Gases PRO Sensor Guide
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Sensors

Starting with the gas sensors

In this section we are going to explain the first steps to start with the sensors used in the Gases PRO Sensor Board.

Notes for Calibrated Gas Sensors

1- Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. Libelium keeps a minimum stock of calibrated gas sensors to ensure the maximum durability. Ensambling process and delivery time takes from 1 to 2 weeks in case the current stock is enough for the order and from 4 to 6 weeks in case the order is higher than the stock available and new sensors units need to be manufactured and calibrated. Please inform as soon as possible of your sensor requirements to our Sales agents so that they can order the units needed to factory.
2- Lifetime of calibrated gas sensors is 6 months working at its maximum accuracy as every sensor looses a small percentage of its original calibration monthly in a range that may go from 0.5% to 2% (depending on the external conditions: humidity, temperature, measured gas concentration, if there are another type of gas present which corrode the sensor, etc). We strongly encourage our customers to buy extra gas sensor probes to replace the originals after that time to ensure maximum accuracy and performance. Any sensor should be understood as a disposable item; that means that after some months it should be replaced by a new unit.- Electrochemical calibrated gas sensors are a good alternative to the professional metering gas stations however they have some limitations. The most important parameters of each sensor are the nominal range and the accuracy. If you need to reach an accuracy of ±0.1 ppm remember not to choose a sensor with an accuracy of ±1 ppm. Take a look in the chapter dedicated to each sensor.
4- Libelium indicates an accuracy for each sensor just as an ideal reference (for example, "±0.1 ppm"). This theoretical figure has been calculated as the best error the user could expect, the optimum case. In real conditions, the measurement error may be bigger (for example, "±0.3 ppm"). The older the sensor is, the more deteriorated it is, so the accuracy gets worse. Also, the more extreme the concentration to meter is, the worse the accuracy is. And also, the more extreme the environmental conditions are, the quicker the sensor decreases its accuracy.
5- In order to increase the accuracy and reduce the response time we strongly recommend to keep the gas sensor board ON as electrochemical sensors have a very low consumption (less than 1 mA). So these sensors should be left powered ON while Waspmote enters into deepsleep mode. Latest code examples implement in the new API of Waspmote v15 follow this strategy. If you are using the old version of the API and boards (v12) write in our Forum and we will help you to modify your code.
6- These sensors need a stabilization time to work properly, in some cases hours. We recommend wait 24hours of functioning (always with the gas sensor board ON) to ensure that the values of the sensors are stable.
7 AFE boards for electrochemical gas sensors have different gain options. The system integrator must choose the adequate gain according to the concentration range to measure. For low concentrations, higher gains are recommended. To know how choosing the right gain, see the chapter "How to choose the right gain resistor".
8- A digital smoothing filter based on previous values is interesting to reduce noise. It will increase the accuracy of the Gases PRO sensors. The filter adequate for its application (note that every sample given by the library has already been filtered inside Waspmote) means from 4 to 8 values.
A simple moving average can be used to increase the accuracy and reduce the noise.
Filtered value=samplet+samplet−1+samplet−2+...+samplet−(n−1)n\text{Filtered }\text{value} = \frac{\text{sample}{_t} + \text{sample}_{t - 1} + \text{sample}_{t - 2} + \text{...} + \text{sample}_{t - {(n - 1)}}}{n}
Where:
  • Filtered value is the concentration value with the mean filter applied
  • sample are the measurements taken by the gas sensors being sample_t the last measurement, sample_(t-1) the penultimate measurement, etc.
  • n are the number of samples to calculate the moving mean.
Other filters can be applied according to the project requirements
9- Take into account that developing a robust application for gases detection or measurement may take an important effort of testing and knowing the insights of the sensor probes and code that reads them.

