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  Everything you should know about Power Supply Dips & Spikes but were too afraid to ask.
By Les Rose
  Supply Authorities such as ETSA (Electricity Trust of South Australia) recommend appropriate power conditioners as a normal part of an industrial or commercial computer installation.
  Why would the Electricity Trust of South Australia make this recommendation in their booklet "Computer and Electricity"? Because they acknowledge there is a problem. But do you?
  As computer technology advances it is becoming increasingly apparent that the mains distribution system is very inadequate for modem electronic equipment. It is important for every hardware and software supplier to have a basic understanding of the limitations of the power system and the way in which it interacts with modem electronics. Hopefully this will increase professionalism in supplying 'total" computer solutions and eliminate much of the wasted time, energy, money and confidence that occurs due to power related problems.
  The previous decade has seen dramatic changes in computer technology and the direction of computing as a whole. In their infancy, computers were basically used for data storage and retrieval, and number crunching. In today's hi-tech society they are employed as on-line devices in a real time capacity.
  Therefore any downtime caused by software failures tend to have immediate and often catastrophic effects on industry productivity and profitability.
  Technical advances in integrated circuitry have produced phenomenal processing power and memory capacity in what seems to be ever-diminishing package sizes. However, there has been a corresponding trade-off in that much of the needed protection circuitry has been eliminated to reduce device real estate. As a result these devices have now become more susceptible to damage and degradation due to operating conditions such as excess temperature and power supply disturbances and fluctuations.
  If we look at the basics of our power distribution system we discover some interesting facts.
  First of all the system was originally designed for applications such as lighting, heating and motors; none of which employ predominantly sensitive electronics.
  The electrical supply authorities regularly catty out certain procedures to ensure reliable, quality and cost effective supply for these applications. These measures include generator switching, power factor correction, load redistribution and fault clearing. All of these procedures produce some form of power disturbance or interruption to supply, none of which have any significant effect on lights, heaters or motors, which, in spite of this, accept the electrical supply as a reasonable stable source of power.
  However, sensitive electronic equipment such as computers perceive these power line disturbances as potentially hostile to their reliable and effective operation.
  While this is a problem and an area of concern it has been discovered that the greatest and more common threat to computers and the like stems from lights, heaters and motors, and a wide range of other electric and electronic products.
  In the majority of cases this equipment is located in the vicinity of the computer installation, either in the same office, building or similar geographical location.
  Most devices connected to the power cause some form of disturbance or interruption even if only for a fraction of a second. These may not be discemable to the human eye, but depending on the timing, magnitude and rate of accurance, they can cause havoc with the computer system. One of the most crucial periods occurs the instant a device is switched on. Many pieces of equipment act almost like a short circuit for a fraction of a second and others create extremely high voltages and noise.
  It is a practical and physical impossibility for the electricity supply authority to supply infinite amounts and power and protection solely to accommodate the power requirements of sensitive electronic equipment, which only constitutes a very small percentage of its supply. Hence the need for the consumer to provide suitable protection.
  There are a multitude of interruptions and disturbances, which occur on the mains supply. Here are some of the more common problems encountered.
  Voltage Fluctuations:
Any gradual change above or below the prescribed 240 volt supply is classified as a fluctuation. They are caused by heavy load variations on the system.
  Voltage Sags/Surges:
These are rapid changes in voltage that occur for a fraction of a second and are generally caused by local loads such as air conditioners, compressors, system overloads; etc.
This can be defined as any undesired signal superimposed on the mains supply. It is often referred to as EMI or RH interference. Noise can be applied directly to the power lines by appliances or electrical devices. It can also be picked up by the lines acting as antennae from sources such as radio/N transmitters, medical equipment, welders, lightning, etc
These are very high voltage short term disturbances superimposed on the AC waveform. They can rise to several times the normal mains voltage and are caused by motors, SCR controllers, welders, fluorescent lights, lightning, etc.
  Loss of Supply:
This can occur either as a momentary interruption lasting from a fraction of a second to a few seconds or as a total power failure. It can be caused by situations such as system faults, overloads, generator switching, accidents, storms, etc.
