1. Contact measurement
Contact measurement started with the steel belt float level gauge, and accurately measured the distance of the float through various ways, and later evolved into servo, magnetostrictive and other modern instruments. The earliest liquid level gauge is now facing an upgraded working principle. The float floats on the surface of the medium by buoyancy, and the liquid level value on the graduated steel belt is read through the speed change gear. After the liquid level rises or falls, the float also rises or falls, driving the steel strip to run. The theoretical accuracy is about 2-3mm, the installation is complicated and the reliability is low. Due to many mechanical parts, the steel belt is easy to get stuck. Optical fiber type is to digitize the liquid level of steel strip through the reading of optical encoder.
2. Magnetostrictive type
Magnetostrictive working principle The electronic components at the upper end of the probe generate low-voltage current pulses. When time begins, the generated magnetic field propagates downward along the magnetostrictive line. The float moves up and down along the measuring rod with the change of liquid level. There is a magnet in the float, which will also produce a magnetic field. When two magnetic fields meet, the magnetostrictive line is twisted to form a torsional stress wave pulse, and the pulse speed is known. The calculated pulse propagation time corresponds to the precise change of liquid level. Current travels at the speed of light, so its propagation time is negligible compared with the force wave time. ) The accuracy can be up to 1mm Advantages and disadvantages analysis The magnetostrictive liquid level has high accuracy and can measure the oil-water interface. However, due to its contact measurement method and high installation and maintenance requirements, the market has not been widely popularized.
3. Servo level gauge
Servo level gauge is a new type of level gauge successfully used recently, which is mainly used for high-precision measurement of light oil products. Form a strong competition with radar level gauge. The basic principle is the same as the steel strip level gauge, but it has an accurate force sensor and servo system to form a closed-loop adjustment system. By considering the gravity of the steel strip itself, the height of the float can be accurately adjusted, the buoyancy and gravity can be balanced, and the accurate current height from the liquid level to the tank top can be obtained, thus the liquid surface value can be obtained. The accuracy is high, reaching 65438±0mm, which meets the requirements of measurement grade. Used for calm light and non-corrosive liquid. The installation and debugging are troublesome, and the contact level gauge also has various unfavorable factors, which is expensive.
4. Static pressure level gauge
Static pressure level gauge is special, which uses the proportional relationship between the pressure and height of uniform liquid to convert the liquid level height by measuring the pressure at the bottom of the liquid. P = ρ GH (P pressure) is greatly influenced by medium density and temperature, so its accuracy is often poor. In order to eliminate these effects, many other test instruments are needed. Therefore, it is very expensive to establish a complete static pressure measurement system.
5. Non-contact measurement
Non-contact measurement usually takes the form of emitted waves that can be reflected by the measured medium. Using the known wave propagation speed, the distance between the liquid level and the measuring instrument can be obtained by directly or indirectly measuring the wave propagation time, and then the liquid level value can be obtained. According to the types of emitted waves, there are light wave laser level gauge, ultrasonic level gauge and electromagnetic wave radar level gauge.
6. Radar measurement
Radar measurement adopts the form of emitting electromagnetic waves. Because the dielectric constant of the measured medium is greater than 1 of air and vacuum, there will be reflection at the interface between air and liquid due to the discontinuity of the medium, and the propagation speed of electromagnetic wave in air is basically unaffected by temperature. Therefore, by measuring the time between the emission of electromagnetic waves and the reception of reflection, the height of the liquid level gauge from the liquid level can be measured, and then the liquid level value can be obtained. Radar level gauges are divided into two categories, and the specific measurement principles are different. Radar level gauges are classified into pulse frequency modulated continuous wave mode (FMCW).
7. Pulse radar measurement
The principle of pulse radar is basically the same as that of ultrasonic radar. The radar emits a short microwave pulse, which is reflected on the liquid surface. The radar receives the reflected echo and obtains the target distance through signal processing. R=c*(t 1-t0)/2 Generally, the low-priced radar liquid level gauges on the market are all pulsed, such as KROHNE, siemens, E+H, VEGA, etc. Accuracy: 5 ~10 mm.
8. Frequency modulated continuous wave mode (FMCW)
Principle: linear frequency sweep, frequency measurement is equivalent to time measurement, and the propagation time of electromagnetic wave is obtained, and then the distance is obtained. The advantages of FM CW radar are high precision, up to 0.5 mm, strong anti-jamming ability, wide application range, maintenance-free, high reliability, convenient installation and flexible configuration. Different antenna and radar head combinations are suitable for different measurement environments. The high-precision FM CW radar abroad is represented by SAAB-Pro series and saab-rex series of Swedish Saab company in the world. Pro series is a level gauge with control level, and its accuracy is 3 ~10 mm. rex series is a level gauge with trade handover certification and its accuracy is 0.5 mm. It is also the most accurate radar level gauge today. The high-end products of liquid level meter all adopt FM continuous wave mode, which is more expensive.
Magnetostrictive liquid level sensor is mainly used for liquid level measurement of various storage tanks. This kind of liquid level meter has the characteristics of high precision, strong environmental adaptability and convenient installation. Therefore, it is widely used in the field of liquid level measurement such as petroleum and chemical industry, and gradually replaces other traditional sensors and becomes a fine product in liquid level measurement.
General principles of tank liquid level
1. The liquid level measurement of crude oil and heavy oil storage tanks shall be non-contact (radar type, ultrasonic type); Liquid level measurement of light oil and [wiki] chemical raw material products (non -[wiki] corrosive [/wiki]) shall be non-contact or contact (float type, differential pressure type).
2. In-situ liquid level indication of storage tank shall be selected from magnetic float level gauge, floating ball level gauge or direct reading colored glass plate level gauge.
3. For the liquid level measurement of vault tanks and floating roof tanks, heavy hammer type steel strip level gauge, constant force spiral spring type steel strip level gauge or light guide type level gauge should be selected.
4. For the liquid level measurement of inner floating roof tank, outer floating roof tank, pressure tank and tank with agitator or cyclone, servo liquid level meter with conduit installation mode should be selected.
5. When measuring the liquid level of crude oil, refined oil, asphalt, ethylene, propylene, liquefied petroleum gas, liquefied natural gas and other media in large vault tanks and spherical tanks, radar liquid level gauge can be selected.
6. For the measurement of liquid quality, density, volume and level in atmospheric tank, pressure tank, vault tank and floating roof tank, static pressure tank level gauge can be selected, but it is not suitable for high viscosity level measurement.
If you want to seize the opportunity in the fierce competition in the field of gas stations, you can't just pay attention to service and management. To improve the level of reading and other aspects, hardware construction should also be improved. "If a worker wants to do a good job, he must sharpen his tools first." This is the truth. New technologies and equipment are emerging in the field of gas stations. In order to provide decision-making reference for managers in the field of gas stations, we have specially set up a sub-column of "refueling technology" to be good staff. At present, as long as the gas station industry mentions the liquid level gauge, it will be called "magnetostrictive".
Manufacturer of magnetostrictive level gauge: Qingdao Aoke level gauge, in which Vidrut level gauge is the most widely used.