Measurement Computing PCM-DAS08 - Manual (Page 9)

3.3 GROUND LOOP EXAMPLE
Figure 3-3 shows a single-ended analog input connected incorrectly. The resulting
ground loop may introduce an error to the input signal.
Figure 3-3. Incorrect Connections Causing a Ground Loop
3.4 BEWARE OF VOLTAGE SPIKES
Although your Laptop may not be grounded, that does not mean that you can connect
the PCM-DAS08 to a signal that is subject to voltage spikes. Even though the Laptop
has no reference to ground, it has more capacitive mass than the PCM-DAS08 inputs
can bear. If the signal you are measuring suddenly swings greater than +/-15V, the
weak link in the circuit will fail. That weak link is your PCM-DAS08 analog input
circuit.
This is true of any A/D board not protected by isolation amplifiers
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