How do gas density detectors work?
Only by maintaining the optimum amount of gas density in their chambers can the functional reliability and reliability of high-voltage industrial equipment be guaranteed. This article covers the principle of operation of gas density detectors, their components, and the latest research focused on this particular area.
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Principles of Gas Density Detection
Gas density is often estimated indirectly by gas pressure sensors. Since the pressure in a hermetically sealed compartment fluctuates greatly with temperature, such systems require temperature adjustment, introducing a cause for variation.
The most reliable commercially available options include two dominant technologies for accurate gas density measurement and monitoring. Mechanical detectors use the standard/reference chamber feature to accurately determine gas density. To measure density directly, gas density sensors use an electronic quartz tuning fork mechanism. Hybrid technology incorporates the two functional techniques mentioned above.
Reference chamber mechanism for density measurement
Gas pressure, density and temperature have a specific connection specified by isochores. The insulation of a gas-insulated room is achieved through a predetermined density, which results in a fixed pressure at a specific temperature.
A density sensor is often immediately connected to the pressurized chamber of the equipment via a programmable mechanical interface. Metal bellows technology provides immediate thermal bonding of pressure chamber gases and standard chamber gas fill.
The reference gas chamber and the pressure chamber are both hermetically sealed. The principle of operation is not affected by ambient pressure, making it an absolute detection principle.
The external capacity of the bellows is used to analyze the pressure, more particularly the density of the gas chamber. If the density of the gas chamber changes, the bellows system activates up to four separate microswitches via a switch shaft and a spring-loaded switch panel. Each microswitch can be calibrated at the factory to warn in the event of an increase or decrease in pressure.
How is gas density measured by quartz tuning fork technology?
In the mid-1990s, the quartz tuning fork density monitoring technique was invented. This is the preferred option for simultaneous, long-term, drift-free density sensing and data collection. When a vibrating tuning fork is exposed to gases of varying density, its resonant frequency shifts and becomes damped. It is a quantitative density measurement technique.
A configurable mechanical attachment connects the density sensor to the pressurized chamber. As a result, the density in both the insulated gas chamber and the sensor measurement compartment is balanced. Density detectors use physics by contrasting the continuous resonant frequency of a quartz oscillator in vacuum against the resonant frequencies of an equivalent quartz surrounded by a mixture of shielding gases.
The preset resonant frequency of the quartz tuning fork enclosed in the gas mixture is affected by variations in gas density. Monitoring density variations requires less than 10 ms of response time. The resonant frequency shift is proportional to the density of the isolated reaction gas. A temperature sensor has been added to the digital processing unit.
Limitations of Gas Density Detectors
Physical degradation and pollutants that are toxic and aggressive to materials can develop when releases come from pressurized gas chambers. Gaseous sulfur hexafluoride (SF6) is commonly used. Hydrofluoric acid and thionyl fluoride are the two most common pollutants. Both can lead to long-term deterioration due to improper material selection. Abrasion grains can degrade sensor elements.
The substances used for the process gas interconnection, the standard gas chamber and the bellows mechanism are particularly chosen to tolerate hazardous pollutants. Popular materials include high alloy stainless steel. A separate advanced gas filtration process protects against tiny eroding particles and filters out harmful fumes.
How do gas density meters work?
The density sensing component is a narrow metallic cylindrical element that has been stimulated to oscillate in a circular pattern at its inherent frequency. The gas is transferred to the outer and inner faces of the cylinder, creating a connection with the oscillating walls.
Gas density determines the amount of gas that resonates with the cylinder, and because increasing oscillating mass reduces the inherent frequency of oscillation, gas density is easily established by monitoring this frequency.
The output signal is provided by an amplification system which is magnetically connected to the sensor module and preserves the oscillation parameters. The amplifier module and signal output circuits are encased in epoxy resin.
What factors should be strictly monitored?
First, the gas in the hydrometer chamber must reflect free flow in terms of gas composition proportions. This is usually best achieved by providing a modest sample gas flow.
Since density varies proportionally to absolute pressure in an ideal gas, the sample gas pressure should be approximately equal to the pipeline pressure. Also, since densities fluctuate inversely to absolute temperature, sample temperatures should be roughly equivalent to the temperature of the pipe gas.
An article published in Mathematical problems in engineering A density calculation framework based on viscoelastic correction has been proposed to balance the detection performance of the tuning fork density sensor. Research has identified a better group of tuning fork proportions to improve its performance over typical tuning fork density sensors.
Although the accuracy of the measurement was improved, the effect of viscosity on the resonant frequency of the tuning fork increased as the proportions of the tuning fork decreased. The researchers used the least partial solution that corresponds to the method of estimating density by the frequency-density characterization test to solve this problem.
In short, gas density measurement is very essential in various industries and researchers are committed to fabricating highly optimized density sensors with higher efficiency and accuracy.
References and further reading
Yang, H. et. Al. (2020). Research on optimization of tuning fork dimensions and density calculation model based on viscosity compensation for tuning fork density sensor. Mathematical problems in engineering, 2020. Available on: https://doi.org/10.1155/2020/7960546
Emerson, n.d. Micro Motion® 7812 Gas Density Meter. [Online]
Available at: https://www.emerson.com/documents/automation/configuration-manual-gas-density-meter-model-7812-micro-motion-en-63108.pdf
Mettler Toledo, 2022. Everything you need to know about density measurement. [Online]
Available at: https://www.mt.com/sg/en/home/applications/Application_Browse_Laboratory_Analytics/Density/density-measurement.html
STS sensors, 2020. Density measurement in gas flowmeters. [Online]
Available at: https://www.stssensors.com/blog/2020/07/01/density-measurement-in-gas-flow-meters/
Truedyne, 2022. Density-Measurement-Basics-Part 2. [Online]
Available at: https://www.truedyne.com/density-measurement-basics-part-2/?lang=en