1.1.1. The Necessity of Tank Level Monitoring
With the sustained and steady development of China's economy, infrastructure projects to prevent the situation of fuel tensions, oil depots around the increase in capacity to increase the delivery of oil to ensure the supply of crude oil. So how is the oil depot in order to ensure the supply of crude oil supply? The answer is the oil depot monitoring system. The following is the workflow:
Oil depot is the base of unloading, storage and supply of oil, and crude oil is explosive, flammable, volatile, easy to accumulate static and other properties, so the reservoir area is large, the route is far, resulting in the monitoring station away from the tank area Operation layer, so that the need for on-site information can be timely and effective transmission to the monitoring station, to facilitate the main station quickly give instructions. In general, according to the infrastructure of the infrastructure automation system, the entire depot can be divided into three different levels, namely, the underlying operating layer, the monitoring layer and the management. The operation layer includes on-site monitoring equipment, automatic detection and automatic control system. The concrete implementation includes the operation process of metering, closing and oiling, automatic control part, oil field security, oil and gas alarm equipment. The monitoring layer collects the data and information collected by the operation part in the network environment, provides the system unified monitoring platform, meets the centralized management requirements, provides the data for the most senior management system, supports the daily business management and the decision (Shanghai Unionwell electronic technology Co., Ltd. 2017).
At present the main level measurement methods are:
Liquid level measurement is widely used in petroleum, chemical, meteorological and other departments, especially in the chemical process control of the closed container level measurement. JJG971-2002 Level gauge verification procedure gives the definition of a level gauge, “the level gauge is used in industrial process measurement and control systems to indicate and control the level of the instrument.” With the continuous improvement of the accuracy of the liquid level instrument and the oil industry on the tank level measurement automation requirements continue to improve, liquid level meter began to apply to the tank level measurement. Currently used for oil tank measurement of the liquid level meter are the following:
- 1.
Manual Scale: Artificial scale method is the basic method of tank level measurement. Is currently widely used in the world, it can be used for on-site inspection of other means of measurement reference. The measurement method is: first use the immersion scale steel tape to measure the liquid level, sampling the measured oil temperature and specific gravity, and then through the formula to get the volume and weight of the liquid storage. Its measurement accuracy is generally considered to be ± 2mm artificial reading error.
- 2.
Mechanical Steel Belt Level Gauge: Mechanical steel level gauge began to develop and use in the 20th century, 60 years to the early 80s. Currently used in the storage of corrosive liquids often, high pressure storage tanks. Its measurement principle is the use of a large and heavy float connected to a porous steel belt, through the steel belt drive mechanical equipment as a field display, driving the electric transmitter to the level measurement information remote. Mechanical steel gauge level measurement accuracy is generally ± (4 ~ 10) mm.
- 3.
Servo Level Gauge: Servo level gauge is the use of buoyancy balance principle, by the servo motor to drive a smaller float for liquid level measurement. It uses the gravity measuring device to know whether the small float is completely immersed in the liquid, or half immersed in the liquid or completely above the liquid level, control the servo motor to drive the float with the liquid lift and lift, tracking the changes in the liquid level, and finally send the measurement signal. The servo level gauge uses intelligent technology to compensate for the difference in the weight of the wire rope produced when the liquid level is raised and lowered, thus further improving the measurement accuracy. Servo level gauge measurement range has reached 40m, measurement accuracy of 0.7mm.
- 4.
Ultrasonic Level Gauge: Ultrasonic level gauge is currently the fastest growing, high precision measurement of a non-contact level gauge. It uses liquid transmission and acceptance of the time difference for liquid level measurement. The current ultrasonic level gauge through the intelligent software to receive signal processing and analysis, can be a variety of interference signal filtering, identify multiple echo, analysis of signal strength and ambient temperature and other information, and ultimately to the level of accurate measurement. As the ultrasonic level gauge is a non-contact level gauge, with easy installation, wide adaptability and other advantages (Xiao Cezhou & Qiao Fengchun, 2015). High accuracy of the ultrasonic level gauge measurement accuracy of up to ± 1mm.
- 5.
Radar Level Gauge: Radar level gauge is another kind of non-contact level gauge commonly used in tank metering. It uses high-frequency radar to measure the liquid level. It usually needs to install the antenna at the top of the tank, the high frequency microwave pulse is transmitted and received through the antenna system, the radar wave running time can be converted into the level signal through the electronic component. It ensures a stable and accurate measurement of microwave emission recovery time through a special time-handling approach. The use of microelectronic processing technology and a high degree of debugging software package can accurately identify the level echo signal. High accuracy radar level gauge measurement accuracy can reach ± 1mm. Radar level gauge for high viscosity, high pollution products, liquid level measurement.
- 6.
Laser Level Gauge: Laser level gauge and ultrasonic level gauge measurement principle is roughly the same, the difference is that the laser level gauge with a light wave instead of acoustic measurement. The laser level of the laser emitter is irradiated to the measured level and receives the reflected laser signal. Will eventually be converted from laser to laser receiving time into liquid level. This is the laser level gauge measurement principle. In the liquid level measurement to the laser into a 20mm wide laser beam, the purpose of doing so can be encountered in the surface of the measured object is very rough, there have been a lot of diffuse light, the laser beam can still be received by the receiving device.