Abstract: A method for controlling an air sampling pump includes establishing from empirical measurement a family of sets of data relating speed of the pump to the flow rate of air through the pump as a function of pressure drop of the air at the pump inlet and storing the data in an electronic memory. The pump is then operated at a selected speed corresponding to a desired air flow rate and selected inlet pressure drop. The actual pressure drop is measured and a pair of sets of pressure drop values are identified in the stored data, which values bracket the actual measured pressure drop. The desired air flow rate and corresponding pump RPM value for each of the identified pair of sets of differential pressure values are located and extrapolation is used to locate a new value of RPM for delivering the desired air flow rate at the actual measured value of pressure drop. The pump is then operated at the new RPM value.

Abstract: A microprocessor controlled air sampling pump utilizes a PWM controlled DC electric motor for regulating air flow generated by a diaphragm-type air pump. The control system regulates air flow as a function of RPM of the motor by establishing a table of values which relate motor RPM to air flow rates. The control system maintains RPM at the desired value but includes a control loop which senses deviations in RPM and adjusts the PWM signals to the motor to regulate RPM. The system also senses large changes in RPM and treats such changes as blockages in the air sampling pump lines which prevent accurate environmental sampling. This system enters a cycling mode which turns the pump motor off for different time intervals until the detected blockage has been removed or until a predetermined time has expired. This procedure minimizes battery drain in the event of blockage of the air sampling pump lines.

Abstract: An improved primary gas flow calibrator measures the flow rate of a gas source through a fixed volume by monitoring the travel time of a liquid soap film. The device comprises a novel mechanism for generating a single film of soap across a first end of a flow tube and an infrared light beam responsive timing system for determining the speed of a soap film moving through a portion of the flow tube. The device is a microprocessor-based system which comprises settable adjusting DIP switches for avoiding exacting dimensional tolerances of the flow tube during manufacture.