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<html xmlns:tei="http://www.tei-c.org/ns/1.0">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<link rel="stylesheet" type="text/css" href="./css/css.css">
</head>
<body>
<div id="encoInfo"><div class="modalContent">
<span class="close" onclick="hideEnco()">x</span><h1><center>Keep Power-Line Pollution Out of Your Computer</center></h1>
<center><p>
1' edition, Byte Magazine, 1983.
</p></center>
<center><p>
Converted to XML encoding by
Alessandro
Mazzeo
</p></center>
<br><p><b>Project Description</b>
The project was born as an exercise for the exam of text encoding. The choosen text is a stretch from an article of Byte Magazine,
December 1983, the text speak about a common matter of computer users, the power-line pollution.
This inconvenience is a interference inside power line that could cause voltage anomalies, the consequence is damage to home computer.
Infact in '80 years this problem was the principal cause of guaste in feeder.
Steve Ciarcia in this article propose his solution.
</p>
<br><br><p><b>Based on:</b><br>Keep Power-Line Pollution Out of Your Computer by
Steve
Ciarcia
<br>Byte<br>the small systems journal<br>
Byte Publications
A McGraw-Hill Publication
U.S.A.
Canada
U.K.
1983-12-01
<br>vol:
8<br>num:
12<br>page:
36-44<br></p>
<p>Document typology:
Article,
Tech article,
</p>
<p>Language:
English,
</p>
<p>Licence: Public Domain</p>
<h3>Editorial Declarations: </h3>
<ul>
<li>
Errors in transcription have been controlled manually, and there were not errors.
</li>
<li>
Many of end-line hyphenations have been removed.
</li>
<li>
All technical information have been expanded with a gloss, and all abbreviations have been further expanded.
</li>
<li>
Measure units and other text elements have been normalized.
</li>
<li>
All punctuation marks in the source text have been retained.
</li>
<li>
All quotations in the source text have been retained.
</li>
<li>
The text has been subdivided in macrosection (eg. advertises-section, addresses-section ecc..) and in microsection identfied by paragraph elements or other elements.
</li>
</ul>
<h3>Revisions Description</h3>
<ul>
<li>When: 2017-12-03, What: Wrote text introduction, Who: #AM</li>
<li>When: 2017-12-05, What: Text encoding, Who: #AM</li>
<li>When: 2017-12-06, What: Text encoding correction and adding other elements, Who: #AM</li>
<li>When: 2017-12-07, What: Donwload an upgrade of my DTD from TEI ROMA and
adding images, creating xslt, Who: #AM</li>
<li>When: 2017-12-08, What: Started translation in Italian, other
corrections., Who: #AM</li>
<li>When: 2017-12-09, What: Completed Italian translation but aborted in final
project, rebuilding xslt., Who: #AM</li>
<li>When: 2017-12-10, What: Complete document revision, Who: #AM</li>
<li>When: 2018-02-12, What: Rewriting a new xslt, Who: #AM</li>
<li>When: 2018-02-23, What: Text encoding correction, Who: #AM</li>
<li>When: 2018-03-16, What: Removing translation section, Who: #AM</li>
<li>When: 2018-04-06, What: Corrections on DTD, Who: #AM</li>
<li>When: 2018-05-17, What: Encoding new elements, Who: #AM</li>
<li>When: 2019-03-26, What: Expanding teiHeader, various corrections, Who: #AM</li>
<li>When: 2019-03-27, What: generating new DTD from TEI ROMA, rebuilding xslt, Who: #AM</li>
<li>When: 2019-03-28, What: Improoving xslt, css adaption, Who: #AM</li>
<li>When: 2019-03-29, What: Adding facsimile, Who: #AM</li>
<li>When: 2019-03-30, What: Building xslt, Who: #AM</li>
<li>When: 2019-04-01, What: Improoving xslt, Who: #AM</li>
<li>When: 2019-04-02, What: Other corrections in xml, Who: #AM</li>
<li>When: 2019-04-03, What: Restyling CSS, correcting js, Who: #AM</li>
<li>When: 2019-04-04, What: Generated html output, Who: #AM</li>
</ul>
</div></div>
<div id="bodyText">
<div class="introduction">
<div class="figure" id="IM1">
<img src="./img/fig1.png">
<p class="figDesc"><i> Photo 1: Your computers and other electronic equipment are vulnerable
to disturbances transmitted through the power line. Most of the components
necessary for transient and noise suppression can be purchased from Radio
Shack. Shown here are a commercial <abbr title="Electro Magnetic Interference">EMI</abbr><span class="expan">Electro Magnetic Interference</span>/<abbr title="Radio Frequency Interference">RFI</abbr><span class="expan">Radio Frequency Interference</span> line filter made by Corcom and
two General Electric metal-oxide varistors. </i></p>
</div>
<h2>Keep Power-Line Pollution Out of Your Computer</h2>
<hr>
<div id="showInfo"><a href="#" onclick="mostraEnco()">Show information about encoding</a></div>
<hr>
<center><p><i>by Steve Ciarcia</i></p></center>
<p> A visitor once called the Circuit Cellar my
mountaintop wilderness retreat. Since he lived in the
center of Manhattan, the few oak and birch trees around my
house seemed to him like a forest, and because he could view scenery further
away than a block or two he must have felt like he was on Mount
Whitney. Well, my area is one of the higher points in
Connecticut, but that isn't very high. It's barely a
prairie-dog mound to someone from Montana. Life in a rural
location has its special pleasures. I get to plow the snow from
my own driveway, trim back the ever-encroaching foliage and rake the leaves,
pile four cords of wood for the stove each winter (<a href="#refe1">see reference 1</a>), fight off
the local animal population, and spend large sums of money repairing damage done
to my electronic equipment by electrical disturbances. This last item is the
only one that really annoys me. Every year I can count on experiencing some
equipment failure attributable to an external electrical impulse, usually coming
in through the power line. </p>
<p> For three years, just like clockwork, the first thunderstorm in
June wiped out a DECwriter II terminal connected to one of my computers. After
the first two times of spending a few hours replacing blown chips, I got smart
and installed <i>sockets</i>. (Now I even know
in advance which chips will be blown.) Last summer I kept the printer
unconnected when I wasn't using it. But the elements were not to be denied.
