External CO2 sensor for GX-A1+ or GX-HS warning devices, detects CO2 from used air or CO2 exhaled by humans, as a timely reminder to ventilate at about half the TLV (2500 ppm).
Performance features
- External sensor for the gas detectors GX-A1 and GX-HS
- Detection for carbon dioxide indoors / living room-like
Scope of delivery
1 gas sensor with cable and mounting material
1 Operating instructions
Technical data
Operating voltage: | 5 V |
Sensor type: | NDIR - Infrared |
Trigger concentration: | Pre-alarm 2000 ppm, main alarm 2500 ppm |
Humidity (ambient): | 5-90 % RH (non-condensing) |
Functional area: | -10 °C / +50 °C |
Storage temperature: | -20 °C / +70 °C |
Lifespan: | approx. >5 years |
Protection class: | IP 20 |
Cable length: | 2,5 m |
Cable Ø: | 3.5 mm |
Dimensions (HxWxD): | 52x27x29 mm |
WEEE NO.: EN91394868
The external NDIR sensor is suitable for the gas detectors GX-A1 and GX-HS and is connected to them by cable and screw terminals. The trigger concentration is 2000 - 2500 ppm.
The connecting cable of the sensor can be extended. The following minimum cross-sections apply depending on the length of the cable
on the length of the cable:
Cable cross section 3 x 0.75 mm²: maximum length 10 m
Cable cross section 3 x 1.5 mm²: maximum length 20 m
Description of the mode of operation for technically interested persons
An NDIR sensor is a non-dispersive infrared sensor consisting of an IR diode as light source, an optical wavelength filter and an IR detector. Ambient air diffuses through a membrane into a chamber. Each gas has its own wavelength in which it optimally absorbs light in the infrared spectrum. The extent is measured electro-optically, providing a reference for the concentration present.
The optical filter ensures that only the narrow spectrum of interest is evaluated. A pure air mixture is enclosed in a second chamber. Now the same measurement is performed alternately in the two chambers at a low pulse frequency of just under 1 Hz.
External influences such as temperatures affect both chambers and are thus compensated for as far as possible, since only the difference between the two chambers is evaluated. A powerful
microcontroller system first converts the low detector currents into a voltage, which is then converted into digital signals by an AD converter. Here, a first filtering takes place, which checks the signals for plausibility and smoothes strong fast, possibly unusual signal changes
and replaces them with intermediate values. The voltage values read in are now related to a concentration that can be represented in ppm according to an internal reference and output as a pulse width modulated continuous signal. By means of an analog low-pass filter, the pulses are converted back into a modulated DC voltage, whereby in this case approximately 1 mV per ppm is achieved.
Fresh air contains about 400 ppm CO2, so the sensor should output about 0.4 volts when the air is fresh, which is about what appears on the display of the GX-A1 warning device. Since the GX-A1 in particular has an additional signal filter for smoothing and avoiding false alarms, displays of 0.2 - 0.6 volts are possible. All gas detectors from Elektrotechnik Schabus are in fact warning devices and not measuring devices, therefore such a deviation is okay and does not represent a fault. The values are displayed to show a tendency to determine whether, for example, ventilation measures achieve the desired effect.
Gas detectors from ES switch from 2 volts to the pre-alarm, if this is provided for in the device, and from 2.5 volts to the main alarm. Here also possibly existing relays switch and inserted Piezotöner emit strong acoustic warning tones. These thresholds correspond to about 2000 and 2500 ppm. These values are far below the limits at which it becomes dangerous for humans. For example, the maximum workplace concentration MAK in Germany is 5000 ppm CO2 for an exposure of 8 hours. Thus, a warning device with the sensor GX-DS is an early warning system.
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