Comparative between Libelium hardware with Alphasense sensors and Alphasense hardware with Alphasense sensors

Ozone
Sensor 1 -Alphasense (blue)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
0 ppm
-1.641
1.641
1 ppm
-0.815
1.815
6 ppm
5.77
0.221
Sensor 2 - Libelium (red)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
0 ppm
0.861
0.861
1 ppm
0.210
0.789
6 ppm
7.039
1.039
NO
Sensor 1 -Alphasense (blue)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
7 ppm
6.182
0.818
2 ppm
1.840
0.160
0 ppm
-0.4098
0.4098
Sensor 2 - Libelium (red)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
7 ppm
6.478
0.521
2 ppm
1.919
0.08
0 ppm
-0.260
0.260
CO
Sensor 1 -Alphasense (blue)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
10 ppm
10.76
-0.766
0 ppm
0.826
-0.826
1 ppm
1.718
-0.718
Sensor 2 - Libelium (red)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
10 ppm
10.66
-0.066
0 ppm
0.790
-0.790
1 ppm
1.636
-0.636
SO2
Sensor 1 -Alphasense (blue)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
4 ppm
4.183
-0.183
0 ppm
0.373
-0.373
8 ppm
7.85
0.146
Sensor 2 - Libelium (red)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
4 ppm
4.451
-0.451
0 ppm
0.5779
-0.5779
8 ppm
7.614
0.358
NO2
Sensor 1 - Libelium (red)
Real Input (ppm)
Medium Measured Value (ppm)
Error (ppm)
1 ppm
0.721
0.278
3 ppm
2.776
0.223
0 ppm
-0.163
0.163

Understanding the sensor accuracy and the range of operation

Metering gas concentration in the range of low ppb (close to 0 ppb) is still a complex technical challenge. Electrochemical sensors deliver tiny currents (in nA) which need to be amplified. And like any other electronic system, there is an inherent error inside the sensor signal. This error has 2 mathematical components: the constant error (bias) and a random/unpredictable component too (ripple).
This error is given by the sensor itself. It is complicated to remove the error. The best practice is to calibrate the sensor: our API applies equations with the correction factors calculated by the manufacturer on their gas chambers (these values are unique, obtained for each sensor; the values are hard-coded on a chip soldered on the sensor's AFE). But this calibration may not be enough for certain applications that require extreme accuracy (the customer can create an additional calibration process to meet his special needs, targeting especially the constant error).
Libelium obtained the accuracy value of its sensors experimentally: we visited a chemical laboratory and measured the error our sensors made at different gas concentrations provided by standard gases (with known and controlled ppb). We observed most of Libelium's sensors feature an accuracy as good as ±0.2 ppm in good conditions (or even ±0.1 ppm for certain models). That is, the typical error we measured in these experiments is as low as ±200 ppb in such favorable conditions (±100 ppb in selected top models).
Figure: Example of work at low concentrations - Sensor's uncertainty is huge compared to the real concentration
As we can see in the figure above, the red dotted line represents the real concentration of a certain gas. The concentration is not constant over time, but remains in a very low range: it starts at 60 ppb and remains between 70 and 20 ppb. This is a typical range for many pollutant gases (NO2, O3, CO, etc) in not-too-polluted environments, like EU or USA cities.
In the graph we also see 2 green lines. They represent the maximum and minimum readings that we can expect from the Libelium sensor. We obtained these 2 lines easily: we simply added (and subtracted) to the red line (real concentration) the accuracy of the sensor (which we assume here to be 100 ppb). The area between the 2 green lines represents the area of uncertainty: the sensor can give values within this area. This error is inherent to the sensor and cannot be eliminated (additional calibration processes help mitigate it).
A curious effect is the sensor can deliver negative values for the gas concentration. This is common when the sensor is operating at a concentration below to 100 or 200 ppb. Of course, it is physically impossible to have "-40 ppb" of NO2, but on a mathematical level it makes sense: our API's function simply returns a numerical value according to the equation and correcting factors defined by the manufacturer. Previously, our API removed negative values (making them 0 ppb automatically), but we think it is appropriate to give the raw values again, without saturating to 0: this way the user can know that the sensor is working; if negative values are obtained, he knows that the current gas concentration is just below the accuracy of the sensor.
Obviously, the relative error made by the sensor is high at low concentrations: An error of -50 ppb is huge when the gas concentration is 60 ppb. However, the relative error is lower as the concentration increases: a relative error of -50 ppb is almost negligible at 800 ppb.

