Dwyer Instrument Particulate Monitors: Correlating picoAmp Readings to mass Concentration

Dwyer Instruments Particulate Monitors are designed using the Induction (AC) method for measuring particulate matter as it passes the sensing probe. As particles pass by the probe, minute currents are induced relative to the amount of particulate in the air flow. This induced current is what is being measured by the device, and the subsequent scale range is in the units of picoAmps (pA). The signal is not significantly affected by velocity variations in fabric filter applications. This measurement method is a proven way of determining when leaks or holes develop in baghouse filters, however some regulatory agencies require that particulate is measured in concentration terms;  i.e. mg/m³ . Since the mass concentration of particulate is a function of the specific material being measured, the best practice is to audit your installation and perform gravimetric tests to set the baseline correlation between the particulate monitor reading and the actual mass concentration of the process. The following is a brief review of the steps taken by one 3^rd party entity to prove that a particulate monitor utilizing induction technology was capable of measuring concentrations below 1 mg/m³, that it could detect small leaks of increasing size, and that the induced current measured in pA is reasonable linear in correlation to actual mass. By following similar steps a mass concentration correlation can be determined when required, and the pA readings from the particulate monitor can be converted in mass concentration. Please review your local regulatory requirements for specific standards and test methods that are acceptable for your installation.