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INTRODUCTION/TABLEOFCONTENTS StepOne
Offered in liquid and gas sensor types, the general purpose flow switch provides reliable low or no‐flow
detectionofrelativelyclean,non‐coatingmediawithone1Arelayoutput.Liquidexamplesincluedwaterand
aceticacid.Availablein Polypropylene‐PPS or PVDF, the short flow sensor isusedinpipeorductingfrom½”
to1‐1/2”,andthelongflowsensorisusedin2”andup.Theflowswitchsetpointmaybeadjustedfrom0.,04
to3fps in liquids or 1to90 fps in gases asalow‐flow alarm.The flow sensor isbestappliedin applications
withrelativelyconstanttemperatures.
NewFeatures
RuggedPolypropylene‐PPSorPVDFsensorforcorrosiveliquidsandgasses.
AdjustablesetpointwithLEDforfloworno‐flowstatusindication.
60VArelayselectableNOorNCviapowersupplywiringpolarity
SolidStatesensorisnotdamagedbyover‐rangingflowvelocities.
TableofContents
Specifications:........................................................................................................................................................4
MakeaFail‐SafeSystem:...........................................................................................................................4
Dimensions: .........................................................................................................................................................5
Configurations:...........................................................................................................................................5
SafetyPrecautions:................................................................................................................................................6
Introduction: .........................................................................................................................................................7
Technology:................................................................................................................................................7
InitializingSequenceforFST‐200Series:...................................................................................................7
SetPoints:..................................................................................................................................................7
Installation: .........................................................................................................................................................8
Wiring: .........................................................................................................................................................9
SupplyVoltage:..........................................................................................................................................9
SignalOutput:............................................................................................................................................9
WiringtoanOmegaEngineeringController:.............................................................................................9
WiringtheRelayOutput:..........................................................................................................................10
WiringasaP‐ChannelorN‐ChannelOutput:..........................................................................................11
Calibration: .......................................................................................................................................................12
SetPoint:..................................................................................................................................................12
Maintenance:.......................................................................................................................................................13
CleaningProcedure:..................................................................................................................................13
TestingtheSensor(FST‐200SeriesOnly):...............................................................................................13
TestingtheSensor(FST‐300SeriesOnly):...............................................................................................14
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SPECIFICATIONS StepTwo
Setpointrange: FST‐200:.04to3fps(.012to.91mps)
FST‐300:1to.90fps(.3to27mps)
Factorysetpoint: FST‐200:.2fps(.06mps)
FST‐300:10fps(3mps)
Repeatability: ±.5%ofsetpoint@fixedtemp.
Responsetime: 1‐10seconds
Setpointadjust.: Potentiometer
LEDindication: FlowStatus
Viscosityrange: 1‐200centipoise(FST‐200seriesonly)
SupplyVoltage: 14‐36VDC
Consumption: 70mAmaximum
Contacttype: (1)SPSTrelay
Contactrating: 60VA,1Amax
Contactoutput: SelectableNO/NC
Processtemp.: F:32°to140°
C:0°to60°
Electronicstemp. F:‐40°to140°
C:‐40°to60°
Pressure: 150psi(10bar)@25°C.,derated@1.667
psi(.113bar)per°C.Above25°C.
Sensorrating: NEMA4X(IP65)
SensorMaterial: FST‐211/‐221/‐321/‐323: PP‐PPS
FST‐212/‐222/‐322/‐324: PVDF
Cablejacketmat.: FST‐211/‐221/‐321/‐323: PP
FST‐212/‐222/‐322/‐324: PFA
Cabletype: 4‐conductor,#22AWG(shielded)
Cablelength: 10’(3m)
Processmount: 3/4"NPT(3/4”G/Rp)
Mount.Gasket: FKM(Gversiononly)
Classification: Generalpurpose
CEcompliance: EN61326EMC
EN61010‐1safety
Make a Fail‐Safe System:Design a fail‐safe system that accommodates the possibility of switch and/or
power failure.OMEGA ENGINEERING recommends the use of redundant backup systems and alarms in
additionto the primarysystem.Addingaredundantalarm switch tothesystemis a costeffectivemeans
topreventcostlyrun‐dryissues.
