GPM is used to monitor the charged particle flux during the flight of satellite, particularly the flux when the satellite passes through the South Atlantic Anomaly (SAA). When it (GPM count rate) exceeds a certain threshold, a command is executed to shut off the high voltage of the payload detector, protecting key components such as the PMT of the GRM main detector from being "fatigued" or damaged by excessively high flux. The schematic diagram of GPM is as Fig2:

Fig 2：schematic diagram of GPM

According to the scientific objectives, the main technical specifications of GPM are as table2:

Table 2: technical specifications of GPM