In many industries, liquid and bulk materials are used as process media. In the regimes of continuous production of products and especially with automatic controls, constant monitoring of the parameters of working materials is required. The most common means of such control is level measurement, during which the degree of filling of one or another capacitive equipment is monitored.
Technology implementation
In this case, the level is understood as the filling height of the technological installation (tank, tank, tank, piston) with the working medium. In itself, knowledge of this quantity is necessary for the management and control of the production process. In particular, such measurements are a necessary operation in the chemical, oil refining and food industries. Knowing the filling level of the tank for collecting refined oil, for example, the operator can set the optimal parameters for the operation of the pumping pump station. And again, many industries operate on automation, so the output can be processed by controllers, which even without the participation of the operator give instructions to the executive units, taking into account the information received about the level of filling of the controlled device. Depending on the specific technological operation and accounting requirements, different level measurement units can change - for example, there are methods with a wide measuring range from 0.5 to 20 m, as well as specialized laboratory control schemes that take into account a narrow spectrum from 0 to 500 mm Direct measurement is carried out by physical, electromagnetic and ultrasonic devices, some of which also record the properties of the medium - chemical composition, pressure, temperature, etc.
Visual control methods
The simplest way to solve the problem, in which it is enough to use a standard measuring tool. Roulettes, rulers, sight glasses and other devices are used, which, in principle, can be used in the given conditions of a specific production environment. The most technological means of measuring the level of this type is a remote or bypass indicator. It is installed in the side of the tank by means of threaded, flanged or welded joints. The indication process is ensured by a transparent tube, which is filled as the liquid level in the target tank rises. More modern bypasses use cylindrical floats with a magnetic reading system. But such a design is considered obsolete due to significant limitations in communication capabilities of interfacing with control electronics and automation.
Float measurement method
It is also one of the simplest traditional methods of controlling the level of filling with liquid media. It is based on fixing the position of the float on the surface of the serviced liquid. Control is carried out according to different principles - mechanical, magnetic and magnetostrictive. During the movement, the nature of the connection between the float and its controlling element changes, for example, with a rigidly fixed lever. The mounting angle changes when the float rises, which is fixed by the metering system. Typically, a level measurement of this type occurs during the conversion of the same angle into an electrical signal. Most often, this is not even about taking into account specific indications, but about registering the moment of reaching a specific value. In other words, when the float reaches the set height level, the level indicator is activated. In the simplest schemes, contact closure occurs, leading to certain technological actions - for example, the function of a pump pumping a liquid stops.
Hydrostatic measurement of media
The key measurement factor in this level gauge system is hydrostatic pressure. That is, a pressure gauge with suitable characteristics and an immersible pressure sensor is used. Moreover, an important condition for monitoring is the separation of the sensor from the working medium with a special membrane on the one hand, and on the other hand, atmospheric pressure must be supplied through the capillary inlet from the filler. In the process of measuring the level of this type, overpressure is monitored, the indicator of which affects the characteristics of the generation of a unified signal. An electrical appliance with a converter is also connected to the pressure gauge, which is responsible for notifying about certain changes that have occurred in a controlled environment. As an alternative to this method of measuring hydrostatic pressure, it is possible to control the pressure of the gas, which is pumped into the analog of the capillary tube from the side of the liquid filling the tank. This model of the hydrostatic pressure gauge is called piezometric.
Level Radar
In some industries, a universal approach is applied to the measurement of high-altitude filling levels with technological media. For working with liquids, gases and bulk materials, radar equipment is optimally suited, the action of which is based on the analysis of frequency-modulated oscillations. The time of propagation and return of undamped oscillations from special antennas to the medium served is measured. The wavelength ranges can vary from one to tens of GHz. Transmitting antennas themselves can have a different device and radiation characteristics. To measure the level of liquids in chemical plants, for example, rod antennas with a height measurement range of up to 20 m are used. For environments whose control is subject to increased requirements in terms of accuracy, parabolic and planar devices are used. Usually these are areas of technical accounting, where it is important to fix measurements up to 1 mm.
The use of radioisotope methods
The main specialization of this type of level gauge is the control of bulk materials and liquid media in closed tanks. The principle of operation of the radioisotope apparatus is based on the absorption of gamma rays that pass through the layer of the target medium. Technically, the measurement process is organized using a radiation source and a receiver. Two devices are suspended or mounted on a supporting structure and are controlled by a reversible electric motor, which changes their height position depending on the current filling level. If the system for measuring the level of the working medium is located above its surface, then the radiation from the receiving signal will be strong, since there is no obstacle in its path. Therefore, the electric motor from the controller is given a signal to lower the equipment. The position of the measuring tool will control the signal in the tank by means of a constant supply and processing of wave oscillations.
Ultrasonic Testing Methods
The principle of operation in this case is largely similar to radio frequency control, in which a radio signal is released and the degree of filling of the production capacity is recorded by the characteristics of its reflection from the medium being measured. However, with the ultrasound method, special acoustic instruments are used to measure the level of fullness. That is, sound waves propagate, and the functioning of the equipment is similar to the principles of location. The indicators are fixed according to the time it takes for the oscillations of the distance from the emitter to the media dividing line and back to the receiver. The location of the interface is determined from the sides of the air (gas) and the target working environment. This is how combined high-precision devices work, but in the very group of ultrasonic level gauges there are devices that can purposefully control only gas-air (unfilled) or only the working medium.
Microwave methods
One of the most popular non-contact measurement technology, which combines the techniques and principles of radar electromagnetic control. The most promising technique of this class can be called directional electromagnetic measurement, in which the signal reflection coefficient is determined on the basis of microwave pulses that can penetrate to the bottom of the tank, bypassing all kinds of undesirable impurities and sludge particles. The returned signal or part of it is measured by the characteristics of completeness and speed. Given the time of its passage, the degree of fullness is determined. Microwave methods for measuring the level of working media are widely used in technological problems of controlling the filling of granular and powder materials. In such industries, probes with single suspension on ropes are used, while with respect to liquids, double and rod supporting structures are used. In general, the optimization of equipment when working with solids justifies itself for reasons of physical and mechanical properties, which are associated with technical limitations in the organization of measurement processes.
Conclusion
In recent years, the technology for developing level gauges for monitoring technological environments has undergone several fundamentally important stages of development, which have changed the principles of such measurements. Among the most important of them can be called the transition to non-contact measurement methods and the expansion of capabilities when working with aggressive fluids. Today, using the same non-contact radio frequency or electromagnetic method, precise control of crude oil, acid, molten sulfur and liquid ammonia can be ensured.