Connecting Floating Signal Sources; What Are Floating Signal Sources; When To Use Differential Connections With Floating Signal Sources; When To Use Non-Referenced Single-Ended (Nrse) Connections With Floating Signal Sources - National Instruments SCB-68 User Manual

Connecting Floating Signal Sources

© National Instruments Corporation

What Are Floating Signal Sources?

A floating signal source is not connected to the building ground system, but
has an isolated ground-reference point. Some examples of floating signal
sources are outputs of transformers, thermocouples, battery-powered
devices, optical isolators, and isolation amplifiers. An instrument or device
that has an isolated output is a floating signal source.
When to Use Differential Connections with Floating
Signal Sources
Use differential input connections for any channel that meets any of the
following conditions:
• The input signal is low-level (less than 1 V).
• The leads connecting the signal to the device are greater than 3 m
(10 ft).
• The input signal requires a separate ground-reference point or return
signal.
• The signal leads travel through noisy environments.
• Two analog input channels, AI+ and AI–, are available for the signal.
Differential signal connections reduce noise pickup and increase
common-mode noise rejection. Differential signal connections also allow
input signals to float within the common-mode limits of the NI-PGIA.
Refer to the Using Differential Connections for Floating Signal Sources
section for more information about differential connections.
When to Use Non-Referenced Single-Ended (NRSE)
Connections with Floating Signal Sources
Only use NRSE input connections if the input signal meets the following
conditions:
• The input signal is high-level (greater than 1 V).
• The leads connecting the signal to the device are less than 3 m (10 ft).
Differential input connections are recommended for greater signal integrity
for any input signal that does not meet the preceding conditions.
Chapter 4 Adding Components for Special Functions
4-7 SCB-68 User Manual for Advanced Functions