During an August thunderstorm, lightning struck my house. I can't say for sure
where the bolt ac <p class="pb"><b>36</b> December 1983 © Byte Publications Inc.</p>
<p id="epgh">
An expensive lesson produces the cheapest Circuit Cellar
project yet
</p>
tually hit (there were no burn marks or other visible clues),
but I suspect the point of entry was the power line. I remember seeing an
indistinct flash of light, hearing a tremendous crash, and then standing in
darkness. My assistant Jeanette saw a bright blue glow
behind one of the computers. Such a tremendous power surge is not kind to
semiconductor-based equipment. The casualties included one computer, one video
camera, two video monitors, a microwave receiver, and probably several other
assorted items I haven't found yet. The damage did not include the DECwriter
(safely unplugged since May), but it was over $3000. In December, thunderstorms
are not an immediate threat, but as I write this in early September the memory
is still fresh and I still have a month of potentially violent weather to
contend with. I am forced to consider some defensive measures. Perhaps by
relating my experiences I can save you from a similar fate. Of course, lightning
isn't the sole cause of electrical disturbances; you don't have to wait for a
thunderstorm to be a victim. Many kinds of trouble can be ducted into your
computer through the power line. In the January 1981
Circuit Cellar article (<a href="#refe2">reference 2</a>), I wrote about <span class="glossOver" onclick="showGloss('#intfM')">electromagnetic interference</span>
<abbr title="ElectroMagnetic Interference">(EMI)</abbr>
<span class="expan">ElectroMagnetic Interference</span>
and <span class="glossOver" onclick="showGloss('#intfR')">radio-frequency interference</span>
<abbr title="Radio-Frequency Interference">(RFI)</abbr>
<span class="expan">Radio-Frequency Interference</span>
. This month I'd like to pick up the saga by describing
other forms of electrical pollution that occur on power lines. Afterward, I'll
describe a few simple, inexpensive means of dealing with them. </p>
</div>
<div class="article">
<div id="sez1" class="sezione">
<b>The Power Line: A Hostile Environment</b>
<p> The lines leaving your local utility company's generating plant carry
electrical power that in most respects is pure, smooth, and constant.</p>
<p> However, as the power is routed through the distribution network, it comes
<p id="cpy"> Copyright © 1983
Steven A.
Ciarcia. All rights reserved.</p> under the increasing aberrant influence of external
forces and the connection or shedding of electrical loads. Your
susceptibility to these aberrations depends on your location in the
distribution system. If you are close to the power plant, you should have
relatively few, with the low <span class="glossOver" onclick="showGloss('#src-imp')">source-impedance</span> of the generator and short
distance of the transmission line limiting the influence of external forces.
But rural customers at the end of the line usually experience the full
effect. While the utilities try to distribute power evenly, the presence of
a large-scale user of electrical power along the line between the generator
and you can greatly affect the quality and quantity of the power you get. If
you own a personal computer, you should be concerned about the quality of
the power you feed it. Power-line irregularities cause problems for
computers and other digital equipment because certain kinds of extraneous
electrical pulses can be interpreted as data or instructions, causing errors
in operation. You face hazards every time you plug in a piece of electronic
equipment, but there are certain precautionary measures that can protect
your computer. The degree of sensitivity depends somewhat on the type of
equipment and the type of disturbances. As the operating speed of digital
equipment increases, its tolerance to power-line pollution lessens.
High-speed processors and memory components are susceptible to fast
transients. (Dynamic memories, which must be periodically refreshed, are
particularly susceptible.) Disk drives and displays, on the other hand, are
more affected by lasting surges and sags in operating voltage. </p>
</div>
<div id="sez2" class="sezione">
<b>Common Sources of Woe</b>
<p> Electrical power-line disturbances can come from either natural or manmade
sources. Of the many ways the power line can be disturbed, the several
varieties of voltage fluctuation most often cause problems
with computer equipment. These fluctuations can be categorized by source and
severity, as follows: </p>
<ul>
<li style="font-weight: bold;"> Blackouts.</li>
<li>
<p> A blackout is a total power outage—the voltage goes to zero.
Obviously if no alternate source of power is available as a backup,
computer equipment will be severely affected, and data will be lost.
Blackouts generally affect only a small number of utility customers
(fewer than 5 percent) during a year and generally last less than 10
seconds. </p>
</li>
<li style="font-weight: bold;">Brownouts.</li>
<li>
<p> A brownout is typically a corrective action taken by the utility
when power demand exceeds generating capacity. The utility reduces
the output voltage from a <span class="glossOver" onclick="showGloss('#nomV')">nominal 120 V (volts)
by 5 to 15 percent</span>. When the voltage is thus reduced, the
resistive load presented to the generators by the distribution
network consumes less power. Generally speaking, most consumer and
industrial equipment designed for use in North America
functions properly when supplied with current within the range from
105 to 130 V. But when operating at either extreme, the equipment is
more vulnerable to disruption from some other power-line anomaly.
