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Teledyne - Technical Manual - Model T300 Family CO Analyzers ESD
Teledyne Analytical Instruments 319
Always wear an Anti-ESD wrist strap when working on the electronic
assemblies of your analyzer. An anti-ESD wrist strap keeps the person
wearing it at or near the same potential as other grounded objects in the
work area and allows static charges to dissipate before they can build to
dangerous levels. Anti-ESD wrist straps terminated with alligator clips are
available for use in work areas where there is no available grounded plug.
Also, anti-ESD wrist straps include a current limiting resistor (usually
around one meg-ohm) that protects you should you accidentally short
yourself to the instrument’s power supply.
Simply touching a grounded piece of metal is insufficient. While this
may temporarily bleed off static charges present at the time, once you stop
touching the grounded metal new static charges will immediately begin to
re-build. In some conditions, a charge large enough to damage a component
can rebuild in just a few seconds.
Always store sensitive components and assemblies in anti-ESD storage
bags or bins: Even when you are not working on them, store all devices
and assemblies in a closed anti-Static bag or bin. This will prevent induced
charges from building up on the device or assembly and nearby static fields
from discharging through it.
Use metallic anti-ESD bags for storing and shipping ESD sensitive
components and assemblies rather than pink-poly bags. The famous,
pink-poly bags are made of a plastic that is impregnated with a liquid
(similar to liquid laundry detergent) which very slowly sweats onto the
surface of the plastic creating a slightly conductive layer over the surface of
the bag.
While this layer may equalize any charges that occur across the whole bag,
it does not prevent the build up of static charges. If laying on a conductive,
grounded surface, these bags will allow charges to bleed away but the very
charges that build up on the surface of the bag itself can be transferred
through the bag by induction onto the circuits of your ESD sensitive device.
Also, the liquid impregnating the plastic is eventually used up after which
the bag is as useless for preventing damage from ESD as any ordinary
plastic bag.
Anti-Static bags made of plastic impregnated with metal (usually silvery in
color) provide all of the charge equalizing abilities of the pink-poly bags but
also, when properly sealed, create a Faraday cage that completely isolates
the contents from discharges and the inductive transfer of static charges.
Storage bins made of plastic impregnated with carbon (usually black in
color) are also excellent at dissipating static charges and isolating their
contents from field effects and discharges.
Never use ordinary plastic adhesive tape near an ESD sensitive device
or to close an anti-ESD bag. The act of pulling a piece of standard plastic
adhesive tape, such as Scotch
®
tape, from its roll will generate a static
charge of several thousand or even tens of thousands of volts on the tape
itself and an associated field effect that can discharge through or be induced
upon items up to a foot away.
14.4.2. BASIC ANTI-ESD PROCEDURES FOR ANALYZER REPAIR
AND MAINTENANCE