National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual
Page 38
Chapter 3
Signal Connections
© National Instruments Corporation
3-7
Lab-PC+ User Manual
When the Lab-PC+ is configured 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. The DIFF input configuration should be used
when any of the following conditions are present:
•
Input signals are low-level (less than 1 V).
•
Leads connecting the signals to the Lab-PC+ are greater than 15 ft.
•
Any of the input signals requires 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.
Differential Connections for Grounded Signal Sources
Figure 3-3 shows how to connect a ground-referenced signal source to a Lab-PC+ board
configured for DIFF input. Configuration instructions are included under Analog Input
Configuration in Chapter 2, Configuration and Installation.