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DIMENSIONS StepThree
LongSensor(FST‐221/‐222/‐323/‐324)
ShortSensor(FST‐211/‐212/‐321/‐322)
Configurations(LiquidFlowSwitches):
Part
Number
Length
Material
(body)
Material
(cable)
Thread
(insidexoutside)
FST‐211‐SPST Short(3”) PP‐PPS Polypropylene ¾”NPTx¾”NPT
FST‐212‐SPST Short(3”) PVDF PFA ¾”NPTx¾”NPT
FST‐221‐SPST Long(4.5”) PP‐PPS Polypropylene ¾”NPTx¾”NPT
FST‐222‐SPST Long(4.5”) PVDF PFA ¾”NPTx¾”NPT
Configurations(GasFlowSwitches):
Part
Number
Length
Material
(body)
Material
(cable)
Thread
(insidexoutside)
FST‐321‐SPST Short(3”) PP‐PPS Polypropylene ¾”NPTx¾”NPT
FST‐322‐SPST Short(3”) PVDF PFA ¾”NPTx¾”NPT
FST‐323‐SPST Long(4.5”) PP‐PPS Polypropylene ¾”NPTx¾”NPT
FST‐324‐SPST Long(4.5”) PVDF PFA ¾”NPTx¾”NPT
Note:Theaboveproductsshipwithastandard10’cablelength.Adding“‐25”totheendofthepartnumber
indicatesthattheproducthasa25’cablelength(ex.FST‐211‐SPST‐25).Adding“‐50”totheendofthepart
numberindicatesthattheproducthasa50’cablelength(ex.FST‐321‐SP
ST‐50).
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SAFETYPRECAUTIONS StepFour
Aboutthis Manual:PLEASE READTHE ENTIRE MANUALPRIOR TO INSTALLING OR USING THIS PRODUCT.
ThismanualincludesinformationonallmodelsofOmegaEngineeringThermalDispersionFlowSwitches:FST‐
200and FST‐300series.Pleasereferto thepartnumber locatedontheswitch labeltoverifythe exactmodel
whichyouhavepurchased.
User’s Responsibility for safety:Omega Engineering manufactures a wide range of flow switches and
technologies, while each of these sensors is designed to operate in a wide variety of applications; it is the
user’sresponsibilitytoselectasensormodelthatisappropriatefortheapplication,installitproperly,perform
tests of the installed system, and maintain all components. The failure to do so could result in property
damageorseriousinjury.
Proper Installation and Handling:Because this is an eclectically operated device, only properly trained
staffshouldinstall and/or repair this product. Useapropersealantwithallinstallations. Note: Always install
the 3/4” FKM gasket with all versions of Flow switches with metric threads. The G threaded version will not
seal unless the gasket is properly installed. Never over tighten the sensor within the fitting, beyond a
maximumof80inch‐poundstorque.Alwayscheckforleakspriortosystemstart‐up.
Material Compatibility:The FST‐200 and FST‐300 series sensors are available in two different wetted
materials. Models FST‐211/‐221/‐321/‐323 are made of Polypropylene (PP) with PPS tips. Models FST‐212/‐
222/‐322/‐324 are made of Polyvinylidene Fluoride (PVDF). Make sure that the model you have selected is
compatible with the application liquid. To determine the chemical compatibility between the sensor and its
applicationliquids,refertoanindustryreferencesuchastheCompassCorrosion.
WiringandElectrical:Thesupplyvoltageusedtopowerthesensorshouldneverexceedamaximumof36
voltsDC. Electricalwiringof thesensorshouldbeperformedinaccordancewith allapplicablenational, state,
andlocalcodes.
Flammable,ExplosiveandHazardousApplications:DONOTUSETHEFST‐200orFST‐300SERIESGENERAL
PURPOSEFLOWSWITCHESINHAZAROUSLOCATIONS.
