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  • New item   Digital duct VOC sensor with LCD display | 4–20 mA, 0–10 V DC, Modbus RS485

    Digital duct VOC sensor with LCD display | 4–20 mA, 0–10 V DC, Modbus RS485

    Code: SKU#165270814946854031
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    Digital duct VOC sensor with LCD display that measures extract air pollution and shows the reading on site. It transmits the signal via 4–20 mA, 0–10 V DC or Modbus RS485 to a ventilation controller or BMS.

  • Product description

    Digital duct VOC sensor with LCD display, 4–20 mA, 0–10 V DC and Modbus RS485 outputs

    The digital duct VOC sensor measures the level of volatile organic compounds (VOC) in the air flowing through a duct, and its LCD display shows the reading on site. The probe is inserted into the extract air duct and shows the average air quality of the whole zone. It has three outputs – 4–20 mA, 0–10 V DC and Modbus RS485 – so it connects to a ventilation controller, a PLC or a BMS.

    ⚠ Measuring range, supply voltage and Modbus register map are not stated in this description – check them in the supplier datasheet delivered with the product before wiring.
    Key point:
    A VOC sensor lets you ventilate according to actual air pollution instead of a timer. When odours, cleaning agents, paints or emissions from furniture increase, the signal rises and the controller increases the airflow. When the air is clean, the fans slow down and heating and electrical energy is saved. Three output types let you use the same sensor in a simple analogue system and in a networked one.
    Measures
    VOC (air quality)
    Analogue outputs
    4–20 mA / 0–10 V DC
    Digital interface
    Modbus RS485
    Mounting
    Duct, with LCD

    Operating principle

    VOC is a collective name for many volatile organic substances: solvents, odours, cleaning agents and compounds released by human activity. Sensors of this type typically use a semiconductor (metal oxide) sensing element whose resistance changes when oxidisable gases reach its surface. The electronics convert this change into an air quality value.

    The result is provided in three ways: a 4–20 mA current signal (robust over long cables and against interference), a 0–10 V DC voltage signal (suits most ventilation controllers and frequency inverters) and Modbus RS485 (digital communication when several sensors share one bus).

    A VOC sensor does not distinguish individual substances and does not measure CO₂ directly – it shows the overall trend of air pollution. That is exactly what demand-controlled ventilation (DCV) needs.

    Why use a VOC sensor?
    It reacts to what people perceive as stuffy or smelly air, even when the CO₂ level is still normal: after cleaning, renovation, cooking or in rooms with new furniture. Ventilation is boosted only when it is really needed.

    Technical specifications

    Product type Digital duct VOC sensor with LCD display
    Measured quantity Volatile organic compounds (VOC), overall air quality value
    Mounting In the duct, probe inserted into the duct
    Analogue current output 4–20 mA
    Analogue voltage output 0–10 V DC
    Digital interface RS485, Modbus protocol
    Display LCD, reading visible on site
    Measuring range, supply, Modbus registers According to supplier datasheet

    Main functions

    • 4–20 mA output – stable signal over long lines, a broken wire is easy to detect (0 mA).
    • 0–10 V DC output – direct connection to the analogue input of ventilation controllers, EC fans or frequency inverters.
    • Modbus RS485 – several sensors on one bus, data straight to a PLC or BMS.
    • Overall VOC value – reacts to odours, solvents, cleaning agents and human activity.
    • Demand-controlled ventilation – fan speed follows the actual air pollution.
    • Energy saving – heated or cooled air is not exhausted unnecessarily.
    • LCD display – the reading can be checked on site without a computer or software.
    • Versatility – the same sensor suits both analogue and networked systems.

    How does it differ from similar products?

    CO₂ sensor measures carbon dioxide only (occupancy); a VOC sensor also reacts to odours, solvents and cleaning agents.
    Gas leak detector designed to detect hazardous concentrations and raise alarms; a VOC sensor is for comfort and ventilation control.
    Duct VOC sensor without display same function, but the reading is visible only via the controller or BMS.

    Where is it used?

