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April 1991

Protect against computer power failure. (uninterruptible power supplies) (The Practitioner & the Computer)

by Greenley, Langdon J.

    Abstract- One of the major causes of computer failure is an interruption in the computer's power supply. Users can protect themselves with an uninterruptible power supply (UPS), which provides a reliable backup power supply during cutoffs of power and provides protection against sag, noise, surges, and spikes. The three main components of a UPS are the battery, the inverter, and the rectifier. Purchasing a UPS can be an expensive proposition, costing anywhere from a few hundred to thousands of dollars. Users should evaluate their need for a UPS by evaluating the value of the computer hardware and software, the value of time lost to outages, and the value of a sustained level of operations.

By Langdon J. Greenley From PH&Z CPA Advisor, Paneth, Haber & Zimmerman, Winter 1990

Computer systems perform many critical day-to-day operations for today's businesses. Companies often spend substantial amounts of money on excess computing capacity and quick and guaranteed responses to breakdowns, in order to protect themselves against processing interruptions that could negatively impact business. However, most of these efforts do not protect the computer user from one of the leading causes of computer failure: an interruption of the electrical power supply.

A severe storm, fallen power lines, nearby repair or construction work, or even other office machines, can all cause power disruption at company location. A disruption at the wrong time can result in considerable loss, depending on the circumstances. Most computer users know enough to back up critical data files and programs on a daily basis, but are not as aware of what protective measures can be implemented to significantly minimize the computer failure risk due to electrical problems. Most power disruptions are the consequence of an event in the power system and the adjustment of the system to that event. Intermittent memory glitches, data errors and shutdowns are good indications of a "noisy" environment, which is a common problem even in quiet offices.

Surge Protector

The cheapest and most common way to solve most of these problems is to install a surge protector or a line conditioner for $200 or less. These devices automatically correct varying input voltage to provide your equipment with a steady flow of regulated AC power, as well as surge, sag, noise and spike protection. This solution, however, does not allow the computer system to function during a power supply cutoff such as a brownout or blackout. An uninterruptible power supply (UPS) is the ultimate backup of PCs and Local Area Networks (LANs). It buffers the computer equipment from power disruptions and cutoffs, and provides an efficient backup power supply if your main source fails.

What is a UPS and How Does It Work?

A UPS backs up the utility power from an electrical outlet with a battery-based power supply. There are three components to UPS:

* Rectifier. Stores line power in the battery after converting the AC power into DC power. Power disruptions only affect the battery charging process because the battery is being charged by the rectifier.

* Battery. Stores the power for use when the power source is interrupted, and determines the length of time the UPS will support your equipment.

* Invertor. Converts the battery DC power into AC power for the equipment. The invertor supplies continuous power to the computer just as the battery provides uninterrupted power to the invertor.

Do You Need a UPS?

A UPS can cost from a few hundred dollars to several thousand dollars, depending on the computer hardware configuration and the desired level of protection. Buying a UPS can be either an unnecessary expense or a critical step in protecting a computer system. Before purchasing, many factors should be considered:

* Computer hardware and software value. Besides the hard cost of the computer hardware, consider what the temporary or permanent loss of valuable data would cost. If power is interrupted while information is being updated, some data could be lost or corrupted. Such an occurrence may require reentering input data, completing a file cleansing process, or restoring the most recent backup and reentering the data since the last backup. This could be a very time consuming process and possibly too complicated for a computer environment with no in-house technical personnel.

* Cost of downtime. Some companies, such as point of sale and medical systems, would find it very difficult to operate without a computer. An entire company could be shut down during a power interruption if it were in a remote location supported by a central computer. The key factor to consider is the importance of the computer to the operation and the alternatives if the system were to become inoperative. For example, can an accounting firm doing its own tax-return preparation switch to a manual backup system during periods of downtime?

* Level of operations. Determine what has to be done during interruptions and the power needed to support the computer hardware. The UPS system required to run a complete system will be more expensive and complicated than maintaining a reduced level of operations. Determine whether it is practical to continue work on the computer during a power outage and calculate how long the battery must power the computer equipment.

Before buying a UPS, decide on the level of protection desired. The length of time that the UPS should be able to boot supply power to the computer depends on whether the objective is to allow for the smooth shutdown and would avoid the normal file corruption and problems associated with a sudden interruption in service. Normally, this type of system would provide power from 10 to 30 minutes to allow users to save their work and terminate processing. Because most power problems are for a very short duration, this type of UPS protection eliminates loss of service for 90% of the electrical problems encountered in most office environments.

Generally, you can purchase UPS systems to provide more than eight hours of backup power for small systems and networks. It all depends on the company's needs and budget. What should be evaluated is the cost and benefit of having that amount of backup power versus the probability of a power interruption lasting up to eight hours.

What to Do When the Power Fails

If a power failure occurs, employees using the computer should adjust their work activities according to the design of the UPS system. If the system was designed for a smooth and orderly shutdown, then the staff should immediately begin shutdown procedures. If the system was designed to support critical operations, then work should be carefully prioritized. In this case, you should establish rules for shutting down the system as the end of the UPS support time approaches. Once power is restored, the staff should act according to established procedures. For example, the system should be backed up and a designated person should verify that all users are properly signed off the system before full operations are restored. There should also be an analysis of the backlog caused by the power failure and the course of action required to catch up.

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