Warning
Theratingfortherelayis60VA,1Ampmax.
Omega Engineering’s Thermal Dispersion flow switches are not recommendable for use with
electricallycharged application liquids.Formostreliable operation, theliquidbeingmeasuredmay
needtobeelectricallygrounded.
Thesensingtipofthesensormustalwaysbesubmersedintheliquidandneverexposedtoair.
Theliquidtemperaturemustremainconstantandnotchangethroughouttheprocess.
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INTRODUCTION StepFive
Technology:TheThermal Dispersion flow switches measure liquidorgas temperaturetodeterminechanges
in flow velocity.As fluid flows across the sensing tips, the temperature is reduced proportionately as a
functionoftheflowrate.Whenatemperatureorvelocityshiftreachestheuserdefinedsetpoint,theswitch
changesstateindicatingtheappropriateflowcondition(flowofno‐flow).
OMEGAENGINEERING’s sophisticated electronicsconvert the temperatureshift into asignal which indicates
whethera flow orno‐flowconditionoccurs.Dependingonhow the sensor iswired,thissignalmay be wired
fornormallyopenornormallyclosedcircuits.
OMEGAENGINEERING’s ThermalDispersionflowswitches havenomovingparts toclogorfoul, makingthem
suitablefor averityofapplications,including non‐coatingandnon‐scalingliquids.The FST‐200 seriesdirectly
measuremassflowand can operate over board rangeofliquidsfrom0.4to 1.2 specific gravity and 1to300
cp.
InitializingSequenceforFST‐200 ser
ies:Whenthe flowswitchis powered up whilesubmersed, the FST‐200
series will immediately indicate flow before switching to its correct state.A time delay may be used to
eliminatetheinitializationsequence.OmegaEngineering’sthermaldispersion relaycontrollersfeaturea0to
60secondti
medelayforyourconvenience.
SetPoints:TheFST‐200seriesliquidflowswitchsetpointisfactorycalibratedto0.2fpsandtheFST‐300gas
flowswitcharesetto10fps.Toconvertfeet/sectoGPM,pleaserefertothechartbelow.
FST‐200Series
FlowRatevs.Velocity
(gpmvs.fps)
FST‐300Series
FlowRatevs.Velocity
(scfmvs.fps)
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Installation StepSix
The FST‐200 series flow switch must always be in contact with
the liquid being measured. The FST‐300 series flow switch must
never be submersed in liquid.Both flow switches featurea 3/4”
NPTthreads which will allowit to be usedwithvarious types of
fittings.Besuretochecktheinsertiondepthofth
eflowswitchin
thefittingafteritisinstalled.Seethediagramtotherightforthe
recommendedinsertiondepth.
Thetwotipofthesensoraretobeperpendiculartothe
flow(asseentotheright).Nevermountthetipswith
oneinfromtoftheothe
r.
When using any type of fitting, the orientation as well as the
insertiondepth of theflow switch in the pipe is critical. See the
diagramtotherightfortherecommendedorientation.
Warning
Theflowswitchtipshaveathinplasticwallwhichmaybedamagedifdroppedorinstalledimproperly.
The FST‐200 series flow switch is designed for use in liquid. For best results, avoid installing the FST‐200
serieswherebubblesarepresentorwherethetipsoftheswitchmaybeoutoftheliquid.
TheFST‐300 series flow switchis designed for usin gas applications. Forbest results, avoid installingthe
FST‐300serieswhereitmaybesubmersedinliquid.
Always install the FKM gasket with all versions of the model FST‐212/‐222/‐322/‐324. The G threaded
versionwillnotsealunlessthegasketisproperlyinstalled.
The two temperature probes (tips) must always be perpendicular to the flow (see the flow at the same
time).
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WIRING StepSeven
Supply Voltage:The supply voltage to the Thermal Dispersion flow switch shouldnever exceed a minimum
outputof14VDCormaximumoutputof36VDC.
