Design and implementation of a mobile automobile exhaust gas analyzer

introduction

Automobile exhaust has become one of the main sources of urban air pollutants. Governments at all levels have taken comprehensive measures from development planning, urban construction, energy supply and other aspects to alleviate the impact of automobile exhaust emissions on the atmospheric environment. Relevant departments are also studying and formulating policies and measures to promote the establishment of a more convenient and fast public transportation system and reduce energy consumption and exhaust emissions in the transportation industry. Mobile automobile exhaust analyzer is a detection device designed to detect exhaust emission indicators of automobiles during driving. It will play a certain role in controlling exhaust emissions and establishing a low-carbon life.

Mobile vehicle exhaust gas analyzer

When the car starts, the mobile car exhaust gas analyzer starts the air pump to sample exhaust gas from the car exhaust pipe. After dust removal, oil removal and water filtration, the exhaust gas enters the gas analysis component IRidium100 for internal infrared processing to collect CO, CO2 and HC concentration data. Then the exhaust gas enters the external O2 and NOx sensors to collect the corresponding O2 and NOx exhaust gas concentration data. These data are converted into digital results after signal detection, amplification and processing, and are transmitted to the microprocessor through the RS-232 serial port of IRidium100. The microprocessor processes and stores the data through statistical and averaging algorithms, encapsulates the data according to the customized environmental protection communication protocol, and transmits it to the designated upper management platform through GSM/GPRS/CDMA data communication or short message communication. There is an operation menu on the LCD of the analyzer. The user can obtain the working status of the equipment and the exhaust gas analysis results by operating the menu through the keyboard. The specific detection data results of CO, CO2, HC, O2 and NOx can be displayed on the LCD. The structure of the mobile car exhaust gas analyzer is shown in Figure 1.

Hardware Design of Mobile Automobile Exhaust Gas Analyzer

The gas analysis component of the exhaust gas analyzer uses the IRidium100 gas analysis module of the British CITY company. It collects the concentration data of CO, CO2, and HC through internal infrared processing. IRidium100 can obtain the concentration data of O2 and NOx through external O2 sensors and NOx sensors.

The single-chip microcomputer system uses C8051F020, which has two serial ports, one of which is connected to IRidium100, and the other is connected to GSM/GPRS or CDMA communication module, using a custom communication protocol to exchange data with the upper management platform.

The input power is directly connected to the car power supply DC12V~DC24V, converted into DC12V and provided to IRidium100, and a set of DC5V power output is provided for the microcontroller and communication module.

The single chip microcomputer controls the operation of the sampling vacuum pump through the relay, mainly controlling the intake and exhaust actions. The relay controls the vacuum pump, which is usually in the disconnected state. When the system starts to perform exhaust gas analysis, the relay is energized to make the vacuum pump work for 5 minutes.

The GSM module uses Siemens' MC37I. This module is a fully functional mobile communication industrial module. The CPU controls it and transmits data through the serial port. It can transmit data including SMS, CSD, GPRS, etc. The CPU controls the module using AT instructions, which complies with ETSI standards GSM 07.07 and GSM 07.05.

Software Design of Mobile Automobile Exhaust Gas Analyzer

Exhaust gas analyzer working mode

The dedicated automobile exhaust gas analyzer is designed with four working modes:

① Manual working mode: when the machine is turned on, the menu is controlled by the keyboard to execute an exhaust gas analysis process;

② Automatic working mode: when the set time is reached every day, the exhaust gas analysis process will be automatically performed;

③ Command working mode: when receiving a command from the upper management platform, an exhaust gas analysis process is executed;

④Calibration working mode: enter through menu selection when the machine is turned on and perform an exhaust gas calibration process.

Among them, the manual working mode and the calibration working mode are triggered by the main menu provided by the LCD, the key value entered by the keyboard on site, and then the corresponding control command is executed.

Manual working mode: when exhaust gas analysis is needed immediately, manually enter the main menu and select one exhaust gas test, or choose to perform n exhaust gas tests (n is entered by the menu setting option) to perform one or more exhaust gas analysis processes.

The automatic working mode compares the configurable "automatic test time" with the real-time clock in the RTC. When the time is equal, it is triggered to perform an exhaust gas analysis process. The automatic working mode is the default mode.

