Flow and Level Sensor

 Flow and Level Sensor

 Level Sensors

level sensor is a device that is designed to monitor, maintain, and measure liquid (and sometimes solid) levels. Once the liquid level is detected, the sensor converts the perceived data into an electric signal. Level sensors are used primarily in the manufacturing and automotive industries, but they can be found in many household appliances as well, such as ice makers in refrigerators.  

What is a Liquid Level Sensor?

Liquid level sensors, also called liquid level switches, are designed to change state when immersed in a liquid. They are used to determine if a liquid or oil exists at a particular level in a container.


Level sensors are useful devices that are used to detect the level of substances such as liquids, powders and granular materials. There is a wide range of level sensors and they are all used in different industries. Some level sensors can be used for any fluid and others can only be used for certain substances.

Level sensors are used to measure substances that are inside a container or in their natural state, e.g. rivers.

Level sensors are used in the following industries:

  • Oil Manufacturing Plants 
  • Water Treatment
  • Paper and Pulp Production Divisions
  • Petrochemical and Chemical Making & Refinery Units
  • Waste Material Handling Industry
  • Beverage and Food Manufacturing Factories
  • Pharmaceutical Processes
  • Power Generating Plants

Below is a list of the most common level sensors:

  • Reflex level sensor
  • Tank level sensor
  • Bi-colour level sensor
  • Transparent level sensor

There are various technologies that are used in the level sensor market. Ultrasonic is the most popular technology; this is due to that fact that ultrasonic sensors are small, mobile and they have no moving parts; they are easy to use, affordable and they do not require much maintenance. Ultrasonic sensors are used to measure thick substances and they can be used in extreme conditions.

Level Sensor Classification

Level Sensors can be broken into two classifications;

  1. Point level measurement
  2. Continuous level measurement

Point level measurement indicates when a product is present at a certain point and continuous level measuring indicates the continuous level of a product as it rises and falls.

The sensors for point level indication are:

  1. Capacitance
  2. Optical
  3. Conductivity
  4. Vibrating (Tuning fork)
  5. Float Switch

The sensors for continuous level measuring are:

  1. Ultrasonic
  2. Radar (Microwave)

Point Level Measurement Sensors

1. Capacitance Level Sensors

These sensors are used to detect the liquid levels like slurries and aqueous liquids. They are operated by using a probe for checking level changes. These level changes are transformed into analog signals. The probes are generally made of conducting wire by PTFE insulation. But, stainless steel probes are extremely responsive and hence they are appropriate for measuring non-conductive substance granular or materials with low dielectric constant. These types of sensors are very simple to use and clean as they do not have any moving components.

Pros and Cons

  • Solid-state, compact, can be non-invasive, accurate
  • Can only be used in certain liquids, May require calibration


They are commonly used in applications like Tank level monitoring in chemical, water treatment, food, battery industries and involving high pressure and temperature.

2. Optical Level Sensors

Optical level sensors are used to detect liquids including poised materials, interface between two immiscible liquids and the occurrence of sediments. They are worked based on the changes of transmission in infrared light emitted from an IR LED. The interference from the produced light can be reduced by using a high energy IR diode and pulse modulation methods.

Continuous optical level sensors, on the other hand, use the highly intense laser light that can infuse dusty environments and notice liquid substances.

Pros and Cons

  • Compact, high pressure, no moving parts, and capability of temperature, can notice tiny amounts of liquids.
  • Invasive as the sensor needs get in touch with the liquid needs power, certain wide substances can reason coating on the Prism.


They are commonly used in applications like leak detection and tank level measurement

3. Conductivity (Resistance) Level Sensor

Another style of point level sensor is conductivity or resistance.

A conductivity or resistance sensor uses a probe to read conductivity. The probe has a pair of electrodes and applies alternating current to them.

When a liquid covers the probe its electrodes form a part on an electric circuit, causing current to flow which signals a high or low level.

The advantages of using a conductivity level sensor are:

  • There are no moving parts
  • They are low cost
  • Fairly easy to use

The disadvantages are:

  • They are invasive (meaning they must touch the product being sensed)
  • They only sense conductive liquids
  • The probe will erode over time

Appropriate use for these sensors would be for signaling high or low levels.

