Differential Channel Connections - Advantech MIC-1816 Series User Manual

Single-ended connections should only be used in the following situations:
All input signals share a common reference point (AGND)

The wire connecting the signals to the device is less than 3 m in length

2.7.2

Differential Channel Connections

The differential input channels operate with two signal wires for each channel, and
the voltage difference between both signal wires is measured. On MIC-1816, when
all channels are configured for differential input, up to 8 analog channels are avail-
able.
If one side of the signal source is connected to a local ground, the signal source is
ground-referenced. Therefore, the ground of the signal source and the ground of the
card will not be at exactly the same voltage. The difference between the ground volt-
ages forms a common-mode voltage (Vcm).
To avoid the ground loop noise effect caused by common-mode voltages, connect
the signal ground to the low input. Figure 2.7 shows a differential channel connection
between a ground reference signal source and input channel on MIC-1816. With this
connection, the PGIA rejects a common-mode voltage between the signal source
and the MIC-1816 ground, denoted as Vcm in Figure 2.7.
Figure 2.6 Single-Ended Input Channel Connections
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