Everything about the level of measurement + types and the best brands (2022)
Level meter, level gauge or level detection sensor is actually a sensor that is used to detect the amount of materials inside tanks and silos. Altimeters are a very important category of instrumentation equipment and have wide applications in industry.
The equipment used to measure the surface is very diverse and can be classified from different aspects. For example, some are used only for liquids, some for solids, and some for both. On the other hand, some level sensors can accurately measure and report the height of the material inside the tank; While some other surface sensors can only detect whether the surface of the material is above a certain point or not.
In this article, we will explain the types of surface sensors and how they work in simple language, and we will help you to have a much clearer view of this category of instrumentation equipment. We will also introduce the best brands of level measuring equipment so that you can buy the best equipment if you need it!
Why is it important to use a level meter?
The first question is, why should we use a level of measurement at all? Controlling the level of reservoirs is essential and important; Because both the overflow and the emptying of the materials inside the tank will cause a lot of financial losses to the production unit. With the increase in the price of raw materials in all industries, this issue has become more important; Therefore, it is very wise to avoid all related damages by spending a reasonable amount.
According to these statements, which industries need a level meter? Oil, gas, petrochemical, power plant, chemical, mining, steel, food and pharmaceutical industries and in general, all industries in which there is a need to check the level of the substance inside the tank!
Imagine there was no such thing as a level sensor. How could we know the level of material in each tank?
Maybe several people were needed every day to visit a tank and observe and report the amount of material inside the tank! Even in this case, in addition to the financial costs (hiring several people!!!), the very long notification period, as well as the very low measurement accuracy, and this also caused an incredible increase in risk!
Types of level of measurement
Level sensors are mainly divided into two categories: level transmitters and level switches. Level transmitters can continuously check the level of items inside the tank and report accurately. Surface transmitters mainly operate based on wave technology and include radar and ultrasonic types.
On the other hand, level switches are used for level point detection. These sensors are installed in certain points of the tank and can only determine if the level of the material inside the tank is higher than this point or not. In the following article, we will discuss the types of level transmitters and level switches so that you can get to know them completely!
radar level transmitters
radar level transmitter are level transmitters and are used for continuous level monitoring. The basis of the work of radar altimeters is the technology of electromagnetic waves. In this category of level sensors, electromagnetic waves are sent into the tank, then reflect from the surface of the material inside the tank and return to the level sensor. The level sensor accurately detects the height of the material inside the tank using return waves.
In radar sensors, the frequency of the generated waves is very important. The higher the frequency of the waves generated by the radar level transmitter, the better the equipment can distinguish gases, vapors and disturbing foams from the actual level of the materials in the tank and recognize the height correctly. Currently, the highest frequency available in this equipment is 80 GHz, which can ignore its movements even if there is a mixer inside the tank.
Another effective factor in the accuracy and correctness of the performance of radar level meters is their antenna type. There are different types of dish, horn and capsule antennas, which are selected depending on the dimensions of the tank. The smaller the diameter of the antenna in this equipment, the more the waves propagate in a straight line. For example, the power of focusing waves in trumpet antennas is more than that of dish antennas.
The standard output level of radar transmitters is usually 4–20 milliamps. This output can be received and displayed by a programmable display or PLC, or commands can be programmed for each specific level of material in the tank.
In summary, radar level transmitters are by far the most widely used type of level sensor in the industry. With the entry of cheap and high-quality types of these equipments into the market, it is expected that this trend will continue and increase even more!
What are the advantages of radar level sensors and in what cases are they used?
Radar surface sensors are widely used in the industry due to their reliable performance, reasonable cost, and non-contact surface detection method. Also, based on the frequency of the waves sent from the sensor and the design of the equipment, they can be used for a wide range of materials such as solids or liquids. Since most of these equipments have anti-dust and moisture standards (IP66–67–68), you don’t need to worry about these particles penetrating inside the equipment!
Among the most important industries in which radar transmitters are used, we can mention petrochemical, refinery, steel, dams, cement, glass production, food, pharmaceutical, chemical industries, as well as water and sewage and waste management.
Among the disadvantages of radar altimeters, we can mention the relatively high price, although depending on the conditions of the tank or silo, there are also economical and reliable choices in this field.
Ultrasonic level transmitters
Ultrasonic level meters are also a family of level transmitters and are used for continuous level detection. Unlike radar, ultrasonic altimeters use mechanical waves. These mechanical waves are sent into the tank and reflected by hitting the surface of the material. By receiving and interpreting this information, the sensor can detect the height of the materials in the tank with relatively high accuracy.
