Category
Duct Smoke Detector for AHUs
Stop smoke spreading through ductwork: shut down AHUs as soon as smoke is detected.
A duct smoke detector samples air from inside a duct and shuts down the air handling unit, or closes fire dampers, as soon as it detects smoke. The Produal KRM-X-2 uses a scattered-light optical sensor with a 0.16 m sampling tube, in standard relay, Modbus RTU and BACnet MS/TP versions, stopping smoke spreading through ductwork.
1 Product · Duct Smoke Detector
Selection guide
Duct Smoke Detector for AHUs Guide
How a duct smoke detector works
Air is drawn from the duct through a sampling tube into an optical chamber, where a scattered-light (optical) sensor detects smoke particles crossing an alarm threshold. The KRM-X-2 tracks that threshold over time, extending its service life as dust slowly builds up, and its contamination relay warns you when cleaning is needed, before the sensor gets dirty enough to false-alarm.
How to choose a duct smoke detector
- Output: the standard KRM-X-2-0,16 gives one changeover alarm relay (8 A, 250 VAC/DC) and a normally-closed contamination relay, for direct wiring to a fan starter or fire panel.
- Protocol: choose the KRM-X-2-MOD for Modbus RTU over RS-485, or the KRM-X-2-BAC for BACnet MS/TP, when the detector needs to report status to the BMS rather than just trip a relay.
- Supply and environment: all versions run on 24 VAC/DC and operate from -20 to +50 °C, in an IP65 housing suited to plant rooms and duct-mounted locations.
- Testing: the sensor supports a test spray without opening the cover, so routine checks don't need access to live ductwork.
- Approval: the KRM-X-2 carries VdS approval to DIN EN 54-27, relevant where a fire certifier specifies it.
For other AHU and BMS sensors, see HVAC & BMS sensors.
FAQ
Common questions
How does a duct smoke detector work?
It draws a small air sample from the duct through a sampling tube into an optical chamber, where a scattered-light sensor detects smoke particles. Once the signal crosses the alarm threshold, an alarm relay trips, which is normally wired to stop the AHU fan or close a fire damper.
What does the contamination relay on a duct smoke detector do?
It's a separate normally-closed relay that signals when the optical chamber has picked up enough dust or dirt to need cleaning, before that build-up is enough to cause a false alarm. It gives maintenance staff a warning ahead of any nuisance trips.
Can a duct smoke detector report to a BACnet or Modbus BMS?
Yes. The Produal KRM-X-2-MOD adds a Modbus RTU RS-485 interface and the KRM-X-2-BAC adds BACnet MS/TP, alongside the standard alarm and contamination relays, so status and alarms reach the BMS as well as the fan starter.
Where should a duct smoke detector be installed?
In the supply or return duct of an AHU serving more than one room, ahead of any branch to individual spaces, so a fire in one area is caught before smoke spreads through the shared ductwork. It works alongside, not instead of, point smoke detectors inside rooms.
What is the alarm relay rating on the Produal duct smoke detector?
One changeover contact rated 8 A at 250 VAC or VDC, enough to interrupt most fan starter or damper actuator control circuits directly, or to signal a fire alarm panel. The detector itself is powered separately, from a 24 VAC/DC supply.
Need help?
Can't find what you need?
Our team helps you select the right duct smoke detector products for your application. Request a quote or discuss your requirements.
Expert product guidance
Tailored selection of duct smoke detector instruments
Custom solutions
Instruments customized for your specific industrial setup
Trusted global brands
Full warranty and official documentation support