Fortunately, power companies rarely reduce the voltage by more than
7 percent. </p>
</li>
<li style="font-weight: bold;">Voltage transients.</li>
<li>
<p> The phenomena of voltage transients include surges of voltage above
the specified normal, voltage sags below, and instantaneous voltage
spikes that leap far above the nominal levels. Surges and sags are
long-duration events occurring at some point in the distribution
network when electrical equipment is routinely turned on or off
nearby. The magnitude of the surge or sag depends upon the size of
the load being removed from or placed on the network. Sags are often
produced by the turning on of electric motors, which have high
starting currents. (You've probably noticed lights dimming
<p class="pb">December 1983 © Byte Publications Inc. <b>37</b></p>
<div class="appendix">
<h3>How Lightning Strikes</h3>
<div class="introduction">
<p>A lightning flash is characterized by one or more strokes with typical peak
currents of 20 kA <span class="glossOver" onclick="showGloss('#kA')">(kiloamperes)</span> or higher. In the immediate vicinity of the
stroke's impact on the earth, hazardous voltage gradients exist. It is
difficult to establish a definite grounding-conductance
value necessary to protect equipment and personnel. The current in a
lightning strike is so high that even 1 ohm of resistance can theoretically
produce hazardous potentials. When lightning strikes a building unprotected
by a lightning rod, the stroke seeks out the lowest-impedance path to earth
(most likely through the electric wiring or water pipes).</p>
</div>
<div class="figure" id="appeIm">
<img src="./img/appendice.png">
<p class="figDesc"><i> The important element in lightning protection is the lightning rod, a
pointed shaft of copper to which a half-inch copper cable is fastened. The
cable in run down the side of the building, where it is clamped to an
8½-foot copper-plated steel rod driven into the earth. The rod system
pictured here costs $150. </i></p>
</div>
<div id="sez9" class="sezione">
<b>How It Starts</b>
<p>As the electric charge builds up in a cloud, the electric field in the
vicinity of the charge center increases to the point where the air starts to
ionize. A column of ionized air, called a <span class="glossOver" onclick="showGloss('#pltStamr')">pilot streamer</span>, begins to extend
toward the earth at a velocity of about 100 miles per hour. After the <span class="glossOver" onclick="showGloss('#pltStamr')">pilot
streamer</span> has moved perhaps 100 feet to 150 feet, a more intense discharge
called the stepped leader occurs. This discharge inserts additional negative
cluzrge into the region around the <span class="glossOver" onclick="showGloss('#pltStamr')">pilot streamer</span> and allows the <span class="glossOver" onclick="showGloss('#pltStamr')">pilot
streamer</span> to advance for another 100 to 150 feet, after which the cycle
repeats. As its name indicates, the stepped leader progresses toward the
earth in a series of steps, with a time interval between steps on the order
of 50 microseconds. </p>
<p> In a cloud-to-ground flash, the <span class="glossOver" onclick="showGloss('#pltStamr')">pilot steamer</span> does not move in a direct line
toward the earth but instead follows the path through the atmosphere where
the air ionizes most readily. Although the general direction is toward the
earth, the specific angle of departure taken by each succeeding <span class="glossOver" onclick="showGloss('#pltStamr')">pilot
streamer</span> from the tip of the previous streamer is unpredictable. Therefore,
each 100- to 150-foot segment of the stroke will likely approach the earth
at a different angle. This changing angle of approach gives the overall
flash its characteristic zigzag appearance.</p>
<p> As a highly ionized column, the stepped leader is at essentially the same
potential as the charged area from which it originates. Thus, as the stepped
leader approaches the earth, the voltage gradient between the earth and the
tip of the leader increases. The increasing voltage further encourages the
air dielectric between the two regions to break down.</p>
</div>
<div id="sez10" class="sezione">
<b>Attracting Lightning</b>
<p>Objects extending above their surroundings are likely to be struck by
lightning. Thin metallic structures, such as flag poles, lighting towers,
antennas, and overhead wires, offer a very small cross-sectional area
relative to the surrounding terrain, but ample evidence exists to show that
such objects apparently attract lightning. The ability of tall structures or
objects to attract lightning serves to protect shorter objects and
structures nearby. In effect, a tall object establishes a protected zone
around it; within this zone, other structures and objects are protected
against direct lightning strikes. As the height differential between the shorter surrounding objects and the tall
one decreases, the protection provided to the shorter objects decreases.
Likewise, as the horizontal distance between the tall and short structures
increases, the protection afforded by the tall structure decreases.</p>
</div>
<div id="sez11" class="sezione">
<b>Lightning Rods</b>
<p>A protective device that makes use of this phenomenon is the lightning rod,
shown in photo. Generally just a sharp copper spike, the lightning rod is
attached to the highest point on the structure to be protected. When
lightning strikes, the current is shunted directly through a heavy copper
wire from the rod to a grounding electrode buried in the earth.
Although the duration of a strike is typically less than 2 microseconds, the
voltage generated is high enough to cause flashover strikes to conducting
objects located as much as 14 inches away from the conducting path. For this
reason, metallic objects in close proximity to down conductors should be
electrically bonded to the conductors.</p>
<p> But circuits not in direct contact with the lightning discharge path can
experience damage, even in the absence of overt coupling by flashover.
Because the high current associated with a discharge builds up so fast,
large inductively produced voltages are formed on nearby conductors.
Experimental and analytical evidence shows that the surges thus induced can
easily exceed the tolerance level of many components, particularly
solid-state devices. Inductive surges can be induced by lightning current
flowing in a down conductor or structural member, by a stroke to earth in
the vicinity of buried cables, or by cloud-to-cloud discharges occurring
parallel to long cable runs, either above ground or buried.</p>
</div>
<div id="sez12" class="sezione">
<b>The Moral</b>
<p>The objective of all lightning-protection systems is to direct the high
currents away from susceptible elements or limit the voltage gradients
developed by the high current to safe levels. In a given area, certain
structures or objects are more likely to be struck by lightning than others;
however, no object, whether man-made or natural, should be assumed to be
immune from lightning. The voltages that could be induced by such discharges
present a definite threat to signal and control equipment, particularly
equipment employing semiconductor components.</p>
</div>
<div class="addressList" id="addrCom">
<div id="sez13" class="section">
<p>
<ul>
<b>Power-Line Conditioner Sources</b>
<li>Cuesta Systems Inc.
