Gas Alarm GX-D250

The professional CO₂ detector with display and relays: keep an eye on indoor air, control ventilation automatically

The Schabus Professional CO₂ Detector GX-D250 is a CO₂ warning device for permanent installation in residential and office spaces and in rooms with regular occupancy, for example classrooms, offices, meeting rooms, medical practices or public facilities. An external, high-precision NDIR infrared sensor continuously measures the CO₂ concentration. An illuminated plain-text display shows the exact ppm value and evaluates the indoor air in understandable language, for example with “good air”. The GX-D250 was developed to detect spent exhaled air and to provide guidance for better ventilation behaviour.

The detector warns in three stages: From as low as 800 ppm the display indicates the need to ventilate. The pre-alarm follows at 1,000 ppm with a discreet acoustic warning; the highest alarm level is at 2,500 ppm CO₂ in line with occupational safety (half MAK). In addition, the device has two potential-free changeover relays: one switches on alarm and can, for example, activate forced ventilation or close a solenoid shut-off valve; the other reports faults to the building management system. This makes the GX-D250 not only a detector but a building block for automatic ventilation management.

The GX-D250 is permanently installed on the wall; installation must be carried out by a qualified specialist. The device has no options or variants.

Measure, display, warn, switch

The GX-D250 clearly reminds you to ventilate and passes its knowledge on to your technology via two relays.

Measure at nose height, display at eye level

With the GX-D250 the measuring point and the display are separate. The sensor measures where people breathe; the control unit is mounted so that the display is easy to read while standing. The sensor cable can be extended up to 50 m. Via the height of the sensor you set the response behaviour:

• Mounted lower the sensor reacts more sensitively
• Mounted higher the sensor reacts more tolerantly

What’s in the box

• GX-D250 CO₂ warning device with pre-mounted external sensor
• Mounting material
• Operating instructions

How the GX-D250 is constructed

The GX-D250 consists of the control unit in a surface-mounted housing and the external sensor, which is connected via a cable. The sensor is already pre-mounted.

Install correctly and put into operation

Read the operating instructions thoroughly before installation and first commissioning. Installation must be carried out by a qualified specialist. The device may only be installed on a wall in dry indoor rooms.

Wall mounting

1. Loosen the four housing screws and remove the front panel. If necessary, unplug the ribbon cable at the connector.
2. Fasten the base shell of the housing to the wall with the enclosed mounting material. The mounting position “at medium height” is chosen so that the display is easy to read while standing.
3. Install the connection cables leading to the gas detector firmly as surface-mounted cables.
4. Connect the mains voltage, relays and sensor to the terminals, then refit and screw on the front panel.

Connecting the relays correctly

Commissioning step by step

1. Ventilate the room well before commissioning.
2. Apply the operating voltage. The display greets you with the manufacturer’s name and device type while all self-tests are completed.
3. Wait for the start phase of 5 minutes. During this time the GX-D250 performs function tests, the external sensor is pre-heated and the software checks itself. The display shows “CO₂: Wait / Prepairing”. Move away from the sensor during the start phase so as not to falsify the starting values.
4. When the green LED lights alone, the warning system is in order and ready for operation.

Even after a short power failure the function test is restarted.

How the GX-D250 evaluates the indoor air

Fresh outdoor air is around 400 to 410 ppm. Depending on the concentration the GX-D250 displays the following:

Behaviour in the event of an alarm

1. Ventilate the room and open all doors and windows. If necessary, inform other people and ask them to leave the room.
2. Stay calm; there is absolutely no reason to panic. Even CO₂ concentrations near 5,000 ppm are not life-threatening. 5,000 ppm for a long time corresponded to the MAK (maximum workplace concentration for 8 hours).
3. Stop all use of combustion appliances and ensure fresh air.
4. If necessary, mute the alarm tone with the RESET button. It remains muted until the system falls back into “pre-alarm” mode as the CO₂ concentration decreases.

Test regularly

For your own safety the manufacturer recommends regularly checking the acoustic alarm transmitter for proper function with the test button. Both relays Re1 and Re2 also drop out during this test.