Understanding the basics of electrochemical sensors

Gas sensors (except the combustible gases sensor and the CO2 sensor) are electrochemical cells that operate in the amperometric mode. That is, they generate a current that is linearly proportional to the fractional volume of the target gas. These sensors are composed of 3 metal strips connecting each electrode to the 3 pins outside of the sensor body and a cell electrolyte. Each electrode has its own specific function:
  • Working electrode reacts with the target gas to generate a current
  • Counter electrode supplies a current that balances that generated by the working electrode current
  • Reference electrode sets the operating potential (bias voltage) of the working electrode
The cell electrolyte provides ionic electrical contact between the electrodes.
To convert the current generated by the working electrode in a voltage for the ADC, the AFE module uses a transimpedance stage with a selectable gain resistor.
The bias voltage is managed by the AFE module and it is automatically fixed by the sensor parameters stored into the EEPROM. These sensors use the 3-electrode AFE board.
Figure: 3-electrode AFE module diagram block
The Ozone , Nitric Oxide (low concentrations), Nitric Dioxide (high accuracy) and Sulphur Dioxide (high accuracy) sensors have a 4th electrode. This electrode, commonly called auxiliary electrode, works as an extra working electrode and it is used to compensate the variations produced by the temperature in the baseline current. The compensation will be performed automatically by the API library. These sensors use the 4-electrode AFE board.
Figure: 4-electrode AFE module diagram block
Electrochemical sensors have a very low consumption (less than 1 mA) so, to increase the accuracy and reduce the response time, these sensors can keep powered while Waspmote enters into deepsleep mode.
These sensors need a stabilization time to work properly, in some cases hours. It implies that the first reads of the sensors may have an offset level.

Understanding the combustible gas sensor

The CH4 and combustible gases sensor uses the pellistor technology to detect the gas concentration. A pellistor consists of a very fine coil of platinum wire, embedded within a ceramic pellet. On the surface of the pellet there is a layer of a high surface area noble metal, which, when hot, acts as a catalyst to promote exothermic oxidation of flammable gases. In operation, the pellet and so the catalyst layer is heated by passing a current through the underlying coil. In the presence of a flammable gas or vapour, the hot catalyst allows oxidation to occur in a similar chemical reaction to combustion. Just as in combustion, the reaction releases heat, which causes the temperature of the catalyst together with its underlying pellet and coil to rise. This rise in temperature results in a change in the electrical resistance of the coil, and it is this change in electrical resistance which constitutes the signal from the sensor.
Pellistors are always manufactured in pairs, the active catalyzed element being supplied with an electrically matched element which contains no catalyst and is treated to ensure no flammable gas will oxidize on its surface. This "compensator" element is used as a reference resistance to which the sensor's signal is compared, to remove the effects of environmental factors other than the presence of a flammable gas. In the case of the CH-A3 gas sensor from Alphasense, detector and compensator are inside the same encapsulated. One pin of each resistor are connected to a pin of the encapsulated. The other pins are connected together inside the sensor to the signal pin.
The AFE module fixes the supply voltage to the resistors and reads the voltage of the signal pin. This sensor uses the pellistor/NDIR AFE board.
Figure: CH4 and Combustible Gases Sensor AFE module diagram block

Understanding the CO2 sensor

The IR series of infrared gas detection sensors use the technique of NDIR (Non-Dispersive Infrared) to monitor the presence of hydrocarbons or carbon dioxide. This technique is based on the fact that the gas has a unique and well-defined light absorption curve in the infrared spectrum that can be used to identify the specific gas. The gas concentration can be determined by using a suitable infrared source and analyzing the optical absorption of the light that passes through the gas. The IRSS-E sensor contains the same optics as the related and simpler model IRSS-X, but is also equipped with incorporated electronics and software in order to provide an output that is linearized and temperature compensated.
In the standard version of IRSS-E, the sensor provides a linearized and temperature compensated analog voltage output that is proportional to the gas concentration. The AFE module sets the supply voltage and reads the voltage of the signal pin. This sensor uses the pellistor/NDIR AFE board.
Figure: NDIR AFE module diagram block