3440 Roberto Court San Luis Obispo,
CA 93401
(805) 541-4160</li>
<li>Dymarc Industries Inc.
21 Governor's Court Baltimore,
MD 21207
(800) 638-9098
(301) 298-2629</li>
<li>Electronic Protection Devices Division CNS Electronics
Corp.
5-9 Centml Ave. Waltham,
MA 02154
(800) 343-1813</li>
<li>Electronic Specialists Inc.
171 South Main St. Natick,
MA 07160
(800) 225-4876 (orders) (617) 655-1532</li>
<li>Isoreg Corporation
410 Great Rd. Littleton,
MA 01460
(617) 486-9483</li>
<li>RKS Industries
4865 Scotts Valley Dr. Scotts
Valley,
CA 95066
(800) 892-1342
(408) 438-5760</li>
<li>Sun Research Inc.
POB 210 Old Bay Rd. New Durham,
NH 03855
(603) 859-7110</li>
</ul>
</p>
<p>
<ul>
<b>Power-Line Filter Sources</b>
<li>Cornell-Dubilier Electronics
Box B-967 New Bedford,
MA 02741
(617) 996-8561</li>
<li>Corcom Inc.
1600 Winchester Rd. Libertyville,
IL 60048
(312) 680-7400</li>
<li>Curtis Industries Inc.
8300 North Tower Ave. Milwaukee,
WI 53223
(414) 354-1500</li>
<li>Genisco Technology Corporation
18435 Susana Rd. Rancho Dominguez,
CA 90221
(213) 537-4750</li>
<li>Hopkins Engineering Company
12900 Foothill Blvd. San Fernando,
CA '91342
(213) 361-8691</li>
<li>The Potter Company Division of Varian
POB 337 Wesson,
MI 39191
(601) 643-2215</li>
<li>Siemens Corporation
8700 East Thomas Rd. Scottsdale,
AZ 85252
(602) 941-6366</li>
<li>Sprague Electric Company
87 Marshall St. North Adams,
MA 01247
(413) 664-4411</li>
<li>Stanford Applied Engineering
3520 De La Cruz Blvd. Santa Clara,
CA 95050-1997
(408) 988-0700</li>
</ul>
</p>
</div>
</div>
</div><p id="cpy"> Copyright © 1983
Steven A.
Ciarcia. All rights reserved.</p>
<p class="pb"><b>38</b> December 1983 © Byte Publications Inc.</p>
when an air conditioner comes on.)</p>
<p> Surges are generally the result of network switching by the utility
or of a sudden reduction in demand for power in the network; during
the period necessary for the utility's electromechanical
compensation system to function, an overvoltage transient condition
can exist. The most damaging power-line disturbance is the
high-speed, highenergy voltage spike. People speaking loosely about "power-line transients" are probably
talking about this type of event. Lasting usually less than 100
microseconds, spikes can be up to 6000 volts. Such high-energy
transients are produced by the switching off of inductive loads by
the opening of switch contacts, short circuits, or blown fuses;
severe network load changes; or lightning. Inductive-load switching
accounts for the majority of spikes. </p>
<p class="pb">December 1983 © Byte Publications Inc. <b>39</b></p>
<div class="figure" id="IM2">
<img class="solImg" src="./img/fig2.png"><p class="figDesc"><i> Photo 2: You can save approximately $40 on the price of a
transient-protected power strip by adding the protection yourself, as
demonstrated on the Radio Shack Archer 61-2620 unit. First, unscrew the end
plates. </i></p>
</div>
<div class="figure" id="IM3">
<img class="solImg" src="./img/fig3.png"><p class="figDesc"><i> Photo 3: Open the strip case, exposing the four receptacles and the
white circuit-breaker block. The three wires conducting power run the length
of the strip: black is the hot side, white is the neutral return, and the
green wire is earth ground. </i></p>
</div>
<div class="figure" id="IM4">
<img class="solImg" src="./img/fig4.png"><p class="figDesc"><i> Photo 4: Using an X-acto knife or similar tool, strip insulation from
the wires between the receptacles (which I number 1 through 4, from left to
right) according to the following system: between 1 and 2, strip the green
and black; between 2 and 3, strip the green and white; between 3 and 4,
strip the black and white. </i></p>
</div>
<p> When the coil of an inductive load such as a transformer or motor is
suddenly deenergized, the collapsing magnetic field must dissipate
its energy, and it does this by placing a large voltage back into
the circuit that energized it. Let's examine the process in detail.
