Level measurement is a heavy production data in industrial production, especially in coal powder silo, limestone powder silo, ash storage, desulfurization system dewatering silo, etc. in thermal power plants, which is one of the common problems faced by level manufacturers today. There is no ready-made control mode for reference. Therefore, it is not simple to really choose a good type, and design, install, use and maintain a good level measurement instrument. In recent years, with the development of automation control technology, a continuous level measurement instrument based on radar wave measurement mode has been widely used in power plants, oil fields, petrochemicals and other industrial production fields. The level measurement of solid particles, ash powder and slurry mixture always has the problems of large dust viscosity, high temperature and small dielectric constant, etc. How to reasonably select and design a new type of level measurement sensor suitable for power plant ash storage and dewatering silo and successfully apply it has become the key.

I. Product principle

Radar level meter is to measure the distance from the sensor to the surface of the measured medium by measuring the emission and reflection time of microwave pulses. The pulsed radar level meter transmits microwaves from the antenna at a fixed frequency, and the time difference between the transmitted signal and the returned signal reflects the interface between 2 materials with different dielectric constants. The return wave is passed through a receiver that detects the transmission time and is used to calculate the level. The reflected radar wave is digitally converted to generate an echo pattern, and the echo shape is analyzed to determine the distance from the media surface to the instrument reference point. Formula: 71-2Dl / formula, the time difference between the launch and received reflection: D is the measured medium and the sensor distance; C is the electromagnetic wave propagation speed. Radar level meter in the time interval of the launch, the antenna system used as a receiving device. The instrument analyzes and processes the echo signal with a running time of less than one billionth of a second and analyzes and processes the echo in a very short instant. The radar sensor uses a special time interval adjustment technique to amplify and locate the same wave signal per second. Then analyze and process. Therefore, radar sensors can accurately and carefully analyze and process these amplified echo signals within 0.Is. Do not need to spend a lot of time to analyze the frequency.

II.the radar characteristics

High frequency radar level meter (26GHz) has the advantages of high energy, small beam angle, small antenna size and high accuracy. 26GHz radar wavelength 11mm, radar level meter in the measurement of bulk material level, radar wave reflection is mainly from the material surface of the diffuse reflection, the intensity of the diffuse reflection is proportional to the size of the material. The intensity of diffuse reflection is proportional to the size of the material and inversely proportional to the wavelength, while the diameter of most bulk materials is much smaller than 50ram. This is the reason why 26GHz radar is a good choice for measuring the level of bulk materials. Because the radar level meter adopts advanced echo processing and data processing technology, coupled with the high frequency of the radar wave itself and good penetration performance, the radar level meter has better performance than the contact level meter and similar non-contact level meter. Radar level meter has the following advantages in use.

1. continuous and accurate measurement: radar level meter does not contact with the measured medium, and is very little affected by temperature, pressure, gas, etc.

2. with suppression function for interference echoes: interference echoes caused by joints in the beam range and interference echoes caused by noise of incoming or outgoing material, etc. can be suppressed automatically by internal fuzzy logic control.

3. Learning function of false wave: input the actual material level of the material surface. The software can automatically identify the false echoes from the material level to the antenna to eliminate the interference of these waves.

4. Convenient parameter setting: easy operation keys on the level meter can be used for setting, or set by HART protocol with a PC equipped with special software remotely or directly connected to the communication end of the level meter, which is very convenient.

5. accurate and safe. Energy saving: radar level meter can be measured under vacuum and pressure, and it is accurate and safe, reliable, and can be applied to various occasions without any limitation.

6. Easy installation: In various industries, the radar level meter can be installed directly on top of the tank.

7. Maintenance-free and strong availability: Microwave is almost interference-free and does not come into direct contact with the measurement medium. Can be used in almost all kinds of applications, such as vacuum measurement, liquid level measurement or level measurement; due to the use of advanced materials, the situation is extremely complex chemical and physical conditions are durable, can provide accurate and reliable, long-term stable analog or digital level signal.

8. Convenient maintenance and simple operation: the radar level meter has fault alarm and self-diagnosis function, which analyzes the fault according to the error code prompted by the operation display module and determines the fault to be eliminated in time, making the maintenance and correction more convenient and accurate and guaranteeing the normal operation of the meter.

III.the field application analysis

In the military grain city power plant ash bin formerly used in the radio frequency conductivity level meter, because of its working conditions, subject to temperature, pressure, dielectric constant, dust and other factors, radio frequency conductivity level meter often for hanging material and other issues, resulting in false signals make the instrument output fluctuations, the effect is not ideal, found that the data drift serious, and even in the display of "dead" data phenomenon. The system can not rely on the meter output accurate and stable parameters to automatically control the material level, but only rely on the experience of the operator and time to control the material level, so it is easy to cause the bin level topping, control efficiency is low. After a period of trial, the radar level meter was used and proved to have achieved more satisfactory results. Since the adoption of radar level meter for half a year, continuous and accurate measurement can be carried out, the meter output is relatively stable, and the system can rely on the stable and accurate parameters of the meter output to automatically control the material level. When the ash bin is in and out of the material, the meter output is stable and can accurately reflect the position of the powder level, so that effective and reliable control can be carried out.

Problems have occurred in the application and how to deal with them.

1. The instrument does not indicate. Check whether the power supply and communication cable are normal, and set the echo position parameter. 2.

2. The parameter setting is not reasonable. Reset the instrument and reset the parameters. Before putting into use, the basic parameters must be set correctly, such as whether the empty slot and full slot are set correctly, and whether the application conditions meet the actual situation.

3. The instrument is not displayed correctly. Check whether there are obstacles in the tank, set rVTSETUP, let it learn false echo suppression automatically and eliminate false echo.

4. The meter indication is unstable, incorrect or no echo. Echo processing ECHOPROOC. Select the suitable echo algorithm BestofLargestorFirstecho to find out its correct echo, then the display is normal.

5. antenna pollution. Add a special dust cover to prevent dusty materials hanging on the antenna and reduce its sensitivity.

Radar detection technology as an advanced level measurement technology, can be used for non-contact continuous measurement of the level of high dust, slurry particles, granular materials. Radar level meter is resistant to wear and aging; it is suitable for vacuum, temperature and pressure changes, with gas, steam, dust and other harsh conditions.