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Setup and Installation
Application Precautions
Unavoidably, data acquisition systems are intimately tied to the computer.
Because of this, it is VERY IMPORTANT that signal inputs NOT be
mixed with AC line current. As an aid to avoiding this problem:
1. Avoid direct connections to the AC line.
2. Ensure all signal wire connections are tight and sound to avoid shorts
to high voltages.
3. Use isolation amplifiers and transformers where necessary to ensure
isolation.
There are two ground connections (DIG. COM. and L.L. GND.) on the
rear connector (DAS-8 Series boards implement the L.L. GND. only
when in the single-ended input mode). Digital common is the noisy or
“dirty” ground that is meant to carry all digital signal and heavy current
(power supply). Low level ground is the signal ground for all analog input
functions. It is only meant to carry signal currents (less than a few mA)
and is the ground reference for the A/D channels. Because of connector
contact resistance and cable resistance, there may be several millivolts
difference between these two grounds even though they are eventually
connected to each other, the computer, and power line grounds on the
DAS-8 Series board.
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