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'Static electricity' arises when contacting surfaces are separated. If the charge that arises
from differences between the surfaces cannot run away to earth quickly enough then it is trapped - it
is 'static'. The 'quickly enough' relates to the time for the charge to leak away to earth - or to the
time for the charge to spread out over the surface of a material.
Examples of 'static electricity' are the picking up of small pieces of paper by a rubbed comb or piece
of plastic and the cling of thin light fabrics after they have been rubbed.
Static Electricity is important in industry as it can cause risks and problems that need to be avoided.
It is also the basis for many useful applications.
Explore this Website to find out about making electrostatic
measurements, about JCI instruments and to access
lots of supporting information about static electricity.
Many materials, in particular
plastics, easily become electrostatically charged when rubbed against other materials. Such 'triboelectric'
charging can be used constructively - for example, in photocopying, electrostatic clamping and the
retention of powder in electrostatic precipitation and paint spraying. Retained electrostatic charge also
creates risks and causes problems in many areas of industry. It can cause ignition of flammable gases and give shocks
to personnel. It can make thin films and light fabrics cling, attract airborne dust and debris, damage semiconductor
devices and upset the operation of microelectronic equipment.
Most of the uses and problems of static electricity relate to the influence of charge retained on surfaces via the surface voltage created. The 'suitability' of materials thus needs to be judged in relation to charge retention and surface voltage.
The way to assess the charge retention performance of materials is to measure the 'charge decay time' - how quickly any charge put on the material dissipates over and through the material and away to earth. (Note: we are talking about 'decay time' - not 'resistivity'!). To avoid risks and problems it is necessary to ensure that static charge can dissipate more quickly than charge is generated. For normal manual handling and body motion activities this means the charge decay time needs to be ¼ ; second or less.
The above approach to assessing the suitability of materials is in use by many major companies in a wide variety of industries all around the world. For example for industries making and handling paper, packaging, retail as well as cleanroom garments, pharmaceutical powders and protective materials for microelectronics.
The voltage arising on the surface depends upon the 'capacitance' experienced by the charge. A new concept, relevant to risk control, is that if static charge experiences a high capacitance on a material then only low surface voltages will be observed - and many problems and risks will not arise (see JNC papers for the IEEE-IAS meeting Oct, 1999 and for the ESA meeting at Niagara Falls, June 2000).
Another area of interest relates to the ability of materials to provide shielding against electrostatic discharges and transient electric fields.
Measurements enable you to find out if, where, when and how much static electricity is present.
They tell you whether materials are suitable, or not.
With reliable and appropriate measurements you can assess risks, can design and check the effectivenss of remedial
measures and can be confident in the selection and performance of materials.
Without reliable measurements it is all guesswork...!<
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Latest site update: 20/10/2003. © John Chubb Instrumentation.
Number of visitors since 25 Feb, 2000
