Electrostatic And Electromagnetic Interference

 INTERFERENCE BY RADIATION.

 Interference by electromagnetic radiation becomes important at cable lengths greater than 1/7 of the wavelength of the signals. At frequencies beyond 30Mhz, most of the interference occurs by e.m. radiation

 Principle of the coupling by e.m. Interference.

 INTERFERENCE BY ELECTROSTATIC CHARGE.

 Charged persons and objects can store electrical charges of up to several micro- Coulombs, which means voltages of some 10kV in respect to ground. Dry air, artificial fabrics and friction favour these conditions.When touching grounded equipment, an instantaneous discharge produces arcing with short, high current pulses and associated strong changes of the e.m. field.

 REDUCTION OF INTERFERENCE

 There are a number of methods to prevent interference. But all of them only reduce

 the interference and never fully prevent it. This means there will never be a system which is 100% safe from interference. Because the efforts and the cost will rise with the degree of reduction of interference, a compromise has to be found between the effort and the result.

 The requirement for the reduction of interference will depend on:

 -     The strength of the interference source

-     The sensitivity of the interference sink

-     The problems caused by interference

- The costs of the equipment

 We will discuss ways of preventing interference, their effect, and the main aspects for the optimum efficiency of each method.