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DSL-EM (Environmental Monitor)

DALI powered CO2, temperature, humidity, pressure and lux meter

The only DALI-powered CO2 sensor (Modbus also available)

Purpose An aim of BMS is to create a pleasant environment using minimum energy. Environmental quality measures include temperature, humidity, light level and CO2 level. Basic automation only maintains temperature (via thermostats) and sometimes light level (daylight harvesting), but significant discomfort and mental impairment of staff and visitors is just as likely if humidity and CO2 levels are not controlled. Tiredness and poor decision making occur at just 0.1% CO2 (just twice the level in fresh air) and in a poorly ventilated room the CO2 level can rise to this in minutes. Ventilation reduces CO2 level but wastes energy in the heating or cooling of outside air brought into the building. Demand Controlled Ventilation saves energy by controlling the amount of outside air brought into a building based on CO2, temperature and humidity levels in each room. Read about the need for CO2 control here.
The DSL Difference The DSL-EM allows real-time monitoring of all environmental quality parameters anywhere on the DALI lighting network with no need for additional power supplies or solar energy.

CO2 sensing is done by the most accurate non-dispersive infrared (NDIR) method at two wavelengths, which normally requires too much power to be practical on bus-powered devices. Low-power single-wavelength sensing using LEDs exists, but is inaccurate due to ageing of components and the need for regular re-calibration with fresh air. By harvesting energy, the DSL-EM can measure absolute CO2 level using the most accurate technique, twice a minute without taking any more power from the DALI bus than a proximity sensor.

Unlike other CO2 sensors, which are not compensated for air density (meteorological pressure, temperature and altitude), which can introduce large errors, the DSL-EM compensates for these effects. The dual-wavelength technique used eliminates the need to calibrate or “zero” on fresh air, or ever re-calibrate as the unit ages. Inferior CO2 sensors use “Automatic Baseline Correction” (ABC) which assumes that rooms experience fresh air (<400 ppm CO2) regularly. ABC is not required with this technology, making it appropriate for environments which may never experience fresh air (rooms in use 24 hours, factories, urban environments, agricultural facilities).

The unit has a strobe light and audible alarm to indicate CO2 levels above BMS-defined limits, a mute switch, and an optional backlit LCD display.

CO2 concentration Technology: Dual-channel Infrared Spectroscopy (3.9/4.2 um)
Reported resolution 20 ppm, Accuracy +/- 5% (20 ppm minimum)
Temperature Reported resolution 0.1 C
Accuracy +/- 0.4 C
Humidity Reported resolution 1%
Accuracy (0-80% RH) +/- 2% typical +/- 3% maximum
Light level
(Black body source)
Reported resolution 2 lux
Reported range 1 lux to 8000 lux
Accuracy 2% (above 100 lux)
Air pressure Reported resolution 0.1 mb
Accuracy 2 mb
DALI Bus Power (20 V DALI) Quiescent: 7 mA. Audible alarm sounding: 17 mA. CO2 Sampling: 24 mA for 1 second. Sensor cleaning: 37 mA for 1 minute each day. All non-quiescent operations are co-ordinated by BMS driver so that devices cannot draw high current simultaneously. For network planning, assume quiescent 7 mA and ensure that the DALI network would not be overloaded by an additional 30 mA for one minute to allow for sensor cleaning.
Electromagnetic Compatibility (EMC) EN 61326 (Electromagnetic Compatibility)
EN 55024 (Information Technology Immunity)
Isolation DALI Version: DALI is the only connection to the product.
RS485/Modbus Version: 16-24 V DC power isolated from RS485 by 2500 Vrms. 7kV bus ESD protection.
Environment Operating ambient temperature: 0-50 C
Humidity: non-condensing
Forced ventilation not required
RoHS, Conflict Minerals and WEEE compliant