Index: firmware/App/Controllers/AirTrap.c
===================================================================
diff -u -r408247fba0f81c8ca77fb3144694ac8d7358d87b -re300530d917868cdf690421673e3efcd48fd3f67
--- firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision 408247fba0f81c8ca77fb3144694ac8d7358d87b)
+++ firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision e300530d917868cdf690421673e3efcd48fd3f67)
@@ -21,6 +21,7 @@
 #include "FPGA.h"
 #include "ModeTreatmentParams.h"
 #include "OperationModes.h"
+#include "PersistentAlarm.h"
 #include "Switches.h"
 #include "SystemCommMessages.h"
 #include "TaskGeneral.h"
@@ -41,7 +42,7 @@
 #define AIR_PUMP_ON_ERROR_MAX_CNT           6                                                   ///< Maximum number of air pump on events within time window before alarm triggered. Do not exceed MAX_TIME_WINDOWED_COUNT.
 #define AIR_PUMP_ON_ERROR_TIME_WIN_MS       ( 60 * MS_PER_SECOND )                              ///< Time window for Air Pump on count error.
 /// Persistence period for illegal level sensors fault.
-static const U32 AIR_TRAP_ILLEGAL_LEVELS_PERSISTENCE = ( MS_PER_SECOND * 2 / TASK_GENERAL_INTERVAL );
+#define AIR_TRAP_ILLEGAL_LEVELS_TIMEOUT_MS  ( 2 * MS_PER_SECOND )                               ///< Air trap illegal values timeout (in ms)
 
 /// Volume (in mL) of venous portion of blood circuit line.  TODO - get actual volume from Systems.
 #define VENOUS_LINE_VOLUME_ML               ( 200.0F )
@@ -63,7 +64,7 @@
 static U32 airTrapDataPublicationTimerCounter;                                              ///< Used to schedule air trap data publication to CAN bus.
 
 /// Interval (in ms) at which to publish air trap data to CAN bus.
-static OVERRIDE_U32_T airTrapDataPublishInterval = { AIR_TRAP_DATA_PUB_INTERVAL, AIR_TRAP_DATA_PUB_INTERVAL, 0, 0 };
+static OVERRIDE_U32_T airTrapDataPublishInterval = { AIR_TRAP_DATA_PUB_INTERVAL, AIR_TRAP_DATA_PUB_INTERVAL, AIR_TRAP_DATA_PUB_INTERVAL, 0 };
 static OVERRIDE_U32_T airTrapLevels[ NUM_OF_AIR_TRAP_LEVEL_SENSORS ];                       ///< Detected air trap level for each level sensor.
 
 static BOOL pendingStartAirTrapController = FALSE;                                          ///< Flag indicates an air trap controller start request is pending.
@@ -72,7 +73,6 @@
 static U32  fillStartTime = 0;                                                              ///< Time stamp for start of air trap fill.
 
 static U32 airPumpUpperLevelCtr = 0;                                                        ///< Timer count for air pump persistence.
-static U32 airTrapIllegalLevelSensorsCtr = 0;                                               ///< Timer counter for illegal level sensor fault.
 
 // ********** private function prototypes **********
 
@@ -93,8 +93,8 @@
     U32 i;
 
     resetAirTrap();
-    airTrapIllegalLevelSensorsCtr = DATA_PUBLISH_COUNTER_START_COUNT;
-    airPumpUpperLevelCtr = 0;
+    airTrapDataPublicationTimerCounter = DATA_PUBLISH_COUNTER_START_COUNT;
+    airPumpUpperLevelCtr               = 0;
 
     for ( i = 0; i < NUM_OF_AIR_TRAP_LEVEL_SENSORS; i++ )
     {
@@ -103,6 +103,9 @@
         airTrapLevels[i].ovInitData = 0;
         airTrapLevels[i].override = OVERRIDE_RESET;
     }
+
+    initPersistentAlarm( ALARM_ID_HD_AIR_TRAP_ILLEGAL_LEVELS, AIR_TRAP_ILLEGAL_LEVELS_TIMEOUT_MS, AIR_TRAP_ILLEGAL_LEVELS_TIMEOUT_MS );
+
 }
 
 /*********************************************************************//**
@@ -181,6 +184,8 @@
 void execAirTrapMonitor( void )
 {
     BOOL lower, upper;
+    bool isAirTrapLevelsValid = FALSE;
+    AIR_TRAP_LEVELS_T lowerAirTrap, upperAirTrap;
 
     // Get latest level readings
     getFPGAAirTrapLevels( &lower, &upper );
@@ -190,27 +195,21 @@
     if ( STATE_OPEN == getSwitchStatus( PUMP_TRACK_SWITCH ) )
     {
         // If the pump track on open, zero the persistent counter to not check the air trap illegal level alarm
-        airTrapIllegalLevelSensorsCtr = 0;
+        checkPersistentAlarm( ALARM_ID_HD_AIR_TRAP_ILLEGAL_LEVELS, FALSE, 0.0, 0.0 );
     }
-
-    // Check level readings are valid
-    if ( ( AIR_TRAP_LEVEL_AIR == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_LOWER ) ) &&
-         ( AIR_TRAP_LEVEL_FLUID == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_UPPER ) ) )
+    else
     {
-        if ( ++airTrapIllegalLevelSensorsCtr >= AIR_TRAP_ILLEGAL_LEVELS_PERSISTENCE )
-        {
+        lowerAirTrap         = getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_LOWER );
+        upperAirTrap         = getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_UPPER );
+        isAirTrapLevelsValid = ( ( AIR_TRAP_LEVEL_AIR   == lowerAirTrap ) && ( AIR_TRAP_LEVEL_FLUID == upperAirTrap ) ) ? TRUE : FALSE;
+
 #ifndef _RELEASE_
-            if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_ILLEGAL_AIR_TRAP_ALARM ) != SW_CONFIG_ENABLE_VALUE )
+        if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_ILLEGAL_AIR_TRAP_ALARM ) != SW_CONFIG_ENABLE_VALUE )
 #endif
-            {
-                activateAlarmNoData( ALARM_ID_HD_AIR_TRAP_ILLEGAL_LEVELS );
-            }
+        {
+            checkPersistentAlarm( ALARM_ID_HD_AIR_TRAP_ILLEGAL_LEVELS, isAirTrapLevelsValid, lowerAirTrap, upperAirTrap );
         }
     }
-    else
-    {
-        airTrapIllegalLevelSensorsCtr = 0;
-    }
 }
 
 /*********************************************************************//**