In industry and everyday life, there is always a need to determine various levels in containers. Level sensors are used for these tasks various designs. Depending on the filling environment of the tank, one or another sensor is used; sometimes, for the sake of simplicity and saving money and time, combined sensors are used, that is, made by hand. These are simple designs that use completely different types of sensors. Basically, such sensors are used where there is no easy access to the measurement environment or the measurement location is very aggressive for human health.
Types of level sensors
Most modern level sensors have an electronic relay with a converter in their design. Electronic circuit designed to convert the measured value into a standard signal. The signal can be analog or discrete. Analog can be a current 0..20mA and a signal called a current loop 4..20mA or a voltage 0...5V, 0..10V.
Level sensors are used to protect the pump motor from dry running, regulate the motors of well pumps that fill any containers with water and more in the cold and hot water supply system.
DIY water level sensor
Let's see, using the example of pumping water from a pit, how we can control the automatic cycle of maintaining the water level not higher than the required one.
We have a pit with very little clean look a liquid consisting of water and coolant impurities for the cutters of a metal-cutting machine.
All types of sensors were considered, however, in terms of price and ease of execution, a combined design consisting made of wire three meters long(depth of the pit), attached to a float (large plastic container with air), on the surface the wire is attached to a spring with a petal.
The signal is taken as a conventional discrete 24V signal from a conventional inductive sensor. He works on the petal. When the water level in the pit rises, the float rises, weakening the spring. A petal is attached to the end of the spring; it rises due to the extension force of the spring. The petal, in turn, receives feedback from the inductive sensor, feeding the pump motor relay to the coil, causing it to pump out water from the pit. In order to avoid frequent switching on and off of the engine, in the sensor-coil circuit there is a switch-off delay relay set to 10 minutes.
Thus, the next time the sensor is triggered, the relay will work again and the cycle will repeat.
Of course, to protect the engine from dry running it is advisable install a leakage sensor in the pipe, through which the emulsion is pumped out. But in our case, simplicity of design was important. Instead of an inductive sensor, you can use two plates in contact with each other, which will be even more economical.
If water or other liquid has a homogeneous composition, then a metric single-electrode level sensor can be used.
For example, DU-1N manufactured by Relsib, designed for measuring levels in various types liquids. The sensor can operate over a wide temperature range. The body is not subject to corrosion, consists of high quality of stainless steel. Ceramic and fluoroplastic are used as insulation, this provides excellent insulating protection. Resistant to many mechanical loads. The measurements are independent of liquid density. And does not require additional care during operation.
To regulate and control the liquid level or solid(sand or gravel) in production, in everyday life used special device. It is called a water level sensor (or other substance of interest). There are several varieties of such devices, which differ significantly from each other in their operating principles. How the sensor works, the advantages and disadvantages of its varieties, what subtleties you should pay attention to when choosing a device, and how to make a simplified model with a relay with your own hands, read in this article.
The water level sensor is used for the following purposes:
Possible methods for determining tank load
There are several methods for measuring liquid level:
- Contactless- often devices of this type are used to control the level of viscous, toxic, liquid or solid, granular substances. These are capacitive (discrete) devices, ultrasonic models;
- Contact- the device is located directly in the tank, on its wall, at a certain level. When the water reaches this indicator, the sensor is triggered. These are float, hydrostatic models.
Based on the principle of operation, the following types of sensors are distinguished:
- Float type;
- Hydrostatic;
- Capacitive;
- Radar;
- Ultrasonic.
Briefly about each type of device
Float models are discrete and magnetostrictive. The first option is cheap, reliable, and the second is expensive, complex design, but guarantees an accurate level reading. However general disadvantage float devices - this requires immersion in liquid.
Float sensor determining the liquid level in the tank
- Hydrostatic devices - in them all attention is paid to hydrostatic pressure column of liquid in the tank. The sensitive element of the device senses pressure above itself and displays it according to a diagram to determine the height of the water column.
The main advantages of such units are compactness, continuous operation and availability price category. But they cannot be used in aggressive conditions, because they cannot do without contact with liquid.
