Switching unit

Limit switch with loop power supply


from €122.24
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    • 2 relays for setpoint monitoring (with changeover contacts)

    • LC display for alarm setpoints and bargraph

    • Front end setup using 3 push buttons

    Specs at a glance

    Limit function 2 relays
    Input Current, voltage
    Transmitter power supply Optional
    Time delay 0 to 99 s
    Product / VersionPrice / pcs. in EUROrder code
    Loop Power SupplyPower Supply1 to 34 to 1011+
    without196-250VAC138.91129.19122.24 RTA421-A11A
    98-126VAC138.91129.19122.24 RTA421-A21A
    20-250VDC/AC170.28158.36149.85 RTA421-A31A
    with196-250VAC170.28158.36149.85 RTA421-A12A
    98-126VAC170.28158.36149.85 RTA421-A22A
    20-250VDC/AC201.65187.53177.45 RTA421-A32A


    Product / VersionPrice / pcs. in EUROrder code
    Housing Field, R4 182x180x165, 5xM20, PC Protection housing Minitec. Synthetic housing with transparent cover. Protection IP66. 4x22.5mm / 2x45mm. Usage: FTL825.74.96 52010132

    Prices valid until 31.12.2020 in EUR per unit (not including shipping and applicable sales tax). See
    Endress+Hauser Terms and Conditions

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  • Application

    The RTA421 contactor is used to monitor and protect industrial processes. The unit has two independent relays which offers a number of cost-effective applications such as pump control in wastewater technology and level monitoring in containers. The quick setup feature allows for changes of limit values and the unit is particularly suited for use in plant and engineering applications as well as switching cabinets.


    The instrument evaluates current signals (0/4 to 20 mA) and voltage signals (0/2 to 10 V) and switches upon going over or under the predefined limit values. Both limit values are shown on the display. The bargraph displays the connected signal in percentages. A 2-digit bar code is available as an option to prevent entry of limit value.

    Application Example

    Limit switch - application example
  • Technical data


    Current: 0/4 to 20 mA, 20 to 0/4 mA, max. 150 mA, Ri: 5 Ω;

    Voltage: 0/2 to 10 V, 10 to 0/2 V, max. 50 V, Ri: 1 MΩ;

    Integration time: 4/s

    Accuracy 0.5 % FSD
    Temperature drift 0.02 % / K ambient temperature
    Output (option) 24 V ± 20 %, 30 mA
    Output (Relays) 2, binary, switches when alarm setpoint is reached, 1 potential free changeover contact per relay,
    Contact load ≤ 250 V AC, 8 A, 30 V DC, 5 A
    Mechanical construction
    Housing (W × H × D) 45 × 110 × 112 mm (1.77" × 4.33" × 4.41")
    Weight Approx. 150 g (5.29 oz)
    Materials Housing Plastic PC/ABS, UL 940
    Electrical connection Keyed, plug on screw terminals, core sizes flexible to 1.5 mm²
    User interface

    Operation, 1 × green (2 mm/0.08")

    Fault condition, 1 × red (2 mm/0.08")

    Alarm setpoint, 2 × yellow (2 mm/0.08")

    LC display

    Numeric display 4 × 7 segment (6 mm/0.24”);

    alarm setpoint condition 2 × channel number, 4 × 1 segment;

    bargraph 10 x 1 segment

    Display range 2 × 0 to 99 %
    Operation 3 pushbutton operation
    Power supply
    Supply voltage

    196 to 250 V AC, 50/60 Hz

    98 to 126 V AC, 50/60 Hz

    20 to 250 V DC/AC, 50/60 Hz

    Power consumption Max. 9 VA

    Dimensions (in mm)

    Dimensions of a contactor RTA421

    Installation according to instruction manual

    Electrical connection

    Electrical connection of a contactor RTA421

    a) Power supply

    b) Relays (internal circuit)

    c) Relay 1

    d) Relay 2

    e) Contact condition shown in alarm or power out

    f) Current input

    g) Current input with loop power supply (option)

    h) Voltage input

  • More documents for RTA421