4. Vibrating (Tuning Fork) Level Sensor

Vibrating or tuning forks is another type of point level sensor.

They use a fork-shaped sensing element with two tines. The fork vibrates at its natural resonant frequency. As the level changes, the frequency of the fork will change detecting the level. 

These sensors are:

  • Cost effective and compact
  • Invasive to the product, meaning they have to touch the material to sense the level
  • Easy to install
  • Essentially maintenance-free

They have unlimited uses based on the material that they can sense. Mining, food and beverage, and chemical processing industries use these sensors for their applications.

5. Float Switch

The last point level sensor that we will talk about is a float switch.

Float switches use a float, a device that will raise or lower when a product is applied or removed, which will open or close a circuit as the level raises or lowers moving the float.

Advantages of a float switch are:

  • They are non powered device
  • They provide a direct indication
  • They are inexpensive

Disadvantages are:

  • They are invasive to the product
  • They have moving parts
  • They can be large in size

Float switches will only give an indication for a high or low level, they cannot measure a variable level. A great use for float switches is in liquid storage tanks for high or low-level indication.

Continuous Level Measurement Sensors

1. Ultrasonic Level Sensors

Ultrasonic level sensors are used to detect the levels of sticky liquid substances and bulkiness materials as well. They are worked by producing audio waves at the range of frequency from 20 to 200 kHz. These waves are then replicated back to a transducer. The ultrasonic sensor’s response is influenced by turbulence, pressure, moisture, and temperature. In addition, the transducer is necessary to be increased appropriately to obtain a better response.

Pros and Cons

  • Compact, cost-effective
  • Invasive, numbers of users are limited

The advantage of using this type of sensor is that:

  • These sensors have no moving parts
  • They are compact
  • They are reliable
  • Non-invasive (Non-contact)
  • Unaffected by the properties of the material they are sensing
  • Self-cleaning because of the vibrations they give off

The disadvantage of using this type of sensor is that:

  • They can be expensive
  • In some situations, the environment can have a negative effect on them


The ultrasonic level sensors are used to control the liquid level, fine-grained solids within mining and powders, food and beverage industries and chemical processing.

2. Microwave Optical Sensors

These types of sensors are used for applications like varying temperature, pressure, dirty and moist environments, as microwaves can easily go through under these situations without involving air molecules for energy transmission. Microwave Optical sensors can notice conductive water & metallic substances. The measurements are accepted using time domain or pulse reflectometry.

Pros and Cons

  • No calibration required, very accurate, multiple output options
  • Costly, limited detection range, and can be affected by the environment.

The advantages of radar sensors are that:

  • They are not affected by temperature, pressure or dust
  • They can also measure liquids, pastes, powders, and solids
  • They are very accurate and require no calibration
  • They are non-invasive because they do not have to touch the product that it is sensing

The disadvantages of radar sensors are that:

  • They are expensive
  • They have a limited detection range


  • They are commonly used in applications like vaporous, Moist, and dusty environments. 
  • They are also used in systems in which temperatures differ.

Flow Sensor

Water Flow

Water flow sensors are installed at the water source or pipes to measure the rate of flow of water and calculate the amount of water flowed through the pipe. Rate of flow of water is measured as liters per hour or cubic meters.
Water flow sensor consists of a copper body, a water rotor, and a hall-effect sensor. When water flows through the rotor, rotor rolls, its speed changes with different rate of flow.


Flow is defined as the quantity of fluid (gas, liquid, vapour or sublimate) that passes a point per unit time
It can be presented by a simple equation: Flow (Q) = quantity/time
It is the rate of change of a quantity. It is either volumetric or mass flow rate.