Lifetime of the Gas sensors

All sensors provided by Libelium for the Gases PRO Sensor Board have been calibrated in the origin factory by the manufacturer. Calibration parameters are stored inside the EEPROM (non-volatile memory) of each AFE board for a unique gas sensor. Thus, changing the AFE boards between gas sensors is forbidden.
The maximum accuracy for each sensor is valid only for 6 months. Every sensor loses a small percentage of its original calibration monthly in a range that may go from 0.5% to 2%.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. Manufacturing process and delivery may take from 4 to 6 weeks. Lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensor probes to replace the originals after that time to ensure maximum performance.
Remember that damages caused by external agents (animals, fire, flooding, gases, etc) are not covered under the Warranty. High concentration of corrosive gases (for example, NH3 -ammonia-, present in pig farms due to swine manure), causes early degradation of the devices, especially the most sensitive or exposed ones, such as sensors.
Libelium indicates an accuracy for each sensor just as an ideal reference (for example, "±50 ppm"). This theoretical figure has been calculated as the best error the user could expect, the optimum case. In real conditions, the measurement error will be bigger (for example, "±90 ppm"). As stated before, the older the sensor is, the more deteriorated it is, so the accuracy gets worse. Also, the more extreme the concentration to meter is, the worse the accuracy is. And also, the more extreme the environmental conditions are, the quicker the sensor ages. The sensors have been tested at 20 ºC / 101300 Pa. Cross sensitivity gases are not target gases. Relation can change with aging. The cross sensitivity may fluctuate between +/- 30% and may differ from batch to batch or from sensor's lifetime. The cross sensitivities are including but not limited to the gases from the tables. It may also respond to other gases. The data offered solely for consideration, investigation, and verification. Any use of these data and information must be determined by the user to be in accordance with federal, state, and local laws and regulations. Specifications are subject to change without notice.

Temperature, Humidity and Pressure sensor

The BME280 is a digital temperature, humidity and pressure sensor developed by Bosch Sensortec.
Figure: Temperature, Humidity and Pressure sensor

Specifications

Electrical characteristics
Supply voltage: 3.3 V Sleep current typical: 0.1 μA Sleep current maximum: 0.3 μA
Temperature sensor
Operational range: -40 ~ +85 ºC Full accuracy range: 0 ~ +65 ºC Accuracy: ±1 ºC (range 0 ºC ~ +65 ºC) Response time: 1.65 seconds (63% response from +30 to +125 °C) Typical consumption: 1 μA measuring
Humidity sensor
Measurement range: 0 ~ 100% of Relative Humidity (for temperatures < 0 °C and > 60 °C see figure below) Accuracy: < ±3% RH (at 25 ºC, range 20 ~ 80%) Hysteresis: ±1% RH Operating temperature: -40 ~ +85 ºC Response time (63% of step 90% to 0% or 0% to 90%): 1 second Typical consumption: 1.8 μA measuring Maximum consumption: 2.8 μA measuring
Figure: Humidity sensor operating range
Pressure sensor
Measurement range: 30 ~ 110 kPa Operational temperature range: -40 ~ +85 ºC Full accuracy temperature range: 0 ~ +65 ºC Absolute accuracy: ±0.1 kPa (0 ~ 65 ºC) Typical consumption: 2.8 μA measuring Maximum consumption: 4.2 μA measuring
You can find a complete example code for reading the Temperature, Humidity and Pressure sensor in the following link:
GP v30 05: Temperature, humidity and pressure sensor
GP v30 05 – Temperature, humidity and pressure sen

Carbon Monoxide (CO) Gas Sensor for high concentrations [Calibrated]

Figure: Image of the Carbon Monoxide Sensor for high concentrations mounted on its AFE module
This sensor was discontinued in 2017. Its substitute is the Carbon Monoxide (CO) Gas Sensor for high concentrations [Calibrated]. The information about this alternative sensor can be found in the next section of this guide.

