Water level indicators. LED Water Level Indicator Water Level Indicator Circuit Working Principle

To automate many production processes, it is necessary to control the water level in the tank, the measurement is carried out using a special sensor that gives a signal when the process medium reaches a certain level. It is impossible to do without level gauges in everyday life, a vivid example of this is the shut-off valves of the toilet bowl or automation to turn off the well pump. Let's look at the different types of level sensors, their design and principle of operation. This information will be useful when choosing a device for a specific task or making a sensor with your own hands.

Design and principle of operation

The design of measuring devices of this type is determined by the following parameters:

  • Functionality, depending on this device, is usually divided into signaling devices and level gauges. The former monitor a specific tank filling point (minimum or maximum), the latter continuously monitor the level.
  • The principle of operation, it can be based on: hydrostatics, electrical conductivity, magnetism, optics, acoustics, etc. Actually, this is the main parameter that determines the scope.
  • Measurement method (contact or non-contact).

In addition, the design features determine the nature of the process environment. It is one thing to measure the height of drinking water in a tank, and another thing to check the filling of tanks for industrial effluents. In the latter case, appropriate protection is needed.

Types of level sensors

Depending on the principle of operation, signaling devices are usually divided into the following types:

  • float type;
  • using ultrasonic waves;
  • devices with capacitive level detection principle;
  • electrode;
  • radar type;
  • operating on the hydrostatic principle.

Since these types are the most common, we will consider each of them separately.

float

This is the simplest, but nevertheless effective and reliable way to measure liquid in a tank or other container. An example implementation can be found in Figure 2.


 Rice. 2. Float switch for pump control

The design consists of a float with a magnet and two reed switches installed at control points. Briefly describe the principle of operation:

  • The tank is emptied to a critical minimum (A in Fig. 2), while the float drops to the level where the reed switch 2 is located, it turns on the relay that supplies power to the pump that pumps water from the well.
  • The water reaches the maximum mark, the float rises to the location of the reed switch 1, it works and the relay turns off, respectively, the pump motor stops working.

It is quite simple to make such a reed switch on your own, and its setting comes down to setting on-off levels.

Note that if you choose the right material for the float, the water level sensor will work even if there is a layer of foam in the tank.

Ultrasonic

This type of meter can be used for both liquid and dry applications and can have an analog or discrete output. That is, the sensor can limit the filling to a certain point or monitor it constantly. The device includes an ultrasonic emitter, a receiver and a signal processing controller. The principle of operation of the signaling device is shown in Figure 3.


 Rice. 3. The principle of operation of the ultrasonic level sensor

The system works as follows:

  • an ultrasonic pulse is emitted;
  • reflected signal is received;
  • the duration of the signal attenuation is analyzed. If the tank is full, it will be short (A fig. 3), and as it empties it will begin to increase (B fig. 3).

The ultrasonic signaling device is non-contact and wireless, so it can be used even in aggressive and explosive environments. After the initial adjustment, such a sensor does not require any specialized maintenance, and the absence of moving parts significantly extends the service life.

Electrode

Electrode (conductometric) signaling devices allow you to control one or more levels of an electrically conductive medium (that is, they are not suitable for measuring the filling of a tank with distilled water). An example of using the device is shown in Figure 4.


 Figure 4. Liquid level measurement with conductometric sensors

In the given example, a three-level signaling device is used, in which two electrodes control the filling of the tank, and the third one is an emergency one, to enable the intensive pumping mode.

capacitive

With the help of these signaling devices, it is possible to determine the maximum filling of the container, and both liquid and loose substances of a mixed composition can act as a technological medium (see Fig. 5).


 Rice. 5. Capacitive level sensor

The principle of operation of the signaling device is the same as that of a capacitor: the capacitance is measured between the plates of the sensitive element. When it reaches the threshold value, a signal is sent to the controller. In some cases, the “dry contact” version is involved, that is, the level gauge works through the tank wall in isolation from the process medium.

These devices can operate in a wide temperature range, they are not affected by electromagnetic fields, and operation is possible at a great distance. Such characteristics significantly expand the scope of application up to severe operating conditions.

Radar

This type of signaling devices can really be called universal, since it can work with any process medium, including aggressive and explosive ones, and pressure and temperature will not affect the readings. An example of the operation of the device is shown in the figure below.


The device emits radio waves in a narrow range (several gigahertz), the receiver catches the reflected signal and determines the capacity of the container by its delay time. The measuring transducer is not affected by pressure, temperature, or the nature of the process fluid. Dust also does not affect the readings, which cannot be said about laser signaling devices. It is also necessary to note the high accuracy of devices of this type, their error is not more than one millimeter.

Hydrostatic

These alarms can measure both the limit and the current filling of tanks. Their principle of operation is shown in Figure 7.


