Fixed Combustible Gas Monitor

Fixed Combustible Gas Monitor

The Fixed Combustible Gas Monitor is used for continuous, real-time online monitoring of the concentration of various flammable and explosive gases in a fixed installation.

Applied to the detection of flammable gas concentrations, it can accurately detect the concentration of flammable gases and display the real-time concentration value on-site. It issues an audible and visual alarm when the concentration of flammable and explosive gases exceeds the standard. The signal is remotely transmitted and synchronously displayed on the monitoring host in the duty room, showing the concentration value and alarm status. It also automatically interlocks to control the exhaust fan for ventilation.

★★★★★

  • Short delivery time
  • Better price
  • Customizable parameters

Features

  • Misoperation recovery function allows restoring settings changed within a specific timeframe to their previous state;
  • Operates normally in extreme environments from -40°C to +70°C with automatic temperature compensation;
  • Features dual-level lightning protection, IP65 waterproof rating, dustproof and explosion-proof capabilities, and resistance to strong electromagnetic interference and static electricity generation;
  • Transmits monitored concentration data to the controller host in the monitoring control room via 4-20mA analog, RS485, or digital outputs for synchronized display and alarms;
  • Includes a standard infrared remote control for remotely silencing alarms, modifying alarm thresholds, and restoring factory settings;
  • Features reverse-connection protection, preventing damage to the fixed combustible/explosive gas detector from any incorrect wiring configuration;
  • Incorporates an independent gas chamber to prevent particulates and impurities from entering the instrument alongside the measured gas, enhancing service life and reliability.

Specifications

Gas DetectionCombustible gas, Ex. (methane, CH4)
Optional: Expandable to 1-6 gas concentrations and temperature/humidity settings
Measuring Range & ResolutionEx. (CH4): 0-100%LEL, 0.1%LEL, industrial-grade catalytic combustion principle sensor
Or Ex. (CH4): 0-1000ppm, 0.1ppm, imported high-precision infrared principle sensor (optional 0-5000ppm, 10000ppm, etc.)
Or Ex. (CH4): 0-5%VOL, 0.01%VOL, imported high-precision infrared principle sensor (optional 0-50%VOL, 100%VOL, etc.)
Other ranges, scales, principles, and resolutions can be customized.
Detection Accuracy≤±3% F.S. (higher accuracy available upon request)
Repeatability≤±2%
Linearity≤±2%
Uncertainty≤±2%
Response TimeT90 ≤ 20 seconds
Recovery Time≤ 30 seconds
Signal OutputRS485 (Modbus-RTU) bus-based, 4-20mA split-line system.
Optional features: 0-20mA, 1-5V, 0-5V, 0-10V, wireless transmission, network transmission, SMS alarm.
Operating ModeFixed installation, online detection, diffusion-type measurement; optional pipeline, flow-through, and pump-suction measurement.
Display Mode1.7-inch high-definition color screen display on-site; optional no on-site display, or optional ERUN-PG32E controller for remote display, control, and alarm.
Alarm ModeDefault 1-channel output, optional 2-channel passive contact (dry contact) output, three-level alarm, alarm points can be set.
On-site audible and visual alarm.
Installation MethodPipe-mounted and wall-mounted types. The working pressure for pipe-mounted devices is atmospheric pressure ±30%; pressure reduction is required for pressures exceeding this range.
Operating Voltage12～30VDC DC; standard power supply for a single unit is 24V, 1A or greater DC regulated switching power supply.
Operating EnvironmentTemperature: -40℃～+70℃; Humidity: ≤10～95%RH (normal) non-condensing environments.
For use in condensing environments, customization is required or the operating environment must be specified when ordering.
Electrical Interface3/4NPT, optional M20*1.5 internal thread, 1/2NPT
Connecting CableFor 4-20mA, select a three-core shielded cable; for RS485, select a four-core cable. For distances exceeding 1000 meters, the diameter of a single wire should be ≥1.5mm; the shielding layer should be grounded.
Protection ClassIP65 waterproof and dustproof rating.
Explosion-proof TypeExplosion-proof type, Ex d IIC T6 Gb (gas explosion-proof); Ex tD A21 IP65 T80℃ (dust explosion-proof)
Dimensions210×170×85mm (L×H×W)
Weight1600g

Combustible Gas Sensors and Their Working Principles

Combustible gas detection sensors primarily operate on three principles: catalytic combustion, infrared, and semiconductor. We will now introduce the characteristics of each principle.

Catalytic Combustion Principle

Catalytic combustion sensors are commonly used in the %LEL range. Their main component is two bridge arms composed of two pairs of bridges. When the gas sensor comes into contact with a combustible gas, the resistance within the bridge changes, causing a change in the bridge’s output voltage. The magnitude of the output voltage is directly proportional to the combustible gas concentration. Some catalytic combustion sensors also incorporate a compensation reference compensator to effectively prevent signal degradation caused by environmental changes, ensuring the overall bridge output is proportional to the concentration.

The characteristics of this type of sensor are stable signal, zero-point stability, good repeatability, and a lifespan of approximately 3 years.

