In various areas of production, liquid and bulk media are used. This raw material can perform different functions, but often the technology of its use involves controlling the filling of containers, bunkers and reservoirs with them. For this, special signaling devices are used, which can also be considered as sensors and monitoring relays. In this case, the methods of indication and the principles for determining the filling levels may be different. There are level switches on the market that differ in design, type of sensor and the presence of additional functions.
Capacitive Sensors
These are the most common universal signaling devices, which, depending on the model, are suitable for either bulk or liquid media. In particular, using a capacitive signaling device, the levels of powders, granular products, viscous oils, cement mortars, etc. are estimated. Some modifications also allow detecting the presence of foreign bodies, signaling this to the control panel. The principle of operation is based on fluctuations in the electric capacity indicator.
As a rule, this type of level switch has a sensitive element that directly contacts the target material, constantly monitoring the dielectric parameters of the air. Fluctuations in the recorded frequencies are converted into a signal supplied to the output control relay. The design of the capacitive sensor is diverse - manufacturers produce tubular, flexible, cable and other models.
Float alarms
The version of the signaling device, which is also simple in design and universal in application. The standard device of such a sensor provides for a float that connects to the switching mechanisms of the electromagnetic contacts. In the working environment, float detectors can be located both vertically and horizontally, which also expands the range of applications. Nevertheless, there are restrictions on the use of sensors of this type.
For example, they are rarely used in technological processes where high accuracy of readings and additional indication of the properties of the working environment are required. On the other hand, the float level switch is resistant to adverse operating conditions. For this reason, it is used as a recorder of levels of aggressive chemical products, kerosene, seawater, etc. On average, the maximum temperature for using a float alarm is 200 ° C.
Buoy signaling devices
In a way, a kind of float alarms, but having its own characteristics. The basis of the structure is formed by a buoy, which is suspended on a cable and, in the same way as float counterparts, is connected to contact mechanisms for transmitting readings. The process of immersing the device in a working liquid medium contributes to a change in the load on the cable, which leads to the opening of the contacts.
The model is quite simple in design, but it has significant advantages. For example, a buoy water level switch is capable of operating at high pressure indicators - about 20 MPa. As for the protection against aggressive environments and temperature effects, these qualities are determined by the design and materials of manufacture of a particular model.
Vibration alarm
A more technological design of the signaling device, which can be used in different environments - bulk and liquid. The principle of operation, as the name implies, is based on oscillatory movements. In the process, the sensitive element of the device produces mechanical vibrations under conditions of a resonant frequency. The sensor is driven by a piezoelectric generator or other energy source.
The immersion of the vibration level switch provokes a change in the activity of frequency oscillations and electrical parameters in the circuit connected to the sensor. Further, the changed parameters of the electric circuit are recorded in the relay as a discrete output signal. The advantages of vibration alarms include resistance to temperature influences, high pressure and aggressive environments. For many consumers, the high accuracy of such devices also matters - the error on average is 1 mm.
Optical sensors
Optical signaling devices use a light beam as a level detector. The source may be an infrared small lamp or laser. The measurement principle itself is based on the ability of the target material to reflect, refract or transmit light fluxes through itself.
It is important to emphasize that optical devices include both contact and non-contact analysis. Since this is an electronic level switch, you can count on the high accuracy of the results provided. As for working materials, these can be both traditional media and specific ones - for example, foam or oil products. In addition, optics makes it possible to record the density, viscosity and transparency of materials.
Ultrasonic sensors
Like other ultrasonic measuring equipment, level sensors of this type operate on the basis of an assessment of acoustic vibrations. A special receiver acts as a radiation source. It is installed in a container, after which the process of background propagation of the ultrasonic field is started. At the moments of fixing deviations in the parameters of sound waves, the electronics access the output relay, closing or opening the circuit.
The error of ultrasonic level switches is on average 2 mm, but this indicator can be improved in the process of finding the most favorable location. As practice shows, ultrasonic models of signaling devices are very exacting to working conditions in rooms. But otherwise they demonstrate stability in performance.
Rotary Models
This is one of the most common versions of electromechanical signaling devices, which is most often used for working with bulk mixtures. Such devices can be used in explosive and food industries to service materials with a density of about 100 g / l and a fraction of up to 50 mm. In particular, a rotary level switch is used to equip tanks for sugar, grain, powders, animal feed, etc.
The sensitive element in such models is represented by a rotor blade, which rotates as a result of the transfer of force from a synchronous electric motor. Actually, the moment the level in the tank changes is recorded as a result of the fixation of the blade by the target medium. Next, the electromechanical filling comes into play, which opens the contacts, sending a signal to the controller relay.
Varieties by type of switch
Most signaling devices operate with indicator contact switches, 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 ability to work with large spectra of voltages and currents, which increases the accuracy of the measurement.
At the same time, such contacts are not affected by evaporation, therefore, a liquid level switch with electromechanics is allowed to work in rooms with high thermal conditions. Solid state switches, in turn, have no moving mechanical elements that are subject to wear. That is, in the process of using this device, regular updating of consumables is not required. In addition, solid state devices switch faster and respond to the signal registration system.
Conclusion
In choosing a suitable device for fixing the level of filling containers with certain materials, it is worth considering many parameters. It’s worth starting with the characteristics of the environment and the operating conditions of the device. This will provide an idea of the optimal design and measurement scale.
The principle of operation of the level switch, as well as the method of transmitting information to the relay, also affects a lot of choices. At a minimum, these parameters will determine the accuracy of the measurement. Do not ignore the additional functionality. The more complex and expensive the detector, the more opportunities it will provide for recording environmental characteristics. So, in addition to the level of physical filling of the tank, the same optical and ultrasonic models can transmit information about the density, degree of viscosity and other qualities of the material.