Combustible gas alarm with dual sensor compensatio

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Combustible gas alarm with dual sensor compensation

key words: dual sensors, temperature compensation, static characteristics, dynamic characteristics, gas alarm

Abstract: This paper introduces a combustible gas alarm with two same type of gas sensors to realize temperature compensation. One gas sensor is sealed as a temperature sensor, and the temperature of the other gas sensor is corrected to eliminate the influence of ambient temperature on the characteristics of the gas sensor in a wide range. The alarm adopts the mc68hc05p6a single chip microcomputer of Motorola as the core control component, and the user program based on a certain algorithm is embedded to achieve the characteristic compensation, software correction and real-time control of a specific gas sensor. This paper analyzes and discusses the temperature compensation principle of combustible gas sensor and the correction and control method of MCU software

1. preface

the characteristics of the gas sensor will always change under the influence of the ambient temperature and humidity. In order to effectively monitor the ambient atmosphere, effectively avoid false alarms and missed alarms, and improve the accuracy of measurement, the gas sensor must be effectively compensated and corrected for temperature and humidity. Generally, the characteristics of combustible gas sensor are less affected by humidity and can often be ignored, so this paper mainly considers how to effectively realize the temperature compensation of the sensor

traditional compensation methods generally include hardware compensation and software compensation. The so-called hardware compensation refers to the direct use of the temperature sensor to compensate the gas sensor in the circuit. Although this method is simple, it can be well compensated only when the temperature characteristics of the temperature sensor and the gas sensor are consistent; It is difficult to match the characteristics of a wide range of gas sensors and temperature sensors. The software compensation method carries out algorithm compensation by fitting the temperature characteristic curve of the sensor. This method is based on a certain characteristic curve. For different working environments and temperature characteristics of different sensors, algorithm processing and table lookup correction are used to obtain different compensation effects. This method is complex, and the fitting effect is poor for sensors with discrete characteristics. In order to solve this problem, according to the plan, this paper proposes to adopt the dual sensor compensation method, specifically to select two gas sensors with the same characteristics (in fact, they can only be very close) to realize compensation, and seal one gas sensor a instead of the temperature sensor to compensate the other gas sensor B. This compensation method can not only better fit the static temperature characteristics of the gas sensor, but also synchronously compensate the dynamic temperature response of the sensor

2. Design principle

the value measured by the gas sensor often changes. It may be stable in a short period of time, but it may fluctuate slowly in a long period of time, or it may fluctuate periodically, or even have sudden peaks. The gas sensor mainly reflects this variability of the sensor through two basic characteristics -- Static Characteristics and dynamic characteristics

static characteristics are usually reflected in sensitivity. The so-called sensitivity refers to the output generated by its unit input under static working conditions, which is expressed in S

dynamic characteristic is a unique problem of gas sensor, which reflects the response characteristics of gas sensor to input varying with time. The output characteristic curve of a gas sensor with good dynamic characteristics changes little with time. The input-output relationship of dynamic characteristics is not a constant, but a function of time, which changes with time, so it is often represented by "transfer function"

it can be seen that the input and output relationship of the gas sensor is not a simple linear or curvilinear relationship, and it is very difficult to establish an accurate temperature correction mathematical model for the gas sensor. In general, the dynamic characteristics of the gas sensor are ignored, and certain measures are taken to compensate it according to its static temperature response sensitivity. For example, the temperature of the environment is measured by the temperature sensor, and the output characteristic curve of the gas sensor is corrected; Or directly compensate the hardware of the sensor

the dual sensor compensation method can effectively compensate the dynamic characteristics of the gas sensor. Because the two gas sensors have the same material components and processes, their static and dynamic characteristics are basically the same, and a more complete compensation can be obtained

the combustible gas alarm with dual sensor compensation adopts two combustible gas sensors of the same type, and the mc68hc05p6a micro control chip of Motorola is used for data acquisition, processing, correction and alarm control. The schematic diagram of the system is shown in Figure 1

the system samples two gas sensors respectively, removes the temperature response part of the measured value of the sensor through certain algorithm processing, and obtains the complete gas response number. When the requirements of material experiment are simple and there are not many experimental items, it can take spatial data

set the measured value of the sensor va=a, vb=b, then the gas response VO without temperature influence is: vo=|va vb

judge whether to alarm according to the value of VO. The system can choose which problems we need to pay attention to or multi-point delay alarm mode according to MCU program settings. The alarm output adopts the form of sound and light alarm. In this system, due to the algorithm processing and software compensation method of embedded MCU, not only trivial hardware circuits are saved, but also the reliability and anti-interference ability of the system are greatly improved, and the intelligent control of the system is strengthened

3. hardware design

alarm is mainly composed of sensor, MCU and alarm circuit. The circuit uses mc68hc05p64 as the core control chip. It has 4 channels of 8-bit a/d ports. The gas and temperature sensitive signals are directly collected by the a/d port, and then some algorithm correction and software compensation are carried out. The alarm circuit is shown in Figure 2

the partial voltage resistors R1 and R2 connected in series on the induction resistors of the two sensors should be adjustable resistors. During commissioning, under a certain temperature and standard environment without combustible gas, adjust R1 and R2 to make the output voltage of the two sensors equal, so as to make effective compensation

4. control flow

the MCU control flow of the alarm with dual sensor compensation is shown in Figure 3

mcu can sample the sensor for many times to reduce the error; When judging the alarm, use multiple judgments. Only when the gas concentration is higher than the limit value for three consecutive times within a certain time can the state be confirmed and the alarm be given, so as to reduce the false alarm rate

5 diversity means that I didn't expect a grass-roots entrepreneur. Conclusion

this combustible gas alarm adopts the dual sensor compensation method; In order to achieve better temperature correction effect, the cooperation of sensor manufacturers is often required, and the sensors are produced in pairs during production to ensure the consistency of sensor characteristics. In the design, mc68hc05p6a is used as the control chip, and its a/d conversion circuit is placed in the chip, and the software compensation method is adopted. Therefore, the overall design of the system is small, low power consumption, simple peripheral circuit and strong dry resistance


semiconductor technical data for mc68hc05p6a Motorola semiconductor 1998

2 Lin Youde, Guo Xiangli sensors and their application technology Shanghai Science and Technology Literature Press 1992.1

3 Zhu Mingcheng, et al. Principle and design of intelligent carbon monoxide alarm. Journal of electronic technology application, 1998 3 P

The Design and Implementation on Combustible Gas Alarm made up of Double Gas Sensor

Zhu mingcheng Li kunhua Lo chuntao

(The EDA Technology Center of Shenzhen University, Shenzhen, 518060)


This paper introduces a combustible gas alarm made up of double gas sensor for temperature compensation. In the gas alarm, the Motorola MCU-MC68HC05P6A is used as core controlling unit. A algorithm program for temperature compensation and software correct and real time control are embeded. In this paper, we also discuss the fundamental of temperature compensation of the combustible gas alarm, and analyze the methods about MCU's software correcting and controlling.

Key wards double gas sensor temperature compensation static charactteristic dynamic characteristic gas alarm

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