Hydrostatic liquid level sensor
- Capacitive devices - plates are provided to control the water level in the tank. By changing the capacity indicators, you can judge the amount of liquid. Lack of moving structures and elements, simple circuit devices guarantee durability and reliable operation of the device. But one cannot fail to note the disadvantages - this is the necessity of immersion in liquid, and demanding temperature conditions.
- Radar devices - determine the degree of increase in water by comparing the frequency shift, the delay between the radiation and the achievement of the reflected signal. Thus, the sensor acts as both an emitter and a reflection collector.
Such models are considered the best, accurate, reliable devices. They have a number of advantages:
The only disadvantage of the model is its high cost.
Radar tank liquid level sensor
- Ultrasonic sensors - the principle of operation and the design of the device are similar to radar devices, only ultrasound is used. The generator creates ultrasonic radiation, which, upon reaching the surface of the liquid, is reflected and reaches the sensor receiver after some time. After some mathematical calculations, knowing the time delay and speed of the ultrasound, the distance to the water surface is determined.
The advantages of a radar sensor are also inherent in the ultrasonic version. The only thing is that the indicators are less accurate and the operation scheme is simpler.
Subtleties of choosing such devices
When purchasing a unit, pay attention to the functionality of the device and some of its indicators. Extremely important questions when purchasing a device, this is:
Options for sensors for determining the level of water or solids
DIY liquid level sensor
You can make a basic sensor to determine and control the water level in a well or tank with your own hands. To perform the simplified version you need:
A self-made device can be used to regulate water in a tank, well or pump.
Sometimes human laziness can make you think, so to speak, create. And they came up with the wheel, probably out of laziness, when they got tired of carrying everything on themselves.
So I’m tired of standing in front of water barrels filling with water. Summer is dry, there are 4 barrels, each fills in about half an hour. It’s too lazy to entangle the area with wires from the level sensors, and making a control unit in such heat. I tried to let this matter take its course, but at the fifth step from the barrel I already forgot that the barrel was being filled and the pump was on. I started thinking about how to make a wireless barrel fill alarm. I thought for a long time until the radio call came through the gate. Everything that immediately came to mind, look at photo 1. 
The entire structure required two welding electrode And empty bottle from alcohol. In short, everything that came to hand. I hope you find it all more aesthetically pleasing. First, a rocker arm is made and a float is attached to it. Then they make a blank for the bracket. Cutting off a piece of the electrode required length, sharpened on both sides and bent in the shape of the letter “L”, a rocker arm with a float is put on one end and then this end is bent to form a bracket. Next, this bracket is hammered into the board. It took me about twenty minutes to do everything. The call button on the board just lies there. I hope the principle of operation of the entire device is clear. The water is poured, the float rises, the rocker presses the button, the bell rings, you run out of the house and transfer all the equipment to the next barrel. The disadvantage here is that the call is powered from a 220V network. It wouldn’t be a bad idea to switch it to autonomous power supply, then you’ll be able to catch crucian carp in the pond for a whole half hour. Good luck. K.V.Yu.
To automate many production processes, it is necessary to monitor 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 live without level meters in everyday life; a striking example of this is shut-off valves toilet cistern or automatic system to turn off the well pump. let's consider different kinds level sensors, their design and operating principle. This information will be useful when choosing a device for a specific task or making a sensor yourself.
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 alarms and level meters. The former monitor a specific tank filling point (minimum or maximum), while the latter continuously monitor the level.
- The operating principle can be based on: hydrostatics, electrical conductivity, magnetism, optics, acoustics, etc. Actually, this is the main parameter that determines the scope of application.
- Measuring method (contact or non-contact).
In addition, the design features are determined by the nature of the technological environment. It's one thing to measure height drinking water in the tank, another is to check the filling of industrial wastewater tanks. In the latter case, appropriate protection is necessary.
Types of level sensors
Depending on the principle of operation, alarms are usually divided into the following types:
- float type;
- using ultrasonic waves;
- devices with a capacitive level detection principle;
- electrode;
- radar type;
- working on the hydrostatic principle.
Since these types are the most common, let's look at each of them separately.
Float
This is the simplest, but nevertheless effective and reliable way measuring liquid in a tank or other container. An example implementation can be found in Figure 2.
