The rate of pulses is used to measure concentration. More closely spaced the pulses are higher the concentration. So pulse count per second relates to particle count per second (pcs/s). The particle count per second can be converted to particle concentration (pcs/ml) using flow rate information (ml/s).

A similar analog front end can be used in photometer and optical particle counter. The functioning of sensor varies based on flow rate as flow rate is a critical parameter to ensure single particle presence at a time in sensing volume of the optical chamber. Tuning the circuit for desired flow rate is critical to ensure that a particle doesn’t dwell for longer duration in the sensing volume. The passband frequency range of the AFE should be able to support the flow rate requirement of optical PM measurement sensor.