Heart Attacks and Defibrillators

Posted by PITHOCRATES - May 29th, 2013

Technology 101

Moving Electrons from one Atom to another creates a Positively and a Negatively Charged Atom

Too much humidity can make one uncomfortable.  It can labor your breathing.  Make you sweat so much that you stick to everything.  Making it feel hotter than it is (it’s not the heat; it’s the humidity).  And play havoc with well-coiffed ladies.  As excessive humidity can straighten the finest curl.  That’s why we like the spring and fall.  When there are warm days without the humidity.  Winters, on the other hand, are just too cold.  And uncomfortable humidity-wise.  They’re not too humid.  But too dry.  Giving us dried and cracked skin.  Bloody noses.  And painful electrical shocks.  As anyone can attest to who has slid out of a car only to get a big static spark when they pushed the door close.

What causes that static electric spark?  When you slide your buttocks over the car seat to get out of the car you are charging a capacitor.  By stripping electrons away from atoms.  Leaving atoms with fewer electrons than protons.  Giving them a positive charge.  And atoms with more electrons than protons.  Giving them a negative charge.  Atoms prefer to be electrical neutral.  Which is why when we reach for that metal door those excess electrons jump the air-gap as soon as they can.  So both atoms can return to a neutral state.  Until the next time we drag our buttocks across the seat.

These electric discharges can be painful.  And annoying as they scare the bejesus out of you when you’re not expecting it.  But this is not all that capacitors do.  As it turns out this charging ability has a lot of uses.  They are in pretty much every piece of electrical and electronic equipment we use.  We use them to condition power.  For power factor correction.  Signal processing.  Noise filters.  Tuned circuits (as used in a radio dial to tune in a station).  And energy storage.  Which is what we do when we drag ourselves across a car seat.  We’re storing energy that we discharge later.  In a car it just annoys us.  But it can act like a temporary battery when we change the batteries in something with a volatile memory.  So we don’t lose the songs on our MP3 player when we change the batteries.  And the energy they store can even save lives.

A Defibrillator sends an Electric Charge through an Irregularly Beating Heart to Shock it back into Rhythm

In the movie The Matrix the machines took over the world.  And used humans as batteries to power their machines.  Because a human is a little like an electrical battery.  It creates electricity that operates the human body.  For the human body is controlled by electrical impulses sent along our nervous system.  These electrical impulses even make our hearts pump.  The heart itself is ‘wired’ to transmit this pulse in a delayed mode to the various tissue in the heart.  First a pulse contracts the two top chambers (atria).  This contraction empties the blood they hold into the two bottom chambers (ventricles).  Then after a delay that same pulse contracts the ventricles.  Pushing the blood out and through the body.  When a doctor looks at an EKG he or she can see how that pulse propagates through the heart.  And determine if it’s healthy (showing a normal sinus rhythm).  Or if there was some cardiac event that has altered the normal sinus rhythm.

If a heart doesn’t have a normal sinus rhythm it can lead to cardiac arrest (i.e., a heart attack).  An arrhythmia (irregular heartbeat) can be a fast heartbeat.  A slow heartbeat.  Or it may be an irregular heartbeat.  Which is due to abnormal electrical activity in the heart.  And can lead to ventricular fibrillation.  Where the muscles don’t contract in a coordinated fashion with the proper delays propagating through the heart tissues to pump the blood.  But instead contract without this coordination.  Causing the heart muscles to quiver instead.  If this continues more than a few seconds the heart may stop.  With an EKG showing a flat line.  With no blood flowing organs begin shutting down.  Causing irreversible damage.  And if a normal sinus rhythm isn’t restored within 90 seconds once a person goes into v-fib the chance of survival from this cardiac event are pretty much zero.