Required Cable Length:Determine the length of the cable required between the Thermal Dispersion flow
switch and its point of termination. Allow enough slack to ensure the easy installation, removal and/or
maintenance of the sensor. The cable length may be extended up to a maximum of 1000 ft, using a well‐
insulated14to20gaugeshieldedfourconductorcable.
WireStripping:Usinga10gaugewirestripper,carefullyremovetheouterlayerofinsulationfromthelast1‐
1/4” of the sensor’s cable. Unwrap and discard the exposedfoil shield fromaround the signal wires, leaving
the drain wire attached if desired. With a 20 gauge wire stripper, remove the last 1/4” of the colored
insulationfromthesignalwires.
SignalOutput(RelaySwitching):
Allows the sensor to switch a small load on or off
NormallyOpenWiring:
directly, using an internal relay rated below 60 VA.
TheNO/NC status issetbythe polarity ofthevoltage
feedingtheredandblackwires.Thegreenwireisthe
commonfortherelayandthewhitewireistheNOor
NC,dependingonthepolarityofredandblack.
WiringtoanOmegaEngineeringController:
LVCN‐131/‐141SeriesController
FLCN‐100SeriesController
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WIRING StepSeven
WiringtheRelayOutput:TheFlow switch relay output can be wired as adrycontacttoaVDCorVACpower
source. The flow switch does require 14‐36 VDC power to operate the sensor and switch the relay. All
installationsbelowidentifyadryswitchstateasthenormalpositionoftherelay.
SwitchingaNormallyOpenDCLoad(OpenduringFlow,ClosedduringNo‐Flow):
The Red wire connects to Positive (+) of the power
supplyandtheBlackwireconnectstoNegative( ‐).The
LOAD can be attached to either the Green or White
wires.Completeth
ecircuitbyconnectingtheGreento
(+) VDC power or White to (‐) VDC power (see
illustrationtotheright).
SwitchingaNormallyClosedDCLoad(ClosedduringFlow,OpenduringNo‐Flow):
The Black wire connects to positive (+) of the power
supplyandtheRedwireconnectstoNegative(‐).Th
e
Load can be attached to either the Green or White
wires. Complete the circuit by connecting the Green
to (+) VDC power or White to (‐) VDC power (see
illustrationtotheright).
SwitchingaNormallyOpenACLoad(OpenduringFlow,ClosedduringNo‐Flow):
TheRed wire connects toPositive (+) of theDC power
supplyandtheBlackwire connectstoNegative(‐).The
LOADcanbeattachedtotheGreenwireandtheHotof
the VAC power. Connect the white to the Neutral of
the VAC power (see illustration to the right).Low
voltageVACislessthan36VAC.
SwitchingaNormallyClosedACLoad(ClosedduringFlow,OpenduringNo‐Flow):
The Black wire connects to Positive (+) of the DC
powersupply and theRed wire connectsto Negative
(‐).The LOAD canbeatt
achedto the Green wireand
theHot of the VAC power. Connectthe White tothe
Neutral of the VAC power (see illustration to the
right).LowvoltageVACislessthan36VAC.
ForallSensorWiringdiagramsabove:
SensorPower:RedandBlackWires(36VDCMax.)
Rela
yRating: GreenandWhiteWires(60VA,1AMax.)
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WIRING StepSeven
WiringasaP‐ChannelorN‐Channeloutput:TheFlowswitchcanbesubstitutedforeither aP‐Channel(PNP,
Sourcing)outputorN‐Channel(NPN,sinking)output.
NormallyOpenDCLoadasaP‐ChannelOutput(OpenduringFlow,ClosedduringNo‐Flow):
To wire as a NO P‐Channel o
utput follow the
directions below. The Red Wire connects to Positive
(+) of the power supply and the Black wire connects
toNegative(‐).TheGreenwireis jumping to the Red
wire while theWhite wire is connected tothe LOAD.
JumpertheLOADbacktotheNegative(‐)tocomplete
thecircui
t.