Properties Affecting Fluid Flow

Velocity of Fluid – the fluid speed in the direction of flow. The fluid velocity depends on the head pressure that is forcing the fluid through the pipe. The greater head pressure, the faster fluid will flow.
Pipe size – the larger the pipe, the greater the potential flow rate
Pipe friction – reduces the flow rate through the pipe. Flow rate of the fluid is slower near walls of the pipe that at the center.
Fluid viscosity – its physical resistance to flow.
The specific gravity of fluid – at any given operating condition, the higher fluid’s specific gravity, the lower its flow rate.
Fluid condition – the condition of fluid (clear or dirty) is one of the limitations in flow measurement, some measuring devices blocked/plugged or eroded if dirty fluids are used.
Velocity Profiles – it has major effect on the accuracy of most flow meters. It can be laminar, transitional or turbulent flow. Properties Affecting Fluid Flow

Importance of Fluid Measurement

Measuring flow is one of the most important aspects of process control
The most diverse substances are transported and distributed in piping system
The fluid flowing through pipes have different properties, so different flow measuring devices are used
The maintenance of definite rates of flow is important for maximum efficiency and production

What is Water Flow Sensor?

Huge industrial plants, commercial and residential buildings require a large amount of water supply. The public water supply system is used to meet this requirement. To monitor the amount of water being supplied and used, the rate of flow of water has to be measured. Water flow sensors are used for this purpose.
Water flow sensors are installed at the water source or pipes to measure the rate of flow of water and calculate the amount of water flowed through the pipe.

Differential pressure flow meters

  • Coriolis Flow meter
  • Vortex Flow meter
  • Ultrasonic Flow meter
  • Electromagnetic Flow meter
  • Thermal Flow meter

Working Principle

Water flow sensor consists of a plastic valve from which water can pass. A water rotor along with a hall effect sensor is present the sense and measure the water flow.
When water flows through the valve it rotates the rotor. By this, the change can be observed in the speed of the motor. This change is calculated as output as a pulse signal by the hall effect sensor. Thus, the rate of flow of water can be measured.
The main working principle behind the working of this sensor is the Hall effect. According to this principle, in this sensor, a voltage difference is induced in the conductor due to the rotation of the rotor. This induced voltage difference is transverse to the electric current.

When the moving fan is rotated due to the flow of water, it rotates the rotor which induces the voltage. This induced voltage is measured by the hall effect sensor and displayed on the LCD display.
The water flow sensor can be used with hot waters, cold waters, warm waters, clean water, and dirty water also. These sensors are available in different diameters, with different flow rate ranges.
These sensors can be easily interfaced with microcontrollers like Arduino. For this, an Arduino microcontroller board for processing, a Hall effect water flow sensor, a 16×2 LCD display, and Breadboard connecting wires are required. The sensor is placed at the water source inlet or at the opening of the pipe.
The sensor contains three wires. Red wire to connect with supply voltage. Black wire to connect to ground and a yellow wire to collect output from Hall effect sensor. For supply voltage 5V to 18V of DC is required.

Compact, Easy to Install
High Sealing Performance
High Quality Hall Effect Sensor
RoHS Compliant

Applications of Water Flow Sensor

  • Water flow sensors can measure the rate of flow of water either by measuring velocity or displacement. These sensors can also measure the flow of water like fluids such as measuring milk in a dairy industry etc…
  • There are various types of water flow sensors available based on their diameter and method of measuring. A cost-effective and most commonly used water flow sensor is Paddlewheel sensor. It can be used with water-like fluids.
  • For the type of applications where a straight pipe is not available for inlet, Positive displacement flow meter is used. This type of water flow sensor can be used for viscous liquids also.
  • For working with dirty water and wastewater which may be conductive, Magnetic flow meter is used. For applications such as sewage water, slurries, and other dirty liquids Ultrasonic flow meters are used.
  • The LCD display is used to display the measurements. The magnetic hall effect water flow sensor outputs a pulse of every revolution of the rotor. The hall effect sensor present in the device is sealed from water to keep it safe and dry.

Example of Water Flow Sensor

YFS201 Hall effect sensor is an example of this sensor. These sensors also require a display to display the measurements. This sensor outputs 4-5 pulses for every liter of liquid flowing through it per minute. It has a working flow rate of 1-30liters per minute. Easy to use and cost-effectiveness are the important characteristics of this sensor.