As the circuit through the inductor is broken, current in the
inductor continues to flow, charging the distributed capacitance in
the windings. At some point, the charge voltage becomes sufficient
to leap across the switch gap as a spark. This sudden shorting
action discharges the winding's capacitive charge back into the
circuit until the spark ceases. This process repeats in a cycle
until there is too little energy left in the coil to create an arc
across the contacts. The waveform of inductance-generated transients
is oscillatory. For example, a contact opening while conducting 100
mA <i>(milliamperes)</i> in a 1-H
<i>(henry)</i> inductance
will produce a 3000-V spike, assuming about a 0.001-µtF <i>(microfarad)</i> stray winding
capacitance. Whenever you plug in a vacuum cleaner, hair drier, or
other appliance (even your computer), you could be creating some
potentially serious transient disruptions for other equipment on the
same power line. The equipment need not even be on the same wiring
circuit. The capacitance of household wiring is often sufficient to
couple a transient from one wire to another <span class="glossOver" onclick="showGloss('#diffMode')">(differential mode)</span> or from the wire to the ground <span class="glossOver" onclick="showGloss('#commMode')">(common mode)</span>. Lightning is the most
violent and most destructive source of transient energy. A direct
lightning hit is catastrophic, but direct hits seldom occur. A more
frequent danger is that a lightning strike on a power line miles
away may result in a thousandvolt spike rushing throughout your
home. Such hits happen frequently enough to cause much grief.</p>
<p> (Because lightning is such a significant source of transients, I've
explained it in detail in the text box <a href="#appe">"How
Lightning Strikes."</a> A secondary, and more widespread,
effect of a lightning hit on a power line is a voltage sag over a
large part of the
<p class="pb"><b>40</b> December 1983 © Byte Publications Inc.</p>
<div class="figure" id="IM5">
<img class="solImg" src="./img/fig5.png"><p class="figDesc"><i> Photo 5: You can now solder a varistor between each of the stripped
wire pairs, mounting it fiat against the back face of the receptacle so that
the case will fit together again. </i></p>
</div>
<div class="figure" id="IM6">
<img class="solImg" src="./img/fig6.png"><p class="figDesc"><i> Photo 6: The outlet strip with three MOVs installed provides both
common-mode and differential-mode transient suppression. After you have
finished soldering, carefully reassemble the power strip's enclosure and
screw it back together. </i></p>
</div>
network as the power company's safety circuits
compensate for the spike.) </p>
</li>
<li style="font-weight: bold;">Electrical noise.</li>
<li>
<p> Miscellaneous electrical noise is the final source of power-line
disturbances. It is best understood as high-voltage highfrequency
interference. Noise in the range from 10 kHz <i>(kilohertz)</i> to 50 MHz <i>(megahertz)</i> is the most common cause of
computer failures. Because of its frequency, noise can be either
broadcast through free space from its source or conducted directly
through the power lines. Digital electronic equipment is a prime
source of high-frequency noise. </p>
</li>
</ul>
</div>
<div id="sez3" class="sezione">
<b>Power-Line Protection.</b>
<p> I'm not trying to make you afraid to plug your computer into the wall
outlet. There are remedies for virtually all the problems I've mentioned,
although some are more practical for some computer users than others. If
surges or sags are a constant problem for you, you can try having the power
company change the tap on your local step-down transformer or installing a
constant-voltage transformer on your premises. These measures, although
expensive, are effective. If you are plagued by blackouts or have equipment
that should never be shut down, I suggest that you consider obtaining an
<span class="glossOver" onclick="showGloss('#UPS')">uninterruptible power supply</span>, abbreviated <abbr title="Uninterruptible Power Supply">UPS</abbr><span class="expan">Uninterruptible Power Supply</span>.
Using a <abbr title="Uninterruptible Power Supply">UPS</abbr><span class="expan">Uninterruptible Power Supply</span> gives you confidence in the quality of your power and
effectively isolates your computer from damaging perturbations. However, a
<abbr title="Uninterruptible Power Supply">UPS</abbr><span class="expan">Uninterruptible Power Supply</span> is also quite costly. In the case of electrical noise and <abbr title="ElectroMagnetic Interference">EMI</abbr><span class="expan">ElectroMagnetic Interference</span>, there are
filters and construction techniques that can be employed to reduce
interference, but a better answer is to find the pollution at the source and
eliminate it. My article in the January 1981
BYTE outlined most methods of filtration and preventive design.
While I'll try not to belabor the point, a power-line filter is an important
noise- and transient-suppression device. The best answer to transients is to
suppress their voltages to a harmless level, either with filters or a
special category of components called <i> transient suppressors.</i>
</p>
</div>
<div id="sez4" class="sezione">
<b>Power-Line Filters</b>
<p> A power-line interference filter is an electronic circuit used to control
<abbr title="Radio Frequency Interference">RFI</abbr><span class="expan">Radio Frequency Interference</span> and <abbr title="ElectroMagnetic Interference">EMI</abbr><span class="expan">ElectroMagnetic Interference</span> conducted into and out of equipment. The filter is intended to
provide unwanted interference signals with a high series impedance (into the
vulnerable equipment) and low shunt impedance (to ground). It generally
consists of a set of passive components that act as a mismatching network
for high-frequency signals-a low-pass filter. The network attenuates <abbr title="Radio Frequency">RF</abbr><span class="expan">Radio Frequency</span>
energy above 10 kHz, while passing the 60-Hz power.</p>
<p> The simplest possible filter is a single capacitor wired in parallel or a single coil wired in series with the power line. More
typically, several <span class="glossOver" onclick="showGloss('#cond')">capacitors</span> and/or coils are
used together, connected into different configurations variously called L,
ℼ, and T filters. Though containing only a few components, such <span class="glossOver" onclick="showGloss('#pasBilNet')">passive
bilateral networks</span> have complex transfer characteristics that are extremely
dependent upon the impedances of the source and load. Because you can't
predict these impedances for all applications, it is not possible to
unequivocally state that a specific filter configuration will work the same
way in two different environments. But to allow
<p class="pb">December 1983 © Byte Publications Inc. <b>41</b></p>
<div class="figure" id="IM7">
<img class="solImg" src="./img/fig7.png"><p class="figDesc"><i> Photo 7: For quicker and easier, though incomplete, protection, you
can plug your computer into a simple voltage-spike protector such as the
Radio Shack 61-2790. As you can see from the disassembled unit, the
metal-oxide varistor (wrapped in fiberglass tape) is connected between only
the hot and neutral lines (black and white). It has no varistor connection
to the ground lead and therefore does not protect against common-mode
transients. </i></p>
</div>
<div class="figure" id="IM8">
<img class="solImg" src="./img/fig8.png"><p class="figDesc"><i>Photo 8: Some line filters are made to work in specific circumstances.