 Figure 7. Filling measurement with a gyro sensor

The device is built on the principle of measuring the pressure level produced by a liquid column. Acceptable accuracy and low cost have made this type quite popular.

Within the framework of the article, we cannot examine all types of signaling devices, for example, rotary-flag ones, to determine bulk solids (there is a signal when the fan blade gets stuck in a loose medium, after the pit has been pulled out). It also makes no sense to consider the principle of operation of radioisotope meters, all the more so to recommend them for checking the level of drinking water.

How to choose?

The choice of a water level sensor in the tank depends on many factors, the main ones are:

  • Liquid composition. Depending on the content of foreign impurities in the water, the density and electrical conductivity of the solution may change, which is likely to affect the readings.
  • The volume of the tank and the material from which it is made.
  • The functional purpose of the container for the accumulation of liquid.
  • The need to control the minimum and maximum levels, or monitoring of the current state is required.
  • Admissibility of integration into the automated control system.
  • Switching capabilities of the device.

This is not a complete list for the selection of measuring instruments of this type. Naturally, for domestic purposes, it is possible to significantly reduce the selection criteria by limiting them to the volume of the tank, the type of operation and the control scheme. A significant reduction in requirements makes it possible to independently manufacture such a device.

We make a water level sensor in the tank with our own hands

Suppose there is a task to automate the operation of a submersible pump for the water supply of a summer residence. As a rule, water enters the storage tank, therefore, we need to make sure that the pump turns off automatically when it is full. It is not at all necessary to buy a laser or radar level indicator for this purpose; in fact, you do not need to purchase any. A simple task requires a simple solution, it is shown in Figure 8.


To solve the problem, you will need a magnetic starter with a 220 volt coil and two reed switches: the minimum level - for closing, the maximum - for opening. The connection diagram of the pump is simple and, importantly, safe. The principle of operation was described above, but we repeat it:

  • As the water fills, the float with the magnet gradually rises until it reaches the maximum level reed switch.
  • The magnetic field opens the reed switch, turning off the starter coil, which leads to a de-energization of the motor.
  • As the water flows, the float drops until it reaches the minimum mark opposite the lower reed switch, its contacts close, and voltage is supplied to the starter coil, which supplies voltage to the pump. Such a water level sensor in the tank can work for decades, unlike an electronic control system.

Sometimes you need to know how much water or other conductive liquid is left in a closed container. For example, in a metal barrel buried in the ground or raised to a height so that it is not possible to determine its contents. To solve this problem, I recommend assembling a circuit of a simple water level sensor. The device consists of only a few radio components: resistors, transistors and three LEDs.


Due to the changing pressure in the heating system and the heating of the liquid, the expansion barrel is made open, therefore, after some time, part of the water boils away, and this leads to a stop in the circulation of water and overheating of the heating elements. This device will show when the water level drops below the sensor.

VT1 and VT2 are almost any low-power, BC547, BC337-40 or C9014. IC1- LM358 or 741. Any LEDs for voltage 3-4V. All resistors are 0.125W.

Transistors VT1 and VT2 form a galvanically coupled amplifier. Resistance R2 sets the bias to the base of the second transistor and at the same time being the load of the first one. Resistor R3 is designed to load VT2.

If the contacts of the device are in water or other conductive liquid, then the power plus will be connected to the resistor R1 through water, so voltage is supplied to the base of the transistor VT1 and it is unlocked, while VT2 remains closed and the non-inverting input of the operational amplifier will be connected to the minus through the resistance R3. The output of the op-amp will have a logic zero and the first LED will light up, indicating a normal water level.

If the liquid level drops and the water contact opens, then the bias voltage of the junction at the base of VT1 will disappear and it will close. Accordingly, the VT2 base will be connected to the power plus and it will unlock by connecting the non-inverting input of the op-amp to the plus, and therefore a logical unit level is formed at its output, the second LED starts to signal a decrease in the liquid level.

The water level indicator can also be connected to the sound indication. By connecting the OUT terminal of the level indicator to the output of the audio signaling unit ().

In the role of a sensor, the usual two wires are suitable, you can use a thick two-wire wire, exposing the ends. Sensor mounted on the level of control we need.

DIY water level sensor

The appearance of the liquid level sensor is shown in the photographs below. Stainless steel wire is used as probes, which is soldered to the connector contacts, after which this space is filled with sealant or glue.


Three probes are a part of a design: - the general, - inclusion and - switching off. The insulating sleeves are made from the internal insulation of a large diameter coaxial cable. The structure is connected to the automation unit using a shielded cable with two insulated cores. The shielding braid is connected to a common probe.

Liquid level sensor with audible alert

Two metal rods immersed in liquid are used as a sensor. The principle of operation of the converter is based on the ability of the vast majority of liquids to conduct current. The high sensitivity of the converter is ensured by the use of a CMOS logic microassembly on field-effect transistors with an insulated gate. Domestic microassembly K561LA7 consists of four logical elements "AND-NOT". On DD1.1 and DD1.2, a classic rectangular pulse generator is assembled, operating at a frequency of 3 Hz.

