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What are the level switch and level meter?

What are level switches, level meters and level sensors? Where are they used?
This page explains how level switches, level meters, and level sensors are used in various locations including industrial factories and plants.

 

What are level switch and level meter?

Factories, plants, various equipment, rivers, and utility water tanks all need to monitor and control the levels and remaining volume of liquids, powder, or granulated materials. Level switches and level meters detect and measure materials such as liquids, powder, and granulated materials in tanks, vessels, and plumbing.

What are level switch and level meter? Figure 1

The switch captures the electrical difference between empty and full of material to detect the level. When material is empty, electrical status of detecting electrode and grounding electrode is: resistance (Ro) is infinite, and capacitance (Co) will be specific capacitance value determined by installation status.


What is level switch?

A level switch is a sensor that detects the presence of liquids, powder, or granulated materials at a specific location.(It is also referred to as level sensor) For example, when a tank is supplied with liquid, it overflow.In order to prevent overflows, a level switch is installed near the top of the tank. When the liquid touches the level switch, it outputs a signal to keep the liquid from overflowing the tank. (To detect that a tank is filled with material is referred to full detection, or upper limit detection.) On the other hand, when the liquid level drops as the liquid is discharged, a level switch is used to prevent completely draining the tank. This is referred to as an empty detection or lower limit detection.

What is the level meter?

Different from level switches, level meters these devices continuously measure the volume of liquid, powder, or granulated materials. (This is also referred to continuous level meter, liquid meter, or powder meter.) Although a level switch can detect the presence of material at a certain point, a level meter outputs a reading of the total liquid volume in a tank, usually from 0 to 100%. So, a level meter can monitor and control the volume in greater detail than a level switch. The level meter usually outputs its reading as a small current of 4 to 20mA. (4mA represents 0%, 20mA represents 100%, and 12mA represents 50%,)

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Importance of level switches and level meters

As production facilities put more emphasis on energy saving, they are using lots of various types of sensors.
Among these types of sensors, level sensors are used in harsh conditions with extreme temperatures, pressures, vibration, and surrounding environments. The objects measured by level sensors are greatly diversified. Under these conditions, level sensors are required to be extremely reliable. Our level sensing equipment meets these requirements. They are manufactured using lots of experience and technical skill. We are proud of their quality and reliability.

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Introduction of level sensors with various operating principles

However, you cannot detect substances if you do not select optimum sensor depending on substance to detect (liquid, or powder) and detecting conditions (use temperature, etc.).

This page describes which method and which product (level switch or liquid meter) is best for the substances and conditions you want to detect, taking some typical examples.

Detecting liquids (liquid level meter, water level meter)

Introduction of level sensors with various operating principles Figure 1

Typical examples for measuring and detecting liquids are as follows:

  1. Float type
    : Uses a float that rests at the water level
  2. Ultrasonic wave type
    : :Uses reflection of an ultrasonic wave
  3. Capacitance type
    ; Uses the dielectric constant of the liquid
  4. Pressure type
    : Uses pressure (water pressure) of the liquid

..


Each type has advantages and disadvantages. Therefore, we must choose the detection method depending on the liquid type and conditions of use.
Features of each method and precautions for selection are described below.

 
Method 1. Float type (switch, continuous)
2. Ultrasonic wave type (switch, continuous)
3. Capacitance type (switch, continuous)
4. Pressure type (switch, continuous)
Float type Ultrasonic wave type Capacitance type Pressure type
Principle A float moves up and down due to buoyancy. A reed switch is actuated by a magnet in the float, and outputs a detection signal Emits an ultrasonic wave and receives it after it is reflected off the liquid surface. Then it converts the time difference between sending and receiving the wave to a measuring signal and outputs the data. Detects and measures the difference between a material’s specific capacitance dielectric constant and the present liquid’s dielectric constant to detect the liquid level and output. Install it in the lowest position of a tank and it detects liquid pressure and outputs the results.
Advantages Low cost and easy to use. Measure without contact material. Easy to handle. Can detect and measure under hard conditions of high temperature and high pressure.It can also measure highly viscous liquid. Easy to use.
Disadvantages May not be used for viscous liquid, liquids of low specific gravity, or in high temperature or high pressure situations Cannot be used in vacuum.May not be used under high temperature, high pressure, vapored, dusty environment, and obstacles. Cannot measure when the dielectric constant of the liquid changes. May not measure at high temperature and high pressure as difference may be large.With a continuous indicating type, the sensor shall be installed at lower position of a tank
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Detecting other than liquid (level switch)

Introduction of level sensors with various operating principles Figure 2

Typical examples for measuring and detecting powder and granulated materials

  1. Vibration type
    : Uses the principle of attenuation of a vibrating bar
  2. Capacitance type
    ; Uses the dielectric constant of the powder
  3. Paddle type
    : Uses the principle of slowing or stopping a rotating vane
  4. Ultrasonic wave type
    : Uses reflection of an ultrasonic wave

Each type has advantages and disadvantages. Therefore, we must choose the detection method depending on the liquid type and conditions of use.
Features of each method and precautions for selection are described below.

 
Method 1. Vibration type (switch)
2. Capacitance type (switch, continuous)
3. Paddle type (switch)
4. Ultrasonic wave type (switch, continuous)
Vibration type Capacitance type Paddle type Ultrasonic wave type
Principle A rod vibrates at a specific frequency. When material touches the rod the vibration is attenuated. The unit detects this attenuation and outputs detection signals. Detects and measures the difference between a material’s specific capacitance dielectric constant and the air dielectric constant to detect a level and output it. A shaft with a vane at the end rotates. When the vane touches material, the vane stops rotating and outputs a detection signal. Emits an ultrasonic wave and receives it after it is reflected off the liquid surface. Then it converts the time difference between sending and receiving the wave to a measuring signal and outputs the data.
Advantages Can detect even physical property is changed.No need for initial adjustment and maintenance. Can detect and measure under hard conditions of high temperature and high pressure. Also can measure adhesive powder and granulated materials. Low cost and easy to use. Measure without contact material
Disadvantages Cannot be used in locations with a lot of external vibration, at high temperatures, or under high pressure. Cannot measure levels if the dielectric constant of the material changes As this is mechanical type, it may need maintenance. Cannot be installed at location with much vibration. Cannot be used in vacuum.May not be used under high temperature, high pressure, vapored, dusty environment, and obstacles.
Related links Production information
Standard examples of use
Special examples of use
Product information
Standard examples of use
Special examples of use
Precaution for use
Production information
Standard examples of use
Product information
Standard examples of use
Special examples of use
Precaution for use

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