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4.0 Principles of operation
4.1 Noise and surge suppression
The UPS contains high performance EMI/RFI (Electro-Magnetic and Radio
Frequency Interference) noise and surge suppression circuitry to protect your
computer equipment. The UPS provides this suppression continuously, whether
or not it is turned on. Normally, the UPS suppresses noise and surges without
your notice; that is, the UPS doesn’t transfer your load to its internal power
source. Instead, the suppression circuitry reduces the amplitude of noise and
surges to a level well below that which can be tolerated by your relatively delicate
computing equipment.
The illustration above shows what a typical “medium” amplitude surge or spike
looks like when present on the utility voltage. Surges up to 15 times larger than
this are easily suppressed by the UPS. Surges are commonly caused by nearby
lightning activity and motor load switching created in air conditioners, elevators
and heat pumps.
The illustration above shows what EMI/RFI noise looks like when present on the
utility voltage. The UPS “filters” out this noise with components whose electrical
resistance is very high at radio frequencies. EMI/RFI noise is commonly created
by the same activity which produces surges but can also be caused by nearby
radio transmitters and blinking neon bulbs and signs.