Gas Pressure Sensor

Working principle of gas pressure sensor

The core working principle of gas pressure sensors is to convert gas pressure signals into measurable electrical signals. The key is to utilize the physical properties of pressure-sensitive components that change with pressure, and then convert this change into standardized electrical signals through subsequent circuits for output.

The current mainstream sensing principles include the following:

• Piezoresistive Effect: Utilizing the piezoresistive effect of semiconductor silicon materials - when a silicon chip deforms under pressure, its resistance value changes accordingly, and the resistance change is converted into voltage output through a Wheatstone bridge circuit. This is currently the most widely used technology route in the industrial field, with the advantages of high sensitivity, fast response speed, and relatively low cost, suitable for gas and liquid general working conditions with a range of 0-1000 bar.

• Capacitive: detects changes in capacitance values by causing changes in the spacing between capacitor plates through pressure. Strong anti overvoltage ability and good long-term stability, suitable for measuring low and micro pressures or corrosive media.

  

• Piezoelectric: Some materials (such as quartz crystals) generate charges under pressure and output electrical signals, suitable for dynamic pressure measurement.
• Optical: Utilizing the optical characteristics changes of optical fibers or gratings under pressure to achieve measurement, suitable for strong electromagnetic interference environments.

Types of gas pressure sensors

According to different measurement standards, gas pressure sensors are mainly divided into the following categories:

• Absolute pressure sensor: measures the pressure relative to absolute vacuum, commonly used for atmospheric pressure monitoring and altitude measurement.
• Gauge pressure sensor: measures pressure relative to ambient atmospheric pressure, such as tire pressure monitoring (TPMS).
• Differential pressure sensor: measures the difference between two pressure points and is widely used in pipeline flow control and filter pressure drop monitoring.
• Sealed pressure sensor: Based on a fixed sealed reference pressure, suitable for specific industrial scenarios.

Typical application scenarios of gas pressure sensors

1. Oil and gas industry

The oil and gas industry is one of the most challenging application areas for gas pressure sensors. The working pressure of natural gas long-distance pipelines can reach up to 35-100 bar, and the pressure rating, explosion-proof certification, and material selection requirements for pressure transmitters are extremely strict. The transportation process of natural gas spans five pressure ranges: high-pressure long-distance gas transmission trunk lines (35-100 bar), provincial gas transmission pipelines (16-35 bar), urban high-pressure pipelines (1.6-4 bar), medium pressure distribution pipes (0.1-1.6 bar), and low-pressure end users (below 0.1 bar), each with completely different instrument requirements.

In oil and gas applications, explosion-proof certification is the primary prerequisite for selection. Natural gas belongs to Group IIC gas, and explosion-proof instruments with Ex db IIC T6 level must be selected for hazardous areas (Zone 1/Zone 2). In addition, natural gas often contains trace amounts of hydrogen sulfide (H ₂ S), which is corrosive to ordinary stainless steel membranes. Therefore, it is necessary to use 316L stainless steel material for liquid receiving components.

2. Industrial Automation and Process Control

In the field of industrial automation, gas pressure sensors are widely used in pipeline pressure monitoring, pneumatic system control, compressor operation monitoring and other scenarios. Whether it is pressure monitoring of reaction vessels in chemical plants or pipeline pressure control of air compressor systems, high reliability gas pressure sensors are indispensable.

3. Automotive Electronics

Automotive electronics is an important application market for gas pressure sensors, mainly including engine intake manifold pressure monitoring (MAP sensor) and tire pressure monitoring system (TPMS).

4. Medical equipment

In the field of healthcare, equipment such as ventilators, anesthesia machines, and blood pressure monitors rely on high-precision gas pressure sensors to achieve precise gas flow and pressure control.

5. Environmental monitoring and HVAC

The pressure measurement of meteorological stations, pressure detection of air quality monitoring systems, and pressure and differential pressure monitoring of HVAC systems all rely on gas pressure sensors.

General guide for selection of gas pressure sensors

The correct selection is the key to ensuring measurement accuracy, stability, and safety. The following are six common elements that need to be considered when selecting:

1. Pressure Range

Range is the most basic specification parameter of gas pressure sensors. When selecting, it is necessary to ensure that the measurement range of the sensor covers the maximum value of the target pressure, while leaving a certain safety margin. The common range varies from kPa to MPa.

2. Output Signal Type

Select the appropriate output signal according to the interface requirements of the control system (PLC/DCS):

• 4-20 mA two-wire current signal: the most commonly used standard signal in industrial fields, with strong anti-interference ability and suitable for long-distance transmission
• 0-5 V/0-10 V voltage signal: suitable for short distance transmission
• HART digital communication: can overlay digital communication on 4-20 mA signals, supports remote parameter configuration and diagnosis
• RS-485 Modbus: Suitable for multi-point networking and remote centralized monitoring

3. Media Compatibility

The chemical properties of the measured gas directly determine the material selection of the sensor. When measuring corrosive gases (such as natural gas containing H ₂ S, chlorine gas, ammonia gas, etc.), it is necessary to use 316L stainless steel or special alloy materials for the contact parts. When measuring special gases such as hydrogen, hydrogen embrittlement issues also need to be considered.

