Check manual page of entity_sensors.fan
ENTITY-SENSORS MIB: Fan Speed RPM
This check monitors the temperature of devices
which support the ENTITY-SENSORS MIB such as
Palo Alto Networks Series 200/3000.
The lower default levels are set to 2000, 1000 RPM.
The upper and lower levels are configurable.
The name or index of the sensor.
One service per sensor is created.