This Radio Shack powerline- filter strip (stock number 26-1451) was devised
to cure interference problems with the TRS-80 Model I computer; it contains
two separate LC (inductancelcapacitance) interference filters but no
varistors. If you have this strip, I suggest you install some MOVs.
</i></p>
</div>
electrical specifications to be minimally compared,
however, resistive source and load impedances of 50 ohms each are generally
used. Two similar power-line filters, even built with the same circuit
topology and component values, may not perform identically; the mounting and
wiring of the filter can be critical influences on its performance. A
power-line filter is best installed at the point in your equipment where the
power line comes inside the case rather than at the far end of a long cord.
The filter's purpose is to attenuate high-frequency signals: this purpose is
defeated if these parasitic signals can gain access to the equipment by
capacitively coupling to the power cord at a point behind the filter. It's
not always possible to disassemble your computer to add a line filter, but
the best location for a power-line filter is bolted to the chassis of the
electronic equipment it protects, or at least in the immediate vicinity,
such as at the power receptacle. While you could construct a line filter
using the formulas and designs from a magazine article, I heartily recommend
that you buy a packaged unit instead.</p>
<p> The selection is easier and much more controlled using commercial line
filters <a href="#addrCom">(see the text box on page 39)</a>. So much
depends upon component selection and layout that the only way to make sure
power-line interference has been eliminated is to actually test the filter
in your equipment. A circuit designed according to theory
using a 50-ohm assumed impedance probably won't work as well as one
empirically derived using the actual equipment and power line.</p>
</div>
<div id="sez5" class="sezione">
<b>Transient Suppressors</b>
<p> Protection from. the various kinds of line transients is obtained by
suppressing or diverting them. The three types of circuits most often used
for this are filters, <span class="glossOver" onclick="showGloss('#crowB')">crowbars</span>, and <span class="glossOver" onclick="showGloss('#VolClamp')">voltage-clampers</span>. As I previously alluded,
filters comprising inductances and capacitances are widely used for
interference protection, including transients. Since most transient signals
are high frequency, the suppression by a filter is often effective, provided
it can withstand the associated high voltages.</p>
<p> Crowbar circuits use a switching action, such as turning on a thyristor or
arcing across a spark gap, to divert transients. But <span class="glossOver" onclick="showGloss('#crowB')">crowbars</span> that
incorporate <abbr title="(silicon-controlled rectifiers)">SCRs</abbr>
<span class="expan">(silicon-controlled rectifiers)</span> and triacs are much too slow
to effectively suppress 100-µs (microsecond) transients. Most often they
are incorporated in low-voltage
<abbr title="Direct Current">DC</abbr>
<span class="expan">Direct Current</span>
power-supply output circuits where overvoltage conditions occur at
more manageable speeds (milliseconds). Spark-gap devices, which include
carbon blocks and gas tubes, are fast
<p class="pb"><b>42</b> December 1983 © Byte Publications Inc.</p>
<div class="figure" id="IM1A">
<img class="solImg" src="./img/fig1a.png"><p class="figDesc"><i> Figure la: The Radio Shack four-outlet power strip can be easily
modified to protect equipment from high-energy power-line transients. Three
General Electric V130LA10A metal-oxide varistors (MOVs-Radio Shack number
276-570) are connected between the hot, neutral, and ground wires of the
power line. </i></p>
</div>
<div class="figure" id="IM1B">
<img class="solImg" src="./img/fig1b.png"><p class="figDesc"><i> Figure 1b: For added protection against low-energy electromagnetic and
radio-frequency interference, the Corcom 5VK1 line filter (Radio Shack
273-100) can be installed in the circuit. </i></p>
</div>
and effective, but they trigger at relatively high voltages,
making them unsuitable as the sole protection for semiconductor
circuitry.</p>
<p> Voltage-clamping devices, on the other hand, have impedances that vary as a
function of either the voltage across or the current through them. The
circuit being protected is unaffected by the presence of the clamping device
unless the incoming supply voltage exceeds the clamping level, as would be
the case when a transient hits. The various kinds of high-speed
voltage-clamping devices include selenium cells, zener diodes,
silicon-carbide varistors, and metaloxide varistors. Of these, the
metaloxide varistors, or <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span>, hold a Significant price/performance
advantage and are highly applicable in personal computing applications.</p>
</div>
<div id="sez6" class="sezione">
<b>MOVsMetal Oxide Varisistors to the Rescue</b>
<p>Metal-Oxide Varistors are voltagedependent nonlinear devices that behave
somewhat like a back-biased zener diode. When a voltage lower than its
conduction threshold is applied across it, the <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> appears as a
nonconducting open circuit. But if the applied voltage becomes greater than
this set point (when a transient hits), the <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> begins to conduct, clamping
the input voltage to a safe level. In effect, the <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> absorbs the transient
and dissipates the energy as heat.</p>
<p> An <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> is made of zinc oxide combined with small amounts of bismuth, cobalt,
and manganese. The individual zinc-oxide grains form many p/n
(positive-doped/negativedoped) junctions that combine in a multitude of
series and parallel arrangements. This diversity of microstructure causes
its nonlinear semiconducting characteristics. An <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> is inherently more
rugged than a single-junction semiconductor device (a zener diode, for
example) because energy is uniformly absorbed throughout the bulk of the
component.</p>
<p> The physical dimensions of the <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> determine its characteristics, its
conduction-threshold voltage varying as a function of thickness, and its
energy-dissipating capacity varying according to
volume.</p>
<p> <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span> are available in operating voltages from 6 to 2800 V, with peak current
capacities of up to 50,000 A (amperes). <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span> respond to transients in only
a few nanoseconds and are relatively inexpensive. The chief producer of <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span>
is the General Electric Company.</p>
</div>
<div id="sez7" class="sezione">
<b>Protect Your Computer</b>
<p>Large companies sometimes solve power-line problems by producing their own
power. In the home or small office, it's more practical to protect your
computer and peripherals through comprehensive application of filtering and
transient suppression. Most of the commercially available filtered power
strips contain <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span> as their primary suppression device. Even those costing
$50 or $75 rarely contain more than $5 worth of transient protection. By
purchasing the suppression components separately and installing them
yourself, you can save a lot of money.The majority of the
projects I've presented in Circuit Cellar articles can be built
for $50 to $2000, but the project this month wins hands down for economy.
