Index: firmware/App/Controllers/AirTrap.c
===================================================================
diff -u -r8f2b9d878195896cf41091e97630e264f11394bb -r213af8d663da48931adb07f641ebacf8d0f3b4aa
--- firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision 8f2b9d878195896cf41091e97630e264f11394bb)
+++ firmware/App/Controllers/AirTrap.c	(.../AirTrap.c)	(revision 213af8d663da48931adb07f641ebacf8d0f3b4aa)
@@ -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"
@@ -39,7 +40,7 @@
 #define AIR_TRAP_FILL_TIMEOUT_MS            ( 6 * MS_PER_SECOND )                               ///< Air trap fill timeout period (in ms).
 #define AIR_PUMP_UPPER_LEVEL_PERSISTENCE    ( 100 / TASK_GENERAL_INTERVAL )                     ///< Persistence time for air pump operation after air trap upper level reads air.
 /// Persistence period for illegal level sensors fault.
-static const U32 AIR_TRAP_ILLEGAL_LEVELS_PERSISTENCE = ( MS_PER_SECOND * 2 / TASK_PRIORITY_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 )
@@ -70,7 +71,6 @@
 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 **********
 
@@ -91,7 +91,6 @@
     U32 i;
 
     resetAirTrap();
-    airTrapIllegalLevelSensorsCtr      = 0;
     airTrapDataPublicationTimerCounter = DATA_PUBLISH_COUNTER_START_COUNT;
     airPumpUpperLevelCtr               = 0;
 
@@ -102,6 +101,9 @@
         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 );
+
 }
 
 /*********************************************************************//**
@@ -180,6 +182,8 @@
 void execAirTrapMonitor( void )
 {
     BOOL lower, upper;
+    bool isAirTrapLevelsValid = FALSE;
+    AIR_TRAP_LEVELS_T lowerAirTrap, upperAirTrap;
 
     // Get latest level readings
     getFPGAAirTrapLevels( &lower, &upper );
@@ -189,27 +193,21 @@
     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;
-    }
 }
 
 /*********************************************************************//**