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THE WAY I SEE IT By NEVILLE WILLIAMS Are surges & spikes on the mains a hazard to personal computers? Don't be surprised if the following article raises more questions than it answers. Unfortunately, that seems to be the way it is when one tries to quantify the problem of surges and spikes which occur on the supply mains and the hazards they present to personal computers. First let me emphasise that I boast no special expertise in the subject. I am aware, though, of certain commonsense precautions that can help safeguard personal computers in a home or office situation. They are set out in a separate panel for your consideration and I suggest that you read through them at this point. My day-to-day involvement with personal computers has mainly to do with word processing and allied tasks, where such precautions can be observed without undue hassle. They may be less practical in offices, in educational situations or in other computing applications. I set up my first word processor about five years ago and considering the modest cost, it worked very well. I subsequently replaced it with a more ambitious system using an Apple IIc. I'm still using that system, along with its normal monochrome monitor, Appleworks and other software, external disc drive, printer, modem, mouse and a conventional RF line filter. When first installed, a small serial/parallel converter was also included, allowing the Apple to drive the same BMC BX-80 printer that had formed part of the earlier system. 44 SILICON CHIP In the new situation, the BMC printer failed on three separate occasions, with no obvious explanation but always with the same symptoms: when self-tested, it would print out its full character set in the normal way but would not accept drive from the computer. When it failed a fourth time, so did my patience and I replaced both it and the associated converter with a new Epson LX-800 printer, retrofitted to be Apple-compatible. Since then, as per the old saying, it's been "working like a bought one" on both text and graphics! There's a point to this tale: I never did find out the real reason for the repeated breakdown of the original BMC printer. Predictably, the suppliers of the printer and the serial/parallel converter maintained that such failures were uncharacteristic of their respective products. But they did seem to agree on a couple of points: • Such things do happen on occasions (what a brilliantly perceptive remark)! • Surges and spikes on the power mains could well have had something to do with the problem. (Logical explanation or a cop-out? Take your pick!) That's about as far as their in- terest seemed to extend. I gained the distinct impression that when something faiied (in this case a printer), somebody, somewhere replaced suspect ICs or suspect boards until the fault disappeared. If it failed several times, you fixed it several times. The how, when, where or why of the breakdowns received scant consideration. A major failure I would probably have written the whole thing off as "one of those things" had it not been for a subsequent system failure of a quite different kind. During that (for some) delightfully relaxed period after the Christmas festivities, I fired up the Apple II with the intention of transcribing my hand-written notes about Peter Wright's "Spycatcher" (for the March issue). Everything was behaving normally when, pausing to rethink a particular observation in my notes, I heard an uncharacteristic "grunt" from the printer, much as happens when it is first switched on. But it was already on and the system was just sitting there waiting for me to make up my mind. When I did try to use the keyboard, I realised that the computer had locked up. Unfortunately, switching off and re-booting did not fix the problem. A couple of foreign semi-colons on what should have been blank areas of the screen indicated that something was amiss and while the word processor still worked in a fashion, any attempt to feed the text to either disc or Surges On the Phone Lines Reference: "Characteristics and Rate of Occurrence of Lightning-Caused Induced Voltage Surges in a Telephone Line" by D. Mackerras. Journal of Electrical and Electronics Engineering, Australia, Volume 5, No.3, September 1985. The line which provided the basis for Mackerras' observations over a period of about four years comprised about 3km of overhead cable and 20km of underground cable, including an exchange. A sketch map accompanying the article shows the position of nearby 50Hz high voltage power mains. It is not possible to adequately summarise the contents but the paper indicates that the pulse energy can be attributed mainly to the induced effect of ground printer simply triggered another lock-up. At that point it dawned on me that the computer could hardly have picked a worse time to break down. That became all the more evident when I discovered that just about every Apple PC repairman that I could think of was on holidays until after the new year break! Fortunately, I was able to borrow another Apple lie from a relative for a few days and that allowed me to carry on. But it also gave me time to reflect on what had happened. While I had to concede that the failure might have been purely spontaneous ["one of those things") the circumstances did seem to suggest a high voltage transient on the supply line. This was subsequently supported by the observations of an Apple dealer service manager who, after an initial examination, said that the computer appeared to have suffered more than a simple failure. With a bit of luck, they might be · able to repair it by replacing ICs, in which case I could expect a bill for around $100. Failing that, it could be a case for board replacement which would run to more like $250. Asked whether he'd seen similar (not cloud) lightning flashes and to superimposed 50Hz energy caused apparently by fault current or unbalanced voltage initiated by the same lightning occurrence. A typical recording, relative to a flash within about 1 km of the aerial section of the phone line and close to the 11 0kV cable, shows a prominent 9 cycles of mains frequency at about 200V peak-to-peak present on the phone line . Other such events involved from 4 to 48 cycles at amplitudes ranging from 1 5V to 320V. More than half of all observed lightning events involved multiple surges, the mean average number being 2. 