become charged and readily release their charge to the grounded collection plate. Both extremes in resistivity impede the efficient functioning of ESPs. ESPs work best under normal resistivity conditions. Resistivity, which is a characteristic of particles in an electric field, is a measure of a particle's resistance to transferring charge (both accepting and giving up charges). Resistivity is a function of a particle's chemical composition as well as flue gas operating conditions such as temperature and moisture. Particles can have high, moderate (normal), or low resistivity. Bulk resistivity is defined using a more general version of Ohm’s Law, as given in Equation () below: Where: E is the Electric field strength.Unit:-(V/cm); j is the Current density.Unit:-(A/cm2); and ρ is the Resistivity.Unit:-(Ohm-cm) A better way of displaying this would be to solve for resistivity as a function of applied voltage and current, as given in Equation () below: Where: ρ = Resistivity.Unit:-(Ohm-cm) V = The applied DC potential.Unit:-(Volts); I = The measured current.Unit:-(Amperes); l = The ash layer thickness.Unit:-(cm); and A = The current measuring electrode face area.Unit:-(cm2). Resistivity is the electrical resistance of a dust sample 1.0 cm2 in cross-sectional area, 1.0 cm thick, and is recorded in units of ohm-cm. A method for measuring resistivity will be described in this article. The table below, gives value ranges for low, normal, and high resistivity. Dust layer resistance Resistance affects electrical conditions in the dust layer by a potential electric field (voltage drop) being formed across the layer as negatively charged particles arrive at its surface and leak their electrical charges to the collection plate. At the metal surface of the electrically grounded collection plate, the voltage is zero, whereas at the outer surface of the dust layer, where new particles and ions are arriving, the electrostatic voltage caused by the gas ions can be quite high. The strength of this electric field depends on the resistance and thickness of the dust layer. In high-resistance dust layers, the dust is not sufficiently conductive, so electrical charges have difficulty moving through the dust layer. Consequently, electrical charges accumulate on and beneath the dust layer surface, creating a strong electric field. Voltages can be greater than 10,000 volts. Dust particles with high resistance are held too strongly to the plate, making them difficult to remove and causing trapping problems. In low resistance dust layers, the corona current is readily passed to the grounded