In the movies and on television when a patient goes into v-fib they sometimes show the patient flat-lining when they rush in the crash cart.  They rub gel on the paddles of a defibrillator.  Yell ‘clear’ and shock the patient.  Sometimes with the patient jerking wildly from the jolt from the paddles.  They may do this a couple of times until they hear the flat-line begin beeping again in a sinus rhythm.  It doesn’t really happen like that, though.  If a person is flat-lining a jolt from a defibrillator won’t bring them back.  Some medicine shot into the heart and chest compressions might.  But not an electric shock.  The use of a defibrillator sends an electric charge through a heart beating with an irregular rhythm to shock it back into a normal rhythm.  Sort of like banging on an electronic device to get it working properly again.  With the physical shock perhaps jiggling a loose component back into connection with something.  It can sometimes make the device work again.  But it won’t make it work if the cord is unplugged or if the batteries had been removed.

Portable Defibrillators have a Charged Battery that Charges a Capacitor

Early defibrillators were AC devices that plugged into a wall outlet.  They had a big transformer to step up the voltage.  But they were big and bulky and difficult to move around in a crowded room.  And they didn’t work that well.  Rarely pulling a patient out of v-fib.  And sometimes damaged the heart tissue as much as the heart attack.  In 1959 the AC defibrillator was replaced with one using charged capacitors.  This is the type we see in the movies and on television.  And use in real life.

If a patient goes into cardiac arrest they set the charge level for the given arrhythmia.  As the capacitors charge the person who will use it removes the paddles while someone else applies an electrically conducting gel to the paddles.  The person then places the paddles on the patient with force to ensure a good electrical connection.  And waits for the unit to finish charging.  Once charged anyone working on the patient breaks any contact they have with the patient so they won’t get shocked, too.  When everyone one and everything is clear the person will focus on the EKG for the appropriate point in the rhythm to press a button that discharges the capacitors.  Causing the stored energy to flow from one paddle to the other through the heart.  To reset the arrhythmia into a normal sinus rhythm.

Time is critical in surviving a heart attack.  So using a defibrillator as soon as possible increased a person’s chances of surviving from a heart attack.  Making defibrillators portable allowed paramedics to use them in the field.  Before they got the patient to a hospital.  These portable units have a charged battery that charges a capacitor.  Electronics and computer controls even allow ordinary people to use an automated external defibrillator (AED).  You will see AEDs in crowded areas like airports, shopping malls, casinos, etc.  Anywhere a large concentration of elderly men (the most likely to suffer cardiac arrest) may congregate.  This device often triggers a security alarm when removed to alert first responders.  Someone who witnesses a person suffering a heart attack can follow automated voice instructions from the AED and hook it up on the patient.  The AED will analyze the arrhythmia.  Set the appropriate charge level.  But usually requires someone to press a button for the shock.  To give everyone a chance to get clear from the person before the capacitor discharges its energy.  Because if they are in contact with that body when that charge hits it they may have more than a bad hair day afterwards.  Perhaps even sending their own heart into arrhythmia.  As this shock will be nothing like the one they get after sliding out of a car on a dry winter’s day.



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DC Power Supply

Posted by PITHOCRATES - February 13th, 2013

Technology 101

Every DC Power Supply has a Transformer, a Rectifier Circuit and a Voltage Regulation Circuit

Alternating current (AC) power is one of the greatest technological developments of mankind.  It gives us the modern world we live in.  We can transmit it over very long distances.  Allowing a few power plants to power large geographic areas.  Something Thomas Edison’s direct current (DC) power just couldn’t do.  Which is a big reason why he lost the War of Currents to George Westinghouse and Nikola Tesla.  AC power also allows the use of transformers.  Allowing us to take the one voltage produced by a power plant and convert it to any voltage we need.

AC power can power our home lighting.  Our air conditioning.  Our electric stove.  Our refrigerator.  Our doorbell.  Pretty much all of the non-fun things in our house.  Things with electric motors in them.  Heating elements.  Or solenoids.  But one thing AC power can’t do is power the fun things in our homes.  Televisions.  Our audio equipment.  Our cable/satellite boxes.  Pretty much anything that doesn’t have an electric motor, heating element or solenoid in it.  These things that process information or audio and video signals.  Or all of the above.  Things that have circuit boards.  With electronic components.  The kind of things that only work with DC power.