4. Accuracy level

The accuracy of industrial gas pressure sensors is usually expressed as a percentage of full scale (% FS), with common accuracy levels including ± 0.1% FS, ± 0.25% FS, ± 0.5% FS, etc. For high-precision applications such as trade measurement, it is recommended to use products with a grade of 0.1 or 0.25.

5. Explosion Proof Certification

Pressure sensors used in flammable and explosive gas environments must pass the corresponding explosion-proof certification:

• Explosion proof type (Ex d): The shell can withstand internal explosions without damage and will not ignite external explosive environments
• Intrinsic safety type (Ex ia/Ex ib): The electrical sparks or thermal effects generated under normal operation and fault conditions are not sufficient to ignite explosive environments
• When selecting, it is necessary to specify the type of hazardous gas, temperature group, and zone level (Zone 0/1/2) in the installation area.

6. Operating Temperature Range

Gas pressure sensors need to adapt to different environmental temperatures. The typical operating temperature range for industrial grade products is -40 ° C to 85 ° C. In extreme environments with high or low temperatures, wide temperature products should be selected.

Special selection guide for different gas media

The chemical properties of different gases vary greatly, requiring vastly different materials, processes, and designs for sensors. The following is a detailed analysis of common industrial gas pressure measurement selection:

Nitrogen Pressure Sensor

Nitrogen is one of the most widely used inert gases in industry, and its pressure measurement itself is not complicated, but it has special requirements in high-purity and high-pressure scenarios.

• Conventional measurement: For ordinary nitrogen pipelines, a universal pressure sensor is sufficient to meet the requirements.
• High purity nitrogen: In industries such as semiconductors that require extremely high purity (such as ≥ 99.999%), sensors made of SUS 316L all stainless steel must be selected to avoid gas pollution caused by copper alloy joints and other materials.
• High pressure gas cylinder: When measuring the pressure of high-pressure nitrogen gas cylinders, it is recommended to choose products with a range of 1.5 to 2 times the working pressure, and prioritize shock-absorbing liquid filling (such as glycerin) to cope with pressure shock and vibration during gas cylinder filling and discharging.
• Explosion proof requirements: In hazardous areas such as petrochemicals, explosion-proof products certified by ATEX or IECEx must be selected.

Air/Oxygen Pressure Sensor

Air measurement is the most common, but pure oxygen measurement has the highest and most specific safety requirements among all gases.

• Compressed air: As the most common measuring medium, a universal pressure sensor is usually selected. In pneumatic systems such as air compressors, it is recommended to choose sensors with standard signal outputs such as 4-20mA to adapt to variable frequency control.
• Oxygen: Oxygen itself is not flammable, but it has strong combustion assisting properties. Under high pressure, it reacts violently with organic substances such as oils and fats, posing a risk of explosion.
• Core requirement: "Oil ban" treatment: This is the top priority for oxygen selection. Sensors need to be produced, cleaned, and packaged using a 'no oil process'.
• Special filling fluid: To avoid oxidation reaction between ordinary silicone oil and oxygen, the sensor needs to be filled with inert oil (such as Fluorolubricant) inside ® Oil).

Carbon dioxide pressure sensor (CO ₂ Pressure Sensor)

The pressure measurement of CO ₂ is mainly divided into two directions: environmental monitoring and industrial refrigeration, with significant differences in technical requirements.

• Environmental monitoring: mainly measures low concentrations (such as 400-10000 ppm), often using CO ₂ concentration sensors rather than pure pressure transmitters.
• Industrial refrigeration: In CO ₂ refrigeration systems, the pressure is very high (usually exceeding 30 bar), and pressure sensors specially designed for high pressure must be selected to ensure their pressure resistance and overload protection capabilities can meet extreme pressure requirements.

Hydrogen Pressure Sensor

• Hydrogen measurement is a major challenge in the field of industrial instruments, with the core being to solve the two major problems of "hydrogen embrittlement" and "hydrogen permeation".
• Hydrogen Embrittlement: Hydrogen atoms infiltrate the metal lattice, causing the membrane to become brittle and suddenly fracture under stress far below normal strength.
• Hydrogen Permeation: Hydrogen atoms will penetrate the stainless steel membrane and enter the internal silicone oil chamber to form bubbles, causing zero point and range drift of the sensor, ultimately leading to failure.
• Gold plated membrane: Gold plating on the surface of stainless steel membrane is an effective method to suppress hydrogen permeation.
• Special materials: In high-pressure or high-purity hydrogen environments, it may be necessary to use materials with better resistance to hydrogen embrittlement, such as Hastelloy and Inconel.