    • Extract ducts of air handling units (AHU)
    • Zoned ventilation of office buildings
    • Shopping centres
    • Restaurant dining areas (not kitchen hoods)
    • Schools and public buildings
    • General ventilation of production areas

    Use by experience level

    Beginner.
    The simplest option is to connect the 0–10 V DC output to the analogue input of a heat recovery unit or ventilation controller – only supply and signal wires are needed.
    Advanced installer.
    Use 4–20 mA for long lines, and connect several sensors via a Modbus RS485 bus using shielded twisted-pair cable.
    Energy engineer / designer.
    Combine the VOC sensor with a CO₂ sensor: CO₂ indicates occupancy, VOC indicates other pollutants. The DCV system then responds to both.

    Practical application

    An office building AHU serves several floors. The sensor is installed in the common extract duct, its Modbus RS485 signal is sent to the BMS, and during commissioning the installer checks the reading directly on the LCD display.

    Pros / advantages

    • Three output types in one sensor
    • Suitable for demand-controlled ventilation (DCV)
    • Reacts to odours and solvents that a CO₂ sensor does not see
    • Easy integration into a PLC or BMS via Modbus
    • 4–20 mA signal suits long lines
    • Reading visible on site on the LCD display

    Cons / limitations

    • Shows the overall VOC level, does not identify individual substances
    • Does not measure CO₂ – a CO₂ sensor is needed to assess occupancy
    • Semiconductor VOC sensors usually need a warm-up time after power-on
    • Range and supply must be confirmed from the supplier datasheet

    Safety and installation notes

    • ⚡ Carry out wiring with the control panel supply disconnected; installation by a qualified electrician.
    • ⚠ Before wiring, check the supply voltage and output type against the datasheet – a wrong voltage can damage the electronics.
    • ⚠ Use shielded twisted-pair cable for the RS485 line and termination resistors at the bus ends as required by the system.
    • ⚠ A VOC sensor is not a gas leak or explosion detector – do not use in explosive atmospheres without Ex certification.
    • ⚠ Place the probe in a straight duct section, away from bends, dampers and humidifiers.

    Quick selection guide

    VOC – air quality
    4–20 mA
    0–10 V DC
    Modbus RS485
    Suitable when you need to:
    • ventilate according to actual air pollution
    • react to odours, solvents and cleaning agents
    • send an analogue or Modbus signal to a controller
    • see the reading on site and send a signal to a controller
    Check before choosing:
    • supply voltage and current consumption
    • measuring range and how it is scaled to 4–20 mA / 0–10 V
    • Modbus address, baud rate and register map
    • duct dimensions and probe length
    Important reminder: A VOC sensor does not replace a CO₂ sensor or a gas leak alarm: it is intended for comfort and demand-controlled ventilation.
    ☝ Elsprendimai.eu recommends:

    FAQ

    How does a VOC sensor differ from a CO₂ sensor?
    A CO₂ sensor shows how much exhaled air has accumulated in a room. A VOC sensor reacts to odours, solvents, cleaning agents and other organic compounds.
    Which output should I choose – 4–20 mA or 0–10 V DC?
    For long lines and noisy environments – 4–20 mA. When the controller is close and has a 0–10 V input – 0–10 V DC.
    Can Modbus and the analogue output be used at the same time?
    This depends on the specific device settings – check the datasheet.
    Does the sensor detect gas leaks?
    No. It is an air quality sensor for ventilation control, not a safety detector. It must not be used in explosive atmospheres without Ex certification.
    Where can I find the Modbus register map?
    It is provided in the supplier datasheet. If you do not have it, contact us – we will help you get it.
    How long does it need after power-on?
    Sensors of this type usually need a warm-up time before readings stabilise. The exact time is stated in the datasheet.

    Sources: Manufacturer not identified (supplier product). Parameters based on the product name and general VOC sensor operating principles; measuring range and supply according to the supplier datasheet. Checked 2026-10-18.

    Duct VOC sensor with LCD display for demand-controlled ventilation

    The digital duct VOC sensor with LCD display measures extract air quality in the duct and transmits the signal via 4–20 mA, 0–10 V DC or Modbus RS485. The reading is visible on site, making commissioning and checks faster.

    Illustrative image may have been created using AI. The appearance of the product may differ slightly from the image shown. Please refer to the technical specification.

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