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 monitor the level of the liquid. This can be done using special sensors. They give a signal to the control unit at what level the liquid is in the tank. Next, the main types of sensors and the features of their functioning will be described.
Principle of Operation and Design
The design of sensors of this type 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 filling point of a container (for example, maximum or minimum). The second ones allow you to constantly control the amount of fluid.
The principle of action can also be based on 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 in which area the device is used. You need to understand that measuring the level of simple drinking water or combustible material are two different things.
Varieties of sensors
Liquid level gauges in steam boilers can be used different. The main thing is that they withstand the load. There are several types of devices:
- Float.
- Using ultrasound.
- Capacitive sensors.
- Devices with electrodes.
- Working on the principle of radar.
- Hydrostatic devices.
Float devices
These are the simplest devices that can be found literally everywhere. From such devices, you can make a coolant level indicator for the car. Similar are installed in fuel tanks. By the way, even in simple toilets, 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 level sensors of electronic type, they consist of a magnet mounted on the lever of the float, and a pair of reed switches. The principle of operation of the device is as follows:
- When the capacity is emptied to a minimum, the magnet becomes opposite the corresponding reed switch. The contacts close and the electromagnetic relay switches 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 triggered, which sends a signal to open the power circuit. Consequently, the flow of water or other liquid stops.
But if you use not a reed switch, but a wire variable resistor, you can connect it to a voltmeter. And then you can 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 appliance can limit filling when it reaches a point. There is also the ability to constantly monitor the level. The design includes an ultrasonic signal emitter , a receiver and a controller that allows signal processing.
The system operates according to this principle:
- A pulse is emitted from the emitter.
- The signal is received by the device.
- An analysis of the attenuation of the ultrasonic signal is performed. In the event that the tank is full, the signal will be maximum. If it is empty, then minimal.
Ultrasonic liquid level control devices are non-contact and do not have wires, therefore they can be used even in explosive and aggressive environments.
After the initial setup is carried out, there is no need to maintain the device - its life is very high, in particular, due to the lack of movable elements.
Electrode sensors
Sensors of this type allow you to monitor one or more levels in the tank. There is only one feature - the substance, the level of which is measured, must conduct current. Therefore, measuring the level of distilled water will not work with these devices. Such devices are used, for example, in water towers.
When the water level drops below the minimum acceptable value, the lower and middle electrodes are open - a signal is sent to turn on the pump 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 it 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. A liquid level indicator in this case is not needed, as the occupancy rate can be seen. But often this is not possible, therefore, various device designs are used to display the level.
Using capacitive devices, you can determine the maximum filling of the tank. Moreover, it is allowed to measure the amount of both liquid substances and bulk.
The operation of the sensor is very similar to a capacitor - capacitance is measured between two element plates. 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 activated. 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, the electromagnetic radiation can not affect the functioning.
Radar Sensors
Such signaling devices are almost universal, since 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 will not be able to affect the accuracy of the measurement.
The principle of operation is quite simple - there is radiation of radio waves in a very narrow range. As with ultrasonic devices, the level of signal power drop is measured.
Hydrostatic sensors
If it is not possible to use a visual liquid level indicator, you need to use electronic. Hydrostatic allow you to measure both limit levels and the current state. In this case, a pressure measurement takes place, which creates a column of liquid. This type of sensor is quite popular, it can be used all in the same water towers to get rid of electrodes, which are not very convenient.