Specifications

Gas: CO Sensor: 4-CO-500
Performance Characteristics Nominal Range: 0 to 500 ppm Maximum Overload: 2000 ppm Long Term Output Drift: < 2% signal/month Response Time (T90): ≤ 30 seconds Sensitivity: 70 ± 15 nA/ppm Accuracy: as good as ±1 ppm* (ideal conditions)
Operation Conditions Temperature Range: -20 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 90 to 110 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 5 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm CO equivalent)
Hydrogen Sulfide
H2S
24
0
Sulfur Dioxide
SO2
5
0
Cholrine
Cl2
10
0-1
Nitric Oxide
O2
25
0
Nitric Dioxide
NO2
5
0
Hydrogen
H2
100
40
Ethylene
C2H4
100
16
You can find a complete example code for reading the CO Sensor for high concentrations in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Carbon Monoxide (CO) Gas Sensor for low concentrations [Calibrated]

​
Figure: Image of the Carbon Monoxide Sensor for low concentrations mounted on its AFE module

Specifications

Gas: CO Sensor: CO-A4
Performance Characteristics Nominal Range: 0 to 25 ppm Maximum Overload: 2000 ppm Long Term Sensitivity Drift: < 10% change/year in lab air, monthly test Long Term zero Drift: < ±100 ppb equivalent change/year in lab air Response Time (T90): ≤ 20 seconds Sensitivity: 220 to 375 nA/ppm Accuracy: as good as ±0.1 ppm* (ideal conditions) H2S filter capacity: 250000 ppm·hrs
Operation Conditions Temperature Range: -30 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 80 to 120 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 3 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
* Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
* Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm CO equivalent)
Hydrogen Sulfide
H2S
5
< 0.1
Sulfur Dioxide
SO2
5
< -2
Cholrine
Cl2
5
< 0.1
Nitric Oxide
O2
5
< -2
Sulfur Dioxide
NO2
5
< 0.1
Hydrogen
H2
100
< 10
Ethylene
C2H4
100
< 0.5
Ammonia
NH 3
20
< 0.1
You can find a complete example code for reading the CO Sensor for low concentrations in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Carbon Dioxide (CO2) Gas Sensor [Calibrated]

Figure: Image of the Carbon Dioxide Sensor mounted on its AFE module

Specifications

Gas: CO2 Sensor: INE20-CO2P-NCVSP
Performance Characteristics Nominal Range: 0 to 5000 ppm Long Term Output Drift: < ± 250 ppm/year Warm up time: 60 seconds @ 25 ºC At least 30 min for full specification @ 25 °C Response Time (T90): ≤ 60 seconds Resolution: 25 ppm Accuracy: as good as ±50 ppm*, from 0 to 2500 ppm range (ideal conditions) as good as ±200 ppm*, from 2500 to 5000 ppm range (ideal conditions)
Operation Conditions Temperature Range: -40 ºC to 60 ºC Operating Humidity: 0 to 95% RH non-condensing Storage Temperature: -40 ºC to 85 ºC MTBF: ≥ 5 years
Sockets for Waspmote OEM:
  • SOCKET_1
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: 80 mA
The CO2 Sensor and the Methane (CH4) and Combustible Gas Sensor have high power requirements and cannot work together in the same Gases PRO Sensor Board. The user must choose one or the other, but not both.
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.
You can find a complete example code for reading the CO2 Sensor in the following link:
GP v30 02: NDIR gas sensors
GP v30 02 – NDIR gas sensors

Molecular Oxygen (O2) Gas Sensor [Calibrated]