NormallyClosedDCLoadasaP‐ChannelOutput(ClosedduringFlow,OpenduringNo‐Flow):
To wire as a NC P‐Channel output, follow the
directionsbelow. The Blackwireconnects to Positive
(+)of the power supply andtheRedwire connects to
Negative (‐). The Green wire is jumping to the Black
wire while theWhite wire is connected tothe LOAD.
JumpertheLOADbacktotheNegative(‐)tocomplete
thecircuit.
NormallyOpenDCLoadasaN‐ChannelOutput(OpenduringFlow,ClosedduringNo‐Flow):
To wire as a NO N‐Channel output, follow the
directions below. The Red wire connects to Positive
(+) of the power supply and the Black wire connects
toNegative( ‐).ThewhitewireisjumpingtotheBlack
wirewhile the Greenwire is connectedto the LOAD.
JumpertheLOADbacktothePositive(+)tocomplete
thecircuit.
NormallyClosedDCLoadasaN‐ChannelOutput(ClosedduringFlow,OpenduringNo‐Flow):
To wire as a NC N‐Channel output, follow the
directionsbelow. The Blackwireconnects to Positive
(+) of the directions below. The Black Wire connects
toNegative (‐). The white wire is ju
mping to the Red
wire while theWhite wire is connected tothe LOAD.
JumpertheLOADbacktoPositive(+)tocompletethe
circuit.
ForallSensorWiringdiagramsabove:
SensorPower:RedandBlackWires(36VDCMa
x.)
RelayRating: GreenandWhiteWires(60VA,1AMax.)
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CALIBRATION StepEight
Set Point:If the preset factory calibration is not adequate for your application, follow the calibration steps
listedbelow.
Note: The switch’s internal LED will be on when the switch detects no‐flow and will off when the switch
detects flow, regardless of the polarity of the Red and Black wires.Reversing the Red and Black wires will
reversethepolarityoftherelayswitch,butnottheinternalLED.
1. Install the fitting and flow switch as described in the Installation section of this manual. Turn the flow
switch and controller power on and adjust the flow rate to the application setting. If the medium to be
sensed is likely to be subject to any temperature variation, the flow switch should be set as the highest
normaltemperaturelikelytobeencountered.
2. Locate the potentiometer knob at the top of the flow switch. The red LED is visible through the
potentiometer.Theadj
ustmentisasingleturn270°potentiometer.Theinitialresponsetimeoftheflow
switchafter adjustment is 1 to10seconds.Adjustthepotentiometer in slow increments and wait for the
response.
a. LEDisON‐IftheLEDison,slowlyadjustthepotentiometercounter‐clockwise,withasmallflathead
screwdriveruntiltheLEDturnoff.
b. LED is OFF‐
If the LED is off, slowly adjust the potentiometer clockwise. with a small flat head
screwdriveruntilthelightturnson.
3. AdjustthepotentiometerbackandforthwheretheLEDisswitching,eventuallysettlingforwheretheLED
isOFF(thisisthelowflowstatefortheswitch).
a. Iftheflowisincreased,theLEDwillremainOFFindicatingaflowcondition
b. Iftheflowisdecrease,theLEDwillturnONindicatingano‐flowcondition.
4. Verifythatthenewcalibrationiscorrectbyloweringthesystemflowratebelowthesetpointandcheckto
seethattheredLEDturnson.Then increasetheflowrateabovethe setpointand verifythatthe redLED
turnsoffaccordingly.
FST‐200SeriesFlowSwitch
(LiquidOnly)
Potentiometer
Location
FST‐300FlowSwitch
(GasOnly)
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MAINTENANCE StepNine
General:TheFlow switch requires no periodic maintenance exceptto cleanoffany deposits or scaling from
the sensor tip as necessary. It is the responsibility of the user to determine the appropriate maintenance
schedule,basedonthespecificcharacteristicsoftheapplicationliquids.
CleaningProcedure:
1. Power: Make sure that all power to the sensor, controller and/or power supply is completely
disconnected.
2. Sensor Removal: Make sure that the flow is off and the pressure is down prior to removing the Flow
switch.Carefully, remove the sensor from the installation. Replace the sensor with a 3/4” NPT plug to
insure that the liquid doe
s not leak out during this procedure. Do not re‐install the Flow switch if the
threadsaredamaged.
