Electromagnetic Interference

29 Oct

Noise on Circuit

The topic this month is “NOISE”.  Not the racket coming from your kid’s bedroom down the hall but the insidious corruption of an electrical signal in a circuit.  EMI or electromagnetic interference commonly referred to as “noise” can be a nuisance.  Electrical noise currents on data communication cables are a real problem.  They can cause corruption of the desired signals being sent across the cable by the equipment connected to its ends.  In extreme cases, these noise currents may even become great enough to cause electrical damage, such as component burnout, to the circuit elements used at either end of the cable.

Electrical noise is the result of more or less random electrical signals getting coupled into circuits where they are unwanted, i.e. where they disrupt information-carrying signals.  Noise occurs on both power and signal circuits, but generally speaking, it becomes a problem when it gets on signal circuits.  Signal and data circuits are particularly vulnerable to noise because they operate at fast speeds and with low voltage levels.  The lower the signal voltage, the less the amplitude of the noise voltage that can be tolerated.  The signal–to-noise ratio describes how much noise a circuit can tolerate before the valid information, the signal, becomes corrupted.


Electrical noise, in its various forms, can adversely affect any product using electronic circuitry. Its potential to cause damage or dysfunction is increasing today as electronic circuits become

In Offices, the laser copier/printer is a well-recognized “bad-guy” on the office branch circuit.  It requires an internal heater to kick in whenever it is used and every 30 seconds or so when it is not used.  This constant switching has two effects: the current surge or inrush can cause repetitive voltage sags; the rapid changes in current also generate transients that can affect other loads on the same branch.more and more complex. Today’s computers and microprocessor-based systems operate at higher speeds and provide more features with reduced size and weight through the use of complex solid state components, both analog and digital. These are inherently fragile and susceptible to damage and/or malfunction from electrical noise.

How can I Protect My Equipment?

Proper grounding of the electrical system is essential.  If your business doesn’t have grounded three-pronged outlets, the first step is to install them.  It is best to put printers on its own dedicated circuit.

Fuses and circuit breakers protect building circuits from overheating and causing fires.  However, damaging spikes and surges occur so quickly that they pass through circuit breakers.  To catch spikes and surges before they damage your equipment, you need surge suppressors.  Surge suppressors react within one billionth of a second (called a nanosecond) to divert the excess voltage to the buildings ground.  Good surge suppressors also filter line noise.

In the Video below you can hear an example of electrical noise


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