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Teledyne API M100E Analyzer Operation Manual A Primer on Electro-Static Discharge
297
Potentially damaging electro-static discharges can occur:
Any time a charged surface (including the human body) discharges to a device. Even simple contact of a
finger to the leads of a sensitive device or assembly can allow enough discharge to cause damage. A
similar discharge can occur from a charged conductive object, such as a metallic tool or fixture.
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.
As long as my analyzer is properly installed, it is safe from damage caused by static discharges: It
is true that when properly installed the chassis ground of your analyzer is tied to earth ground and its
electronic components are prevented from building static electric charges themselves. This does not
prevent discharges from static fields built up on other things, like you and your clothing, from discharging
through the instrument and damaging it.
04515F DCN6048