3. Cleaning the sensor: Use a soft bristle brush and mild detergent, carefully wash the Thermal Dispersion
flowswitch.Donotuseharsh abrasivessuchassteelwoolorsandpaper,whichmig
htdamagethesurface
sensor.Do notuseincompatiblesolvents whichmaydamage thesurfacesensor.Do notuseincompatible
solventswhichmaydamagethesensor’sPP/RytonorPVDFplasticbody.
4. Sensor Installation: Follow the appropriate steps of installation as outlined in the installation section of
thismanual.
TestingtheSensor(FST‐200SeriesOnly):
1. Immersingtheswitch:Placetheswitchinacupofwater.Makesurethetipsaresubmersedinthewater.
2. Power: Turn on power to the swit ch with Red to (+) and Black to (‐).You can reverse the polarity if
desired.
3. No‐Flow/Flow Test: With the switch setting still in the cup, wait until the Red LED turns ON (no‐flow
condition).
a. SwirltheswitchinthecupandwaituntiltheRedLEDturnOFF(flowcondition).
b. Stop swirling the sensor and let it restinthecupwaitingfor the Red LEDtoturnONagain (no‐flow
condition).
c. Repeattheabovetwosteps.
4. Relay Test: Connectamultimeter(settoread Ohms) to the White andGreenWires.Performthe above
No‐Flow/Flowtestwiththemultimeterconnecttoobservetheactuationoftherelay.
a. With Red to (+) and Black to (‐), the multimeterwill read a small resistance during no‐flow (closed
relay)andOLduringaflowcondition(openrelay).
b. Reverse Polarity [Red to (‐) and Black to (+)] to see the multimeter read OL during a no‐flow state
(openrelay)andasmallresistanceduringaflowcondition(closedrelay).
TheNo‐Flow/Flowtest determines if theswitchiscapableofsensingthechangesbetween no‐flow and flow.
TheRelaytestdeterminestheabilityofthe relaytoswitch betweenano‐flow andflowcondition.Thisisthe
basictesttodeterminefunctionalityofthesensor.
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MAINTENANCE StepNine
TestingtheSensor(FST‐300SeriesOnly):
1. Creating a No‐FlowTest Point: The purpose ofthis step is tocreate a no‐flow state for thesensor tobe
tested against.Since this is a low flow switch, even a buildings HVAC system can create a flow that the
sensorcanread.
a. Placetheswitchonatableandplaceanemptycupoverthesensingtips.
b. Thecupwillactlikeashieldtoprotectthesensorfromairflow.
2. Power: Turn on power to the swit ch with Red to (+) and Black to (‐).You can reverse the polarity if
desired.
3. No‐Flow/Flow Test: With the switchsettingstill under the cup, waituntiltheRedLED turns ON (no‐flow
condition).
a. Remove the cup and move the sensor in air and observe when the Red LED turn OFF (flow
condition).
b. Place the sensoron the tableandplace the cupoverthe sensor and letit rest waiting forthe
RedLEDtoturnONagain(no‐flowcondition).
c. Repeattheabovetwosteps.
4. Relay Test: Connectamultimeter(settoread Ohms) to the White andGreenWires.Performthe above
No‐Flow/Flowtestwiththemultimeterconnecttoobservetheactuationoftherelay.
a. With Red to (+) and Black to (‐), the multimeter will read a small resistance during no‐flow
(closedrelay)andOLduringaflowcondition(openrelay).
b. Reverse Polarity [Red to (‐) and Black to (+)] to see the multimeter read OL during a no‐flow
state(openrelay)andasmallresistanceduringaflowcondition(closedrelay).
TheNo‐Flow/Flowtest determines if theswitchiscapableofsensingthechangesbetween no‐flow and flow.
TheRelaytestdeterminestheabilityofthe relaytoswitch betweenano‐flow andflowcondition.Thisisthe
basictesttodeterminefunctionalityofthesensor.
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