DIFF Configuration)
Differential connections are those in which each PCI-1200 analog input
signal has its own reference signal or signal return path. These connections
are available when you configure the PCI-1200 in the DIFF mode. Each
input signal is tied to the positive input of the instrumentation amplifier,
and its reference signal, or return, is tied to the negative input of the
instrumentation amplifier.
When configuring the PCI-1200 for DIFF input, each signal uses two of the
multiplexer inputs—one for the signal and one for its reference signal.
Therefore, only four analog input channels are available when using the
DIFF configuration. Use the DIFF input configuration when any of the
following conditions is present:
• Input signals are low level (less than 1 V).
• Leads connecting the signals to the PCI-1200 are greater than 10 ft.
• Any of the input signals require a separate ground-reference point or
return signal.
• The signal leads travel through noisy environments.
Differential signal connections reduce picked-up noise and increase
common-mode signal and noise rejection. With these connections,
input signals can float within the common-mode limits of the input
instrumentation amplifier.