The Effects of Common Mode (N-G) Noise on a Data String

Today’s electronics have microprocessors that act as high speed switches. These switches are turned off and on millions of times per second. Microprocessors normally work with 5 Volts DC. The off state (zero DC volts) is called “zero” The on state (five DC volts) is called “one” These series of “ones” and “zeros” (0100110010) form the binary language by which the microprocessors function.

The zero voltage in PC boards is connected to the ground wire. Any spike between NEUTRAL and GROUND (common mode) higher than 1 volt confuses the logic in microprocessors. As the graph below shows, any pulse higher than 2.5V (2.5 to 5V) is consider as “1” and bellow 2.5V (0 to 2.5V) is consider as “0”. The logic mistakenly reads “1” as “0” or the “0” as “1”.

Logic Confusion - Normal

Logic Confusion - Noisy

Logic confusion causes error codes in electronic equipment. A logic error produces unintended output or other behaviors. A logic error in a point of sale system could manifest as a system crash. In a copier, it could manifest as a paper jam.

These problems are sometimes interpreted as equipment problems when in fact they are actually power quality problems. Any service call made in which the problem can not be duplicated by the technician is commonly referred to as a “no problem found” service call.