There are different types of ultrasonic sensors for measuring the level of solids and liquids. But because solids usually create a lot of dust, which makes it difficult to measure the sensor, this equipment is usually used for liquids.
Due to the use of mechanical waves, many factors can be effective in surface monitoring by these tools. Dust, disturbing gases and vapors, medium to high intensity sounds, wind and rain are among the most important of these factors. On the other hand, the range of ultrasonic level meters is usually not very high (certainly less than 20 meters) due to the lower speed of mechanical waves.
Ultrasonic height measurement are usually used in closed tanks where there are no disturbing factors in the measurement. Tanks for water, oil, gasoline, flammable substances, milk and some petrochemical substances that do not produce thick vapors are among the most important uses of this equipment in the industry. But in the distant years, they were mistakenly used in water treatment plants and outdoor pools due to their low price compared to radar transmitters.
Capacitance level switch (weight) or rod capacitance
Capacitance levelswitch with towed wire or rod are from the category of level switches and are used for point detection of the level. The basis of the work of capacitive level sensors is electrical capacity; But what does this mean in simple language?
As you know, capacitors have two positive and negative surfaces (called anode and cathode). The electric charge is collected in these two levels and is used in the circuit when necessary. If a dielectric material is placed between these two levels, the electrical capacity of the capacitor will change based on the specific dielectric coefficient of that material.
In capacitive level sensors, this issue is used to detect the level. The question is: how? In the level of capacitive switches, the probe that is placed inside the tank plays the role of one surface and the wall of the tank plays the role of another surface.
When the material is placed between the tank wall and the point where the equipment is installed, the electric capacity changes compared to the absence of the material, and the sensor detects the presence of the material at the specified point.
Advantages, disadvantages and applications of capacitive level switches
Capacitive level switches are used in a wide range of industries. Also, due to the strength of the probe, they can be used in cement tanks and tanks where there is paste, slurry or lumps. But these types of level measurement also have their own limitations.
As you probably noticed by now, capacitive height meters are used exclusively for tanks that are made of metal; Therefore, they cannot be used in plastic tanks. Of course, it should be noted that some models of capacitive sensors such as Vega EL4 or Vega Cap 69 are multi-cathode and despite being capacitive, they can also be used in tanks with non-conductive walls.
Capacitive level meters can be installed and operated even at extremely high temperatures and pressures that few equipment can withstand. For example, some capacitive sensors can withstand even 400 bar pressure.
But for rod capacitor switches, the conditions inside the tank are much more important than the weight type, and the following points must be taken into account when choosing: Temperature and type of material inside the tank (corrosiveness or acidity)
Radar or microwave level switches
Just like radar transmitters, radar switches use wave technology to detect the surface; But they have fundamental differences with radar transmitters. Microwave surface switches consist of an electromagnetic wave transmitter and a wave receiver that must be installed on the sides of the point where we want to detect the surface of the material.
When the material reaches this particular point, the equipment detects the presence of the material at that point by using the changes in the amount of waves received by the receiver. As you can see, unlike transmitters, radar level switches cannot measure the level of materials continuously and are of switch type.
Range or vibration level switches
Range level switch detect the level pointwise and are actually level switches. The operation of this type of level switches is based on vibration; In such a way that a motor causes vibration in the range section. If the material reaches the part of the range that is placed inside the tank, the vibration level of this part will decrease compared to the initial state. In this way, the sensor detects the presence or absence of the material at the desired point. In recent years, vibration level switches have also been designed and built, and the purpose of this type of level switches is to correct the disadvantages of range sensors, which are mainly caused by the possible failure of the probes due to the passage of time. (As we said, the probes of the range sensor are in direct contact with the material)
Vibrating level switches are widely used in tanks containing powdery materials and corrosive liquids.
Range sensors are used in tanks whose contents are liquids, granules or powders in which there is no possibility of creating lumps. It is necessary to do the necessary research when buying a range level switch in order to prevent damage in the future.
Level measurement using differential pressure
Differential pressure level meter belong to the level transmitter category and are used for continuous detection of the level of liquid tanks. It is interesting to know that differential pressure level sensors are actually pressure meters! But how do we know the surface of the material from the pressure measurement?
To use differential pressure level transmitters, it is necessary to install one sensor at the top and another at the bottom of the tank. Then by considering the contents of the tank and also measuring the pressure difference between the two sensors, the height of the materials in the tank can be easily measured.
Differential pressure level sensors are used in tanks that cannot use other equipment due to high pressure and closed tank. Also, in combination with other instruments, it is possible to measure, for example, the intensity of liquid flow in a tank. This type of tube transmitters are only used for liquids.
