TM 10-6640-215-13 2-2.       OPERATOR CONTROLS AND INDICATORS - continued. Table 2-6.  Purge System and Gas Alarm Controls and Indicators Control or Indicator Function Purge Doors Limit Switches Provides signal to purge alarm buzzer if one of purge doors is not opened when purge cycle is initiated. Gas Alarm Green Pilot Light Provides  indication  when  the  instrument  power  is  on  and detector circuit is energized. Gas Alarm Blue Fail Light Provides   indication   when   there   is   equipment   failure   or malfunction. Yellow Warn/Test Light Provides    indication    when    a    combustible    gas    condition exceeding   the   low   alarm   setting   exists   at   the   remote detector, or when the alarm test switch has been activated. When depressed, provides a simulation of an alarm level of gas concentration at the remote detector.  It also provides a functional check of the analyzer and remote alarm circuit. Alarm Reset Switch When   depressed,   deactivates   the   holding   circuits   of   the alarm  and  warning  relays  if  a  safe  gas  condition  has  been restored at the remote detector.  If a safe condition does not exist, the unit cannot be reset. Indicator Meter Provides indication of the concentration of combustible gas at detection point. e. Air System Controls and Indicators.  Figure 2-7 and Table 2-7 list the controls and indicators for the air system. 2-13