Based on the operating principle of ultrasonic level meters—emitting high-frequency sound waves (typically 20 kHz – 80 kHz) that reflect off the liquid surface and return, with distance calculated via the time difference ($t = \frac{2d}{v}$)—key factors influencing measurement results include the ultrasonic probe, the distance between the probe and the medium, and the medium itself.
1. What factors affect the probe?
1.1 Water vapor and condensation
When highly volatile water vapor rises and encounters the cooler surface of the probe, it condenses into water droplets. Droplets on the probe’s radiating surface can absorb sound wave energy or impede the vibration of the piezoelectric crystal.
1.2 Corrosion
A corroded probe can directly trigger electrical safety faults, cause measurement failure, or even lead to total system paralysis.
1.2.1 Corrosive gases or condensates can penetrate the probe’s interior, directly eroding the piezoelectric ceramic element and its electrodes; damage to the piezoelectric transducer results in a complete loss of signal.
1.2.2 Deformation of the housing surface generates false echoes and expands the “blind zone.” Surface deformation causes severe “internal multiple reflections” or “near-field clutter” at the probe’s emission point. The instrument may mistake the clutter caused by probe corrosion for the liquid level echo, causing the measured value to lock at the maximum level (false blind zone reading) or fluctuate erratically.
1.2.3 Compromised explosion-proof sealing, leading to safety incidents. Corrosion reduces the structural integrity of the explosion-proof housing and causes sealing gaskets (e.g., nitrile rubber, fluororubber) to age and crack, thereby destroying the explosion-proof seal barrier.
1.2.4 Damage to the mechanical interface, leading to probe detachment or medium leakage. If the probe cannot be securely fastened, it may fall directly into the reactor or storage tank; in slightly pressurized vessels, corrosive gas may leak heavily through the damaged interface, polluting the workshop environment and endangering operator safety. 1.3 Temperature Limits
The operating temperature of ultrasonic probes is typically limited to the range of -40°C to +70°C/80°C (with a few special high-temperature models capable of reaching around 100°C). If the medium temperature exceeds 80°C, intense vaporization occurs, making the probe susceptible to damage.
1.3 Viscosity and Splashing
If the medium is highly viscous (e.g., heavy oil, asphalt, thick syrup), it tends to splash and adhere to the vessel walls during filling. Once the viscous medium sticks to and solidifies on the probe’s emitting surface, it can prevent ultrasonic transmission or generate false echoes within the blind zone.
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2. What factors affect the distance between the ultrasonic probe and the medium?
2.1 Vacuum Environment
Gas molecules inside the vessel are extremely sparse or virtually non-existent. Without a physical medium to transmit vibrational energy, ultrasonic waves cannot propagate through the space between the probe and the liquid surface—much like how sound cannot travel in outer space.
2.2 Volatile Media Affecting Propagation Speed
Highly volatile organic solvents (e.g., acetone, benzene, gasoline, concentrated ammonia): The liquid evaporates rapidly, causing drastic changes in the composition and density of the gas above the liquid surface. Since the propagation speed of ultrasonic waves in these gases (such as ammonia or benzene vapor) differs significantly from that in air—and changes dynamically with concentration—this leads to massive linearity errors or serious measurement inaccuracies.
2.3 High Concentrations of Suspended Dust
Examples include cement dust, fly ash, and flour: Fine particles suspended in the air cause severe scattering and attenuation of high-frequency sound waves. With such media, the ultrasonic signal attenuates rapidly, compromising measurement data.
3. What factors relate to the medium itself?
3.1 Surface Morphology and State (Surface Reflectivity)
Sound waves require effective specular or diffuse reflection from the medium’s surface to be received by the probe.
Highly suitable: Calm, continuous liquid surfaces (water, oil, mild chemicals). Surface foam (a critical factor): If the medium’s surface is covered with a thick layer of fine foam (e.g., fermentation broth, beer, or wastewater containing surfactants), the foam acts like sound-absorbing material, completely absorbing the ultrasonic energy and causing a “Loss of Echo.”
Sloped solid material: When measuring solid particles (e.g., plastic pellets, sand, or gravel), the material’s angle of repose (slope) can cause the sound waves to deflect.
3.2 Medium Properties
Liquid media: High sound wave reflectivity; the probe can achieve its maximum rated measurement range (e.g., 10m, 15m).
Measurement range must be derated for solid particles/powders.
Not suitable for media with high levels of suspended dust.