Prevention Methods - Honeywell VPR100 User Manual

B.3 Prevention Methods
Introduction
There are three ways to prevent electrical noise from interfering with the operation of the electronic digital
equipment.
•
Built-in noise rejection
•
Separation of signal and power lines
•
Noise suppression at source
Built-in noise rejection
The first method is to design the digital equipment with a high degree of noise rejection built in. This
includes housing the equipment in a case that will provide shielding, liberal use of noise rejection filters and
opto-isolators, and the use of noise suppressors on potential noise sources within the equipment itself. This,
of course, is the responsibility of the manufacturer who usually performs extensive laboratory and field
testing of newly designed digital equipment to insure the adequacy of its immunity to noise. As a minimum
requirement, the equipment should be able to pass the tests outlined in the IEEE Standard 472-1974 (Surge
Withstand Capacity Tests).
Signal and power line separation
The second method is to prevent noise from getting on the signal and power lines that are connected to the
equipment. This is achieved by proper separation and shielding of those lines. In some cases, separate
power lines or special power line regulation or filtering may be required for satisfactory electronic digital
equipment operation. It is the responsibility of the installer to follow good wiring practices.
Suppression at the source
The third prevention method is to suppress the noise at its source. This is the most effective but also the
most difficult because it is not easy to identify all of the potential noise sources in a typical industrial
installation. Therefore, ''suppression'' is usually a last resort for those extreme situations where the other
methods are insufficient by themselves. See Noise Suppression at Source which follows.
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Appendix B
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