Chapter 7: Converter Applications
Manual Number: 00650-014-4
Page 7-3
Precautions - Noise, Ground Loops, and Overloads
Unavoidably, data acquisition applications involve connecting external things to the computer.
DO NOT
get inputs mixed up with the AC line. An inadvertent short can instantly cause extensive
damage. Industrial Computer Source cannot accept liability for this kind of accident. As an aid to
avoid this problem:
a. Avoid direct connection to the AC line.
b. Make sure that all connections are secure so that signal wires are not likely to come loose and
short to high voltages.
c. Use isolation amplifiers and transformers where necessary. There are two types of ground
connections on the rear connector of AD12-8. These are called Power Ground and Low Level
Ground. Power ground is the noisy or dirty ground that is meant to carry all digital signals and
heavy (power supply) currents. Low Level Ground is the signal ground for all analog input
functions. It is only meant to carry signal currents (less than a few milliamperes) and is the
ground reference for the A/D converter. Due to connector contact resistance and cable resistance
there may be many millivolts difference between the two grounds even though they are connected
together and to the computer and power line grounds on the AD12-8 card.
