Guide [Magazine] Everyday Practical Electronics. Volume 30. Issue 11

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We cannot, however, guarantee it and we cannot accept legal responsibility for it. A number of projects and circuits published in EPE employ voltages than can be lethal. You should not build, test, modify or renovate any item of mains powered equipment unless you fully understand the safety aspects involved and you use an RCD adaptor. We advise readers to check that all parts are still available before commencing any project in a back-dated issue.

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The Publishers regret that under no circumstances will the magazine accept liability for non-receipt of goods ordered, or for late delivery, or for faults in manufacture. The laws vary from country to country; readers should check local laws. Scientific studies have shown that by the time you hear the most distant rumble of thunder, or see the most distant flash, it may already be too late. You are already within range of the next lightning strike.

That is, as humans we are incapable, through our five senses, of receiving timely warning of a possible strike. Two leading lightning researchers in Japan N. Kitagawa and A.

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This phenomenon is so common that it has become an idiom of the English language. At Risk Lightning is not an insignificant risk to humans. It causes more deaths than do most other natural hazards, including hurricanes and tornadoes. The author knows several people who experienced near misses from lightning — including his wife, who was once missed by a mere four metres! She was sitting outside to admire the storm at the time. The risk is particularly acute if you should be standing out in the open, or should find yourself on open waters when a thunderstorm approaches.

Patrons of golf clubs, soccer clubs, and boating clubs are at particular risk — not to speak of the clubs themselves, which might be held liable for injury or death if they have no early-warning system or lightning safety policy in place. Alas, you are not necessarily safer indoors. Another major cause of lightning strikes on humans is electrical equipment they happen to be handling at the time — a leading offender being the telephone.

No less than one in four lightning injuries in the UK is caused through the telephone. Having said this, direct strikes on humans are not the only hazard. Lightning poses a significant risk to livestock, forests, power transmission and distribution apparatus, buildings, electrical equipment, and in particular computer equipment. This is now considered inadequate, with a minimum of ten kilometres being considered more realistic. Principle of Operation There are two broad approaches to lightning detection.

The design presented here represents the less common of the two. The most common approach is to detect electromagnetic pulses emitted by lightning flashes, and this is the method most often used by meteorological met offices. However, while it is very effective, it is still by no means a failsafe warning system — the reason being that it relies on the detection of prior lightning discharges. That is, if you should be extraordinarily unlucky, the first large discharge of a storm might be the one to strike you! The alternative is to monitor atmospheric charge — or, related to this, instability of atmospheric charge.

The present circuit takes the approach of detecting and reporting an unusually high charge on the atmosphere — or rather, an unusually high potential difference between the atmosphere and the earth. At first the author sought to detect instability of atmospheric charge, which is typical of a building thunderstorm. This instability may in some cases be considerable. However, not much is lost by this, since it is not a given phenomenon that thunderstorm activity will cause significant unsteadiness of atmospheric charge — and conversely, ordinary cumulus clouds, and sometimes sudden and unexplained shifts in atmospheric charge may be reported by a circuit as instability — not to mention people walking past the antenna, or electromagnetic pulses e.

What seemed to be the most dependable indicator of a looming thunderstorm was the overall level of atmospheric charge, which was thought to offer fair warning of potential lightning strikes. After all, without a significant potential difference between the atmosphere and the earth, there can be no lightning strike.

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Usually this potential difference covers a large part of the sky, so that the Thunderstorm Monitor would report a raised charge many tens of kilometres away from the epicentre of any electrical activity. In theory, therefore, the circuit should have a range well beyond that of our five senses. However, it needs to be borne in mind that sometimes a raised atmospheric charge may be localised, and the potential difference between the atmosphere and the earth can change very quickly that is, within minutes as a charged thunderhead races across the landscape.

Observations The author found one common factor between most of the storms which he monitored. This was a greatly increased charge on the atmosphere, which easily exceeded the average daily maximum. On an average day, at sea level, the average daily minimum charge will be roughly V per metre elevation, and the average daily maximum charge roughly V.