Command working mode, triggered by the command issued by the upper management platform, executes the corresponding exhaust gas analysis process. In command working mode, the instrument receives the "collect exhaust gas" remote command from the communication module through the serial port, and then the instrument automatically performs an exhaust gas analysis process.

In the calibration working mode, when the analyzer is turned on for the first time or when there is a need for calibration, the standard exhaust gas is connected to the inlet of the vacuum pump, and the calibration range is selected manually in the main menu to perform a calibration process. The calibrated exhaust gas analyzer has a benchmark test reference point, which can improve the accuracy of exhaust gas detection.

Key command sequence selection for exhaust gas analysis module

According to the user manual of IRidium100, the key command sequence for data acquisition of CITY IRidium100 exhaust gas analysis module is described as follows.

Range calibration of exhaust gas analyzer

①RESET (command number: $30), use this command before calibrating the exhaust gas analyzer. After issuing the reset command, a response is received, indicating that the reset is successful.

②ZERO ($35), calibrate to zero before sampling. Start the vacuum pump for half a minute and then send the zero calibration command. If the zero calibration completion response is received within 1 minute, the zero point calibration is successful. At this time, stop the vacuum pump.

③SPAN SPECIFIED CHANNELS ($36), calibration range command. After the zero calibration is completed, manually connect the exhaust standard gas and perform the calibration operation. At this time, start the vacuum pump. After ventilation for 15 seconds, send the calibration command to the exhaust analysis module. The LCD displays the instantaneous value. After receiving the calibration completion response, stop the vacuum pump and stop the operation of the serial port.

The collection of exhaust gas data, that is, the exhaust gas analysis process

①RESET ($30), issue this command before executing each exhaust gas analysis command. The reset is considered successful only when a response is received after issuing the reset command.

②ZERO ($35), calibrate zero before sampling. Start the vacuum pump for half a minute and then send the zero calibration command. If the zero calibration is completed after 1 minute, the zero calibration is successful. Stop the vacuum pump at this time.

③COMPENSATED DATA ($31), after zero calibration, data collection can be performed. Let the vacuum pump work for half a minute before sending the data collection command. Collect data again after 10 seconds, and collect a group every 10 seconds. The LCD displays the instantaneous value. After the collection process is completed (collecting 5 times of data), the average value is calculated as the final display. After collecting 5 times, stop operating the serial port and stop the vacuum pump at the same time.

Software process design and implementation

The basic logic of the program flow is that the main program is triggered according to the conditions in the four working modes, and sends the corresponding command to the CITY IRidium100 exhaust gas analysis module. After the module executes the command, it returns the execution result/status data. The main program displays the result data on the LCD on the one hand, and sends it to the communication device on the other hand, which transmits it to the upper management platform.

When receiving a command from the upper management platform, or when the keyboard triggers manual exhaust gas detection, or when the automatic detection time is reached, the exhaust gas detection action is started. After an exhaust gas analysis process, a flag that has been tested on that day is set.

The main menu of the LCD is shown below. Use the up key, down key, + key, - key and confirm key to operate the keyboard menu to trigger the execution of corresponding commands.

"1.Show Settings", //Parameter display
"2.Setup", //Parameter setting
"3.Analysis 1 time", //Manually perform one exhaust gas test
"4.Analysis n times", //Manually perform multiple exhaust gas tests
"5.Calibration Zero", //Calibration"6.Calibration
Span", //Calibration range
"7.Show Date/Time", //Display RTC time
"8.Setup Date & Time", //Set RTC time
"9.Factory Default", //Restore the default detection range
"10.RETURN", //Return
The result data measured in the four working modes are sent to the communication module through the serial port. The test result data format is as follows:
"CO=xx.xx%; CO2= xx.xx%; HC= xxxxxppm; O2= xx.xx%; NOx= xxxxxppm;".

Conclusion

This design uses the C8051F020 as the core of the single-chip system to control the Iridium 100, and realizes the detection of CO, CO2, HC, O2, and NOx concentrations in automobile exhaust, and transmits the detected concentration data to the remote upper management platform through SMS data transmission. The prototype designed and implemented was tried in a local environmental protection bureau in Xinjiang, and the data from the on-site test was recognized by the environmental protection department.