Influence of particle electrification on AC-based capacitance measurement and its elimination

• The influence of particle electrification on the capacitance measurement is analyzed theoretically and experimentally.
• Experimental studies are carried out on a V-belt pulley rig.
• The influence can be eliminated by removing the electrostatic signal superimposed on the capacitance signal.
• A modified capacitance measurement circuit is proposed.

Based on the variations of equivalent electrical permittivity with different phase concentrations in two-phase or multiphase flow, the capacitance sensor has been successfully used for the phase concentration measurement due to its advantages of non-invasion, low-cost, high reliability and non-radiation. However, solid particles are charged due to the collisions between particles and pipe wall in gas–solid flow system. The charge carried by solid particles will induce a certain amount of charge on the electrode of capacitance sensor, which causes an additional output in the capacitance measurement circuit. Hence, the particle electrification causes errors in capacitance measurements, and even leads to the failure of the measurement system for solid concentration and tomography system based on capacitance sensor. In this paper, the influence of particle electrification on the AC-based capacitance measurement circuit is theoretically and experimentally investigated based on a capacitance sensor with helical surface-plate electrodes. The results indicated that the capacitance signal and the electrostatic induction signal have different frequency band ranges. The influence of charge on capacitance measurements can be eliminated by rationally designing the capacitance measurement circuit, and further accurate and reliable capacitance measurement can be achieved.