19 |
Non-grounded
reference
single-ended
input
（
NRSE
）
3.3.
Floating grounded signal source
A floating grounded signal source is not connected in any way to the building ground system but,
it has an isolated ground-reference point. Common floating grounded signal sources are
transformers, thermocouples, battery equipment, optical isolators, and isolation amplifier output.
An instrument or device with isolated output is a floating-ground signal source.
Attention
When measuring the floating ground signal source, it is important to
connect the negative end of the signal source directly or indirectly
through the resistor to the AGND
。
Using differential mode (DIFF) connection
When any of the following conditions are true, a differential mode should be used to connect the
floating signal:
Analog input AI+ and AI- are all valid signals.
Low input signal voltage while higher accuracy demanded
The cable length of the connection signal to the acquisition
device
exceeds 3 meters
The input signal requires a separate ground-reference point or a return signal
There is obvious noise in the environment of the connection wire
Differential connection mode can reduce noise interference and improve the common-mode
suppression ability of acquisition
device
.
For a floating signal source with less than
100ΩF
internal resistance, you can directly connect the
negative end of the signal to AI- and AI-GND ports and connect the positive end of the signal to
AI+ ports, as shown below in figure 3.2.