HPLC HINTS & TIPS for Chromatographers
Tip# 105: Power and Surge Protection for Computers & Analytical Instruments:
(1) When selecting an Uninterruptible Power Supply (UPS) for your computers and analytical instruments, only purchase one which outputs a true sinewave voltage (just like real AC power). Most of the UPS systems sold at the local office and electronic supply stores output either square wave A/C or pseudo-sine wave (which is not the real thing). Some brands will tell you they offer true sinewave outputs right in the model number or package, but always double-check the specifications (e.g. APC's "Smart-UPS" offer sinewave outputs, but NOT the Smart-UPS SC models). Using a UPS that outputs something other than true sinewave power can damage the power supply of what it is attached to and possibly leading to premature failure of system you are trying to protect.
(2) Calculate the maximum load of the system being protected in Volt amps (VA) and purchase a system that can provide power well above that load for the time period you want to protect (*I think 20 or 30 minutes of run time, at load, is a realistic guideline to go by). A 700 VA UPS will usually power most desktop computers and a monitor for that amount of time. Most brownouts last for just seconds, but that is enough time to shut everything down or loose communication. If a power outage is more than five minutes in length, then it may be a while before it is restored. In this case, be sure to safely shut everything down manually before you run out of battery reserve power. Once everything has been turned off, remember to turn OFF the UPS system to stop it from slowly draining the battery (most computers are still turned ON and using power when they are OFF). Doing so will preserve the remaining battery capacity. Just turn the UPS back 'ON' when power has been restored.
(3) Unless you want to spend really BIG dollars, just put a high quality UPS system on the computer. A high quality UPS system designed for a single high current draw instrument like a chromatograph may cost thousands of dollars. If the system must be maintained at all times, then a serious back up source of energy should be invested in. High current UPS systems are available from a number of manufacturers so it would be wise to investigate these for your application. For everything else, use a dedicated, high quality power conditioner and surge suppressor on the analytical instrument circuits ($85 and up each, not the $20 models sold at most box stores). The computer system is really what you want to protect first. If the computer gets knocked out you loose communication and control of the analytical system. This usually means it will continue to run on and on without stopping. If the computer is protected by a UPS and the power gets glitched (such as a voltage drop/brown-out) or goes out entirely, then the computer may sense this and abort the run or shut the system down (if it has not been shut down). This is the type of approach we have used in our labs for twenty years and it works great during brown outs and black outs. The computers stay on long enough to properly and safely shut down everything without loosing data (which is the key). The instruments are all connected to individual power conditioners/surge suppressors (Tripp lite brand units in our case) so are protected from brown outs and surges. To protect our equipment from large surges, our electrician installed a high amperage DELTA lightning arrestor (100,000 AMP, 3000 joules per pole, unlimited number of surge capacity) on the breaker panel and individual Delta surge capacitors on each critical 20A circuit that supplies power to laboratory equipment. These extras steps provide protection from direct lightning strikes and surges to the panel and equipment.
(4) The UPS Batteries: The batteries in your UPS system have a finite life. Mark them with a date and keep records on battery changes. Depending on the quality, temperature and load over time, they may need to be replaced in as little as one year or perhaps last as long as four years. When the batteries loose their ability to hold a charge your on-battery run time will drop dramatically so replace them early rather than late. The battery pack can be (and should be) tested on a regular basis. To test the UPS, select a time when the computer is not running any critical applications or providing any networked services (such as right before you would normally shut it off for the day). Once it is safe to do so, go ahead and remove the UPSs A/C plug from the wall. This will remove the UPS systems source of input power just as if a real power failure had occurred. Your computer system should behave as if nothing has happened. Monitor how long the system stays on until the available UPS runtime shows 15 to 20% remaining time left and you will know how long the system can handle a complete power outage. The system will need overnight to fully recharge after this test and you should repeat this test a few times each year to monitor the status of the system. *Many of the modern UPS systems offer a software application that continuously monitors the UPS modules which are connected to your computer or entire network. This can provide a record of the systems used, battery change dates and current charge levels right from your desktop. > Bill Letter,
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