In various spheres of industrial activityliquid and bulk media are used. This raw material can perform different functions, but often the technology of its application provides for the control of the filling of tanks, bins and tanks. To do this, special alarms are used, which can also be considered as sensors and monitoring relays. However, the methods of indicating and the principles of determining the levels of filling may be different. On the market level alarms are presented, differing in design, type of sensing element and the presence of additional functions.
These are the most common universalsignaling devices, which, depending on the model, are suitable for either bulk or liquid media. In particular, the levels of powders, granular products, viscous oils, cement mortars, etc. are estimated using a capacitive alarm. Some modifications also allow the foreign bodies to be detected, signaling this to the control panel. The principle of operation is based on fluctuations in the electric capacity indicator.
Typically, a level indicator of this typehas a sensitive element that directly contacts the target material, constantly monitoring the dielectric parameters of the air environment. The oscillations in the recorded frequencies are converted into a signal fed to the output control relay. The design of the capacitive sensor is diverse - manufacturers produce tubular, flexible, cable and other models.
Also simple in design and versatile inapplication version of the alarm. A standard device of such a sensor provides for the presence of a float, which is connected to the switching mechanisms of electromagnetic contacts. In the working environment, the float detectors can be located both vertically and horizontally, which also expands the range of their applications. Nevertheless, there are restrictions on the use of sensors of this type.
For example, they are rarely used in technologicalprocesses where high accuracy of indications and additional indication of properties of the working environment are required. On the other hand, the level float switch is resistant to unfavorable operating conditions. For this reason, it is used as a registrar of levels of aggressive chemical products, kerosene, sea water, etc. On average, the maximum temperature for using the float switch is 200 ° C.
In some way a kind of floatsignaling devices, but having its own characteristics. The basis of the construction is a buoy, which is suspended on a cable and in the same way as the float analogs, is connected to contact mechanisms for transmitting readings. The process of immersing the device in a working liquid environment contributes to changing the load on the cable, which leads to the opening of the contacts.
The model is simple enough for the device, but itthere are significant advantages. For example, buoy water level indicator is able to operate at high pressure values - about 20 MPa. With regard to protection from aggressive media and temperature effects, these qualities are determined by the design and materials of the specific model.
More advanced design of the alarm,which can be used in various environments - bulk and liquid. The principle of operation, as the name implies, is based on oscillatory movements. During operation, the sensing element of the device produces mechanical oscillations at resonant frequency. The sensor is driven by a piezoelectric generator or other power source.
Dive level vibratorprovokes a change in the activity of frequency oscillations and electrical parameters in the circuit connected to the sensor. Further, the changed parameters of the electrical circuit are registered in the relay as a discrete output signal. The advantages of vibration alarms include resistance to temperature effects, high pressure and aggressive media. For many consumers, the high accuracy of such devices is also important - the average error is 1 mm.
In optical signaling devices, a lightray as a level detector. The source can be an infrared small lamp or laser. The very principle of measurement is based on the ability of the target material to reflect, refract or pass light streams through itself.
It is important to emphasize that optical devicesprovide both contact and non-contact analysis. Since this is an electronic level indicator, you can count on the high accuracy of the provided results. As for working materials, it can be both traditional environments, and specific ones - for example, foam or oil products. In addition, optics makes it possible to record the density, viscosity and transparency of materials.
Like other ultrasonic measuringequipment, level sensors of this type operate on the basis of the evaluation of acoustic oscillations. As a source of radiation is a special receiver. It is installed in a container, after which the process of background propagation of the ultrasonic field is started. At the moments of fixing the deviations in the parameters of sound waves, electronics turns to the output relay, closing or breaking the circuit.
Inaccuracy of ultrasonic level alarmsan average of 2 mm, but this figure can be improved in the process of finding the most favorable location. As practice shows, ultrasonic alarm systems are very demanding for indoor conditions. But otherwise they demonstrate the stability of performance.
This is one of the most common versionselectromechanical signaling devices, which is most often used for working with loose mixtures. Such devices can be used in explosive and food industries to handle materials with a density of about 100 g / l and a fraction up to 50 mm. In particular, the rotary level indicator is used in equipping reservoirs for sugar, grain, powders, mixed fodders, etc.
The sensing element of such modelsis represented by a rotor blade, which rotates as a result of force transfer from the synchronous motor. Actually, the moment of level change in the tank is recorded as a result of the fixation of the blade by the target medium. Further, the electromechanical stuffing enters into the case, which opens the contacts, sending a signal to the controller relay.
Most signaling devices work withswitches of indication contacts, which are of two types - electromechanical and solid state. In the first case, mechanical contacts or a control relay are used. The strengths of electromechanics include the possibility of working with large spectra of voltages and currents, which increases the accuracy of the measurement.
At the same time, such contacts are not affectedevaporation, so the liquid level indicator with electromechanics is allowed to work in rooms with high temperature. In turn, the solid state switches do not have moving mechanical elements subject to wear. That is, in the process of using this device, regular updating of the consumables will not be required. In addition, solid state devices switch more quickly and respond to the signal recording system.
In selecting a suitable fixing devicethe level of filling of containers with these or other materials should take into account a number of parameters. It begins with the characteristics of the environment and the operating conditions of the device. This will give an idea of the optimal design and measurement scale.
Much of the choice is affected by the principle of actionlevel indicator, as well as a way to transfer information to the relay. At a minimum, these parameters will determine the accuracy of the measurement. Do not ignore the additional functionality. The more complex and expensive the signaling device, the more opportunities it will provide for recording the characteristics of the environment. So, in addition to the level of physical filling of the tank, the same optical and ultrasonic models can transmit information about the density, viscosity and other qualities of the material.