Where the difference between radar level meter and ultrasonic level sensor? What are the two measurement principles? Radar level gauge and ultrasonic level gauge are used in what kind of conditions? Radar level gauge and ultrasonic level gauge measurement accuracy is how much? Here we explain these issues and we explain these two kinds of level gauge.
Radar level gauge with emission-reflection-receive mode. Radar level meter antenna emits electromagnetic waves, these waves are reflected on the surface of the object to be measured, antennas, electromagnetic waves from the transmitter to receiver is proportional to the distance to the surface, relations are as follows:
D--radar level gauge the distance to the surface
C—— the speed of light
T--electromagnetic wave running time
Radar level meter records the elapsed time of the pulse wave while the transmission speed of the electromagnetic wave is constant, the distance from the liquid level to the radar antenna can be calculated to know the liquid level.
In actual application, the radar level meter has two ways that the FM continuous wave and pulse wave. The use of FM continuous wave technology level gauge, power consumption, to be four-wire system, the complexity of electronic circuits. The use of radar pulse wave technology level gauge, low power consumption, available two-wire 24VDC power supply, easy to achieve intrinsically safe, high accuracy, wider scope of application.
Ultrasound is the use of sound waves, radar is the use of electromagnetic waves, this is the biggest difference. And the penetration of ultrasound and the direction of the electromagnetic waves are much stronger, and this is the reason that ultrasonic detection is more popular now.
The main application of the difference:
1. Ultrasonic accuracy than radar.
2. The relative price of radar is higher.
3. When using the radar to consider the dielectric constant.
4. Ultrasound can not be applied to the vacuum, the steam content is too high or the foam surface conditions.
Radar measurement range is much larger than ultrasound.
6. The radar has a horn, rod, cable, relative ultrasonic can be applied to more complex conditions.
We generally call the sound wave frequency of more than 20kHz sound waves, ultrasonic is a mechanical wave, that is, mechanical vibration in a flexible media in the propagation process, which is characterized by high frequency, short wavelength, diffraction phenomenon is small, the other Good direction, can become a ray of directional transmission. Ultrasound in liquid, solid attenuation is small, and therefore penetrating ability, especially in the opaque solid, ultrasonic can penetrate the length of tens of meters, encounter impurities or interface will have significant reflection, ultrasonic measurement Level is to take advantage of this feature.
In the ultrasonic testing technology, no matter the kind of ultrasonic instrument, it must transmit the ultrasonic energy to the electric energy conversion and receive it back and transform it into the electric signal. The device that accomplishes this function is called ultrasonic transducer, also called probe. As shown in the figure, the ultrasonic transducer is placed above the liquid to be measured and the ultrasonic wave is emitted downward. The ultrasonic wave passes through the air medium, is reflected back when encountering the water surface, and is also received by the transducer and converted into an electrical signal, Electronic detection part of this signal is detected as a liquid level signal to display and output.
According to the propagation principle of ultrasonic waves in the medium, the propagation speed of the ultrasonic waves in the medium is a constant if the conditions of the medium pressure, temperature, density, humidity and the like are constant. Therefore, when measuring the time required for the ultrasonic wave to be received by the reflection of the liquid surface, the distance through which the ultrasonic wave passes can be calculated, that is, the data of the liquid level can be obtained.
Ultrasonic has a blind spot, the installation must be calculated to set aside the sensor installation location and the distance between the measurement of liquid.