Figure: Image of the Molecular Oxygen Sensor mounted on its AFE module

Specifications

Gas: O2 Sensor: LFO2-A4
Performance Characteristics Long Term Output Drift: < 1% signal/3 months Response Time (T90): ≤ 17 seconds Sensitivity: 80-130 μA @ 20.9% O2 Accuracy: as good as ±0.1% (ideal conditions)
Operation Conditions Temperature Range: -30 ºC to 50 ºC Operating Humidity: 5 to 95% RH non-condensing Pressure Range: 80 to 120 kPa Storage Temperature: 3 ºC to 20 ºC, 6 months Expected Operating Life: 2 years until 85% original output of 20.9% O2
Note: Previously, Libelium offered the equivalent O2 sensor 4-OL, by Eurogas.
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.
You can find a complete example code for reading the O2 Sensor in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Ozone (O3) Gas Sensor [Calibrated]

Figure: Image of the Ozone Sensor mounted on its AFE module

Specifications

Gas: O3 Sensor: OX-A431
Performance Characteristics Nominal Range: 0 to 18 ppm Maximum Overload: 50 ppm Long Term sensitivity Drift: -20 to -40% change/year Response Time (T90): ≤ 45 seconds Sensitivity: -200 to -550 nA/ppm Accuracy: as good as ±0.2 ppm* (ideal conditions) High cross-sensitivity with NO2 gas. Correction could be necessary in ambients with NO2.
Operation Conditions Temperature Range: -30 ºC to 40 ºC Operating Humidity: 15 to 85% RH non-condensing Pressure Range: 80 to 120 kPa Storage Temperature: 3 ºC to 20 ºC Expected Operating Life: > 24 months in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm CO equivalent)
Hydrogen Sulfide
H2S
5
< 10
Nitric Dioxide
NO2
5
70 to 120
Cholrine
Cl2
5
< 30
Nitric Oxide
O2
5
< 3
Sulfur Dioxide
SO2
5
< -6
Carbon Monoxide
CO
5
< 0.1
Hydrogen
H2
100
< 0.1
Ethylene
C2H4
100
< 0.1
Ammonia
NH3
20
< 0.1
Carbon Dioxide
CO2
50000
0.1
Halothane
Halothane
100
< 0.1
This sensor has a very high cross-sensitivity with NO2 gas. So, the output in ambients with NO2 will be a mix of O3 and NO2. A simple way to correct this effect is to subtract NO2 concentration from O3 concentration with an NO2 gas sensor. The measure from the NO2 sensor must be accurate in order to subtract the right value. See the related section in the "Library for gas sensors" chapter to use the right function.
You can find a complete example code for reading the O3 Sensor in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Nitric Oxide (NO) Gas Sensor for high concentrations [Calibrated]

This sensor was discontinued in March 2017. Its substitute is the Nitric Monoxide (NO) for low concentrations Gas Sensor [Calibrated]. The information about this alternative sensor can be found in the next section of this guide.
Figure: Image of the Nitric Oxide Sensor for high concentrations mounted on its AFE module

Specifications

Gas: NO Sensor: 4-NO-250
Performance Characteristics Nominal Range: 0 to 250 ppm Maximum Overload: 1000 ppm Long Term Output Drift: < 2% signal/month Response Time (T90): ≤ 30 seconds Sensitivity: 400 ± 80 nA/ppm Accuracy: as good as ±0.5 ppm* (ideal conditions)
Operation Conditions Temperature Range: -20 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 90 to 110 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 2 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output signal (ppm NO equivalent)
Carbon Monoxide
CO
300
0
Sulfur Dioxide
SO2
5
0
Nitric Dioxide
NO2
5
1.5
Hydrogen Sulfide
H2S
15
-1.5
You can find a complete example code for reading the NO Sensor for high concentrations in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Nitric Oxide (NO) Gas Sensor for low concentrations [Calibrated]

Figure: Image of the Nitric Oxide Sensor for low concentrations mounted on its AFE module