For the most part, line filters and <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span> are available off the shelf, and
adequate transient suppression for your computer might cost as little as
$1.59!</p>
<p> You can take two approaches in installing suppression. If you are interested
in protecting only a few items of equipment, <abbr title="Metal Oxide Varisistors">MOVs</abbr><span class="expan">Metal Oxide Varisistors</span> can be wired across the AC
line where it enters the enclosures. You can find the General Electric
V130LA10A <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span> component at Radio Shack for $1.59 (stock number 276-570).
This device is ideally suited to 120-VAC applications. It has an energy
rating of 38 joules (watt-seconds) and will clamp to 340 V at 50 A within 35
ns (nanoseconds). Its peak-current rating is 4500 A. (For heavier duties,
you'll need to use V130LA20A or V130PA20A <abbr title="Metal Oxide Varisistor">MOV</abbr><span class="expan">Metal Oxide Varisistor</span>.) (As a rule, if you are
going to be
<p class="pb">December 1983 © Byte Publications Inc. <b>43</b></p>
<p class="topLeft">Circle 239 on inquiry card.</p><div class="advertising">
<h3>COMPUTERS</h3>
<div id="sez14" class="section">
<p><br><b>Packages: Create your own</b>
<br><b>configuration. CALL</b></p>
<ul>
<br><li style="font-weight: bold;">IBM PC:</li>
<li>
(in Slack) 256k. (2) 320k disk
drives. Monochrome Display <br>& Controller with printer port. C.
Itoh F10-40ps letter quality printer, <br>Diagnostic & Basic manuals
. . . . . . . . . . . . . . . . . . . <b>$4999</b>
</li>
<br><li style="font-weight: bold;">COLUMBIA MPC 1600-1: </li>
<li>
128k. (2) 320k disk drives. Amber or <br>Green video display and controller. (2) serial
& (1) parallel port. C. <br>Itoh F10-40cps letter qual. prnter.,
<b>$3000</b> of free software <b>$3999</b>
</li>
<br><li style="font-weight: bold;">COLUMBIA HARD DISK MPC 1600-4: </li>
<li>
XT Compatible 128k, <br>(1) 320k disk drive. 10meg Hard disk drive. Amber
or Green video <br>display and conlroller. (2) serial & (1) parallel
port. C. Itoh F10-<br>40cps letter quality printer, and <b>$3000</b> of free
software .... <b>$5699</b>
</li>
<br><li style="font-weight: bold;">COLUMBIA PORTABLE COMPUTER VP:</li>
<li>
128k. (2) 320k
<br>half height disk drives. Monochrome display and controller. (1)
<br>serial & (1) parallel port. C. ltoh F10-40cps letter qualily printer, and
<br><b>$3000</b> of free soltware .................................<b>$3795</b>
</li>
<br><li style="font-weight: bold;">EAGLE PC- 2:</li>
<li>
128k. (2) 320k disk drives.
monochrome display & <br>conlroller. (2) serial & (1) parallel
port. DKIDATA 92a near letter <br>quality printer, with free software .
...................... <b>$3399</b>
</li>
<br><li style="font-weight: bold;">APPLE IIe:</li>
<li>
128k, 80 columns display, Amber
or Green screen, half <br>height disk drive & controller, Fan and
electrical surge protector, <br>Gemini Star 10X dot matrix printer
.................... <b>$2199</b>
</li>
<br><li style="font-weight: bold;">CANON AS100 </li>
<li>
128k, (2) 640k disk drives
& controller. color dis-<br>play. (1) parallel port. with color
printer ............ <b>$3599</b>
</li>
<br><li style="font-weight: bold;">DEC RAINBOW 100:</li>
<li>
64k, (1) dual disk drive.
