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Teledyne API T803 CO2/O2 Analyzer Operation Manual A Primer on Electro-Static Discharge
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When static charges accumulated on a sensitive device discharges from the
device to another surface such as packaging materials, work surfaces, machine
surfaces or other device. In some cases, charged device discharges can be the
most destructive.
A typical example of this is the simple act of installing an electronic assembly
into the connector or wiring harness of the equipment in which it is to function.
If the assembly is carrying a static charge, as it is connected to ground a discharge
will occur.
Whenever a sensitive device is moved into the field of an existing electro-static
field, a charge may be induced on the device in effect discharging the field onto
the device. If the device is then momentarily grounded while within the
electrostatic field or removed from the region of the electrostatic field and
grounded somewhere else, a second discharge will occur as the charge is
transferred from the device to ground.
13.3. COMMON MYTHS ABOUT ESD DAMAGE
I didn’t feel a shock so there was no electro-static discharge: The human
nervous system isn’t able to feel a static discharge of less than 3500 volts. Most
devices are damaged by discharge levels much lower than that.
I didn’t touch it so there was no electro-static discharge: Electro Static charges
are fields whose lines of force can extend several inches or sometimes even feet
away from the surface bearing the charge.
It still works so there was no damage: Sometimes the damaged caused by
electro-static discharge can completely sever a circuit trace causing the device to
fail immediately. More likely, the trace will be only partially occluded by the
damage causing degraded performance of the device or worse, weakening the
trace. This weakened circuit may seem to function fine for a short time, but even
the very low voltage and current levels of the device’s normal operating levels
will eat away at the defect over time causing the device to fail well before its
designed lifetime is reached.
These latent failures are often the most costly since the failure of the equipment
in which the damaged device is installed causes down time, lost data, lost
productivity, as well as possible failure and damage to other pieces of equipment
or property.
Static Charges can’t build up on a conductive surface: There are two errors in
this statement.
Conductive devices can build static charges if they are not grounded. The charge
will be equalized across the entire device, but without access to earth ground,
they are still trapped and can still build to high enough levels to cause damage
when they are discharged.
A charge can be induced onto the conductive surface and/or discharge triggered
in the presence of a charged field such as a large static charge clinging to the
surface of a nylon jacket of someone walking up to a workbench.
07276B DCN6418