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S281 Coolant Level Switch – Capacitance Type

Coolant Level Switch providing sink and/or source output. Fitted with DIN 72585 4 pin connector.

The S281 is an active device designed to give an alarm signal if coolant falls below, or rises above, a preset level. It can be specified with a delay to eliminate false alarms due to turbulence.

Containing a factory programmable microprocessor, the switch offers sink to ground or source voltage output. Its small footprint with limited intrusion into the tank means a reduced risk of damage and a wide range of customer specifiable options make it suitable for most applications.

For high accuracy the S281 is ideally mounted horizontally at the point where an alarm or control signal is required. However, the switch can be mounted vertically – contact Fozmula with your application requirements.

Data Sheet

Liquid types

Water based liquids, such as coolant or washer fluid, compatible with brass, PTFE, EPDM and FVMQ.

Electrical rating

Supply voltage: 9-36 VDC.
Supply current: 7 mA + source output.
Max. load current: 1.0 A (sink) or 20 mA (source).
Alarm delay time: 0 to 25 s rising or falling (factory set).
Connection: 4 way DIN 72 585 connector
Power up delay: 0 to 10 s (factory set).
Power up state: ‘In Liquid’ or ‘Out of Liquid’ (factory set).
Output type: Sink (open collector) and/or Source (supply voltage).
Output pin: Pin 3 (sink) or Pin 4 (source).
Output state: Sink Open / Closed in liquid (factory set).
Source On / Off in liquid (factory set).


See diagram below.

Optional accessories

C/K2: Mating connector kit to suit harness wire cross sectional area of 1 to 2.5 mm2, insulation diameter 1.2 to 3 mm: Ø1.60 to 2.15 mm. Comprising of: Crimp Terminals (x4), Cable seals (x4) and Connector assembly 4 way (x1).

Environmental Ratings

Ingress: IP67 (with mating connector fitted).
Max. pressure: 5.0 Bar (72 psi)
Temp. range: -40 °C to +125 °C
Weight: 70 g typical (dependent on thread size)
EMC: ISO13766-1:2018
Vibration (15.3 Grms): 3 orthogonal planes for 3 hours per plane
Testing performed in accordance with BSEN 60068-2-64:1993
Drop test: 1 m to concrete surface.


Body: Brass.
Probe: PTFE.
Terminals: Brass, Tin Plated.
Seals: EPDM & FVMQ.
Connector: PA66 30% Glass Filled Nylon.
Thread sealant: Vibra-Seal 516 (taper thread variants only).

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