TSN-CO2ind Sensor
The TSN-CO2ind-Sensor is a CO2-indicator and a temperature sensor designed to be used in
combination with our AREXX MULTILOGGER-System for permanent monitoring of the CO
level and temperature. Special features of this sensor system are a wireless data-link and a
battery operation!
The sensor’s quality ranges between simple low cost indicators, which may indicate CO2-
levels in standard 3-level traffic-light codes (good, acceptable or bad) and professional
sensors providing highly accurate ppm-levels (in which the shortcut “ppm” refers to “Parts
Per Million”).
Our TSN-CO2ind-Sensor also provides a ppm-value, but it does not meet an according
extreme high accuracy. Besides, our sensor’s response time to changing surroundings is a
little bit slower. Compared to low-cost-sensors however, you will receive a lot more and much
better information. In comparison to other sensors, our sensor will have some advantages
and limitations.
Accuracy and response time will not quite be comparable to highly professional sensor
systems. Compared to low-cost-sensors, which often provide simple traffic-light codes and
rather inaccurate values, our sensor features relatively good accuracy, an excellent trendreporting for CO2-levels, a wireless data-link and a battery operation with two AAA-batterycells, which guarantee good mobility.
Outdoor CO2-levels
In Europe outdoor air will normally provide CO2-levels between 430 and 470 ppm. Of course
these values depend on different environmental conditions. Measurements may result in
different levels between locations in villages, in cities or in forests. CO2-levels will reach
higher values in industrial areas (e.g. near highways) than in nature environments. As a
result, outdoor CO2-levels may fluctuate depending on environmental conditions.
Indoor CO2-levels
Optimal values for indoor CO2-levels will not exceed 800 ppm. In smog areas with high
outdoor CO2-levels this optimal value however is an unrealistic approach! Under such
conditions we might prefer another optimum by aiming at an indoor CO2-level not exceeding
the outdoor-level by more than 1000 ppm. As a standard the maximum level will be set to
1500 ppm.
As a result, standards for CO2-levels in public buildings (e.g. in schools) should not refer to
absolute CO2-levels, but to differences between indoor and outdoor levels of CO2concentrations. As soon as the difference between indoor and outdoor levels exceeds a
value of 1000 ppm it is advised to ventilate the room (e.g. by opening a window).
Testing the CO2-sensors
Testing the CO2-sensors is relatively simple. As soon as you enclose the sensor in a plastic
bag and start breathing in and out at the bag’s opening, your breath will raise the CO2-level
inside the bag, causing the sensor to react. Opening a bottle of carbonated drinks near the
sensor will quickly raise the CO2-level as well. Of course chemical analysis will identify the
bubbles arising from carbonated drinks as CO2. Please pay attention to the fact that if you let
the CO2 level become very high, it can take a long time before the level has adapted to the
regular level again.
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Specification for the TSN-CO2ind sensors;
The CO2-Sensor is designed for environments with temperatures ranging between 10° and
30°C and for relative humidity levels between min. 15% and max. 80%.
CO2-Measurement
Measurement range; from 400 ppm up to 90% (= 400 up to 900.000 ppm)
Accuracy; ± 15%
Response time, regular; 2 up to 5 minutes (if the CO2 variation is small)
Response time, extreme; 30 up to 60 minutes (if the CO2 variation is big)
CO2-Sensortype; based on Gas-Ion-selective electrodes
Lifetime for the sensor; max. 5 years
(Sensors can easily be replaced by technicians)
Temperature measurement
Temperature; from –30 up to +80° Celsius, ± 0,5° respectively 1°.
Supply current; to be delivered by 2 (type AAA) batteries
Lifetime for the batteries approximately 1 year (depending on battery-quality)
RF-frequency; 433 MHz
Range; approximately 50 meters in free field conditions
Operating instructions
Evaluation of the CO2-levels will be restricted to the most recent versions (>v1.86) of our
Logger-software only. Always check for the latest versions at our website www.arexx.com.
Insert the batteries and check if the Temp-Logger-software displays a CO2-level and a
temperature value in the sensor list for the sensor number concerned. First there will appear
one value, approximately 60 seconds later the other value will appear.
IMPORTANT: CALIBRATING THE REFERENCE-LEVEL
Having established good receiving conditions and monitoring the display for the sensor’s
signal, you should calibrate the reference level now. For calibration you must put or hold the
sensor in an outdoor location for approximately 3 minutes (not in rainy weather or under
frostlike conditions). If the sensor already indicates a high starting value, for a accurate
calibration it is better to let it outside longer (30 to 60 minutes). Then press a ballpoint pen or
a sharp pencil at the reference switch at the backside of the sensor! Normally the sensor will
display an outdoor value of 450ppm. After calibration the sensor is ready for use.
It is possible that by temperature and humidity influences the sensor starts drifting (it will
indicate a higher or too high value gradually). In that situation it is best to calibrate the sensor
again.
If the system is inoperable, please start debugging by checking the batteries, to be followed
by the receiver unit and the software. In case of a wrong or strange CO2 value you should
calibrate the sensor again. Try to leave the sensor in clean air outside for a longer period of
time (at least 1 hour) before pressing the reference switch.
© AREXX Engineering Zwolle, NEDERLAND
www.arexx.com
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