January 17, 2022
What is the difference between radar level gauge and ultrasonic level gauge? What are the measurement principles of these two methods? What kind of working conditions are radar level gauge and ultrasonic level gauge used? What are the measurement accuracy of radar level gauge and ultrasonic level gauge? Let's explain these two liquid level gauges to you on these problems.
The radar level gauge adopts the working mode of transmitting reflecting receiving. The antenna of the radar liquid level gauge emits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time from transmission to reception of electromagnetic waves is directly proportional to the distance to the liquid level. The relationship is as follows:
Where D -- distance from radar liquid level gauge to liquid level
c-- speed of light
t - electromagnetic wave operation time
The radar liquid level gauge records the time of pulse wave, and if the transmission speed of electromagnetic wave is constant, the distance between liquid level and radar antenna can be calculated, so as to know the liquid level of liquid level.
In practical application, there are two ways of radar liquid level gauge, namely FM continuous wave type and pulse wave type. The liquid level gauge using frequency modulated continuous wave technology has high power consumption, must adopt four wire system, and the electronic circuit is complex. The liquid level gauge using radar pulse wave technology has low power consumption and can be powered by two-wire 24VDC. It is easy to realize intrinsic safety, high accuracy and wider application range.
Ultrasound uses sound waves, radar uses electromagnetic waves, which is the biggest difference. Moreover, the penetration ability and directivity of ultrasonic wave are much stronger than electromagnetic wave, which is the reason why ultrasonic detection is more popular now.
Differences in main applications:
1. Ultrasonic accuracy is not as good as radar.
2. The price of radar is relatively high.
3. When using radar, the dielectric constant of the medium should be considered.
4. ultrasound can not be applied to vacuum, high steam content or liquid foam.
5. The measuring range of radar is much larger than that of ultrasonic.
6. The radar has horn type, rod type and cable type, which can be applied to more complex working conditions than ultrasonic.
We generally call the sound wave with the sound frequency of more than 20kHz as ultrasonic wave. Ultrasonic wave is a kind of mechanical wave, that is, a propagation process of mechanical vibration in elastic medium. It is characterized by high frequency, short wavelength, small diffraction phenomenon and good directivity. It can become rays and propagate directionally. The attenuation of ultrasonic wave in liquid and solid is very small, so it has strong penetration ability. Especially in light opaque solid, ultrasonic wave can penetrate tens of meters, and there will be significant reflection when encountering impurities or interface. Ultrasonic level measurement uses this feature.
In ultrasonic testing technology, no matter what kind of ultrasonic instrument, it must convert electric energy into ultrasonic wave, transmit it, and then receive it and convert it into electrical signal. The device to complete this function is called ultrasonic transducer, also known as probe. As shown in the figure, the ultrasonic transducer is placed above the measured liquid and emits ultrasonic waves downward. The ultrasonic waves pass through the air medium, are reflected back when they encounter the water surface, and are received by the transducer and converted into an electrical signal. After detecting this signal, the electronic detection part changes it into a liquid level signal for display and output.
According to the propagation principle of ultrasonic wave in the medium, if the medium pressure, temperature, density, humidity and other conditions are certain, the propagation speed of ultrasonic wave in the medium is a constant. Therefore, when the time required for the ultrasonic wave to be received from transmitting to encountering the reflection of the liquid level is measured, the distance through which the ultrasonic wave passes can be converted, that is, the data of the liquid level can be obtained.
The ultrasonic has a blind area, so the distance between the installation position of the reserved sensor and the measuring liquid must be calculated during installation.
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