|
Newsletter (PDF)
Engineering Support
FLX-P™ Innovation
US Office:
31 Winterbrook Road
Mechanic Falls, ME 04256
Phone: 207-998-5140
Fax: 207-998-5143
|
How Is Static Generated?
Friction,
pressure and separation are the major causes of static
electricity. This process is called the Triboelectric
Effect ("tribo" means rubbing). The triboelectric effect
is responsible for the shock you receive from a car door
after you slide out.
The
magnitude of the static charge is determined by material
composition, applied forces, separation rate, and relative
humidity. These factors conspire to cause conveying mechanisms,
and other systems, to act as static generators. Even slow-moving
conveying mechanisms are capable of generating ample static
charge to cause an ESD ( Electrostatic Discharge ) event.
An uncontrolled ESD event can generate enough EMI to damage
electronic components.
Environmental
variables like relative humidity influence the level of
electrostatic charges. When humidity is low, higher static
charges are generated (see Table I). Static becomes more
noticeable in the winter months, in dry climates, and
in air conditioned environments. Increasing humidity to
60% limits static build-up because surface moisture on
materials makes a good conductor. Unfortunately, 60% relative
humidity is extremely uncomfortable, can cause equipment
problems and introduce contaminants into your system.
Fortunately,
static control devices can be located at critical points
to control the ESD event by reducing the static charge
to low levels. Static Control devices allow smoother operation
of conveying mechanisms and eliminate electronic component
damage
caused by ESD events.
|
|
|
|
The
Triboelectric effect is the major cause of static
- the greater the force of friction or pressure,
the more static will be created. Also, faster rates
of separation cause more static.
|
Table
I - Typical Electrostatic Voltage |
| |
Electrostatic
Voltages |
| Means
of Static Generation |
10-20
percent
Relative Humidity |
65-90
percent
Relative Humidity |
| Walking
across carpet |
35,000 |
1,500 |
| Walking
over vinyl floor |
12,000 |
250 |
| Worker
at bench |
6,000 |
100 |
| Vinyl
envelopes for work instructions |
7,000 |
600 |
| Common
poly bag picked up from bench |
20,000 |
1,200 |
|
Static Control Devices
EST
static control devices, such as brushes, work
by induction, much like a lightning rod. Physical
contact between the static eliminator and the
target material is not necessary. The electric
field created by the static charge is focused
on sharp points. If the charge on the material
is high enough, the energy concentrated on the
points will induce ionization. The static charge
must exceed several thousand volts for ionization
to be created using a static control device.
With brushes, the ionizing effect is uncontrolled.
Static control devices can be used in contact
with the material to provide a path to ground,
neutralizing static on isolated conductors.
|
Power
Point™ is a trademark of Microsoft Corporation.
Email: sales@est-static.com |
