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Surface resistivity

Not to be confused with surface resistance, surface resistivity is a measurement of a material’s inherent electrical resistance. For electric current flowing across a surface, the ratio of DC voltage drop per unit length to the surface current per unit width.

In effect, the surface resistivity is the resistance between two opposite sides of a square and is independent of the size of the square or its dimensional units.

To test a material’s electrical resistance, a surface resistivity meter can be used. Surface resistivity measurements are expressed in ohms/square.

Static decay test

A static decay test is a procedure in which an item is first charged to a specified voltage, then allowed to dissipate to a specified voltage while measuring the duration of the discharge.

Surface resistance

Surface resistance is the resistance of a surface measured by a concentric ring electrode test method defined in 61340-5-1 and IEC 61340-2-3: 2000.

It is the ratio of DC voltage to the current flowing between two electrodes of specified configuration that contact the same side of a material. This measurement is expressed in ohms.

Static control

Static control is a generic term for measures taken to diminish the effects of electrostatic discharge. Anti-static products such as ESD mats, ESD bags or conductive flooring are used to create an ESD protected area where static is controlled.

Static dissipative

Static dissipative refers to increased resistance, which protects better against an ESD i.e. between 1 meg-ohm (10^6) and 1000 meg-ohm (10^9). Static dissipative materials allow any static charge to be dispersed. Charge transfers from static dissipative materials are slower than from conductive materials and are significantly faster than from insulators.

Products such as ESD clothing and ESD bench matting are typically made from static dissipative materials, or often a combination of other materials i.e. conductive.

 

Static generation

An example of static generation is when people walk across a floor, the friction between the soles of their shoes and the surface of the floor generates static—also called walking body voltage.

Static electricity

Static electricity is a stationary electrical charge/ field, typically produced by friction, which causes sparks, crackling or the attraction of dust or hair.

All items are made of small atoms. These atoms are made up of even smaller items called protons, neutrons and electrons. The protons are charged positive, the neutrons have no charge and the electrons are charged negative. Under normal conditions, there are the same amount of protons and electrons giving atoms no charge.

However, these electrons can move. When separating or rubbing together materials, electrons can move from atom to atom or from one material to another (triboelectric charges). This can mean that atoms can hold a positive or negative charge. (Dependant on movement and direction of electrons). If the material in question is an insulator, this charge can be held and not move. This is called static electricity.

The rapid movement or decay of these charges can cause expensive problems, whether it is huge and dangerous charges such as lightening or simply an annoying (and sometimes painful) “electric shock” when touching a filling cabinet or when getting out of a car. (These charges are normally on you!).

These charges can be a huge problem for small sensitive electronic devices. Some devices can be damaged or destroyed by as little as 10 volts. Charges on your body simply by walking or even sitting at your chair can be in excess of 5000 volts (human body material). This is because of items of clothing rubbing together or as simple as shoes separating from the ground.

When items are insulators such as carpets, charges are much higher – imagine the damage this could cause. This is why it is important that insulators should be avoided and all possible static electricity generators (such as you) should (must) be grounded to eliminate any build up of charges.

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