Machinery

Choice of liquid level sensors in tanks and reservoirs: examples of use, and make them with your own hands

December 3, 2019

In industry and everyday life there is always a need to determine the different levels in the tanks. Level sensors of various designs are used for these tasks. Depending on the filling environment of the tank, one or another sensor is used, sometimes, in order to simplify and save money and time, combined sensors are used, that is, made with their own hands. These are simple designs, using sensors of completely different types. Mostly such sensors are used there, where there is no easy access to the measuring medium or the measuring point is very aggressive to human health.

Types of level sensors

  • float sensors are the simplest in design, are widespread, combined with an electric relay , are different types of floats, attached through a wire, thread, or hard to the petal contact, which closes when changing the position of the float.
  • capacitive level sensors are plates located on both sides of the tank with the material. The principle of operation is to change the capacity depending on the distribution of the amount or composition of the material in the tank. Such sensors are mainly used to determine the level of bulk materials.
  • radar level sensors work on the principle of "emitter - frequency wave receiver", the surface of the material reflects the radiation of the sensor, the receiver captures this radiation and compares the emitted signal with the reflected and frequency shift determines the level in the tank. The level is determined by a relatively frequent time shift.
  • ultrasonic level sensors work on the principle of radar, only the radiation is ultrasonic. Similar to radar, the signal difference is compared, radiated with reflected and calculated distance to the surface of the material (liquids).
  • hydrostatic level sensors work by measuring the indirect value - the pressure of the liquid column. The pressure is proportional to the liquid level in the tank.

Most modern level sensors have an electronic relay with a transducer in their design. The electronic circuit is designed to convert the measured value into a standard signal. The signal can be analog or discrete. Analog can be 0..20mA current and signal, called current loop 4..20mA or voltage 0… 5V, 0..10V.

Level sensors are used to protect the pump motor from dry running, regulate well pump motors, fill any container with water and more, in the system of cold and hot water supply.

Water level sensor with your own hands

Let's see, on the example of pumping water from the cabin, how it is possible to make management in an automatic cycle of maintenance of water level not above set.

We have a pit from a very clean liquid, consisting of water and impurities of coolant for metal cutting machine cutters.

All types of sensors were considered, however, at the price and simplicity of execution the combined design approached, consisting of a wire three meters long (pit depth), attached to the 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 normal discrete signal 24V 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 extensor force of the spring. On the petal, in turn, works out the inductive sensor, feeding to the coil of the pump motor relay, forcing him to pump water from the pit. For, to avoid frequent engine shutdowns, in a circle the sensor coil, worth the shutdown delay relay with setpoint on 10 minutes.

So, at the next operation of the sensor, the relay will start again and the cycle will repeat.

Of course, to protect the engine from dry running, it is advisable to put a leak sensor in the pipe, through which the emulsion is pumped. But in our case, the simplicity of design was important. You can use two plates instead of an inductive sensor, facing each other, which will be even more economical.

If water or other liquid has a homogeneous composition, then you can apply the end metric single-electrode level sensor.

For example, DU-1N manufacturer "Relsib", designed to measure the level in different types of liquids. The sensor can operate in a wide temperature range. The case is not subject to corrosion, consists of high quality stainless steel. Ceramics and fluoroplastic are used as insulation, this provides excellent insulating protection. Resistant to many mechanical loads. Measurements do not depend on the density of the liquid. And does not require additional care during operation.

Selection of level sensors

When choosing level meters are guided by the following goals:

  • Type of measured liquid. Its characteristics, find the passport density of the measured material. What substances is a substance, what is dangerous for humans or not.
  • Capacity material, in which the measurement is performed. The principle of operation of the level gauge depends on it.
  • Do you need a standard analog signal from the sensor or preferably work as a relay. Some models have built-in circuits for processing an analog signal and converting it into a bit logic signal..
  • It is necessary to know the limits of the measured value, in very long vessels, with rapidly changing volume, the float structure will not work stably. In this case, a radar level gauge is better.
  • Modern level gauges are equipped with a liquid crystal display with the display of parameters in real time and the ability to save maximum and minimum values. The sensor parameters are set by several levels of operation, each level has its own discrete output. The density of the environment in the settings is set.
  • Take into account sanitary norms for the area of ​​application. Example, in the food industry for measuring water, drinks are in high demand. Must be made of stainless steel.
  • The need for certificates. Example, Some meters Rostechnadzor must check and approve for use in hazardous facilities. Some require a permit from the Sanitary and Epidemiological Service, mainly for water and food.
  • Suitability of sensors for use in explosive atmospheres. The following are used in petrochemical industries. The manufacturer guarantees, that such systems will not ignite the combustible medium during the entire service life, in which it is located.
  • You need to consider the possibility of mechanical effects on the system, vibration, electromagnetic waves, aggressive environments.
  • The presence of temperature differences in the system, maximum possible states.
  • How important is the accuracy of level measurements, one of the most important parameters.

Examples of sensors, their parameters and scope

  • Capacitive Sensor DE-1. Scope: in explosive metallurgical environments, chemical industry, etc. Level tracking, as well as the values ​​of the temperature of liquid media and bulk materials. Meals are provided 8 .. 30In direct current. used in emergency protection systems.
  • ESU-1K level indicator. The case is made of fluoroplastic and steel. Placed in explosive atmospheres. The power supply is outside the hazardous environment. power supply 127… 220 V. Measurement of liquid materials such as water, alcohol, oil. The sensitive element is contained in the measured material, the principle of capacitive operation. Power supply material made of aluminum alloy.
  • RU-305 level relay. Monitoring the level of liquid substances. Explosion-proof design. Temperature of use -50 .. + 50C. Not used in chemically aggressive environments. Strictly work in one position, slope is not allowed. The measurement works by moving a float with a magnet. Works by triggering reed switches. Measurement accuracy up to 5 mm. power supply 220V, current 1A.
  • Su-100 level indicator. Measurement of the level of liquids and solids. Supply voltage 24V. It includes an electromagnetic relay, the sensitive element is located directly in the test fluid. Measure the limit position of solids: sand, gravel, grains.
  • Rosemount 5600 radar level gauge. Non-contact measurement of any type of substance. Correct installation is important, the accuracy of measurements depends on it. Power supply 24-240V. The device does not tolerate electromagnetic radiation. Explosive case. Has a display unit. We have developed our own program for the level meter, which simplifies setup . Used to measure the temperature in the tank. Qualified setup of the device is required for the correct full use of the level meter capabilities. You must use the settings when configuring:

    • the distance between the reference point and the level;
    • inner diameter of the pipe;
    • the length of the connection of the level gauge.

There are a huge number of types of sensors on sale . The choice should be based on the most cost-effective option for a particular project.