Figure 1. Structure of AQT400 1 Filter (AQT420 only) 2 Laser particle counter (LPC) (AQT420 only) 3 Pump (AQT420 only) 4 Main electronics board 5 Integrated pressure sensor 6 Combined temperature and humidity sensor 7 Radiation shield 8 Sensor elements (4 sensors per unit) 9 M12 connector