Of course all of these things in our homes plug into AC wall receptacles.  Even though they are DC devices.  So what gives?  How can we use AC power to operate DC devices?  With a little something we call a DC power supply.  And every one of those fun things has one.  Either one built-in.  Or an external power pack at the end of a cord.  Every DC power supply has three parts.  There is a transformer to step down the AC voltage.  A rectifier circuit.  And a voltage regulation circuit.

A Diode is a Semiconductor Device that allows a Current to pass through when there is a Forward Bias

The typical electrical receptacle in a house is 120 volt AC.  An AC power cord brings that into our electronic devices.  And the first thing it connects to is a transformer.  Such as a 120:24 volt transformer.  Which steps the 120 volts down to 24 volts AC.  Where the waveform looks like this.

DC Power Supply AC Input

The voltage of AC power rises and falls.  It starts at zero.  Rises to a maximum positive voltage.  Then falls through zero to a maximum negative voltage.  Then rises back to zero.  This represents one cycle.  It does this 60 times a second.  (In North America, at least.  In Europe it’s 50 times a second.)  As most electronic devices are made from semiconductors this is a problem.  For semiconductor devices use low DC voltages to cause current to flow through PN junctions.  A voltage that swings between positive and negative values would only make those semiconductor devices work half of the time.  Sort of like a fluorescent light flickering in the cold.  Only these circuits wouldn’t work that well.  No, to use these semiconductors we need to first get rid of those negative voltages.  By rectifying them to positive voltages.  When we do we get a waveform that looks like this.

DC Power Supply Rectified

A diode is a semiconductor device that allows a current to pass through when there is a forward bias.  And it blocks current from passing through when there is a reverse bias.  An alternating voltage across a diode alternates the bias back and forth between forward bias and reverse bias. Using one diode would produce a waveform like in the first graph above only without the negative parts.  If we use 4 diodes to make a bridge rectifier we can take those negative voltages and make them positive voltages.  Basically flipping the negative portion of the AC waveform to the positive side of the graph.  So it looks like the above waveform.

All Electronic Devices have a Section built Inside of them called a Power Supply

The rectified waveform is all positive.  There are no negative voltages.  But the voltage is more of a series of pulses than a constant voltage.  Varying between 0 and 24 volts.  But our electronic devices need a constant voltage.  So the next step is to smooth this waveform out a little.  And we can do this by adding a capacitor to the output of the bridge rectifier.  Which sort of acts like a reservoir.  It stores charge at higher voltages.   And releases charge at lower voltages.  As it does it smooths out the waveform of our rectified voltage.  Making it less of a series of pulses and more of a fluctuating voltage above and below our desired output voltage.  And looks sort of like this.

DC Power Supply Capacitor

This graph is exaggerated a little to show clearly the sinusoidal waveform.  In reality it may not fluctuate quite so much.  And the lowest voltage would not fall below the rated DC output of the DC power supply.  Please note that now we have a voltage that is always positive.  And never zero.  As well as fluctuating in a sinusoidal waveform at twice the frequency of the original voltage.  The last step in this process is voltage regulation.  Another semiconductor device.  Typically some transistors forming a linear amplifier.  Or an integrated circuit with three terminals.  An input, an output and a ground.  We apply the above waveform between the input and ground.  And these semiconductor devices will change voltage and current through the device to get the following output voltage (for a 12 volt DC power supply).

DC Power Supply DC Output

All electronic devices that plug into a wall outlet with a standard AC power cord have a section built inside of them called a power supply.  (Or there is an external power supply.  Small ones that plug into wall outlets.  Or bigger ones that are located in series with the power cord.)  And this is what happens inside the power supply.  It takes the 120 volt AC and converts it to 12 volts DC (or whatever DC voltage the device needs).  Wires from this power supply go to other circuit boards inside these electronic devices.  Giving the electronic components on these circuit boards the 12 volt DC power they need to operate.  Allowing us to watch television, listen to music or surf the web.