  It may come as quite a revelation to know that our computers are subjected to such a hostile power environment.
  Before the power can be used to energize logic and memory circuits, and storage devices within the computer, it must first be processed by the systems power supply known as the switched mode power supply, (SMPS).
  Very simply this device converts the 50Hz 240 volt mains to a high frequency in the order of 20-50khz, reduces the voltage and converts it to the 5 and 12 volt DC levels necessary for computer operations. The SMPS is the interface and buffer between the mains and computer hardware and therefore its operating environment must be kept stable in order to maintain satisfactory operation of the system.
  Overseas research has revealed that the majority of hardware and software problems can be directly related to mains disturbances which cannot be tolerated by the SMPA.
All electronic circuits used in computers comprise of digital and analogue devices that simply process electrical signal voltages. The 5 volt facility in the switch mode is used for these devices for the control of all logic functions. The characters which computers produce are represented by a combination of binary digits 0 & I which in turn are generated by certain voltage levels within the 5 volt range. It is therefore not hard to comprehend that a noise burst, high voltage spike/transient severe fluctuation or momentary power loss could cause a voltage change thus confusing the logic, which of course interpret the change as data.
  In most cases disturbances tend to affect software rather than hardware. Noise can introduce an unwanted bit anywhere in the processing train or commands could be modified; intermediate computations may be affected or incorrect memory addresses may be acknowledged and non-programmed jumps m~, be activated.
Where voltage spikes are significantly high in level and energy they can cause immediate damage to sensitive electronics or cause progressive degradation to the pointwhere failure can occur at any time. Because the switches mode operates at high frequency it is relatively easy for high frequency noise to penetrate and cause problems.
  Although the switch mode design enables it to cope with a reasonably wide input voltage range, it nevertheless relies heavily on a continuous noise free supply of power for trouble free operation. The unit does not consume a constant level like heaters or lights. Instead, it draws current in a series of bursts. The peak value of these current burst are quite high and are used for charging the power supply capacitors which in tum supply voltage to the computer. In order for the required charging current to be available, the mains voltage must suffer no significant distortion. Should a hea'vy load be switched on, the resultant voltage from on the mains can prevent the capacitors from receiving their necessary charge voltge resulting in incorrect voltage levels at the logic boards and disk drives.
  This scenario would be one of the major contributory factors towards data loss, corruption and hard disk failure in industry today. Typical loads which cause the problem often exist in or close to the computers own environment such as industrial machinery, air conditioners, photocopiers, heaters, cookers, etc. Whilst a dedicated line can minimise these problems, it is not the total solution as the switchboard still provides a point of common coupling thereby enabling disturbances to be reflected back down the line to the computer.
  Power disturbances are a fact of life and we must acknowledge its existance and take steps to protect both our hardware and software.
  Electricity supply authorities across the country acknowledge the problems and publish brochures and booklets on the subject recommending that suitable precautions are taken.
In spite of the problems that haunt the personal computer user, there are a number of solutions available on the market which can be used in conjunction with the computer system to eliminate or minimise the effects caused by power disturbances.
  Power Filters:
Filters are designed to provide attenuation of undesirable noise on the 240 volt waveform. The most effective filters available incorporate devices which provide protection against high voltage spikes/transients and lightning surges in addition to RFI/EMI noise.
  Line Conditioners:
These devices are designed to compensate for heavily fluctuating mains line voltages by providing a well regulated voltage supply to the load. A well designed line conditioner will also incorporate a good power filter. The majority of computer equipment today is very tolerant to mains fluctuations and therefore these devices are not used to the degree they used to be.
  Unintentiptibie Power Supplies (UPS):
There are basically two types of UPS -On-Line and Standby.
  On-Line UPS:
With this system the computer is normally energised from the mains power supply via filter. When a voltage variation occurs, the load is switched to the integral battery back-up supply. When the main supply returns to normal the computer load reverts to mains.
  Standby UPS:
With this system the UPS generates its own regulated supply and ensures the computer is totally isolated from the mains supply. The battery maintains the output supply without any switching
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