8 with a mean average separation of 1 38 microseconds. damage before, the service manager said it was uncommon but certainly not unique. He still had a couple of other boards on the shelf from computers which appeared to have suffered a similar trauma. His intention was to work through them in detail "one of these days" and bring them back into service. In fact, he managed to salvage my original board and when I got the computer back, it seemed to be working perfectly. That is, until I attempted to feed the text down the line to one of the SILICON CHIP computers. Then, what appeared to leave my screen as perfect ASCII copy showed up on theirs as badly corrupted. So my computer had to go back for further attention, with a suggestion that there was still a fault in the modem output port that had been overlooked. Apparently, that proved to be the case, leaving me with an all-up repair bill of about $170. It seemed likely that the modem port had been damaged at the same time as the remainder of the system but there was another possibility. Thinking back, I realised that while I had been dutifully unplugging the system from the mains, I had As measured in the Queensland University Laboratory, at the end of the underground section of the cable , a maximum voltage exceeding 320V occurred at a rate of 10 events per year. Events exceeding 650V occurred once per year, with the possibility (extrapolated) of 1 400V once per 1 0 years. In · the . Brisbane area, about 84% of all lightning events can be expected in the December/ January period, with 79% of those concentrated in the late afternoon. from 2pm to 6pm . The author lists 9 other references on the same general subject but warns that allowance has to be made for measurement criteria, line configuration and the country or area in which the tests are conducted . been less diligent in disconnecting it from the phone line. So during some of the violent thunderstorms that marked December on the east coast, the system may well have been exposed to lightning induced pulses on the phone line. I might not have been aware of such damage until I actually tried to use the modem. Either that, or a voltage transient may have affected the computer in a more subtle way, rendering it liable to spontaneous failure or vulnerable to, say, a surge or spike on the power mains. Alarming picture If you have a mind to do so, it isn't difficult to put together a deeply disturbing picture of what can happen to your PC from such eventualities. Lightning was discussed in relation to NASA activities on page 30 of the November 1988 issue and again, in more detail, in the February 1989 issue [see also the accompanying panel). But what about spurious pulses on the mains attributable to other causes? With this in mind, I phoned an acquaintance who is usually a mine of information on such matters. He MAY1989 45 Surges On the Power Mains In a 1 984 brochure covering their TRANSIL transient voltage suppressors, Thomson-CSF summarise the problem as follows, presumably based on observations in France. No reference is made to reticulation mishaps. "Externally caused voltage surges are of industrial or atmospheric origin and are transmitted through the supply cables by inductive or capacitive coupling. "On 220V mains, industrially caused voltage surges can have an amplitude of 5 to 1 0kV, with durations of between 0. 1 and recalled that a university student, gaining work experience in the Philips laboratory in Artarmon (NSW), had once built up a device to record the occurrence of spikes on the 240V m::iins. Using mechanical counters (it was back in the 1960s) the circuit was set up to sense the amplitude of peaks in roughly 100V steps above the normal peak of 350 volts to 1000 volts. Apparently, the device worked well but it was amazing to see how many times the 1000 volt counter registered. Next on my list was a schoolteacher friend who has his own Apple Ilc and is involved with several more of them at the school. No, he had never experienced any similar breakdown problems but said I:ie, "I must tell you what happened the other day around this neck of the woods" - out Parramatta way. It seems that a couple of bright lads, poking around a nearby building site, had come upon some loosely rolled bare galvanised fencing wire. Sensing the opportunity for a bit of "fun", they had carriPd it upstairs in a block of units and had landed it neatly, quoit-like, across a nearby llkV power line. What followed was an almighty series of flashes and explosions, which somehow defied the protective cutouts that were supposed to operate in such an emergency. When my ever-inquisitive friend ar46 SILICON CHIP 1 00 microseconds . Their occurrence is variable. Statistics show that, in an area where there is a lot of noise on the mains, 1 kV surges occur between 1 00 and 1 000 times a year and 5kV voltage surges occur on an average of once a year. "In the case of voltage surges of atmospheric origin, lightning can produce amplitudes of 30kV for an average duration of 70 microseconds. In the case of EMP (electromagnetic pulse) voltage surges, the electrical field can reach 1 00kV/m for durations of 1 0 to 50 nanoseconds". rived on the scene a few minutes later, the charred llkV cable ends were draped across the 415/240V consumer wiring beneath. Said he: "I wouldn't like my computer to have copped that lot!" He would have relished, even less, the lot of residents out Manly way, where a truck crashed into a power pole and dropped a 33kV feeder across the 415/240V mains. I understand