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Model 9110T NOx Analyzer Primer on ESD
Teledyne Analytical Instruments 369
14.3. 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 damages 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.
14.4. BASIC PRINCIPLES OF STATIC CONTROL
It is impossible to stop the creation of instantaneous static electric charges. It is not, however difficult to
prevent those charges from building to dangerous levels or prevent damage due to electro-static
discharge from occurring.
14.4.1. GENERAL RULES
Only handle or work on all electronic assemblies at a properly set up ESD station. Setting up an ESD
safe workstation need not be complicated. A protective mat properly tied to ground and a wrist strap are
all that is needed to create a basic anti-ESD workstation.