User Manual

RevA LC900008 11of14
APPLICATIONEXAMPLES StepSeven
LowFlowAlarm:Thegoalistoindicatewhentheflowratefallsbelowacertainpoint.Ifitdoes,analarmis
supposedtosound,alertingtheoperatorofalowflowcondition.
Ifpowerisaccidentallycuttothecontroller,thesensor'sabilitytonotifytheoperatorofalowflowcondition
couldbelost.Thesystemmustalerttheoperatornotonlytolowflow,buttocontrollerpowerloss.
Todothis,connectthehotleadofthealarmtotheNCsideoftherelayterminalofthecontroller.Ifpoweris
lost,therelaywillbede‐energized,andthealarmwillsound(ifthereisstillpowertothealarmcircuititself).
The alarm circuit should have a noninterruptible power supply or some other indicator or backup alarm to
warnofapowerfailureinthealarmcircuit.
In this application,  the normal status is when the sensor is in the flow condition, and the relay will be
energizedholdingthealarmcircuitopen.Pleasenotethattheflowswitchcanbewiredeithernormallyclosed
ornormallyopen(Step5).WhentheswitchiswiredNC,theinputLEDwillbeoffandtherelayLEDwillbeon.
Sofor this application,Invertshouldbe settotheOn position.Whentheswitch iswiredNO, the inputLED 
andtherelayLEDwillbeonsimultaneously.Soforthisapplication,InvertshouldbesettotheOffposition.
LEDIndication:UseLED'slocatedabovetheinputterminalstoindicatewhethertheswitchisinafloworno‐
flow state. When the switch is wired NC, Amber indicates no‐flow and Off indicates flow. Reversing the
polarity(NormallyOpen),AmberindicatesflowandOffindicatesno‐flow.
NormallyClosed(NC)
AmberLEDONforNo‐Flow
NormallyClosed(NC)
LEDOFFforFlow
NormallyOpen(NO)
AmberLEDONforFlow
NormallyOpen(NO)
LEDOFFforNo‐Flow

FlowSwitchLEDON
forNo‐Flow

FlowSwitchLEDOFF
forFlow

FlowSwitchLEDOFF
forFlow

FlowSwitchLEDON

forNo‐Flow
Note:TheLEDinsidetheflowswitchwillalways
beONforNo‐FlowandOFFfor Flow,regardlessofthepolarity
ofthe flow switch.In NCwiring,the switch’sLED will match the controller’sLED.InNO wiring, theswitch’s
LEDwillbeoppositeofthecontroller’sLED.
