Differential Inputs - Xytronix Research & Design ControlByWeb X-16s User Manual

Installation and Connections

2.4.2 Differential Inputs

The differential input mode can be used with sensors that have two analog outputs that are referenced
to each other instead of ground. When making differential voltage measurements, the X-16s is
programmed to use a pair of inputs (2) to make a single differential measurement. With differential
inputs you must make certain both inputs are within the common mode range (0-5V) of the input
amplifiers. Normally this means you must provide some sort of input bias. If no input bias is provided,
even though the differential voltage is correct the absolute voltages may drift into or beyond the 0-5V
power rails of the amplifiers and will produce erratic measurements.
The illustration below shows the connections for a Wheatstone bridge sensor with two output signals.
The outputs are connected to Ain1 and Ain2. The X-16s must be programmed for differential mode on
"Ain1". The analog measurement will be made by the voltage difference between the two inputs (Ain1-
Ain2). For differential measurements the measurement range is ±5V. For example, if Ain1 is 2.0V and
Ain2 is 3.0V, the differential measurement will be -1.0V.
inputs must be in the range of 0-5V for the input amplifiers to work. For example:
Ain1
+5V
0V
When the differential input mode is selected for a pair of inputs, the differential data is output on both
channels. For the example above, Ain1 = Ain2.
In the illustration below the bridge is excited (driven) by the 5.0V reference output. Notice also that the
bridge provides the necessary input bias.
The low input bias and high resolution inputs of the X-16s together with the reference output make the
X-16s workable with many bridge sensors without using a preamplifier or other circuitry.
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Ain2 Measurement
0V +5.0V
+5V -5.0V
Note however, the absolute voltage of both
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X-16s™ Users Manual