Only by maintaining the optimum amount of gas density within their chambers can the functional dependability and reliability of high-voltage industrial equipment be guaranteed. This article covers the working principle of gas density detectors, their components, and the latest research focused on this particular area.
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Gas Density Detection Principles
Gas density is frequently estimated indirectly by gas pressure sensors. Because the pressure in a tightly sealed compartment fluctuates greatly with temperature, such systems require temperature adjustment, introducing a cause of variation.
The most dependable commercially available options include two dominating technologies for precise measurement and monitoring of gas density. Mechanical detectors use the standard/reference chamber function to determine gas density accurately. To measure density directly, gas density sensors use an electronic quartz tuning fork mechanism. The hybrid technology integrates both of the above-mentioned functional techniques.
Reference Chamber Mechanism for Density Measurement
Gas Pressure, density, and temperature have a specific connection specified by isochores. A gas-insulated chamber's insulating is obtained through a predetermined density, which results in a fixed pressure at a specific temperature.
A density sensor is often immediately connected to the equipment's pressurized chamber via a programmable mechanical interface. The metal bellows technology enables immediate thermal linkage of pressure chamber gases and standard chamber gas filling.
Both the reference gas chamber and the pressurized chamber are tightly sealed. The operating principle is unaffected by ambient pressure making it an absolute sensing principle.
The external bellows capacity is used to analyze the pressure, more especially the density of the gas chamber. If the density of the gas chamber changes, the bellows system activates up to four separate microswitches through a switching shaft and a spring-loaded switching panel. Each microswitch can be factory-calibrated to warn for raising or lowering pressure.
How is Gas Density Measured by Quartz Tuning Fork Technology?
In the mid-1990s, the quartz tuning fork density monitoring technique was invented. It is the preferred option for simultaneous and long-term drift-free density sensing and data gathering. When a vibrating tuning fork is exposed to varied density gases, its resonance frequency shifts and dampens. It is a technique of quantitative density measuring.
A configurable mechanical attachment connects the density detector to the pressurized chamber. As a result, the density in both the insulated gas chamber and the sensor measurement compartment is balanced. The density detectors employ physics by contrasting the continuous resonant frequency of a quartz oscillator in a vacuum to the resonance frequencies of equivalent quartz enclosed by a shielding gas mixture.
The pre-set resonance frequency of the gas mixture enclosed quartz tuning fork is affected by changing densities of gas. The monitoring of density variations requires less than 10ms of response time. The resonant frequency shifting is proportionate to the insulated reaction gas density. A temperature sensor has been added to the digital processing unit.
Limitations of Gas Density Detectors
Physical degradation and poisonous and material-aggressive pollutants might develop when discharges originate within pressurized gas chambers. The gas sulfur hexafluoride (SF6) is routinely utilized. Hydrofluoric acid and thionyl fluoride are the two most common pollutants. Both can result in long-term deterioration due to poor material selection. Abrasion grains can degrade sensor elements.
The substances used for the process gas interconnection, standard gas chamber, and bellows mechanism are particularly chosen to tolerate dangerous pollutants. Popular materials include high-alloyed stainless steel. A separate advanced process of gas filtration safeguards against tiny erosion particulates and filters harmful vapors.
How do Gas Density Meters Operate?
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 over the cylinder's exterior and internal faces, creating a connection with the oscillating boundaries.
The gas density determines the amount of gas that resonates with the cylinder, and because raising the oscillating mass reduces the inherent frequency of oscillation, the gas density is easily established by monitoring this frequency.
The output signal is provided by an amplification system that is magnetically connected to the sensor module and preserves the oscillation parameters. The amplification module and signal output circuitry are enclosed in epoxy resin.
Which Factors Should Strictly Be Monitored?
First and foremost, the gas in the density meter chamber should be reflective of the free stream in terms of gas compositional proportions. This is usually best accomplished by assuring a modest sample gas flow rate.
As the density varies proportionally with absolute pressure in an ideal gas, the pressure of the sample gas must be about equal to the pipeline pressure. Furthermore, because densities fluctuate inversely with absolute temperature, the temperatures of the specimen must be about equivalent to the temperature of the pipeline gas.
An article published in Mathematical Problems in Engineering density computational framework based on viscoelastic correction has been proposed to balance the detection performance of the tuning fork density sensor. The research has identified a better group of tuning fork proportions to enhance its performance as compared to typical tuning fork density sensors.
Although the measurement's precision was boosted, the effect of viscosity on the tuning fork's resonance frequency grew as tuning fork proportions shrank. The researchers employed the partial least solution that fits the density estimation method through the frequency-density characterization test to tackle this problem.
In short, the measurement of gas density is very essential in various industries and the researchers are committed to manufacturing highly optimized density sensors with increased efficiency and accuracy.
References and Further Reading
Yang, H. et. al. (2020). Research on tuning fork dimension optimization and density calculation model based on viscosity compensation for tuning fork density sensor. Mathematical Problems in Engineering, 2020. Available at: 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. All 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 flow meters. [Online]
Available at: https://www.stssensors.com/blog/2020/07/01/density-measurement-in-gas-flow-meters/
Truedyne, 2022. Density-Measurement-Basics-Part2. [Online]
Available at: https://www.truedyne.com/density-measurement-basics-part-2/?lang=en