Three Point Speed Relay
Three Point Speed Relay



  • Three speed relays in one compact unit
  • Wide operating frequency
  • Engine RPM meter output




The 3ST provides three independent speed relays in one compact unit. It is designed to work with an engine mounted speed transducer, typically a magnetic pickup. The 3ST measures the transducer signal frequency (which is proportional to engine speed) and compares this with three user-set trip levels. The three non-latching relays then activate or deactivate as appropriate.



Each relay circuit has a front facia LED that lights when the relay is energised. On standard units, the relay functions are designated S1 (crank), S2 (underspeed) and S3 (overspeed): all three relays are energised, and all LEDs lit, when the engine is running at normal speed - see diagram overleaf for relay/LED operation.


Nominal speed calibration and relay trip levels are set via four multi-turn potentiometers - see ‘calibration’ overleaf. The 3ST also features a ‘meter’ output, which may be used for calibration and/or engine speed indication.


The 3ST has a robust, polycarbonate case, designed for DIN rail or surface mounting. Electrical connection is by 12 screw terminals, suitable for stripped panel wires or narrow blade crimps.





The 3ST is designed for use with engines, generators, pumps or any moving machinery where speed related control that requires accurate and repeatable.




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