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Northeasters, Convection Heating, Thunderstorms, Electricity, Electric Charge, Capacitors, Lightning and Lightning Rods

Posted by PITHOCRATES - February 8th, 2012

Technology 101

A Couple of Centuries ago when a Winter Storm Approached we Stocked Up on Wood for our Cast-Iron Heating Stoves

A study of prevailing weather conditions can predict tomorrow’s weather.  Once you’ve learned some basic weather phenomenon.  Weather generally moves from west to east.  Where cold fronts meet warm fronts we can get storms, tornados, rain, sleet, snow, etc.  And if a swirling northeaster buries a town under snow people in a town northeast of this town can expect the same.  Even though the winds are blowing in the opposite direction.

Today in the worst of winter’s weather we can stay warm and snug at work.  And at home.  Amazing when you consider some of our work places have a lot of exterior glass walls.  Glass curtain walls.  Which really transmit the cold.  Of course, even these rooms can be toasty rooms.  Ever wonder how?  Take a look at the floor under the window.  What do you see?  Fin-tube radiation heating registers.  Copper pipes with metal fins soldered to them.  We pump heating hot water through the copper pipe.  And when we do these fin-tube radiators heat the air as it moves through those fins.  As air heats it expands and gets thinner.  Becoming lighter than the cold air.  And rises.  As it moves up it pulls the cold air below through those heated fins.  Heating the cold air.  Where it, too, expands and gets thinner.  And rises.  Creating a heating convection current.  Heating the room.  And the window.  By washing it with warm air.  All without using a fan to move the air.  Heating units that do have fans and move the air are more for circulating the air to prevent the build of carbon dioxide (produced as we breathe).  While fin-tube heating does the lion’s share of heating our buildings.

So when they predict a winter storm we really don’t worry much about staying warm inside.  Of course, it wasn’t always like this.  A couple of centuries ago when we saw a winter storm was moving our way we made sure we had enough wood available.  To burn in our cast-iron heating stoves.  Where we burned our heating fuel in the room we heated.  And vented the products of combustion out through the chimney.  A big difference to using heating hot water and fin-tube radiators.  But the same principle nonetheless.  These wood-burners heated the cold air and created a heating convection current.  Just like those fin-tube radiators.

During Thunderstorms Clouds act like Charging and Discharging Capacitors

In the summertime when a cold front runs into a warm front it often generates some big thunderstorms.  And some dangerous lightning.  Which has started many building fires throughout history.  Especially churches with tall spires.  Which seemed to be magnets for lightning.  Which they were.  In a way.  Because thunder storms are electrical storms.  Which is why we have lightning.  But first a little about electricity.

Electricity flows between a positive and a negative charge.  The greater the difference in charges the greater the flow of electricity.  A battery can store a charge.  A battery has both a positive (plus) and a negative (minus) terminal.  You charge a battery by applying a voltage across these terminals.  The higher the voltage and/or the longer the charge the more energy is stored in the battery.  When we connect a light to a battery it completes the circuit between the plus and minus terminals.  And electricity flows through the light and illuminates it.  The light will stay lit until the battery runs out of charge.  Or until we open the circuit.  Depending on the voltage or amount of stored charge you may see sparks at the point where the circuit opens or closes.  The charge being strong enough to jump a small air gap just before the circuit is closed.  Or just after it opens.