Specifications

Gas: NO Sensor: NO-A4
Performance Characteristics Nominal Range: 0 to 18 ppm Maximum Overload: 50 ppm Long Term Sensitivity Drift: < 20% change/year in lab air, monthly test Long Term zero Drift: 0 to 50 ppb equivalent change/year in lab air Response Time (T90): ≤ 25 seconds Sensitivity: 350 to 550 nA/ppm Accuracy: as good as ±0.2 ppm* (ideal conditions)
Operation Conditions Temperature Range: -30 ºC to 50 ºC Operating Humidity: 15 to 85% RH non-condensing Pressure Range: 80 to 120 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 2 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm NO equivalent)
Hydrogen Sulfide
H2S
15
-1.5
Sulfur Dioxide
SO2
5
0
Cholrine
Cl2
5
1.5
Carbon Monoxide
CO
300
0
You can find a complete example code for reading the NO Sensor for low concentrations in the following link:
SCP v30 01: Electrochemical gas sensors
SCP v30 01 – Electrochemical gas sensors

Nitric Dioxide (NO2) Gas Sensor [Calibrated]

This sensor was discontinued in May 2017. Its substitute is the Nitric Dioxide (NO2) high accuracy Gas Sensor [Calibrated]. The information about this alternative sensor can be found in the next section of this guide.
Figure: Image of the Nitric Dioxide Sensor mounted on its AFE module

Specifications

Gas: NO2 Sensor: 4-NO2-20
Performance Characteristics Nominal Range: 0 to 20 ppm Maximum Overload: 250 ppm Long Term Output Drift: < 2% signal/month Response Time (T90): ≤ 30 seconds Sensitivity: 600 ± 150 nA/ppm Accuracy: as good as ±0.2 ppm* (ideal conditions)
Operation Conditions Temperature Range: -20 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 90 to 110 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 2 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm NO equivalent)
Carbon Monoxide
CO
300
0
Hydrogen Sulfide
H2S
15
-1.2
Sulfur Dioxide
SO2
5
-5
Nitric Oxide
NO
35
0
Chlorine
Cl2
1
-1
You can find a complete example code for reading the NO2 Sensor in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Nitric Dioxide (NO2) high accuracy Gas Sensor [Calibrated]

Figure: Image of the high accuracy Nitric Dioxide Sensor mounted on its AFE module

Specifications

Gas: NO2 Sensor: NO2-A43F
Performance Characteristics Nominal Range: 0 to 20 ppm Maximum Overload: 50 ppm Long Term Sensitivity Drift: < -20 to -40% change/year in lab air, monthly test Long Term zero Drift: < 20 ppb equivalent change/year in lab air Response Time (T90): ≤ 60 seconds Sensitivity: -175 to -450 nA/ppm Accuracy: as good as ±0.1 ppm* (ideal conditions) O3 filter capacity @ 2 ppm: > 500 ppm·hrs
Operation Conditions
Temperature Range: -30 ºC to 40 ºC Operating Humidity: 15 to 85% RH non-condensing Pressure Range: 80 to 120 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 2 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

​
Gas
Formula
Concentration (ppm)
Output Signal (ppm NO2 equivalent)
Hydrogen Sulfide
H2S
5
< -80
Cholrine
Cl2
5
< 75
Nitric Oxide
NO
5
< 5
Sulfur Dioxide
SO2
5
< -5
Carbon Monoxide
CO
5
< -5
Hydrogen
H2
100
< 0.1
Ethylene
C2H4
100
< 1
Ammonia
NH3
20
< 0.2
Carbon Dioxide
CO2
5% vol
0.1
Halothane
​
100
nd
You can find a complete example code for reading the high accuracy NO2 Sensor in the following link:
SCP v30 01: Electrochemical gas sensors
SCP v30 01 – Electrochemical gas sensors

Sulfur Dioxide (SO2) Gas Sensor [Calibrated]

This sensor was discontinued in March 2017. Its substitute is the Sulfur Dioxide (SO2) high accuracy Gas Sensor [Calibrated]. The information about this alternative sensor can be found in the next section of this guide.
Figure: Image of the Sulfur Dioxide Sensor mounted on its AFE module

