| THE PROBLEMYou landed after a rough
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| | The replacement cost of a pcb can be
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| flight, got the last rental car, battled
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| | several hundred thousand dollars!The
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| the snowstorm, and finally arrived at the
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| | front line of defence is the Wrist Strap.
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| Holly Inn. It's nice and warm in there,
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| | This consists of a means of connection
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| you can relax, ready for the conference
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| | to the frame of the machine being worked
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| tomorrow.Out of the elevator, of course
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| | on, linked to some form of bracelet or
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| your room is at the far end of the
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| | band which makes contact with the
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| corridor. No matter, the heating is
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| | worker's skin.The link is not a normal
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| turned up and you are looking forward to
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| | piece of wire, but has a resistance of 1
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| a good night's rest. You make it to the
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| | Megohm. This high resistance is to
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| room door feeling very sleepy. You reach
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| | reduce the current when connecting to the
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| out for the door handle when...Zap! It
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| | frame, so as not to cause problems.The
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| gets you every time!THE CAUSEStatic
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| | wrist strap itself is usually of some
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| electricity. Everyone knows about it,
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| | stretch material, with a metal connector
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| harmless really, happens when you get out
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| | for the wire link, and to connect to the
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| of the car as well. Synthetics are
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| | wrist. Alternatively, some types have an
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| particularly good for generating a good
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| | expanding metal strap, similar to a watch
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| one, along with a dry
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| | strap.The connector to the frame may be a
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| atmosphere.Thousands of volts - harmless?
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| | metal clip, or a plug to fit a receptacle
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| just a little shock? To you, maybe, to an
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| | on the machine, for this purpose.In the
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| electronic circuit static discharge is -
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| | workshop, all work is carried out on an
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| death. Not necessarily instant, more
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| | anti-static mat, made of metalised
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| likely a weakening effect, causing
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| | rubber, so that it is conductive. This
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| intermittent failures, the most difficult
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| | mat is grounded, and connected to the
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| to catch, until the final solid fault.THE
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| | frame of the equipment being worked on.
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| EFFECTThe problem for an electronic
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| | Anyone working on the equipment must
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| circuit is that they work on 2 or 3 volts
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| | first connect his wrist strap to the mat
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| at low currents, so when a kilovolt
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| | via the connectors provided.Another
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| charge turns up, the current which flows
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| | anti-static mat, also grounded, is placed
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| is many times more than it is designed
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| | on the floor at the workstation to stand
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| for. The effect can be like a fuse, a
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| | on.In the computer room, a portable
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| connection to a microcircuit melts, or is
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| | workbench, is provided with an
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| badly damaged. For us there is millions
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| | anti-static mat, connected to the machine
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| of times less current than would be
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| | frame, to place components removed or to
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| required to damage any tissue.The voltage
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| | be installed on. Bags or containers made
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| doesn't need to be enough to cause a zap,
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| | from conductive material are on hand, and
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| an electronic circuit can be damaged by
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| | can also be connected to the mat.A mat is
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| just handling it, touching metal parts.
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| | placed on the floor where work is being
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| The potential for damage has been growing
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| | carried out, connected to the frame. The
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| since transistors, and, particularly
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| | people working on the equipment wear
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| integrated circuits were introduced.
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| | anti-static coats made of conductive
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| Vacuum tube circuits used much higher
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| | material. They also have ankle/heel
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| voltages, such that the circuit was more
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| | straps. These fit around the ankle,
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| likely to zap the careless technician
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| | making contact with the skin, and under
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| than the other way round!THE SOLUTIONWe
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| | the heel of the shoe, to make contact
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| have mentioned, in the history of the
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| | with the mat.Components which have been
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| computer series, the importance of power
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| | replaced for suspect problems are
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| supplies and air conditioning controls.
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| | returned to the factory for failure
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| These are largely there to make sure the
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| | analysis. The failed circuit is examined
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| electronics can work in its designed
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| | through a microscope to observe the
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| range. When the engineer works on these
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| | failing area, and to determine if this is
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| circuits he must take precautions to
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| | a potential problem for other similar
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| ensure this range is not exceeded because
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| | circuits. Failures due to electrostatic
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| of static build-up.In the workshop, all
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| | discharge can also be determined.THE HOME
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| work must be performed in a static free
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| | USERNow you know the precautions the
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| environment, components are to be stored
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| | professionals take, you can understand
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| in anti-static bags or containers, and
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| | the necessity for care to be taken when
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| anyone working on the equipment must
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| | adding memory, or opening your computer
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| ensure he does not allow static discharge
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| | for any other reason. If you have a
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| through it.Similarly, when working on the
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| | wrist strap, use it. If not at least
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| system in the computer room, perhaps
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| | touch the frame of the computer before
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| removing or replacing a circuit board, or
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| | reaching inside. And don't think you
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| adjusting a circuit, the correct
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| | don't need to because it works OK when
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| procedures must be followed.THE
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| | you close it up again. You could be
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| EQUIPMENTThis has become more and more
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| | getting the results of your efforts down
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| complicated as the potential for damage
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| | the track!Tony is an experienced computer
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| has grown, with the reduction in size and
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| | engineer.
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| therefore concentration of circuitry.
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