A capacitor can also hold a charge.  What we used to call a condenser.  Which is a couple of plates separated by an insulator.  When we apply a voltage across the plus and minus terminals the plates charge.  The insulator keeps them from discharging internally.  The bigger the capacitor (i.e., the bigger the surface area of the plates) the bigger the stored charge.  After you charge a capacitor it will hold that charge.  It will dissipate slowly over time.  Or quickly if you short out the plus and minus terminals.  And if you discharge a capacitor quickly you’re going to see some sparking.  As the charge jumps the air gap just before the circuit is closed.  The bigger the capacitor the bigger the sparking.  Funny story.  I saw a kid cutting out the capacitor from an old television set.  The kind your parents had.  With a big glass cathode ray picture tube that used high voltage to move a scanning electron beam to excite (i.e., make glow) the phosphorous coating on the inside of the picture tube.  High voltage and a capacitor mean only one thing.  A very BIG stored charge.  No one turned on that TV for a long time.  But that capacitor held its charge.  As this kid quickly learned.  The hard way.  As he cut the wire going to the plus terminal his un-insulated side cutters touched the metal of the TV chassis.  Which was, of course, grounded.  So you had the plus terminal of a highly charged capacitor coming into contact with the minus terminal of said capacitor (via the grounded TV chassis).  It was like the Fourth of July in the back of that TV.  Threw that poor kid back on his butt.  Funny.  We all had a good laugh.  He was no worse for wear.  Except, perhaps, needing a new pair of undershorts.

All right, back to those electrical storms.  And lightning.  In a nutshell, those ugly black storm clouds are like capacitors.  As the atmosphere churns up these warm and cold weather fronts as they collide something happens.  They charge.  Like a capacitor.  With one plate being on the top of the cloud.  And the other plate being on the bottom of the cloud.  As the charge grows on the bottom of the cloud it induces an opposite charge in the ground below.  The old ‘opposites attract’.  So if a larger and larger minus charge is building up in the bottom of the cloud it attracts (i.e., induces) a larger and larger plus charge on the surface of the earth beneath the cloud.  Until the charges grow so great that they jump the air gap.  But this is no capacitor discharging.  The amount of energy in a lightning strike is so great it can melt sand into glass.  And anything that can do that can play havoc with trees.  And tall buildings.  Igniting a lot of fires along the way.  And killing a lot of people.  Until, that is, we started using lightning rods on our buildings.  Sharp pointed pieces of metal above the highest surfaces of the building.  We attach these rods to conductors running down the sides of the building to ground rods driven below the surface of the earth.  Providing a ‘path of least resistance’ for that charge to discharge through while causing minimal damage to the building.

Ben Franklin gave us Weather Forecasting, Convection Heating and Lightning Rods as well as the United States

Fascinating information, yes?  What’s even more fascinating is that we can trace these developments back to one point in time.  More fascinating still, we can trace them back to one man.  A curious fellow.  With a fascination for scientific experimentation.  Who went by the name of Benjamin Franklin.  Who pioneered weather predicting when a swirling northeaster hit Philadelphia with winds blowing in from the northeast.  Curiously, though, this storm had not yet ravished Boston.  In direct line with those winds.  But the storm moved on to Boston AFTER Philadelphia.  It was Franklin who observed that the northeaster was a counterclockwise spinning storm that moved northeast.  The winds in Philadelphia and Boston were only the top part of that spinning storm.  And weather forecasting was born.

Convection heat goes back to the Philadelphia stove.  What we later called the Franklin stove.  Franklin didn’t discover convection currents.  Or the stove using convection currents.  But he used the available knowledge to make a practical heating stove.  It wasn’t perfect.  But subsequent improvements made it the standard for indoor heating for about a century or two.

Ben Franklin did not discover electricity.  But electricity fascinated him.  And he discovered that lightning was electricity (yes, he actually flew a kite in a storm).  His experimentation gave us the first battery.  The first capacitor.  The standard of using ‘plus’ and ‘minus’ for electrical charges.  The conservation of charge (you can’t create or destroy an electrical charge.  You can only move it around).  The battery.  The capacitor.  Insulators.  Conductors.  Grounding.  All of the fundamentals of electrical circuits we use to this day.  And let us not forget that one other thing.  The effect of points on electrical charges (pointy metallic things help charges jump air gaps).  Which, of course, led to the lightning rod.  This after he set up the U.S. postal service and printed his newspapers and Poor Richard’s Almanac.  But before his political and diplomatic service.  And role as a key Founding Father.  Being the only one to sign the Declaration of Independence, the Treaty of Paris and the U.S. Constitution.  The document that started the Revolutionary War.  The document that ended it.  And the document that created the United States of America.  A busy man that Franklin was.  And a great man.



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