Two-rod capacitive probe for continuous level measurement in liquids

Capacitive probe for level measurement in liquids

Liquicap T FMI21

from €323,-
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    • No calibration needed

    • Corrosion resistant materials (carbon fiber, stainless steel)

    • Safe operation – regardless of tank geometry

    Specs at a glance

    Function Continuous level measurement
    Product Conductive liquids as of 30 μS/cm

    Probe length

    150 to 2500 mm (6 to 98")

    Process pressure

    –1 to +10 bar (–14.5 to 145 psi)

    Product temperature –40 to +100 °C (–40 to +212 °F)
    Viscosity Max. 2000 cSt
    Product / VersionPrice / pcs. in EUROrder code
    ApprovalElectronics; OutputProbe Length; Material1 to 34 to 1011+
    Non-hazardous areaFEI20; 4-20mA..... mm L; PP >316L367,-341,-323,- FMI21-A1A1B1
    FEI20; 4-20mA + display..... mm L; PP >316L408,-379,-359,- FMI21-A1A1C1
    FEI20; 4-20mA..... mm L; PP >carbon fiber (<1000mm)394,-367,-347,- FMI21-A1B1B1
    FEI20; 4-20mA + display..... mm L; PP >carbon fiber (<1000mm)435,-405,-383,- FMI21-A1B1C1
    FEI20; 4-20mA..... mm L; PP >carbon fiber (>1000mm)422,-392,-371,- FMI21-A1C1B1
    FEI20; 4-20mA + display..... mm L; PP >carbon fiber (>1000mm)463,-430,-407,- FMI21-A1C1C1
    Non-hazardous area, WHGFEI20; 4-20mA..... mm L; PP >316L388,-361,-342,- FMI21-B1A1B1
    FEI20; 4-20mA + display..... mm L; PP >316L429,-399,-378,- FMI21-B1A1C1
    FEI20; 4-20mA..... mm L; PP >carbon fiber (<1000mm)416,-387,-366,- FMI21-B1B1B1
    FEI20; 4-20mA + display..... mm L; PP >carbon fiber (<1000mm)457,-425,-402,- FMI21-B1B1C1
    FEI20; 4-20mA..... mm L; PP >carbon fiber (>1000mm)444,-413,-390,- FMI21-B1C1B1
    FEI20; 4-20mA + display..... mm L; PP >carbon fiber (>1000mm)485,-451,-426,- FMI21-B1C1C1


    Product / VersionPrice / pcs. in EUROrder code
    Mounting nut G1-1/2 Hexagon, SW60. Usage: Liquipoint T, Liquicap T, Prosonic M FMU40, Prosonic T FMU30, FMR10, FMR20.22,52 52014146
    Shorting kit FMI21 Usage: Liquicap T.7,69 52024300
    Digital display, holder 4-digit + 0-100% bargraph display. Holder. Please order high transparent cover separately. Usage: FMI21.110,02 52025604
    Cover F16 high, transparent, gasket Display cover, gasket EPDM. Usage: housing Polyester, FMI21, FMI51/FMI52, FMU30.30,92 52025605

    Prices valid until 30.09.2020 in EUR per unit (not including shipping and applicable sales tax). See
    Endress+Hauser Terms and Conditions
    The transaction will be settled with a VAT invoice in PLN after conversion according to the EUR exchange sell rate at the National Bank of Poland on the day of issuing the VAT invoice.

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  • Application

    The Liquicap T FMI21 sensor is used in conductive liquids for continuous level measurement. The Liquicap T FMI21 is particularly suited to small measuring tanks and works independently of the tank's shape or material (plastic, stainless steel, concrete...).

    It is resistant to aggressive liquids like acids or alkalis.


    The probe and medium form an electric capacitor. If the probe is in air, a certain low initial capacitance is measured. When the tank is filled, the capacitance increases the more the probe is covered. The electronic insert of the probe converts the capacitance measured to a 4 to 20 mA signal in proportion to the level.


    Application example

    capacitive probe for continuous level measurement - FMI21 - Application example

    The measuring system consists of:

    • The Liquicap T FMI21 capacitance probe (the probe rods should never be in contact with the tank) with
    • Electronic insert FEI20
    • Display and housing cover (optional)
    • A transmitter power supply unit RN221N, RMA42, RTA421, RIA45/RIA46 or RIA452


    a) Factory calibration

    b) Transmitter power supply

  • Technical Data

    Maximum viscosity 2000 cSt
    Measuring range 0 pF to 2000 pF
    Probe length 150 to 2500 mm (5.9 to 98.43”)
    Permitted span ∆C = 10 pF to 2000 pF
    Measuring frequency 250 kHz
    Input signal

    Probes covered => high capacitance

    Probes exposed => low capacitance

    Output (electronic insert FEI20 / 4 to 20 mA)
    Output signal 3.8 to 20.5 mA
    Switch-on current max. 20 mA (< 500 ms)
    Signal on alarm > 21 mA
    Power supply
    Connection voltage U = 10 to 30 V DC, Reverse polarity protection (integrated)
    Power consumption P < 0.7 W
    Current consumption I < 22 mA
    Cable entries M20×1.5 (screw connection)
    Performance characteristics (with installed electronic insert)
    Reference operating conditions Ambient temperature 23 °C (74 °F), atmospheric pressure, probe installation vertical from above
    Max. measured error ≤ 1 % of full scale value
    Repeatability 0.25 % of full scale value
    Start-up settling time < 2 s
    Influence of ambient temperature < 0.01 %/K (–40 to +70 °C/–40 to +158 °F) probe length 1 m
    Integration time 1 s

    In an installed state, recalibration is only necessary if:

    • the 0 % and 100 % value should be adjusted to suit customer specifications
    • after the probe rods have been shortened
    Operating conditions
    Ambient temperature –40 to +70 °C (–40 to +158°F)
    Storage temperature –40 to +80 °C (–40 to +176°F)
    Climate class Tropicalized as per DIN IEC 68 Part 2-38
    Degree of protection IP 66
    Shock resistance DIN EN 60068-2-27/IEC 68-2-27: 30g
    Vibration resistance DIN EN 60068-2-64/IEC 68-2-64: 20 to 2000 Hz, 1 (m/s²)² /Hz (with min. rod length 150 mm)
    EMC Interference emission to EN 61326, electrical equipment class B; Interference immunity to EN 61326, annex A (industrial)
    Conductivity of medium ≥30 µS/cm
    Process pressure –1 to +10 bar (–14.5 to 145 psi)
    Process temperature –40 to +100 °C (–40 to +212 °F)
    Lateral loading capacity 2 Nm
    Materials in contact with medium
    Probe rods Rod: 1.4404/316L; Optional: carbon fiber CFC; Sealing ring: EPDM; Insulation: PP; Spacer: PP
    Process connections G1½ A (PPS, DIN ISO 228/l)
    Seals Sealing ring for process connection G1½ A: Elastomer fiber asbestos-free (resistant to oils, solvents, steam, weak acids and alkalis)
    Green LED operational status (slow flashing), calibration status (fast flashing)
    Red LED for key enter validation (short flashing), alarm or warning (flashing)
    Display for measured value in % optional
    WHG approval Overspill protection to §19 WHG (Germany)

    Dimensions (in mm)

    capacitive probe for continuous level measurement - FMI21 - Dimensions

    a) Ground rod (uninsulated)

    b) Probe rod insulated

    L = Probe length


    Installation according to operation instructions

    Electrical connection

    capacitive probe for continuous level measurement - FMI21 - Electrical connection

    a) Endress+Hauser transmitter power supply

    b) Measurement display (optional)

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