Differences between ultrasonic level gauges and radar level gauges

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We generally refer to sound waves with frequencies above 20 kHz as ultrasonic waves. Ultrasonic waves are a type of mechanical wave, that is, a process of mechanical vibration propagating through an elastic medium. Their characteristics include high frequency, short wavelength, minimal diffraction, as well as good directionality, allowing them to propagate in a targeted manner as beams. Ultrasonic waves experience very little attenuation in liquids and solids, which gives them strong penetration capabilities; especially in opaque solids, ultrasonic waves can penetrate distances of several dozen meters. They are significantly reflected when they encounter impurities or interfaces, and it is this property that is utilized in ultrasonic level measurement. In ultrasonic testing technology, regardless of the type of ultrasonic instrument, electrical energy must be converted into ultrasonic waves for transmission, and then these waves must be received and converted back into electrical signals. The device that performs this function is called an ultrasonic transducer, also known as a probe. As shown in the figure, the ultrasonic transducer is placed above the liquid to be measured, and ultrasonic waves are emitted downward. These waves pass through the air medium and are reflected back when they encounter the water surface; they are then captured by the transducer and converted into electrical signals. The electronic detection unit detects these signals, converts them into level signals, and displays as well as outputs them. Based on the principle of ultrasonic wave propagation in a medium, if conditions such as medium pressure, temperature, density, and humidity remain constant, the speed at which ultrasonic waves propagate through that medium is a constant. Therefore, by measuring the time it takes for the ultrasonic wave to travel from emission to being received after reflecting off the liquid surface, the distance traveled by the ultrasonic wave can be calculated, thereby obtaining the liquid level data. Ultrasonic waves have blind spots; therefore, when installing it, it is necessary to calculate and leave room for the distance between the sensor’s installation location and the liquid being measured. Radar level gauges operate on a transmit-reflect-receive principle. The antenna of the radar level gauge emits electromagnetic waves, which are reflected by the surface of the substance being measured before being detected by the antenna again. The time it takes for these electromagnetic waves to travel from emission to reception is proportional to the distance to the liquid surface; the formula for this relationship is as follows: D = CT/2, where D represents the distance from the radar level gauge to the liquid surface, C represents the speed of light, and T represents the time it takes for the electromagnetic waves to travel. By recording the time taken by the pulse waves, and since the speed of propagation of the electromagnetic waves is constant, it is possible to calculate the distance from the liquid surface to the radar antenna, thereby determining the level of the liquid. In practical use, radar level gauges come in two types: frequency-modulated continuous wave and pulse wave types. Level gauges that use frequency-modulated continuous wave technology consume a lot of power, require a four-wire system, and have complex electronic circuits. Level gauges that utilize radar pulse wave technology have low power consumption; they can be powered by 24V DC via a two-wire system, are easy to make intrinsically safe, offer high accuracy, and have a wider range of applications. Ultrasonic waves use sound waves, while radar uses electromagnetic waves; this is the biggest difference. Moreover, ultrasonic waves have much greater penetration power and directivity than electromagnetic waves, which is why ultrasonic detection is currently quite popular. Difference in main application scenarios: 1. The radar’s measurement range is much larger than that of ultrasonic waves. 2. Radars come in horn-type, rod-type, and cable-type versions, and can be applied to more complex operating conditions compared to ultrasonic sensors. 3. The precision of ultrasound is inferior to that of radar. 4. Radar has a relatively high price. 5. When using radar, the dielectric constant of the medium must be taken into account. 6. Ultrasonic waves cannot be used in conditions such as vacuum, high steam content, or liquid surfaces with foam.