The device monitors itself

A 32-bit microcontroller continuously monitors the system at around 300 points in hardware and software. Several temperatures, voltages and currents are measured and compensated, results for internal long-term tests are stored, calculated against each other and some of them displayed on the screen. In addition the system performs regular tests on the sensor element. If the result is “good”, you notice nothing. If it is “not good”, the system restarts up to three times, repeats the measurements and then decides whether to issue a fault message.

Maintenance-free, but not care-free

The GX-D250 operates maintenance-free. Only remove dust from it from time to time using dry cloths. Please do not vacuum the device: through the small slots and openings in the housing very high wind speeds could arise inside that would permanently impair the internal temperature sensors through excessive cooling or transmit incorrect values to the processor. Consequences would be an early defect, a severely reduced service life or permanently incorrect measured values.

The external CO₂ sensor should be regularly exposed to fresh air during operation. The lowest CO₂ value measured continuously for at least 20 minutes within each 7 uninterrupted operating days is interpreted as the 400 ppm point, stored and adopted as the new calibration value (zero-point adjustment) for subsequent measurements. If the device is used as intended as a reminder for regular ventilation, it is entirely sufficient to thoroughly ventilate the monitored room once a day and on 2 out of 7 days of a week. The manufacturer also recommends regularly testing infrared sensors and recalibrating them for about 30 minutes in fresh air weekly.

Avoid the influence of moisture (splash or rain water), dust and direct sunlight on the device. Clean it only with a dry linen cloth, which may be slightly dampened in case of heavy soiling. Do not use solvent-based cleaning agents.

Note for maintenance companies: The manufacturer recommends entering all information with date and time in a list at every visit. This allows conclusions to be drawn after some time about the operational safety of the system and about possible manipulations or malfunctions.

What the display shows

After each press of the SERVICE button you move to the next display until the main display appears again. If you remain on a display, the device automatically switches back to the main display after a while, or if you press the SERVICE button a little longer.

Manufacturer’s notes

• Read the operating instructions carefully before installation and commissioning and keep them
• Installation must be carried out by a qualified specialist; the five safety rules must be observed
• Packaging material is not a toy and must be kept away from children
• Intended for residential rooms and rooms with residential-like use
• Intended for residential buildings, sales areas and rooms of small businesses such as workshops and service centres, each connected to the public low-voltage network
• Not suitable for monitoring CO₂ from technical systems under pressure or for dry-ice processing
• Do not use in potentially explosive atmospheres; the device is not approved for other uses
• The measuring cell, evaluation and software were tested by TÜV Süd as part of the development of a CO₂ sensor; safety and stability were certified for the system. The complete warning device GX-D250 was not tested by TÜV
• The declaration of conformity is available for download on the manufacturer’s website

Warranty, guarantee, return and disposal

The GX-D250 is covered by the statutory warranty of at least 2 years in the EU. The manufacturer Elektrotechnik Schabus additionally offers a 5-year guarantee that can be registered online. Repair and spare parts are available directly from the manufacturer, even beyond the statutory warranty. Personal specialist advice is available without a call centre directly from the manufacturer. In the event of a warranty claim, the device is sent in sufficiently packed with a description of the fault, proof of purchase as well as address and delivery address. The device must have been used in accordance with the operating instructions.

Return: In the event of a defect, first contact the manufacturer and state the complete address as well as the reason for return. Within Germany the manufacturer arranges free collection of the parcel. Unpaid parcels will not be accepted, and unjustified returns that do not constitute a complaint will be charged subsequently.

The GX-D250 does not belong in household waste. The crossed-out wheeled bin symbol on the product reminds you to use the take-back systems for waste electrical and electronic equipment (WEEE No. DE91394868). Further information is available from your local waste advice centre or from the manufacturer.

Areas of application

• Classrooms and schools
• Seminar rooms and further education
• Offices and open-plan offices
• Meeting and conference rooms
• Medical practices and waiting rooms
• Public facilities
• Co-working spaces
• Living rooms and home office

The Schabus Professional CO₂ Detector GX-D250: Because good air knows no compromises.

Frequently asked questions