- Nov 01, 2017 -
1 application introduction
Level is one of the important target parameters of industrial process monitoring, a variety of tanks, silos, pools and other continuous level measurement, due to different conditions on-site, it is difficult to meet all the conditions should be bit level meter The
Combined with our steel plant operating conditions, in non-contact measuring instruments, radar and ultrasonic two principle level meter in the steel plant to a wide range of applications. So what is the difference between the radar level and the ultrasonic level meter? What are the two principles of measurement? What are the advantages of the radar level meter and the ultrasonic level meter compared to each other?
Today, on these issues and we explain these two level meter. We are familiar with the regular knowledge of field equipment and colleagues who are concerned with maintenance.
2 ultrasonic level meter
We generally sound wave frequency of more than 20kHz acoustic wave called ultrasonic, ultrasonic wave is a mechanical wave, that is, mechanical vibration in the elastic medium of a propagation process, which is characterized by high frequency, short wavelength, diffraction phenomenon is small, the other Good direction, can become a ray and directional transmission.
Ultrasonic in the liquid, solid attenuation is very small, and thus penetrating ability, especially in the light opaque solids, the ultrasonic wave can penetrate the length of tens of meters, impurity or interface will have a significant reflection, ultrasonic measurement Level is the use of its characteristics.
In the ultrasonic detection technology, no matter what kind of ultrasonic equipment, must be converted to ultrasonic energy transmission out, and then received back into electrical signals, the completion of this function is known as the ultrasonic transducer, also known as the probe.
Work, the ultrasonic transducer placed above the measured object, down the launch of ultrasound, ultrasound through the air medium, in the face of the measured object was reflected back, and was received by the transducer and converted into electrical signals, The electronic detection part detects the signal and converts it into a level signal to display and output it.
3 radar level meter
As with the ultrasonic level meter operating mode, the radar level meter also uses the emission-reflection-receiving mode of operation, the difference is that the radar ultrasonic level gauge is mainly dependent on the ultrasonic transducer, while the radar level meter depends on the tuner And antenna.
The ultrasonic level meter uses mechanical waves, while the radar level meter uses ultrahigh frequency (several G to several tens of G hertz) electromagnetic waves. Electromagnetic waves run at the speed of light, the operating time can be converted into level signals through electronic components.
Another common radar level meter is the guided wave radar level meter.
The guided wave radar level meter is based on the time domain reflection principle (TDR) based radar level meter, radar level meter electromagnetic pulse at the speed of light along the cable or probe transmission, when the surface of the measured medium, the radar A part of the pulse of the level gauge is reflected to form an echo and return to the pulse transmitting device along the same path. The distance between the transmitting device and the surface of the measured medium is proportional to the propagation time between the pulses and the liquid level is calculated.
4 affect the ultrasonic level effect factors
The ultrasonic wave emitted by the sensor is reflected by the measured medium, and the mass of the reflected echo reflects the effect of the meter.
The echo quality is defined as the minimum echo amplitude (the amplitude of the echo in the harshest conditions) than the maximum noise amplitude (false echo, multipath reflection echo, etc.). The greater the echo quality value, the better the level meter application.
1. The more stable the propagation of the media is conducive to the spread
Ultrasonic is a mechanical wave. Mechanical waves in the propagation process will be affected by the stability of the transmission medium. For example: there is a pond water, when the calm, to the pond can be seen in the water ripple, when the wind so that the pond water from the waves, to the pond to throw a large stone are difficult to see the water ripples.
Causing a lot of air fluctuations, such as: dust, air waves, steam, material flow will cause air fluctuations, reduce the quality of the echo, affecting the measurement results.
2. The more smooth the surface of the measured medium, the greater the acoustic impedance is more conducive to reflection echo
Measure the solid, the measured surface is uneven, there is a certain angle of repose. The reflected wave in this condition is a diffuse reflected wave. Since the reflection is related to the wavelength, reflection can occur when the curvature of the reflector can be compared with or greater than the wavelength.
Obviously, the higher the operating frequency, the smaller the wavelength, for smaller materials, more prone to diffuse reflection. For example, the frequency of a mechanical wave with a frequency of 10 kHz in the air is 34 mm, and in most cases, the material's curvature will not be so large.
In addition, low-frequency work, the firing wave angle, the echo will be wide. At this time the measured data are not allowed, sometimes almost a few hundred millimeters or even lm.
Impact Factors on Radar Level
1. The more stable the dielectric constant of the propagation medium is conducive to propagation.
Radar wave is the electromagnetic wave, the electromagnetic wave in the propagation process is not affected by the stability of the transmission medium, only with its dielectric constant. This is a significant difference between radar technology and ultrasonic technology.
2. The more developed the surface of the measured medium, the greater the dielectric constant is more conducive to echo reflection.
Therefore, when considering the field conditions, should pay special attention to: the antenna to the measured medium to ask the distribution of the dielectric constant of the air; the measured surface state and dielectric constant.
Comparison of radar and ultrasonic level meter
Said so much, two level meter comparison, what are the advantages and disadvantages?
1. Ultrasonic accuracy is not as good as radar;
2. Due to the frequency and antenna size, the use of higher frequency radar level meter antenna size is small, easier to install;
3. Because the radar frequency is higher, so the wavelength is shorter, the tilt of the solid surface has a better reflection;
4. The radar measurement blind spot is smaller than the ultrasonic wave;
5. Because the radar frequency is higher, so the radar beam angle is small, energy concentration, enhanced echo ability at the same time is conducive to avoid the interference;
6. Compared with the use of mechanical wave ultrasonic level meter, the radar is basically not vacuum, the air of water vapor, dust (graphite, ferroalloy and other high dielectric dust except), the temperature and pressure changes;
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