TM 10-6640-233-10 Table 2-7. Purge System and Gas Alarm Control or Indicator Function 1.  Purge Doors Limit Switches Provides signal to purge alarm buzzer if one of purge  doors  is  not  opened  when  purge  cycle  is initiated. 2.  Gas Alarm Green Pilot Light Provides indication when the instrument power is on and detector circuit is energized. 3.  Indicator Meter Provides indication of the concentration of combustible gas at detection point. 4.  Gas Alarm Blue Fail Light Provides  indication  when  there  is  equipment  failure  or malfunction. 5.  Yellow Warning/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. 6.  Red Alarm Light Provides test of alarm buzzer. 7.  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. 8.  Detector/Selector Switch Provides  automatic  or  manual  selection  of  individual alarm detectors. 2-9