⚠️  It is strictly prohibited to use ordinary oil filled cores: standard oil filled pressure sensors are strictly prohibited from being used in hydrogen or mixed gases with hydrogen concentration exceeding 30%, as their failure is systematic.

Chlorine/Corrosive Gas Pressure Sensor

For this type of gas, the material selection of the sensor directly determines the safety and reliability of the measurement.

• Corrosive gases (such as chlorine gas Cl ₂): yellow green toxic gases at room temperature and pressure. Dry chlorine gas is still corrosive to steel, iron, etc., but once it contains a small amount of water vapor, it will generate highly corrosive hypochlorous acid and hydrochloric acid. The pressure diaphragm and shell must be made of corrosion-resistant materials such as tantalum or titanium alloy.
• Other corrosive gases (such as ammonia NH3, hydrogen sulfide H ₂ S): Similar to chlorine gas, Hastelloy or PTFE (polytetrafluoroethylene) coated membranes should be used to resist electrochemical corrosion. When measuring natural gas containing H ₂ S, a specialized sulfur resistant pressure gauge should be selected.

Natural Gas Pressure Sensor

Natural gas measurement mainly focuses on explosion prevention and materials, with a pressure range spanning from long-distance pipelines to residential gas.

• Explosion proof certification: Natural gas belongs to Group IIC hazardous gas, and high-level explosion-proof instruments such as Ex db IIC T6 must be selected in Zone 1/2 area.
• Material requirements: If natural gas contains hydrogen sulfide (H ₂ S), the liquid contact material needs to be upgraded to prevent stress corrosion cracking.
• Wide range coverage: From high-pressure gas transmission (>100 bar) to micro pressure of urban gas (<30 mbar), the appropriate range and accuracy need to be selected according to specific operating conditions.

Core challenges and key selection points of gas types

• High purity nitrogen (N ₂) is required, and 316L stainless steel is needed for high-pressure impact high-purity nitrogen; Select 1.5-2 times the range and liquid filled shockproof type for high-pressure scenarios
• Air/oxygen (O ₂) safety risks (combustion assistance) must be treated with "oil prohibition"; Internally filled with inert oil; Adopting specialized cleaning techniques
• Concentration sensor for routine monitoring of carbon dioxide (CO ₂) high-pressure (refrigeration system); The refrigeration system must choose a dedicated high-pressure type
• Hydrogen embrittlement (H ₂) and hydrogen permeation membrane gold plating; Select special alloys for high-pressure scenarios; It is strictly prohibited to use ordinary oil filled cores
• Chlorine gas (Cl ₂) highly corrosive membrane and shell are made of corrosion-resistant materials such as tantalum or titanium alloy
• The risk of natural gas explosion and sulfur-containing corrosion must pass explosion-proof certification (Ex db IIC T6); When containing H ₂ S, sulfur resistant materials should be selected

Installation precautions

Correct installation is the key to ensuring the long-term stable operation of gas pressure sensors:

1. When measuring gas pressure, the pressure tap should be opened at the top of the process pipeline, and the sensor should also be installed at the upper part of the pipeline to facilitate the backflow of accumulated liquid into the pipeline.
2. Before installation, it is necessary to confirm whether the interface size matches. If it does not match, a suitable adapter should be used.
3. Avoid installation within the radiation range of heat sources or near strong vibration sources. If necessary, install insulation covers or vibration reduction devices.
4. Signal cables should not be mixed with power cables, and strong electromagnetic interference should be avoided around sensors.
5. Installation must be carried out without pressure or power supply.
6. For oxygen and other oil free media, it is necessary to ensure that all contact parts undergo strict oil free cleaning before installation.

As a key component of modern industrial measurement and control systems, gas pressure sensors are driving the development of automation and intelligence in various industries through technological advancements. Whether it is long-distance oil and gas pipelines, chemical process control, or automotive electronics and medical equipment, high-precision and high reliability gas pressure measurement solutions are indispensable.

In specific selection, in addition to common parameters such as range, accuracy, and output signal, the type of gas being measured is often the core factor determining the sensor material, process, and safety design. From conventional compressed air to special oxygen, hydrogen, and chlorine gases, each gas has unique technical requirements for its measuring equipment.

Silverinstruments has been deeply involved in the field of industrial instruments for many years, committed to providing customers with high-quality pressure transmitter products. Our gas pressure sensor products cover multiple ranges, output signals, and explosion-proof levels, meeting the full range application needs from general industry to oil and gas, from room temperature to wide temperature, and from ordinary areas to explosion-proof hazardous areas. At the same time, for special gases such as oxygen, hydrogen, chlorine, etc., we can provide customized "no oil" treatment, gold-plated film and special alloy material solutions.