Specifications

Gas: SO2 Sensor: 4-SO2-20
Performance Characteristics Nominal Range: 0 to 20 ppm Maximum Overload: 150 ppm Long Term Output Drift: < 2% signal/month Response Time (T90): ≤ 45 seconds Sensitivity: 500 ± 150 nA/ppm Accuracy: as good as ±0.2 ppm* (ideal conditions)
Operation Conditions Temperature Range: -20 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 90 to 110 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 2 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm SO2 equivalent)
Carbon Monoxide
CO
300
3
Hydrogen Sulfide
H2S
15
0
Nitric Oxide
NO
35
0
Nitric Dioxide
NO2
5
-5
You can find a complete example code for reading the SO2 Sensor in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Sulfur Dioxide (SO2) high accuracy Gas Sensor [Calibrated]

Figure: Image of the high accuracy Sulfur Dioxide Sensor mounted on its AFE module

Specifications

Gas: SO2 Sensor: SO2-A4
Performance Characteristics Nominal Range: 0 to 20 ppm Maximum Overload: 100 ppm Long Term Sensitivity Drift: < ±15% change/year in lab air, monthly test Long Term zero Drift: <±20 ppb equivalent change/year in lab air Response Time (T90): ≤ 20 seconds Sensitivity: 320 to 480 nA/ppm Accuracy: as good as ±0.1 ppm* (ideal conditions)
Operation Conditions Temperature Range: -30 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 80 to 120 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: 2 years in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm SO2 equivalent)
Hydrogen Sulfide
H2S
5
< 40
Cholrine
Cl2
5
< -70
Nitric Oxide
NO
5
< -160
Sulfur Dioxide
SO2
5
< 1.5
Carbon Monoxide
CO
5
< 2
Hydrogen
H2
100
< 1
Ethylene
C2H4
100
< 1
Ammonia
NH3
20
< 0.1
Carbon Dioxide
CO2
5% vol
< 0.1
You can find a complete example code for reading the high accuracy SO2 Sensor in the following link:
GP v30 01: Electrochemical gas sensors
GP v30 01 – Electrochemical gas sensors

Ammonia (NH3) Gas Sensor for low concentrations [Calibrated]

Figure: Image of the Ammonia Sensor for low concentrations mounted on its AFE module

Specifications

Gas: NH3 Sensor: 4-NH3-100
Performance Characteristics Nominal Range: 0 to 100 ppm Long Term Output Drift: < 2% signal/month Response Time (T90): ≤ 90 seconds Sensitivity: 135 ± 35 nA/ppm Accuracy: as good as ±0.5 ppm* (ideal conditions)
Operation Conditions
Temperature Range: -20 ºC to 50 ºC Operating Humidity: 15 to 90% RH non-condensing Pressure Range: 90 to 110 kPa Storage Temperature: 0 ºC to 20 ºC Expected Operating Life: ≥1 year in air
Sockets for Waspmote OEM:
  • SOCKET_1
  • SOCKET_2
  • SOCKET_3
  • SOCKET_4
  • SOCKET_5
  • SOCKET_6
Sockets for Plug & Sense!:
  • SOCKET_A
  • SOCKET_B
  • SOCKET_C
  • SOCKET_F
Average consumption: less than 1 mA
*Accuracy values are only given for the optimum case. See the "Calibration" chapter for more detail.
The electrochemical sensors must be always powered on in order to get optimum measurements. This implies a power consumption, however it improves the performance of the sensor. This should also be applied when entering sleep modes so the sensor is not powered off selecting the proper sleep option.
Calibrated gas sensors are manufactured once the order has been placed to ensure maximum durability of the calibration feature. The manufacturing process and delivery may take from 4 to 6 weeks. The lifetime of calibrated gas sensors is 6 months working at maximum accuracy. We strongly encourage our customers to buy extra gas sensors to replace the original ones after that time to ensure maximum accuracy and performance.

Cross-sensitivity data

Gas
Formula
Concentration (ppm)
Output Signal (ppm NH3 equivalent)
Carbon Monoxide
CO
300
0
Hydrogen Sulfide
H2S
5
1.5
Carbon Dioxide
CO2
5
-3
Hydrogen
H2
15