Rice. 2. Float sensor for pump control The design consists of a float with a magnet and two reed switches installed in control points. Let us briefly describe the principle of operation:
- The container is emptied to a critical minimum (A in Fig. 2), while the float drops to the level where reed switch 2 is located, it turns on the relay that supplies power to the pump pumping water from the well.
- The water reaches the maximum level, the float rises to the location of reed switch 1, it is triggered and the relay is turned off, accordingly, the pump motor stops working.
It’s quite easy to make such a reed switch yourself, and setting it up 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 media and may have an analogue or discrete output. That is, the sensor can limit the filling upon reaching a certain point or monitor it continuously. The device includes an ultrasonic emitter, receiver and signal processing controller. The operating principle of the alarm is demonstrated in Figure 3.
Rice. 3. Operating principle of ultrasonic level sensor The system works as follows:
- an ultrasonic pulse is emitted;
- the reflected signal is received;
- The duration of signal attenuation is analyzed. If the tank is full, it will be short (A Fig. 3), and as it becomes empty it will begin to increase (B Fig. 3).
The ultrasonic alarm is non-contact and wireless, so it can be used even in aggressive and explosive environments. After initial setup, such a sensor does not require any specialized maintenance, and the absence of moving parts significantly extends its service life.
Electrode
Electrode (conductometric) alarms allow you to monitor 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 example given, a three-level alarm is used, in which two electrodes control the filling of the container, and the third is an emergency one to turn on the intensive pumping mode.
Capacitive
Using these alarms, it is possible to determine the maximum filling of the container, and both liquid and bulk solids of mixed composition can act as the process medium (see Fig. 5).
Rice. 5. Capacitive sensor level The operating principle of the alarm 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, a “dry contact” design is used, that is, the level gauge operates through the tank wall in isolation from the process medium.
These devices can operate in a wide range temperature range, they are not affected electromagnetic fields, and operation is possible on long distance. Such characteristics significantly expand the scope of application up to severe operating conditions.
Radar
This type of alarm device can truly be called universal, since it can work with any process environment, including aggressive and explosive ones, and pressure and temperature will not affect the readings. An example of how the device works is shown in the figure below.
The device emits radio waves in a narrow range (several gigahertz), the receiver catches the reflected signal and, based on its delay time, determines how full the container is. The measuring sensor is not affected by pressure, temperature or the nature of the process fluid. Dustiness also does not affect the readings, which cannot be said about laser alarms. It should also be noted high accuracy devices of this type, their error is no more than one millimeter.
Hydrostatic
These alarms can measure both maximum and current filling of tanks. Their operating principle is demonstrated in Figure 7.
Figure 7. Fill measurement with gyrostatic sensor The device is built on the principle of measuring the level of pressure produced by a column of liquid. Acceptable accuracy and low cost made this type quite popular.
Within the scope of the article, we cannot examine all types of alarms, for example, rotary-flag ones, for identifying granular substances (a signal is sent when the fan blade gets stuck in a granular medium, after first tearing out the pit). It also makes no sense to consider the principle of operation of radioisotope meters, much less recommend them for checking the level of drinking water.
How to choose?
The choice of a water level sensor in a tank depends on many factors, the main ones:
- Composition of the liquid. 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 is to accumulate liquid.
- The need to control the minimum and maximum level, or monitoring of the current state is required.
- Admissibility of integration into an automated control system.
- Switching capabilities of the device.
This is far from full list for selection measuring instruments of this type. Naturally, for domestic use it is possible to significantly reduce the selection criteria, limiting them to the volume of the tank, the type of operation and the control circuit. Significant reduction in requirements makes it possible self-production similar device.
Making a water level sensor in a tank with your own hands
Let's say there is a task to automate work submersible pump for water supply to the dacha. Typically, water enters storage capacity Therefore, we need to make sure that the pump turns off automatically when it fills. It is not at all necessary to buy a laser or radar level indicator for this purpose; in fact, you don’t need to purchase any. A simple task requires 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: a minimum level for closing, a maximum level for opening. The pump connection diagram is simple and, importantly, safe. The principle of operation was described above, but let’s repeat it:
- As the water collects, 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 de-energization of the engine.
- 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 a tank can work for decades, unlike electronic system management.