CMA ML60m CO2 Gas Sensor User’s Guide

CMA ML60m CO2 Gas Sensor User’s Guide
CO2 GAS SENSOR ML60M
USER’S GUIDE
CENTRE FOR MICROCOMPUTER APPLICATIONS
http://www.cma-science.nl
Short description
The CO2 Gas sensor ML60m is used to monitor gaseous carbon dioxide levels in the
range of 0 to 5000 ppm1. The sensor uses the Non‐Dispersive Infrared Detection
(NDIR) method and detects the net increase or decrease of light that occurs at the
wavelength where absorption of carbon dioxide takes place. The light intensity is then
correlated to CO2 concentrations. CO2 gas moves in and out of the sensor tube by
diffusion through the six vent holes in it. The tube contains an infrared source at one
end and an infrared detector at the other end. The detector measures infrared
radiation absorbed in a narrow band centered at a wavelength of 4.26 µm. The
greater the concentration of the absorbing gas in the sampling tube, the less radiation
is detected by the IR detector. When the sensor is collecting data, the IR source
blinking on and off – it takes a reading about every 3 seconds.
The sensor is delivered with a 250 ml sampling bottle and rubber stopper to attach the
sensor tube to the bottle.
Do not place the sensor tube directly into any liquid. The sensor is intended only for
measuring gaseous, not aqueous, CO2 concentrations.
The CO2 Gas sensor is an I2C digital sensor, which gives calibrated values of the
measured quantity. This sensor can only be connected to special interfaces that
support I2C digital sensors like the CMA MoLab interface. The sensor cable needed to
connect the sensor to MoLab is not supplied with the sensor, it is supplied with
MoLab.
Sensor specifications
The CO2 Gas sensor ML60m is a digital sensor that converts the measured CO2 in ppm
to a digital value via 12‐bit analog‐to‐digital conversion. The maximal sampling rate of
the sensor is 1 Hz. Due to the measurement process of the sensor the optimal
sampling rate is 20 per minute.
Collecting data
This CO2 Gas sensor works only with specific interfaces. The sensor will be
automatically detected when connected to such an interface. For detailed information
about measurements with sensors consult the User Manuals of the interface and the
Coach 6 software.
The CO2 sensor measures in parts per million (ppm).
In gaseous mixtures, 1 part per million refers to 1 part by volume in 1 million volume units of the whole.
This unit can be recalculated to percent by dividing a value in ppm by 10000. 5000 ppm is equal to 0.5 %.
The level of C02 in the Earth’s troposphere has gradually increased from 317 ppm in 1960 to current
levels of nearly 370 ppm. Exhaled human breath has a C02 concentration of about 50 000 ppm.
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Calibration
The CO2 Gas sensor is supplied with a factory calibration for CO2 level in ppm. The
Coach 6 program allows shifting the pre‐defined calibration if needed. The user
calibration is stored in non‐volatile user sensor memory.
The sensor can be calibrated at one known CO2 level using the calibration button on
the sensor box.
- Place the 250‐ml sampling bottle long enough in the air outside to ensure that its
content is replaced with fresh air. The calibration will be based on the CO2
concentration level of fresh air of about 390 ppm. While still outdoors insert the
sensor with the rubber stopper into the bottle. You can now take the bottle and
the sensor to the location where the measurements are to be done.
- Connect the CO2 sensor to an interface.
- Let the sensor warm up by collection data for at least 90 seconds.
- When the readings are stabilized use a paper clip or a ballpoint to press down the
calibration button. After about 30 seconds, the reading should stabilize at a value
of approximately 390 ppm (plus of min 40 ppm).
- If the reading is significantly lower or higher than 390 ppm (while still in fresh air),
simply press the button again to repeat the process.
Additional information
 The CO2 sensor needs to warm up for 90 seconds anytime when power is
interrupted.
 The sensor requires a large current (120 mA). We recommend that you use the AC
connector for the interface when using the CO2 sensor. Only one CO2 sensor can be
used at a time.
 The sensor cannot take readings at a CO2 concentration higher than 5000 ppm.
Once the CO2 concentration reaches this level the computer will continue to display
a reading of 5000 ppm, until the actual level drops below 5000 ppm again.
 Even though the sensor responds rather quickly to changes in CO2 concentration,
remember that gas has to diffuse through the holes in the sensor tube before any
changes in concentration will be detected. Since diffusion of gases is a fairly slow
process, there is a resulting delay in the readings.
 The sensor is designed to operate between 20°C and 30°C. The sensor can be used
outside of this temperature range; however there will be a loss in accuracy of
readings, even if the 1‐point calibration at the lower level or higher temperature is
done. Allow enough time for the sensor to stabilize at the desired operating
temperatures.
ML60m CO2 Gas Sensor User’s Guide | 3
Suggested experiments
 Measuring CO2 levels (respiration) from small animals and insects.
 Monitoring CO2 changes in a plant terrarium during photorespiration and
photosynthesis in light/dark (combination with the light sensor).
 Measuring CO2 levels during cellular respiration of peas or beans.
 Monitoring production of CO2 during chemical reactions.
 Measuring CO2 levels in classrooms.
Technical Specifications
Sensor kind
Digital 12‐bits resolution
(on‐sensor digital conversion)
communication via I2C
Measuring range
0 .. 5000 ppm
Resolution
2.44 ppm
100 ppm in the range of 0‐1000 ppm
10% of reading in the range of 1000 – 5000 ppm
1 Hz
Accuracy
Maximal sampling rate
Warm‐up time
Respond time
Normal operation temperature
90 seconds (maximum)
faster when air circulates
90% of full scale reading in 60 s
Operating humidity range
25°C
5 – 95% (non‐condensing)
Connection
5‐pins mini jack plug
Warranty:
The CO2 Gas sensor ML60m is warranted to be free from defects in materials and
workmanship for a period of 12 months from the date of purchase provided that it has
been used under normal laboratory conditions. This warranty does not apply if the
sensor has been damaged by accident or misuse.
Note: This product is to be used for educational purposes only. It is not appropriate for
industrial, medical, research, or commercial applications.
Rev. 10/06/2012
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