Overall Functional Design of Laser Dust Sensors

The existing laser dust sensor used in the coal mine safety monitoring system consumes a large amount of power and cannot effectively transmit data over long distances. Based on the principle of laser dust monitor measurement, this paper designs a laser particle sensor with the main features of low power consumption, long transmission distance, and accurate measurement. It meets the various technical requirements of the coal mine safety monitoring system after upgrading and transformation and supports RS485 bus communication and CAN bus communication commonly used in coal mine safety monitoring systems. The sensor has a measurement range of 0-1000 mg/m³ and an accuracy of ±15%. It is a reliable laser dust sensor for coal mine dust concentration monitoring.
 


The design of environmental sensors, after the upgrade and transformation of the coal mine safety monitoring system, should follow national and industry standards such as the "Coal Mine Safety Monitoring System Upgrade and Modification Plans," "General Technical Requirements for AQ6201 Coal Mine Safety Monitoring Systems," "AQ1029 Coal Mine Safety Monitoring System and Detection Instrument Use Management Specifications," and "MT/T 1102 Coal Mine Dust Concentration Sensors." The requirements for the environmental sensor should adhere to the following design principles:

 

The output of the dust concentration measurement is digitized, enabling digital communication with the substation or host computer to achieve the intelligent design of the dust concentration sensor. Digital communication has advantages of good anti-interference ability, low bit error rate, and accurate data transmission. The digital communication protocol designed for the sensor includes a data verification function. The data verification function includes a dual verification mode, incorporating both the verification of the physical address code with the host computer or substation and the parity check function during data transmission to reduce the data transmission error rate. Additionally, it supports both RS485 bus communication and CAN bus communication.
 

The dust concentration measurement is installed at the substation communication interface and adopts a design that enhances its ability to resist electromagnetic interference. The underground transmission space of coal mines is narrow and long, with many large electrical pieces of equipment. When large equipment is started and operated, electromagnetic interference is complex, dust easily gathers, and the air is humid, enabling it to pass the 3-level electrostatic immunity test, the 2-level electromagnetic radiation immunity test, the 2-level electrical fast transient pulse group immunity test, and the 2-level surge (impact) immunity test.

The anti-interference design should align with the characteristics of the dust concentration measurement to minimize interference. On the one hand, it is necessary to prevent interference from intruding, that is, anti-interference; on the other hand, it is necessary to prevent it from becoming a source of interference, that is, to suppress interference. The solution is as follows:
 

The electrostatic anti-interference design should be considered from two aspects: reliable grounding and the structural design of the real-time dust measurement. The structural design incorporates a stainless steel metal shell embedded in an ABS plastic shell. The two shells are integrated, ensuring both the shielding of interference and insulation from the outside world.
 

Fast pulses can damage the core processing chip of the real-time dust measurement, rendering it unable to function normally. If a high-frequency pulse group occurs on the data bus, it can easily cause incorrect timing of the core processing chip, leading to program disorder or more serious consequences. Absorption components are used to reflect and absorb unnecessary interference signals, thereby achieving the purpose of filtering.
 

Surge primarily refers to changes in the power supply current and voltage of Industrial dust monitoring. Whether caused by lightning or high voltage penetration, surges can easily occur and cause significant harm. The relevant design primarily focuses on the filtering function of the power supply, enhancing the power supply filtering circuit, and isolating and filtering the input and output power supplies to achieve anti-surge (impact) objectives.
 

There are three measures to block electromagnetic wave interference: shielding, filtering, and grounding. Grounding and shielding should take into account the structural design of the Industrial dust monitoring, while filtering and suppression should consider the circuit design of the product. Therefore, power supply filtering circuits, surge suppression filtering circuits, and pulse group filtering circuits are added to the circuit design, and anti-static design is incorporated into the structure.
 

The excellent monochromaticity of the laser light source ensures that the conversion coefficient of the environmental mass concentration is unaffected by the color of the dust, thereby ensuring the stability of the detection. Dust measurement sensor technology based on the laser principle is applied to the measurement of dust concentration. The new laser dust sensing technology features low power consumption, accurate measurement, and long-distance transmission. It solves the problem of mining sensors being limited by the intrinsically safe power supply and difficult long-distance transmission. At a typical working voltage of 12V, the working current of the entire machine is no more than 30mA.
 

During coal mining and excavation, dust easily accumulates and the air is humid. To extend the service life of the environmental health sensors, its protection level has been increased to IP65, making it suitable for use in the harsh environments of coal mines. Enhance the protection level of the dust concentration sensor and strengthen its protective capabilities to ensure stable operation in harsh environments over an extended period.
 

The particulate matter detection allows the alarm threshold and power-off threshold to be set through remote control. It emits an audible and visual alarm when the alarm threshold is exceeded and sends a power-off control command when the power-off threshold is exceeded. The alarm threshold, power-off threshold, and physical address of the particulate matter detection can be set and modified using the remote control.
 

The standardized dust sensor supports the mainstream communication methods commonly used in coal mines, including RS485 and CAN bus communication. RS485 communication supports the standard Modbus communication protocol, while the CAN bus protocol supports proprietary protocols.
 

The laser particle sensor can be configured via remote control and can also receive direct commands from the host computer. It provides on-site display and remote transmission functions, including the sensor's measurement value, working status, alarm status, and the operational status of the dust sensor module.
 

The laser particle sensor element is a highly integrated, compact device with a simple interface and easy installation. The element features an open structure that effectively prevents pollution and blockage in the dust measurement chamber. It employs a fanless design and operates with an extremely low current, making it ideal for workplaces with long-distance power supplies. The element uses the photometer principle and a single-line laser light source. It integrates the light source control circuit, photoelectric detection circuit, power management circuit, data acquisition circuit, and signal processing circuit within a volume of 73mm×70mm×36mm. The element features a threaded installation interface. The unique optical path design prevents dust from impacting the core components of the laser particle sensor. The TTL-level UART circuit interface is user-friendly, facilitating continuous dust concentration monitoring on-site in hazardous environments and providing accurate and timely assessments of dust pollution.
 

The stability of the sensor directly affects the overall stability of the system and is crucial for ensuring the safety of coal mine operations. The reliable operation of the laser particle sensor is crucial for the occupational health of coal mine workers and for monitoring and controlling dust explosion hazards in coal mines. A laser particle sensor specifically designed for coal mine environments is proposed. It features accurate detection, good stability, long lifespan, low power consumption, long-distance transmission, and minimal maintenance costs. It significantly reduces maintenance time and costs while enhancing monitoring stability.