Gas detection method and implementation in mobile cabin based on telemetry

In various closed mobile cabin environments, there are a large number of gaseous pollutants, which exist in molecular state, and most of them are inorganic gases, such as CO, NO2, H2S, LEL, VOC, etc. Wireless telemetry technology is used to collect and record the harmful gases, temperature and humidity and other state parameters and environmental parameters in the cabin when the vehicle is stationary and moving in real time, so as to analyze the impact of harmful gases on the physical and mental health of cabin personnel. The system can monitor multiple indicators in the closed cabin environment in stationary and moving in real time, and all test data can be stored, and can be transmitted wirelessly to the monitoring center on the monitoring vehicle several kilometers away in real time.

1 Gas environment in the mobile cabin

According to incomplete statistics, tanks and armored vehicles will produce a large amount of harmful gases in the process of traveling and actual combat, such as CO, NO2, H2S, SO2, CO2, LEL, VOC, NH3, HCN, benzene, formaldehyde and dust pollution. These harmful gases and dust will cause great harm to the physical and mental health of drivers, gunners and crew members. The temperature and humidity in the closed environment of the vehicle also have a certain impact on the human body. In the process of developing tanks and armored vehicles, timely and accurate grasp of various environmental parameters in the mobile cabin provides strong data support for the improved design of the vehicle. Recently, telemetry and remote control technology has been widely used, and the intelligent monitoring technology has been gradually realized. The parameters of the gas in the cabin are shown in Table 1.

2 Test Methods

The monitoring system installs the harmful gas monitor at a fixed position in the cabin in advance. During the monitoring process, the monitor stores the collected signals locally and sends them to the telemetry transmitter through the RS 485 interface protocol. The telemetry transmitter encodes the received data stream to form a standard PCM data stream and sends it to the transmitter. The transmitter converts it into radio waves and transmits it to space. The telemetry ground monitoring center receives these signals, processes them and draws them into curves, so that the environmental changes in the cabin during movement can be intuitively monitored in real time. The system schematic diagram is shown in Figure 1.

The principle block diagram of the telemetry transmission subsystem is shown in Figure 2. The gas sensor subsystem packages the detected gas test data and gives it through the RS 485 data bus interface. All data bus interfaces enter the embedded PCM acquisition encoder for data acquisition encoding.

PCM acquisition coding consists of program control module, timing control module, output module, etc. The serial data stream output by the encoder is sent to the transmitting device for modulation and amplification, and then transmitted from the antenna with sufficient power.

Integration of telemetry ground monitoring subsystem: The telemetry ground monitoring subsystem adopts a vehicle-mounted portable receiving solution. All receiving units of the system except the antenna and low-noise amplifier are placed in the industrial control computer. [page]

3 System composition and implementation

3.1 Sensor selection

The PGM-2000, MultiRAEPGM-54, and UItraRAE PGM-7200 of RAE Company of the United States are selected. These internationally advanced composite/single gas detection modules have an operating temperature of -20 to +50°C and can work normally in an environment with a relative humidity of 0% to 95%. Their lithium batteries can work continuously for more than 10 hours after being fully charged. They have advanced plug-in "intelligent" toxic gas sensors. All of the above instruments have RS 232 interfaces and can provide communication protocols. The technical indicators of the above gas detection instruments are shown in Table 2.

3.2 Sensor Installation

The cabin wireless mobile monitoring system has the following particularities in the system design process: the working environment is harsh, and there are many intersections between the internal subsystems and components; road transportation and climatic conditions make the system face special conditions such as plateaus, mountains, deserts, severe cold, high temperatures and radiation resistance during the design process; the closed cabin space is small, and the volume and shape of the measurement system are strictly required; most of the measurement system equipment is non-standard equipment, and the interior of the mobile cabin cannot provide permanent installation space and specific location for the measurement equipment, and can only be temporarily loaded, which increases the difficulty of reliable installation and operation of the test equipment. Based on sufficient research and banquet car inspection. Different structural designs and installation methods are designed for each type of test equipment. The system consists of two independent units, each of which consists of a main box and a sub-box. The main box and the sub-box are connected by a jumper with a length of about 2 m. The main box can be independently connected to the overall system, and the sub-box can only be attached to the main box. The physical layout of the gas test subsystem is shown in Figure 3.

The test instrument uses EVA cushioning material and flexible sheet metal support to withstand strong impact. The installation diagram of the gas test subsystem in the mobile cabin is shown in Figure 4. Multiple pull rings are configured on the 4 vertical edges of the main box and the auxiliary box, and they are firmly tied to the driving seat with high-strength strapping tape.

3.2 Data collection and transmission

The gas sensor packages the detected gas test data and gives it through the RS 485 data bus interface. All data bus interfaces enter the embedded PCM acquisition encoder for data acquisition encoding.

PCM acquisition coding consists of program control module, timing control module, output module, etc. The serial data stream output by the encoder is sent to the transmitting device for modulation and amplification, and then transmitted from the antenna with sufficient power. This system uses FPGA technology to integrate the interface, acquisition and encoding functions of the measured parameters, so that the encoding module has the characteristics of flexible programming, high integration, fast speed and online programmability. The number of acquisition encoders and the output code rate can be configured online. The transmitter adopts a modular design. The whole machine consists of a modulation module, a linear power amplifier and a secondary switching power supply module. In this way, different modules can be selected to form a transmitter with different point frequencies, different frequencies, different modulation signal forms and different code rates. The vehicle-mounted transmitting antenna adopts an omnidirectional antenna with a gain greater than 5 d Bi. [page]

3.3 Data reception and processing

Data reception and processing are carried out at a remote monitoring station. The system uses an industrial PC as a platform and a PCI bus as a link to connect high-frequency channels, video demodulation and computers to form an organic whole. Except for the antenna and low-noise amplifier , the rest of the system is inserted into the expansion slot of the computer. The main functional components of the system are concentrated in the computer, so the system operation and management are convenient. The antenna and low-noise amplifier are installed on a retractable and movable tripod, so the system is very convenient to carry and set up. The telemetry data processing equipment is shown in Figure 5.

4 Real vehicle installation test

In 2008, a 5 km dynamic real vehicle test was conducted at a certain vehicle standard training ground. The schematic diagram of the fixed-point test vehicle driving process is shown in Figure 6. The monitoring vehicle is stationary at the center of the test field, and the tested vehicle is moving. The distance is less than 5 km, and the tested vehicle is driving at a speed of less than or equal to 100 km/h. During the test driving process, the main functions and indicators of the system are continuously tested and stored. The system is powered by a backup battery or a vehicle battery. The test time is 1 to 2 hours. The telemetry ground station obtains the gas environment parameters in the tested vehicle. Figure 7 is one of the data processing results.

5 Conclusion

By using various gas detection modules and wireless telemetry, the remote monitoring station can reliably obtain environmental data of various harmful gases in the mobile cabin. The test proves that this method is feasible. This test method can provide strong data support for the development and improvement of man-machine-environment of various tanks and armored vehicles.