Measurement Computing CIO-DAS16/M1 - Manual (Page 10)

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Figure 3-2. Cable Shield Grounding
3.2.5 Floating Signal Source
A floating signal source is defined as the low signal having no reference to earth ground (PC Chassis
ground or LLGND). Examples are a battery, an isolated precision power supply or a sensor which is not
earth grounded. See Figure 3-3 for a connection diagram.
Figure 3-3. Floating Signal Source Referenced to Ground
A reference between signal LOW and LLGND must be provided because board inputs are differential.
Failure to supply the reference (10K resistor) will result in unrepeatable readings.
3.2.6 Avoiding Ground Loops
Figure 3-4 shows the wrong way to connect a floating signal and create a ground loop. Any current
caused by a voltage potential between the grounds will be sufficient to interfere with signal readings
Signal High
Signal Low
Channel # High
Channel # Low
Shielded Cable
Instrument
CIO-DAS16/M1/16
Tie Low to GND
LLGND GND
GROUNDED SIGNAL SOURCE - Suggested way to connect
signal and cable shield. Ground is completed through
power ground. Voltage between outlet grounds not to
exceed the common mode range.
Signal High
Signal Low
Channel # High
Channel # Low
Shielded
Cable CIO-DAS16/M1/16
LLGND
FLOATING SIGNAL SOURCE - Suggested way to connect signals
and cable shield. Connection is made to Earth ground through
power ground.
10K