Monochrome dis-<br>play, keyboard. MSDOS or CP/M 86 operating system. DEC
LA50-<br>RA dol matrix printer ......... <b>$3799</b>
</li>
</ul>
</div>
<div id="sez15" class="section">
<h3>IBM PC & COMPATIBLE ACCESSORIES</h3>
<p>
<br>64k memory chips...... <b>$92</b>
<br>additional disk drives <b>$450</b>
<br>DOS 1.1 .............. <b>$40</b>
<br>DOS 2.0 .............. <b>$60</b>
<br>Easywriter ........... <b>$165</b>
<br>Visicalc ............. CALL
<br>dBASE II ............. <b>$430</b>
<br>PFS report ...... <b>$133</b>
<br>PFS filter ...... <b>$110</b>
<br>TK! Solver ...... <b>$250</b>
<br>WordStar ........ <b>$327</b>
<br>MailMerge ....... <b>$165</b>
<br>Memorex disks ... <b>$3.25</b>
<br>3M disk ......... <b>$2.99</b>
</p>
</div>
<div id="sez16" class="section">
<h3>APPLE IIe & COMPATIBLE ACCESSORIES</h3>
<p>
<br><b>JAGUAR half height</b>
<br>drives ................. <b>$249</b>
<br><b>MICRO·SCI full height</b>
<br>drives ................. <b>$220</b>
<br>80 column cards ........ <b>$275</b>
<br>80 column with 64k cards <b>$375</b>
<br>Grappler ............... <b>$140</b>
<br>System Saver Fan ....... <b>$55</b>
<br>WordStar ............... <b>$327</b>
<br>dBASE .................. <b>$430</b>
<br>Memorex disks .......... <b>$3.25</b>
<br>3M disks .................. <b>$2.99</b>
</p>
</div>
<div id="sez17" class="section">
<h3>PRINTERS</h3>
<ul>
<h3>DOT MATRIX</h3>
<li>
<br> C. Itoh ProWriter .... <b>$440</b>
</li>
<li>
<br><b>OKIDATA</b>
<br> MICROLINE 82a ....... <b>$440</b>
<br> MICROLINE 92 ........ <b>$499</b>
<br> MICROLINE 93 ........ <b>$789</b>
<br> RIBBONS ............. <b>$4.99</b>
</li>
</ul>
<ul>
<b> LETTER QUALITY </b>
<li>
<br><b>C. IT0H</b>
<br> F10-40cps ......... <b>$1199</b>
<br> F10-55cps ......... <b>$1499</b>
<br> Single sheet feeder <b>$695</b>
<br> Tractor feed ...... <b>$275</b>
<br> Ribbons-multistrike <b>$6.99</b>
<br> Ribbons-nylon ..... <b>$7.99</b>
<br><b> NEC 3550</b> ... <b>$1899</b>
</li>
<li>
<br><b>GEMINI</b>
<br> STAR 10X ... <b>$335</b>
<br> STAR 15 ........... <b>$490</b>
<br> RIBBONS ........... <b>$4.99</b>
</li>
<li>
<br><b>TRANSTAR</b>
<br>T315 COLOR PRINTER . <b>$499</b>
<br> Ribbon ............ <b>$14.95</b>
</li>
<li>
<br><b>DIABLO</b>
<br> 620 ............... <b>$999</b>
<br> 630 ............... <b>$1999</b>
<br> Single sheet feeder <b>$1350</b>
<br> Tractor leed ...... <b>$215</b>
<br> Ribbons-multistrike <b>$6.99</b>
<br> Ribbons-nylon ..... <b>$7.99</b>
</li>
<li>
<br><b>TTX-1014</b> ...... <b>$499</b>
</li>
<li>
<br><b>SMITH CORONA TP-1</b> .. <b>$499</b>
</li>
</ul>
</div>
<div id="sez18" class="section">
<h3>MONITORS</h3>
<ul>
<h3>ZENITH</h3>
<li> 121 .. <b>$93</b>
</li>
<li> 122 .. <b>$129</b>
</li>
<li> 123 .. <b>$139</b>
</li>
</ul>
<ul>
<h3>TAXAN</h3>
<li> RGB I .. <b>$325</b>
</li>
<li> RGB II .. <b>$520</b>
</li>
<li> GREEN .. <b>$159</b>
</li>
<li> AMBER .. <b>$169</b>
</li>
</ul>
<ul>
<h3>AMDEK</h3>
<li> COLOR I .. <b>$299</b>
</li>
<li> COLOR II .. <b>$429</b>
</li>
</ul>
<br><p><b>GORILLA</b> HI-RES GREEN .. <b>$99</b></p>
<br><p><b>PRINCETON</b> GraphicSys .. <b>$665</b></p>
</div>
<div id="sez19" class="section">
<h3>SOFTWARE</h3>
<ul>
<b>APPLE SOFTWARE</b>
<li>
<br> Temple of Apshai ... <b>29.99</b>
<br> DOS Boss ........... <b>19.99</b>
<br> Type faces ......... <b>14.99</b>
<br> Apple Panic ........ <b>21.95</b>
<br> Chopliner .. . ..... <b>24.95</b>
<br> Raster Blaster ..... <b>21.95</b>
<br> Ultima ............. <b>29.95</b>
<br> MicroWave .......... <b>24.97</b>
<br> Swashbuckler ....... <b>23.95</b>
<br> Zaxxon ............. <b>26.95</b>
</li>
</ul>
<ul>
<b>IBM PC SOFTWARE</b>
<li>
<br><b>ALPHA SOFTWARE</b>
<br> Database ........... <b>99.97</b>
<br> Apple-IBM CnnCtn ... <b>136.75</b>
<br> Data Base Manager .. <b>191.75</b>
</li>
<li>
<br><b>ASHTON-TATE</b>
<br>Financial Planner <b>430.00</b>
<br> Bottom Line Strtgst ...... <b>250.00</b>
</li>
<li>
<br> <b>EPYX</b>
<br> Temple of Apshai .... <b>26.95</b>
<br> Crush, Crumble & Chomp <b>22.99</b>
</li>
<li>
<br> <b>INFOCOM</b> Zork I/II/III .... <b>79.00</b>
<br> Sargon II ................ <b>24.97</b>
</li>
<li>
<br> <b>MICROPRO</b> products WordStar/MailMerge/SpeliStar CalcStar/DataStar/InfoStar
<br> LOWEST PRICES ....... CALL
</li>
<li>
<br> <b>MILTON BRADLEY</b> educational
<br>software. All about Division,
<br> Fractions. Commas. Words.
<br> We have Them all ......... CALL
<br> Pie Writer IIe ........... <b>99.97</b>
</li>