True Duct Smoke Detector with Relay Output and Analogue Output, VSD 301

Duct Smoke Detectors VSD-series

The true duct smoke detector VSD 301 has been developed from a proven design using modern devices to provide effective and reliable detection of smoke in ventilation systems.

Detection of smoke for true duct smoke detector VSD 301 is achieved by monitoring a carefully controlled infrared beam (IR-detection, obscuration) within a perforated tube which is inserted into the ductwork. This method senses smoke directly within the duct, eliminating the problems associated with conventional detectors mounted in sampling boxes.

Circuitry incorporated in the design of the true duct smoke detector controls the infrared beam continuously. This ensures that the true duct smoke detector response will remain constant throughout operation of the system.

sensing probe for duct smoke detector VSD-series

External influences including background pollution, airborne dust and low level electrical interference frequently found in commercial and industrial applications,
a common source of problems with some other types of true duct smoke detectors, are selectively filtered by the electronics thereby providing the highest sensitivity to smoke combined with effective rejection of short term disturbances that would otherwise give a false alarm.


The true duct smoke detector is equipped with a reset botton outside the enclosure.

reset button for duct smoke detector VSD-series


The true duct smoke detectors features variable sensitivity and an advanced signal damping circuit which can be bypassed for testing purposes.

  • Outputs
  • - Relay SPDT 1A@24Vdc, 120 Vac
    - Analogue 2-10 Vdc

  • Relay output for closing fan/damper motor
  • Damped output or undamped output
  • The analogue output signal 2-10 Vdc can transmit
    smoke or service alarm (dirt level) to BEMS system
  • Manual reset or auto reset
  • Power supply 24 Vac/dc
  • Probe lenght 300 mm.
  • The true duct smoke detector is simple to clean and does not need to be removed from the duct work when cleaning is required.

  • pcb for duct smoke detector VSD-series

  • Analogue output status levels
  • < 2 Vdc = Sensor fault
    < 3-7 Vdc = Normal operation
    < 7-9 Vdc = Optics require cleaning
    > 9,5 Vdc = Smoke alarm


    compensation ovk for duct smoke detector VSD-series


Download datasheet

Technical data sheet True Duct Smoke Detector VSD 301.pdf


Download CE declaration of conformity

CE declaration of conformity True Duct Smoke Detector, VSD 301.pdf


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