Reasons and Solutions for Errors of Radar Object (Liquid) Level Meter

Radar level meter is a very commonly used instrument for measuring material level, and inaccurate measurement often occurs in use. So what is the reason for the inaccurate measurement of the radar level meter? How to solve the inaccurate measurement of radar level meter? Usually, the error of the radar level gauge is mainly due to the error in the installation of the instrument, which will cause the echo signal to be disturbed, resulting in measurement error. Therefore, during installation, the height of the tank and the size of the beam angle must be taken into account, leaving enough installation space for the radar level gauge. The following are several common causes of errors and their solutions: 1: Measurement dead zone: the radar level meter outputs a current of 4 to 20 mA during measurement. Due to the measured medium itself and the probe, there are two There are two dead zones, namely the upper dead zone and the lower dead zone. The minimum distance that can be measured between the liquid level in the upper dead zone and the upper reference point is about 0.1m~0.5m; the lower dead zone is at the bottom of the probe. With the change of the actual liquid level in the tank, the measurement results are not part of the change. 2: Error caused by the measured medium: When measuring the interface, the dielectric constant of the liquid above must be 10 larger than the dielectric constant of the liquid surface below. If the dielectric constant of the two interfaces is not much different, it will become a wave mode. During measurement, since the time used for the liquid level and the boundary level is basically the same, the two returned signals will be overlapped, which will affect the measurement result. 3: The viscosity of the liquid to be measured is too large: the medium has a high viscosity, such a liquid medium is likely to adhere to the probe, affecting the transmission of the signal and causing errors in the measurement. If the viscosity is higher, the medium and the probe will appear. Connected together, at this time, the probe must be cleaned regularly. 4: The error generated by the radar level gauge itself: the radar level gauge uses radar technology, and most of the errors come from the installation on site. 5. The roughness of the inner wall of the waveguide causes abnormal radar echoes. The installation requirements of the radar level gauge with the waveguide are relatively high, especially the smoothness of the inner wall of the waveguide. The still-pipe is recommended to be made of stainless steel, and the still-pipe welding method is adopted. In order to effectively avoid these possible problems, when installing the radar level meter, the following points should be paid attention to: 1. When installing the radar level meter, the feed inlet, feed curtain and vortex should be avoided, because the medium will produce amplitude during injection. False echoes that are much larger than the effective echoes reflected by the measured liquid level. At the same time, the irregular liquid level caused by the vortex will scatter the microwave signal, which will cause the attenuation of the effective signal, so they should be avoided; 2. For the container with a stirrer, the installation position of the radar level gauge should not be near the stirrer , because an irregular vortex will be generated during stirring, which will cause the attenuation of the radar signal. At the same time, the blades of the stirrer will also cause false echoes to the microwave signal, especially when the relative permittivity of the measured object is small and the liquid level is low, the impact of the stirrer is more serious; 3. When the radar liquid level When the meter is used to measure the liquid level of corrosive and easy-to-crystallize objects, in order to prevent the influence of the medium on the sensor, the manufacturer generally adopts a structure with a PTFE measuring window and a separation flange. The temperature of these parts should not be too high, the temperature of PTFE is 200 ℃. In order to avoid the influence of high temperature on the radar antenna, and to prevent the crystals existing on the diaphragm from affecting the normal operation of the instrument, a safety distance of at least 100-800mm is required between the flange end face and the high liquid level. How to solve the accuracy problem of the radar level gauge: First of all, when using the guided wave radar level gauge, you must pay attention to the measurement range. Exceeding the range will not only get accurate measurement data, but also may cause damage to the radar level gauge. damage. The measurement range should be calculated from the bottom of the tank touched by the light wave. If the storage tank is special and the bottom is concave, at this time the material level is lower than the calculation point, and the measurement cannot be performed. Secondly, when measuring low dielectric constant medium, if its material level is lower than the liquid level measurement value, and the bottom of the tank is visible, to make the measurement value more accurate, you can adjust the zero point upward to higher than the bottom of the tank. Location. Although it is said that the measurement range value can reach the top of the antenna tip, this is only an ideal situation. In reality, the effect of adhesion needs to be considered, so try to fix the measurement value at least 100mm away from the top of the antenna. If the medium to be measured is in constant motion, in order to ensure the accuracy of the measurement, it is recommended to fix the still-pipe at the bottom of the storage tank on site, and then fix it in the middle. During the welding process, it is necessary to ensure the smoothness of the inner wall of the still-pipe , in order to prevent the bumps from hindering the guided wave, it is also necessary to ensure the flatness of the welding.
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