Infrared Principle

Infrared gas sensors are mainly designed for specific gases. Not all combustible gases can be detected using infrared principles; only certain flammable gases can be detected using infrared sensors. These include point-type gases such as methane, ethane, and propane.

It primarily utilizes non-dispersive infrared (NDIR) light to detect combustible gases in the air. This sensor uses the absorption characteristics of the near-infrared spectrum and the absorption intensity relationship with the combustible gas concentration to determine the gas concentration. It is highly identifiable and can accurately identify the concentration of the target gas in complex background gases.

The main advantages of this type of sensor are its fast response speed, high repeatability, and integrated temperature compensation. Its lifespan is generally over five years, making it superior to catalytic combustion generation products. The sensor outputs an analog signal, which is converted into a gas concentration change by the detector’s A/D conversion circuit.

Metal Oxide Semiconductor Sensors

Metal oxide semiconductor sensors are most commonly used for ppm-level measurements. They consist of three parts: a heating circuit, a load circuit, and a power supply circuit. After the semiconductor device is heated to a stable temperature using the heating circuit, when combustible gas comes into contact with the sensor, the sensor’s conductivity increases with the increase in combustible gas concentration, forming an output signal proportional to the combustible gas concentration. The gas-sensitive material used in this type of sensor is primarily tin dioxide.

The lifespan of this type of sensor can be up to 10 years. The disadvantages are poor stability, long aging time, and large zero-point drift, so it is often used in civilian combustible gas detectors.

Technical Support

Combustible gas (also known as flammable gas) refers to a gas or vapor that, at 20℃ and 101.3kPa, has a certain flammability range when mixed with air. Simply put, a gas is considered combustible if it meets both the conditions of being combustible and potentially explosive when mixed with air.

From a classification perspective, combustible gases are mainly divided into two categories: Category A gases (lower explosive limit less than 10% of volume), such as hydrogen, methane, and acetylene, are more dangerous; the other category consists of vapors formed from the vaporization of Category A and B flammable liquids, such as liquefied petroleum gas (a mixture of propane and butane) and gasoline vapor.

These gases are widely present in industrial production (petrochemicals, coal mining, semiconductor manufacturing) and daily life (kitchen gas, water heaters), making them a double-edged sword.

Many combustible gases are common, including:

Hydrogen (H2), carbon monoxide (CO), methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), ethylene (C2H4), propylene (C3H6), butene (C4H8), acetylene (C2H2), propyne (C3H4), butyne (C4H6), hydrogen sulfide (H2S), and phosphine (PH3).

A Combustible Gas Meter is a safety device used to detect the concentration of flammable and explosive gases in the environment. There are two main types: catalytic combustion type and infrared optical type. The working principle of a Combustible Gas Monitor is to measure the ratio of the gas concentration to its lower explosive limit (LEL), or ppm and VOL. This instrument can detect dozens of flammable gases such as methane and ethane, and is widely used in high-risk locations such as petrochemical plants, production workshops, confined spaces, and wastewater treatment plants.

Understanding combustible gases requires mastering the core concept of “explosive limits.” This refers to the concentration range of a combustible gas mixed with air that can trigger an explosion, and is divided into the Lower Explosive Limit (LEL) and the Upper Explosive Limit (UEL). Below the LEL, the gas concentration is too low to burn; above the UEL, insufficient oxygen also makes an explosion unlikely. However, concentrations between these two limits can pose a danger when exposed to open flames or electrical sparks.

The explosive limits of different combustible gases vary significantly: the LEL of liquefied petroleum gas (LPG) is only 1.0% VOL, meaning that a concentration of 1% in air poses an explosion risk; the LEL of methane (the main component of natural gas) is 5.0% VOL, while that of hydrogen is 4.0% VOL.

National standards clearly stipulate that combustible gas detection must have two levels of alarms: a level one alarm not exceeding 25% LEL indicates a leak; a level two alarm not exceeding 50% LEL requires immediate emergency measures. This explains why specialized detection equipment is central to safety protection.

There are 7 main types of combustible gas detectors:

  1. Point-type combustible gas detectors with a measurement range of 0–100% LEL;
  2. Standalone combustible gas detectors with a measurement range of 0–100% LEL;
  3. Portable combustible gas detectors with a measurement range of 0–100% LEL;
  4. Point-type combustible gas detectors for measuring manufactured gas;
  5. Standalone combustible gas detectors for measuring manufactured gas;
  6. Portable combustible gas detectors for measuring manufactured gas;
  7. Linear combustible gas detectors.

These seven types of combustible gas detectors can be classified according to different characteristics:

(1) Classification by explosion-proof requirements:

  • 1) Explosion-proof combustible gas detectors.
  • 2) Non-explosion-proof combustible gas detectors.

(2) Classification by usage:

  • 1) Fixed combustible gas detectors.
  • 2) Portable combustible gas detectors.

(3) Classification by detector distribution characteristics.

  • 1) Point-type combustible gas detector.
  • 2) Linear combustible gas detector.

(4) Classification by gas characteristics detected.

  • 1) Combustible gas detector for detecting explosive gases.
  • 2) Combustible gas detector for detecting toxic gases.

