Filter Devices - Description

A noise filter is a device placed in the electrical circuit to reduce electrical noise. It allows the basic power frequency of 60 Hz to pass, but filters out other frequencies. Electrical noise is present in almost every power system. This noise is distortion of the standard electrical signal. When it reaches high magnitudes it effects how electronic equipment operates. You may have seen this happen when someone starts a vacuum cleaner in your home while you are watching TV. The picture and sound become distorted due to electrical noise from the vacuum cleaner's motor.

Electrical noise can be caused by motors, loose electrical connections, resistive heating elements, and some transformers. Computers and electronic equipment are often affected by noise. The symptoms of electrical noise are:

  • Static on audio equipment,
  • Wavy lines or snow on TVs or monitors,
  • Random software errors, and
  • Process control shut-downs,

There are two basic types of noise - noise on the power conductor is called normal mode noise and noise between neutral and ground is called common mode noise.