When there is thunderstorm activity nearby, atmospheric charge may rise to hundreds if not thousands of volts per metre elevation. The present circuit switches a relay and any alarm attached to it when an estimated V per metre elevation is detected — i. This avoids meaningless triggering on the one hand, yet is very responsive on the other.

In most cases, the Thunderstorm Monitor picked up the possibility of a thunderstorm well in advance of any thunder or lightning. Different atmospheric activity graphs. A breaking thunderstorm is shown in e and a high speed record of a thunderstorm directly overhead is shown at f. It would seem a shame, for instance, to call off a wedding reception because of some rumbling in the sky, when the atmospheric charge in fact remains within the normal daily variation.

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Activity Log Atmospheric activity was monitored on and off for a year, by means of a computer logger attached to IC1 output pin 6 solder pin C in Fig. In contrast, the final prototype described here offers a full scale deflection readout. Different vertical atmospheric charge and horizontal time axes are shown in the graphs of Fig. On most days, atmospheric charge meanders slowly and steadily up and down Fig.

There are times when readings become very lively, even without a storm.

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Often such episodes are on a small scale, measuring less than 0. The jagged ascending patterns of Fig.

highdergnonpclom.tk Everyday Practical Electronics, November During a thunderstorm, a negative charge builds up in the lower regions of the clouds in relation to the earth. When the electrical difference between a thundercloud and the ground overcomes the insulating properties of the surrounding air, a cloud-to-ground lightning strike occurs, with the cloud discharging to earth. When a cloud discharges to earth, atmospheric charge, within milliseconds, will dramatically drop, then rapidly return close to its original level.

Not only does the charge drop beneath the cloud itself, but it may drop across the entire visible atmosphere. During observations, it was noted that variations in atmospheric charge frequently predicted weather conditions — in particular, giving a good indication of likely flooding at the complex where the author works. This has him puzzled as to why weather stations seldom, if ever, incorporate measurements of atmospheric charge.

It begins with a 5V regulator IC4 , which is required to provide a suitable voltage for IC1 in particular, and to ensure stability for what is a very sensitive circuit. Note that the circuit is ground referenced the earth , since one is measuring the potential difference between the atmosphere and the ground. Atmospheric charge monitors are often complex circuits — however, this does not have to be the case, as this circuit shows. Therefore, when atmospheric charge is low within daily averages , a Green l.

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When it is raised, an Amber l. When it is high, a Red l. Further, when the red l. A relay was chosen here above, say, a pulsed alarm at the output, since one might wish to use the Thunderstorm Monitor in situations where a more powerful alarm would be required, or to switch other circuits. In this case, IC2a is used as a buffer, to prevent the output of IC1 from being skewed through undue loading. These meters all provide full scale deflection f.

The moving coil meters in particular give a very useful visual impression of atmospheric instability. As a thunderstorm approaches, even at a distance, they may visibly begin to twitch. Circuit Details The author first encountered the present approach to lightning detection in an electronics publication of The core of this circuit is shown in all its magnificent detail in Fig. This represents a simple potential divider, with the potential at the emitter varying with atmospheric charge.

The original circuit added a meter at the output.

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The germanium transistor, which is now obsolete, was evidently very carefully selected. However, unsatisfactory results were obtained with a modern-day equivalent and therefore, a j. With the prototype antenna being about 2. However, atmospheric current is so small a mere 2 picoamps per square metre , and the input impedance of most test equipment so low relatively speaking , that this voltage is practically unmeasurable. If, however, input impedance is raised sufficiently, a meaningful result can be obtained, although with much reduced voltage.

Block diagram for the Thunderstorm Monitor. The full circuit diagram for the Thunderstorm Monitor is shown in Fig. The TLCN j. This reduces atmospheric charge at 2. By way of comparison, if one were to use a op.

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At the very height of a thunderstorm, the input voltage at IC1 pin 3 may rise quite high — potentially higher than the supply voltage of IC1 — and IC1 could be at risk.