The output of radar level meter in measurement is 4 ~ 20mA current. Due to the measured medium itself and the probe, there are two dead zones in its measurement, namely upper dead zone and 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 the part at the bottom of the probe where the measurement results do not change with the change of the real liquid level in the storage tank.
2: Error caused by measured medium:
When measuring the boundary, it is required that the dielectric constant of the upper liquid must be 10 greater than that of the lower liquid. If the dielectric constants of the two interfaces are not much different, they will become wave patterns. During measurement, since the time taken for the liquid level and the boundary is basically the same, the two returned signals will overlap and affect the measurement results.
3: The measured liquid viscosity is too large:
The medium has a high viscosity. Such liquid medium is likely to adhere to the probe, affecting the transmission of signals and causing errors in measurement. If the viscosity is higher, the medium will be connected with the probe. At this time, the probe must be cleaned regularly.
4: Error of radar level meter itself:
The radar level meter adopts radar technology, and most of the errors come from the installation on site.
5. Radar echo anomaly caused by rough inner wall of waveguide
The installation requirements of radar level meter with waveguide are relatively high, especially the smoothness of the inner wall of waveguide. It is recommended that the waveguide be made of stainless steel, and the plug-in welding method shall be adopted when the waveguide is welded.
In order to effectively avoid these possible problems, precautions should be taken when installing radar liquid level meter:
1. When installing the radar liquid level meter, the feed inlet, feed curtain and vortex shall be avoided, because the false echo with amplitude much larger than the effective echo reflected by the measured liquid level will be generated when the medium is injected. At the same time, the irregular liquid level caused by the vortex will scatter the microwave signal, thus causing the attenuation of the effective signal, so we should avoid them;
2. For vessels with agitators, the installation position of radar liquid level gauge should not be near the agitator, because irregular vortex will be generated during mixing, which will cause attenuation of radar signal. At the same time, the blades of the stirrer will also cause false echoes to the microwave signal, especially when the relative dielectric constant of the measured object is small and the liquid level is low, the influence of the stirrer is more serious;
3. When the radar liquid level gauge is used to measure the liquid level of corrosive and crystallizable objects, in order to prevent the influence of the medium on the sensor, the manufacturer generally adopts the structure with polytetrafluoroethylene measurement window and separation flange. The temperature of these parts shall not be too high, and the temperature of polytetrafluoroethylene shall be 200 ℃. In order to avoid the influence of high temperature on the radar antenna and prevent the crystal on the diaphragm from affecting the normal operation of the instrument, a safe distance of at least 100-800mm is required between the flange end face and the high liquid level.
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