Compact Low Power Wireless Gas Sensor Node With Thermo Compensation for Ubiquitous Deployment

TLDR: This work presents a wireless gas sensor node in which a widely used Wheatstone sensing circuit based on two sensors is exchanged with a single sensor circuit, as well as the associate gas measurement procedure.

Abstract: Wireless sensor networks (WSNs) have recently been applied for industrial monitoring, including combustible and flammable gases monitoring. In this work, we present a wireless gas sensor node in which a widely used Wheatstone sensing circuit based on two sensors is exchanged with a single sensor circuit, as well as the associate gas measurement procedure. The core of the measurement procedure is the four-stage heating profile, which enables low power consumption of sensing circuit and thermo compensation adjustment. A thermo compensation algorithm is capable of avoiding the effect of the environmental temperature on the measurements by keeping stable zero-offset within $\pm 1\;\hbox{mV}$ and ensuring low absolute error within 0.1% vol. The thorough design of the sensor node allows it to fit into the $5.5\;{\hbox{cm}^3}$ packaging, which ensures its true ubiquitous deployment in outdoor and industrial environment.

Figures

Fig. 5. Sensor response (a) U02 , (b) U 0 4 , and (c) resultant output response S 0 under the environmental temperature change for 38 ◦C at 0% gas concentration in the atmosphere where solid line is approximation and dots are experimental values.

TABLE II ABSOLUTE MEASUREMENT ERROR (% VOL.) OF TEST GAS MIXTURE CH4 WITH (W) AND WITHOUT (W/O) THE APPLICATION OF THERMO COMPENSATION

Fig. 6. Sensor output voltage fluctuation with thermo compensation (SC ) and without thermo compensation (S0) adjustment at 0% vol. methane concentration and ambient temperature change for 38 ◦C.

Fig. 8. Current consumption diagram of the sensing circuit.

Fig. 7. Sensor response to 0.5, 1, 1.5, 2, and 2.5% vol. of methane with and without the application of thermo compensation adjustment algorithm.

TABLE III AVERAGE POWER CONSUMPTION OF THE GAS SENSOR NODE ELECTRONIC COMPONENTS: COMPARATIVE STUDY

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Compact low power wireless gas sensor node with thermo compensation for ubiquitous deployment" ?

In this work, the authors present a wireless gas sensor node in which a widely used Wheatstone sensing circuit based on two sensors is exchanged with a single sensor circuit, as well as the associate gas measurement procedure. 

Q2. What is the advantage of the continuous heating profile?

The continuous heating profile used in [12] addresses the problem of the incomplete moisture evaporation and, due to careful design and power management, improves the power consumption up to 227 mW. 

Q3. What is the advantage of commercial platforms?

The advantage of commercial platforms is the simplified application design available by the code reuse and technical support, as well as the minimum time required for platform debugging. 

Q4. What are the requirements of the components incorporated in the units?

All electronic components incorporated in the units are to meet the following requirements: energy efficiency, small size, compatibility of the components, and their simple interface. 

Q5. What is the advantage of the early generic platform?

The early generic platform proposed by Wobscholl [34] consumes up to 1 W, but allows for automatic sensor (catalytic/ semiconductor) calibration. 

Q6. What are the benefits of WSN technology?

WSN technology has opened up wide vista for environmental sensing and industrial applications including the hazardous gases detection. 

Q7. How many boards are used to build the platform?

The platform consists of two 3 cm2 boards fitting into 5.5 cm3 packaging, which significantly improves the state-of-the-art and ensures the platform ubiquitous deployment including difficult to access areas. 

Q8. What is the proposed method for a temperature compensation circuit?

The extra temperature sensor incorporated in a gas sensor to ensure the precise ambient temperature variation measurement is proposed in [5]. 

Q9. What are the advantages of using a temperature, luminosity, and humidity sensor?

Widely used sensors, such as a temperature, luminosity, and humidity ones, consume even less power than the MCU in the active mode. 

Q10. What are the requirements for the commercial and certified gas sensors?

In fact, the commercial and certified catalytic gas sensors require large casing, e.g., TO-7, and power management circuits to enable their correct functioning. 

Q11. What does the sensor node do when the gas concentration is between 0.5 and 1% vol?

When the measured gas concentration is between 0.5 and 1% vol., the sensor node immediately sends a request to the actuator to close the gas valve and, in parallel, notifies the WSN operator about the dangerous situation via the gateway. 

Q12. What is the advantage of the commercial sensing platform?

Commercial sensing platforms for natural and LPG gases detection FlyPort [21] and WaspMote with the “Gases” extension sensing board [22], though having no automatic calibration option as compared with Wobscholl platform, are characterized by slightly reduced power consumption up to 800 and 280 mW, respectively. 

Q13. What is the disadvantage of the voltage divider circuit?

it has an important disadvantage being unable to compensate for the effect of ambient temperature as compared with the Wheatstone circuit where the resultant response from the active and reference sensors provides this compensation “by default” [4]. 

Q14. What is the maximum drift of the zero offset for this sensing circuit?

The maximum drift of the zero offset for this sensing circuit is 0.33% vol. instead of 0.1% vol. tolerance at the temperature change for 38 ◦C. 

Q15. What are the requirements for the gas sensor nodes?

The sensor nodes for hazardous gases detection at plants, in some cases, have, e.g., to be deployed at various heights including the mixing emission height and difficult-to-access areas in indoor/outdoor conditions [20]. 

Q16. What is the purpose of this experiment?

This experiment demonstrates that the application of the proposed algorithm helps keeping the zero-offset properly to meet the absolute error requirement. 

Q17. What is the energy efficiency of the one sensor-based approach?

The energy efficiencyof the one sensor-based approach can be explained by exploiting just one sensor in the sensing circuit and the application of four stage heating profile instead of continuous one. 

Q18. What is the proposed approach to ensure the proper sensors operation at the ambient temperature?

There are two general approaches to ensure the proper sensors operation at the ambient temperature: 1) sensors calibration in all range of operating temperatures and recording these values in the memory of MCU; and 2) compensation for the ambient temperature proposed in this work.