Hydrostatic level meter
Hydrostatic level of measurement, like the level of differential pressure transmitters, detect the level of the material by measuring the pressure, but there are differences between these two types of equipment. Hydrostatic sensors are also only used for liquids, but unlike other equipment, they are often installed in wells and behind large dams.
As you know, the pressure of a liquid column depends on its height regardless of the cross section. In this type of level sensors, the transmitter level probe is placed in the depth of the well or tank and measures the pressure at the lowest level of the well. Then, taking into account the normal air pressure at the well site, the sensor easily calculates how high the liquid is above the probe.
Hydrostatic altimeters are used in oil and water wells or very high liquid tanks. In this case, the quality of monitoring will also be very high. But you should be careful that the length of the sensor wires should be proportional to the depth of the desired well!
Radiometric level of measurement
Level radiometric transmitters, as their name suggests, use the property of radioactivity for continuous and point detection of level, density and density. Radiometric level gauges are used in environments where it is not possible to use other level measuring equipment. Petroleum coke processing tanks are an example of these environments.
In these surface sensors, a radioactive substance such as cesium 137 or cobalt 60 is used to emit gamma rays. Gamma rays have a lot of energy and penetrate the body of the tank and the materials inside it. Then the radiometric sensor detects exactly where the surface of the material inside the tank is based on the amount of absorption of these rays and the amount of its passage.
Level radiometric transmitters are very expensive equipment and also have very advanced technology. Therefore, when buying equipment from a trusted and experienced center, you should definitely get super-specialized advice on this matter so that you can find the right equipment for your needs.
Magnetic level gauges, floaters and graduated gauges
In the past, other level sensors such as magnetic level gauges, floaters and graduated gauges were used. The operation of these sensors was very simple and analog; For this reason, the error rate was extremely high and the possibility of creating automation was also very limited.
For example, consider the type of graduated gauge. In this equipment, a ball with a specific weight corresponding to the material inside the tank was prepared and placed in the tank. As the material inside the tank rises and falls, this sphere also moves and shows the amount of fullness and emptyness of the tank. This may even seem a little funny today; But before the arrival of newer technologies, there were practically no alternatives for these primitive methods.
Nowadays, due to the advancement of technology, to a large extent, this type of surface sensors is obsolete and they are no longer used in modern companies and productions. It can be said that the most important reason for the obsolescence of this equipment is the issue of analog output.
With the introduction of modern technologies and the increase of automation, less professional and experienced managers are willing to deal with such technologies. Although these equipments may still be found in the market today, their use is not recommended in any way; Because a possible damage resulting from the lack of monitoring quality will be several times the cost saved when purchasing the equipment.
Which type of level meters is best?
If we want to look at the matter realistically, there is no answer to this question! There are different answers to this question depending on the situation in which the equipment is to be used. For example, in aggressive environments, it is better to use non-contact surface measurement methods as much as possible; As a result, level radar transmitters will be the best option. In this case, if it is not possible to use this type of transmitter due to environmental conditions, maybe radiometric sensors are the most suitable type.
In another example, imagine that we need a spot measurement of the level in a cement tank. Since there is a possibility of clogging in these tanks, it is not at all right to use a range switch level, so a capacitive sensor would be the best choice.
In general, level transmitters have high monitoring quality and can report the level to us continuously, so it is safe to say that they are often the best choice available. But it should also be considered that in rare circumstances, due to the special shape and state of the tank or the incompatibility of the control systems, it may not be possible to use them.
When choosing the best type of level meters for your needs, you must pay attention to these things:
- Type of tank
2. Dimensions of the tank
3. The material inside the tank
4. Temperature and pressure inside the tank
5. Other details of the tank (the presence of disturbing gases, the presence of a mixer, the presence of appendages in the tank, …)
5. Contact or non-contact measurement
6. Type of control system
According to these things, it is possible to predict the best type of level sensor according to the need.
What are the best brands ?
Vega, Anders Hauser and Rosemount brands are the most well-known brands of surface measuring equipment in the world. But among all these brands, Vega brand has a very special place. Vega equipment is produced exclusively in the mother company in Germany, and for this reason, they have the highest level of quality and longevity.
Due to the integration in production, unlike other brands, the possibility of selling stock equipment or repairing Vega equipment is close to zero; Because the exact date of production and even equipment testing can be tracked! That is, you can see exactly when this equipment was produced and when the final tests were performed on it in the manufacturing company. But in other brands, due to the lack of integrity in production, it is not known exactly on what date the equipment was produced and tested.