that the accident took out quite a few microwave ovens and TV sets in the area but it would also have been a poor lookout for any computers that happened to be powered up at the time. Distribution problems When I raised the general subject with a technical officer attached to a major electricity distribution centre, incidents like those above held no surprise for him. They were par for the course. As he said, "Our circuit breakers are normally very fast and very effective, able to isolate a high voltage line within a couple of cycles. Having isolated a line", he added, "they can test the circuit again after about 60 seconds, to see whether the problem had disappeared - as it might well have done if a momentary short has been caused by, say, a falling branch". There had been a much larger headache, he said, when they'd lost a major underground cable during the Christmas break. It failed suddenly, without warning, possibly due to unreported damage and subsequent moisture penetration. It really upset things. "Are incidents in the high voltage network reflected in the 240V mains?'' "Most definitely", he said. "Variations, surges and spikes are simply stepped down by the pole transformers''. He went on to say that a blackout involving a major shopping centre posed a particular problem, with thousands of independent fluorescent lights and other appliances sitting across the mains. No-one ever bothers to turn them off when the supply fails. An enormous peak current flows at the instant supply is restored, followed by complex current and voltage variations until everything settles down. In many cases, consumers in areas surrounding large shopping and industrial complexes share the same high-voltage feeders - as a practical and economic necessity. What happens in the shopping or industrial complex is reflected in nearby consumer mains. By the very nature of things, he said, some consumers face greater risks than others of mains supply interruptions and traumas. Too many loose ends As I said, it isn't hard to assemble a disturbing picture by lumping together lightning strikes, reticula-. tion accidents, load problems and switching transients but in the process, I became aware of certain "loose ends". Or if you prefer: questions lacking ready answers. For example, in what way are computers supposed to be especially vulnerable to spikes and surges? By simple failure of the DC power supply, by the application of excessive voltage to other components, by anomalous injection into the data circuits, or all three? A detailed documented analysis would be much more helpful - and convincing - than the usual bald statement that computers are vulnerable and that's that! Again, there 's endless talk and numerous references to spikes and surges on the power mains. But try Personal Computers - Typical Precautions • Don't expose PCs to an environment which can generate high electrostatic charges; eg, synthetic carpets, plastic furnishings, etc, especially in a naturally dry or air conditioned atmosphere. • Don't couple or uncouple units or fiddle with plugs and cables while the system is powered up. • Feed the system through a line filter. It will hopefully liinit to obtain a quantitative assessment of the potential rate, amplitude or duration of spikes and surges and one is met with mainly anecdotal answers. A detailed analysis of all such possible events would shed further light on the whole subject. (In the meantime, see the panels accompanying this article). The w ay I see it Doubts notwithstanding, it seems to me that the precautions as listed make good basic sense and are well worth observing: • Computers should not be exposed needlessly to large electrostatic potentials, or physical changes made to the set-up while it is switched on. • RF filters , preferably including a va ristor limiter, a re affordable and should attenuate most highamplitude spikes from the microsecond to the low millisecond range. If you want to build your own, ref er most of the spurious pulses on the power mains. • If possible, avoid leaving the system switched on during a thunderstorm. Better still, operate the entire system from a multi-outlet cord or filter, which can be readily removed from the power point, should the need arise. • If connected to the telephone system, unplug when not required but especially during thunderstorm activity. to the Mains Muzzler project in the January 1989 issue of SILICON CHIP. • If the system is not going to be used for some hours, switch it off until it is needed again. Reduce the number of hours it sits across the mains and you reduce in direct proportion its exposure to a reticulation mishap that the filter might not be able to cope with. • Don't just disconnect the modem when you hear thunderclaps; leave it unplugged until it is actually needed. What if the equipment needs to operate continuously throughout the whole working day? And during the evenings, or the night as well? I guess that one has to accept the added risk. Either that or you can install a more comprehensive - and expensive - line filter or conditioner, or even an uninterruptible power supply. Few personal computer applications would justify that sort of expense, however. ~ Lightning Monitor System According to a report in a recent edition of the TV series "Beyond 2000" , a system has been set up to automatically monitor the progress of thunderstorm activity across France. Groups of receptors , positioned mainly on airfields, pinpoint cloud and ground flashes , plotting them in real time as dots and crosses respectively on a video display, over which is superimposed a map of France. The intensity, track and present location of thunderstorms can be seen at a glance and precautionary measures taken. No less to the point, the system provides a means by which computers and other lightning-prone systems across France can be isolated automatically as a storm cell moves across their area. 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