The article will talk about liquid level indicators that are used in various industries - from automotive to household and industrial. To automate various processes, it is necessary to control the level of the liquid. This can be done using special sensors. They send a signal to the control unit about the level at which the liquid is in the tank. The following will describe the main types of sensors and features of their operation.
Working principle and construction
The design of this type of sensor depends on its functionality. This parameter affects the type of device - it can be either signaling or measuring. The first ones are needed in order to track a specific point of filling the container (for example, maximum or minimum). The latter allow you to constantly control the amount of liquid.
Based onThe principle of operation may also lie in electrical conductivity, hydrostatics, electromagnetism, acoustics, optics, etc. This is the main parameter that determines the scope of use of devices.
And the measurement method can be non-contact or contact.
It is also worth noting that the design depends on the area in which the device is used. You need to understand that measuring the level of plain drinking water and combustible material are two different things.
Varieties of sensors
Liquid level gauges in steam boilers can be used in different ways. The main thing is that they withstand the load. There are several types of appliances:
- Float.
- Using ultrasound.
- Capacitive sensors.
- Devices with electrodes.
- Working on the principle of radar.
- Hydrostatic devices.
Float instruments
These are the simplest devices that can be found literally everywhere. From such devices, you can make a coolant level indicator for a car. Similar ones are installed in fuel tanks. By the way, even in simple toilet bowls a float sensor is used, only it regulates the operation of a mechanical drive that closes the water supply when the maximum mark is reached.
As for the simplest electronic type level sensors, they consist of a magnet mounted on a float lever and a pair of reed switches. The principle of operation of the devicelike this:
- When the container is empty to a minimum, the magnet becomes opposite the corresponding reed switch. The contacts are closed and the electromagnetic relay is switched on. It is with its help that you can switch the power part of the pump.
- When the maximum point is reached, the second reed switch is activated, which gives a signal to open the power circuit. Consequently, the supply of water or other liquid is stopped.
But if you use not reed switches, but a wire variable resistor, you can connect it to a voltmeter. And then you will be able to control the level in the tank.
Ultrasonic devices
It is worth noting that the requirements for liquid level indicators are quite acceptable - they can be used in a liquid medium. But they work well with dry substances. For level sensors of this type, the outputs can be discrete or analog. In other words, the device can limit filling when it reaches a certain point. It is also possible to constantly monitor the level. The design includes an ultrasonic signal emitter, a receiver and a controller that allows signal processing.
The system functions as follows:
- An impulse comes from the emitter.
- The signal is received by the device.
- The attenuation of the ultrasonic signal is being analyzed. In the event that the tank is full, then the signal will be maximum. If it is empty, then it is minimal.
Ultrasonic non-contact liquid level control devicesand do not have wires, so they can be used even in explosive and aggressive environments.
After the initial setup is carried out, there is no need to service the device - its resource is very high, in particular, due to the absence of moving elements.
Electrode sensors
Sensors of this type allow you to control one or more levels in the tank. There is only one feature - the substance, the level of which is measured, must conduct current. Therefore, it is not possible to measure the level of distilled water with these devices. Such devices are used, for example, in water towers.
When the water level drops below the minimum allowable value, the lower and middle electrodes are open - a signal is given to turn on the pumping station. When the tower is filled, the middle and upper electrodes are closed, the pumps are turned off. The design is simple and reliable, but you need to use wires to work. And if they break off and this happens in a fierce winter? Restoring performance will be problematic.
Capacitive sensors
The easiest way to control the amount of liquid is to cut glass into the container. In this case, a liquid level indicator is not needed, since the filling can be seen. But often this is not possible, so various device designs are used to display the level.
With the help of capacitive devices, you can determine the maximum filling of the tank. Andit is allowed to measure the amount of both liquid substances and bulk.
The operation of the sensor is very similar to a capacitor - the capacitance is measured between the two plates of the element. When the threshold value of the capacitance is reached, a signal is sent to the information processing device - the microcontroller. Sometimes the so-called dry contact is involved. In this case, the meter is isolated from the substance, placed behind the wall of the tank.
Such devices can operate in a fairly wide temperature range. Moreover, electromagnetic radiation cannot affect the functioning.
Radar type sensors
Such signaling devices are almost universal, as they work with all substances. They can be used even in aggressive and explosive environments. And it should be noted that high temperature and pressure cannot affect the measurement accuracy.
The principle of operation is quite simple - radio waves are emitted in a very narrow range. As with ultrasonic devices, the drop in signal strength is measured.
Hydrostatic sensors
If it is not possible to use a visual liquid level indicator, you need to use an electronic one. Hydrostatic allows you to measure both the limit levels and the current state. In this case, the pressure is measured, which creates a column of liquid. This type of sensors is quite popular, it can be used in all the samewater towers to get rid of the electrodes, which are not very convenient.