Combustible gases, flammable gases, and explosive gases are concepts under different classification standards. The main differences lie in their definition scope and hazardous characteristics:

Combustible gases refer to substances that are in a gaseous state at normal temperature and pressure and can burn, such as methane and hydrogen. They can mix with air (or oxygen) and burn under certain conditions.

Flammable gases specifically refer to combustible gases with a lower explosive limit ≤13%. These gases easily form explosive mixtures in air, such as acetylene and hydrogen. Their danger is higher than that of ordinary combustible gases.

Explosive gases refer to substances that, when they reach their explosive limit concentration in a confined space, will undergo a violent oxidation reaction upon encountering an ignition source, releasing a large amount of heat and gas. Their core characteristic is a sudden and violent reaction leading to a rapid increase in pressure.

In reality, many gases, depending on their concentration in air, may simultaneously possess both flammability and explosiveness. The key difference lies in the speed and intensity of combustion. Combustible gases burn, while explosive gases explode.

In gas detectors, LEL% is generally used to detect the concentration of flammable and explosive gases, ensuring a safe working environment. VOL% and PPM are more commonly used for the quantitative detection of non-flammable gases or low-concentration gases, such as in environmental monitoring and industrial hygiene. In practical applications, LEL% and VOL% are typically used for detecting higher concentrations of gases, while PPM is suitable for monitoring low concentrations of toxic and harmful gases.

LEL% (Lower Explosive Limit %)

LEL is an abbreviation for Lower Explosive Limit, representing the lowest concentration of a flammable gas in air that can cause combustion or explosion. LEL% is a relative quantity used to measure the volume percentage of a flammable gas within its explosive range. When the concentration of a flammable gas in air reaches LEL%, it means that the gas mixture is just at the point where it can be ignited or exploded. For example, if the LEL of a flammable gas is 5%, it means that when the gas content in air reaches 5% by volume, it may explode upon contact with an ignition source.

VOL% (Volume Percentage)

VOL% refers to the proportion of a gas in the total volume of a gas mixture. It is an absolute concentration unit, representing the percentage of a particular gas’s volume within the total volume. For example, if an environment contains 2% oxygen, it means that 2 units of every 100 units of gas are oxygen.

PPM (Parts Per Million)

PPM is a unit for expressing the concentration of trace substances, meaning parts per million. In gas detection, 1 ppm is equivalent to 1 part of the analyte gas per million parts of gas. This is a very small concentration ratio, typically used to represent low concentrations of harmful gases or pollutants. For example, if the concentration of a toxic gas is 1000 ppm, it means that the toxic gas accounts for 1000 parts per million parts of gas.

The conversion between VOL and PPM is relatively simple. Since %VOL is a volume percentage, while PPM is a volume fraction (parts per million), therefore:
1% (VOL) = 10000 PPM.

To convert between VOL and LEL, you must first determine the lower explosive limit (LEL) of the flammable gas. When the concentration of a flammable gas in the air reaches its LEL, we say that the flammable atmosphere is 100% explosive. For example, hydrogen’s LEL is 4%VOL, meaning that when its volume percentage in the air reaches 4%VOL, it will explode upon contact with an open flame.

Therefore, considering 4%VOL as 100% hazard, we call it 100%LEL, i.e., 4%VOL = 100%LEL. Thus, 1%VOL = 25%LEL.

PPM and LEL cannot be directly converted. You must first convert LEL to VOL, and then from VOL to ppm. Here’s a formula for PPM: PPM = %LEL × LEL (vol%) × 100. For example, to calculate methane at 20% LEL, we would use: 20 (%LEL) × 5 (%VOL) × 100 = 10000 PPM.

Besides LEL%, VOL%, and PPM, gas detectors may use other units to express gas concentration, depending on the type of instrument and sensor, as well as the measurement range.

Expert Guide: How a Photoionization Detector Works

Posted on
A photoionization detector (PID) is a highly sensitive analytical instrument designed for the broad-spectrum detection of volatile organic compounds (VOCs) and certain inorganic gases. Its operational principle is rooted in…

CO2 Sensor vs. VOC Sensor: What’s the Difference?

Posted on
An examination of indoor air quality monitoring reveals a frequent point of confusion regarding the distinct roles of carbon dioxide (COâ‚‚) and volatile organic compound (VOC) sensors. This analysis clarifies…

As a professional manufacturer with many years of experience in the gas detection field, Sino-Inst consistently provides reliable combustible gas detection solutions for various industries. Covering multiple sensor types including catalytic combustion and infrared, it can accurately detect over 500 combustible gases such as methane, hydrogen, and propane, suitable for all scenarios including petrochemical plants, gas stations, kitchens, and coal mines.

Request a Quote

Shop Products

Fixed Combustible Gas Monitor | Sino-Inst

The Fixed Combustible Gas Monitor is used for continuous, real-time online monitoring of the concentration of various flammable and explosive gases in a fixed installation.

Product SKU: Fixed Combustible Gas Monitor

Product Brand: Sino-Inst

Price Valid Until: 2099-09-09

Product In-Stock: PreOrder

Editor's Rating:
5