Charge dissipation test

The surface resistivity is easy and relatively reproducible to determine with the ring electrode but it is limited for various reasons, for example it is based on a static test with no information about the important charging and discharging behaviour of the textiles. Therefore, combination with a charge dissipation test is favoured. 

An alternate test for charge-dissipating performance is the charge decay test, in which the time of charge decay is measured after a potential of 5 kV has been applied to the specimen (Federal Test Method Standard 101C, Method 4046.1). For many purposes, a... 

The main tests for assessment of electrostatic discharge are (USA) the following. ASTM D 257-75 (reapproved 1983) - standard test methods for DC resistance or conductance of insulating materials. Federal Test Method Standard No lOlC - 13 March 1980, Method 4046.1 - 8 October 1982 (charge notice 1). This measures the charge decay time of materials in film and sheet form. The maximum time accepted for charge dissipation is two seconds (as stated in MIL-B81705B-2,February 1972). 

The static decay test is a good measure of the static dissipative nature of an object. However, the test is controlled by the object s resistance to ground. Objects that have a high resistance, such as insulators, will not readily accept an induced charge or decay an induced charge. The static decay test is most suited for objects with resistances of 10 or less (52). 

Phosphors for cathode-ray tubes, television screens, monitor screens, radar screens, and oscilloscopes are tested under electron excitation. Electron energy and density should be similar to the conditions of the tube in which the screen will be used. The phosphors are sedimented or brushed onto light-permeable screens and coated with an evaporated aluminum coating to dissipate charge. The luminescence brightness and color of the emitted light are measured with optical instruments such as photomultipliers or spectrophotometers. 

Many fuel specifications require the use of static dissipator additive to improve safety in fuel handling. In such cases the specification defines both minimum and maximum electrical conductivity the minimum level ensures adequate charge relaxation whereas the maximum prevents too high a conductivity, because this can upset some capacitance-type fuel gauges in aircraft (ASTM D-2624, ASTM D-4308, IP 274). The standard test methods (ASTM D-2624, IP 274) employ an immersible conductivity cell and field meter intended for measuring the conductivity of fuel in storage tanks. 

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