Design of CO infrared detection system based on CAN bus and MSP430
Abstract: It is proposed a design idea of infrared detection system based on CAN bus interface. The detection system uses the MSP430 ultra-low power microcontroller as the core, using the SM-CO H / M infrared CO gas detector, combined with digital filtering and temperature compensation, to achieve the purpose of accurately measure the CO concentration, and use the CAN bus interface to achieve data. Remote transmission while performing field and remote monitoring. Key words: MSP430; CAN bus; digital filtering; temperature compensation; Delphi1 Introduction Carbon monoxide (CO) is a highly toxic gas, human body tissue and cell hypoxia, resulting in poisoning suffocation. Under the coal mine, CO is also one of the main gases that cause gas explosion. COs have caused huge damage to industrial production or humans. Therefore, CO testing is especially important, especially in coal mines, "Coal Mine Safety Regulations", the CO concentration in the downhole workplaces should be controlled below 0.002 4%. Therefore, in real time, the concentration of CO gas under the well is accurately measured, which is of great significance to protect the safety production of coal mines. The method of currently detecting CO mainly has chemical method, electrochemical method, gas chromatography, etc. These methods are generally priced, unparalleled, and the measurement accuracy is low. A new detection system is designed here, and the infrared Co sensor and the MSP430 single-chip microcomputer are used as the core signal processing circuit, combined with digital filtering, temperature compensation operations. It has the advantages of wide detection concentration range and long service life. The CAN bus has a long and reliability, and the detector has a remote communication capability by expanding the CAN bus interface, which can easily connect contact with the monitoring center, effectively reduce the incidence of accidents, and has promotion and application value. 2 System Composition and Hardware Design The system consists of an infrared CO gas sensor, an MSP430 microcontroller, a CAN bus interface, and a remote monitoring system. The system controls the data detected by the single-chip microcomputer in the detection site, controls the LCD display, the sound and light alarm, and also equipped with the CAN bus controller, it can easily obtain relevant information such as concentration, temperature, and alarm record to achieve intelligent industrial scene, remote Simultaneous monitoring function. The composition block diagram of the system is shown in Figure 1. The principle of the sensor and the selection of each substance has a specific absorption spectrum (such as a very strong absorption peak at a wavelength of 4.5 μm in the wave wavelength), which can be used for measurement. The concentration of the gas can be judged according to some specific wavelengths on various gas spectrum curves. When the infrared light passes through the gas to be tested, these gas molecules have an absorption effect on the perfume of a particular wavelength, and the absorption law follows the Larbon-Bill law style, and I is the energy of transmitted light, L / Mol · cm; IO is infrared radiation The energy of gas absorbed, l / mol. Cm; k is constant associated with gas and radiation wavelength, l / mol · cm: C is the concentration of the gas being measured. Mol / L; L is radiant through the thickness of the gas layer, cm. It can be found in the formula (1), by detecting the radiation intensity after the infrared radiation is absorbed, the concentration of the gas is calculated. The SM-C0 H / M sensor is used, which uses two beam non-lateral infrared (NDIR) detection techniques. It has the advantages of anti-other gas interference, convenient maintenance, good stability, self-contained temperature compensation, MODBUS ASCII protocol digital output and analog output. Suitable for leakage alarms, on-site construction protection, simple gas analysis gases, online monitoring, industrial process analysis and other occasions. 2.2 MSP430 Single Chip Microcomputer Working Principles and Data Processing MSP430 MCU is a 16-bit single-chip microcontroller produced by Texas Instruments (Ti). According to the system function and peripheral circuit interface requirements, the MSP430F449 single-chip microcomputer is selected. The microcontroller has a rich internal hardware resource; the built-in temperature sensor is used to detect the ambient temperature, compensate for the data detected by the infrared sensor; its built-in A / D converter is used to use the sensor The output analog is converted to digital; through the hardware multiplier, the measured A / D sampling data is implemented for high-speed digital filtering and temperature compensation. Digital filtering method adopts a depleted average filtering method. In cases of pulse interference, if the general mean value method is used, the interference will be an average to the results, and the error caused by interference is not easily eliminated. First, the IV sampling value is arranged in size in size, and the "Bubbling Sort Law" can be used to remove the maximum and minimum value in n data, then calculate the average of (n-2) data, that is, Extreme value average filtering method. Temperature compensation processing method; when the static characteristics of the sensor are linear, the characteristics before the temperature compensation can be expressed as: in the formula, X is the input amount of the sensor, y is the output amount, y is the intercept of the characteristic curve on the Y-axis (Ie the output gain caused by ambient temperature), k is a proportional coefficient. The steps of the temperature compensation formula method are as follows: (1) Given (M + 1) Temperature value: T0, T1, T2, ..., Tn, ..., Tm, measure the static characteristic curve of each temperature at the Y-axis The intercept Y0, Y1, Y2, ..., Yn, ... ym; (2) Title Yenda as a temperature T as an argument of the N-Multiplicate (N