The generator, made on DD1.3 and DD1.4, operates at a frequency of 1 kHz. If the submersible sensor comes into contact with the liquid, the container C1 starts charging and starts the generator DD1.1 - DD1.2, which, every 350 milliseconds, starts the generator at DD1.3 - DD1.4. Therefore, an intermittent sound signal appears at the output of the amateur radio homemade product. The sensitivity can be adjusted by selecting the resistance R1. The higher the value, the higher the sensitivity. Capacitance C1 protects the high-resistance input of the microassembly from possible interference.

A simpler version of the scheme:

To assemble this water level sensor, you will need: field effect transistor IRF540N or similar, for example IRFZ44N; Any Active buzzer (beeper); Resistance at 1 MΩ; 12V power supply, such as a battery.


The principle of operation of the liquid level control circuit is shown in the video instruction below:

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In production, it is often necessary to measure the level of a liquid (water, gasoline, oil). In everyday life, it is most often necessary to determine the height of the water in a container; for this, special devices are used - level gauges and signaling devices. Measuring devices are divided into several varieties, they are purchased in stores, but for home use, the easiest way is to make a do-it-yourself water level sensor.

Types of sensors

Sensors differ from each other by the method of measuring the liquid level and are divided into two types: signaling devices and level gauges. The signaling devices monitor the specified filling point of the container and, when the desired volume of liquid is reached, stops its flow (for example, a float in the toilet bowl).

Level gauges continuously monitor the degree of filling of the reservoir (for example, a sensor on a mine drainage).

According to the principle of operation, water level sensors in the tank are divided into such varieties:

These are the most common level sensors, in addition to them, there are capacitive, hydrostatic, radioisotope and other types of devices that are used in various industries.

Selection rules

When buying a liquid level sensor in a tank, several factors must be taken into account, if they are observed, the device will work correctly and without fail. First of all, you need to determine fluid type and its density, the level of danger to humans. The material of manufacture of the container, its volume are of importance - the principle of operation of the selected sensor depends on these parameters.

The next point to pay attention to is purpose of the device, it will be used to control the minimum and maximum liquid levels, or to constantly monitor the filling of the tank.

When choosing industrial sensors, the number of criteria can be expanded; for household signaling devices and level gauges, it is enough to take into account the volume of the tank and the type of device. At home, do-it-yourself devices are used - they work no worse than factory models.

DIY manufacturing

The easiest way is to make your own float sensor of the water level in the tank, or a filling indicator.

The principle of operation of such a device It consists in the fact that the float floats in the liquid, at the maximum filling of the container it closes the contacts and signals a sufficient water level.

Manufacturing sequence:

The above scheme for manufacturing the sensor is the simplest; it is used for small containers.

The disadvantage of such a device is that it does not allow automatic shutdown of the pump. To stop the water supply to the tank, signaling devices are made using magnets and reed switches.

Using your favorite 555 timer, you can make a sensor for water, for washer, antifreeze, etc. It should be noted that such a sensor is useful both in your car and at home. The scheme is quite simple and easy to repeat. The microcircuit has become widespread precisely because of its simplicity.

The following circuit will be used for the water sensor.

The operation of the device is extremely simple. When the electrodes are immersed in a liquid, C1 is a capacitor, shunted. When the electrodes are in the air, the shunt disappears and the microcircuit starts to work.

Rectangular pulses come from the microcircuit. With the help of such impulses, it is possible to control with a larger load. For example, you can apply a signal to a light bulb through a transistor. This technology allows you to include an alarm or indicator in the circuit. With the help of the latter, you can determine the presence of water in the tank. A similar sensor can be installed both in the tank and in the radiator. Sensor power supply - 12 volts. This suggests that there will be no issues with nutrition.

As a rule, sensors are made of fiberglass. But most often they use ordinary copper (wires). For the sensor, two identical pieces of wire with a cross section of 1 millimeter are suitable. It is important to note that you need to clean off the varnish from the wires, which may be on the surface of the metal. This is done with fire or sandpaper. So, the length of the wire should be up to 3.5 centimeters.


To keep the wires in the cork, they are reinforced with silicone. Then the wires are attached to the microcircuit itself. The wires in the cover can be connected to the chip with thinner wires.

The microcircuit can be hinged - without an installation board. When everything is ready, the resulting device is closed with another similar lid. The connection of the covers must be sealed with glue or other means.

Thus, without making unnecessary expenses, you can independently manufacture a sensor that will help not only in the car, but also in everyday life. So, you can save yourself from frequent rises to the shower in order to see the water level in the tank. A homemade water level sensor will solve the problem. It is only important to do all the work carefully and carefully so that the device works properly.

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