Devices that can be used in explosive zones caused by dust are designed according to three application groups. Depending on the nature of the dust causing the danger, it can be:

 flammable, long-threaded particles:   group IIIA

 by conductivity:

                                  non-conductive:    group IIIB

                                  conductive:            group IIIC

Flammable, long fiber particles are characterized by one of their dimensions exceeding 500 µm and their length-to-width ratio greater than three. A good example is cotton, hemp, or carbon fiber. Powders are classified into this group by visual inspection or microscopic examination.

In conductivity classification, the threshold of the defining specific resistance is 10³ Ωm . At a higher value, the port is considered to be non-conductive, and at a lower value it is considered conductive. The specific conductivity is determined by a standard test according to the EN ISO 80079-20-2 standard.

During the determination of conductivity by means of an instrumental test, a constant, defined volume of powder is filled between the two electrodes of a special measuring cell, to which the resistance between the two electrodes can be determined by connecting different measuring voltages. The base plate of the measuring cell is made of Teflon (polytetrafluoroethylene), two electrodes are mounted on it, made of polished stainless steel bars, at a distance of 10 mm from each other. The electrodes are connected to a resistance meter.

KÉPET ILLESZTENI !

For each test voltage, the specific resistance p is determined by the following relationship:

KÉPET ILLESZTENI !

The values obtained at different measurement voltages are recorded in the measurement report after averaging.