Monitoring and Control


A sensor is an input device that records data about the surrounding physical environment. The sensor inputs this data into a computer system to be processed. Once the data has been processed, if necessary, an output can be triggered as a response. Sensors can automatically enter data into a computer system, removing the need for a human to manually enter the data. They can be very beneficial as it can increase the accuracy of the data by removing the possibility of human error.

The readings taken by the sensors are monitored and processed in a certain way the steps are as follow:

  • The sensor will constantly monitor the surrounding environment
  • The data readings from the sensor will normally be analogue. Therefore, they will be converted to a digital signal for a computer system to process. This is done by an analogue to digital converter
  • The digital signal is then sent to a microprocessor. The microprocessor processes the value and compares it to a pre-set value or range of values
  • If the value is outside the acceptable range, the microprocessor will send a signal to an actuator to trigger any action that needs to be taken.

Types of sensors used in monitoring and controlling technologies:

Motion sensors:

A motion sensor detects movement. It can do this either passively or actively.

There are two types of motion sensors:

Passive motion sensor:

  • A passive motion sensor reads the energy in its surrounding environment and detects changes caused by movement.
  • An example of a passive motion sensor is a passive infrared sensor. This is a sensor that detects the presence of infrared energy if it appears in its surrounding environment.
  • Passive infrared sensors are commonly used in security systems. These sensors are normally wall mounted in the corner of a room. As an intruder walks in front of a sensor, the sensor detects the infrared energy emitted by the intruder. The detection of infrared energy by the sensor can then trigger an alarm to sound.

Active motion sensor:

An active motion sensor emits energy into the surrounding environment to detect any movement.

An example of an active motion sensor is a microwave sensor. This is a sensor that emits microwaves and detects the changes in the reflection it receives back when bouncing off nearby objects.

Active motion sensors can also be used in security systems. A microwave sensor continuously emits microwaves into a room. As an intruder walks through the microwaves, they will be reflected back much more quickly to the sensor and it will detect the change. This change in reflection of the microwaves can then cause an alarm to sound.

Pressure sensors:

Measures pressure normally of a liquid or gas. The measure of pressure is usually based upon the force it takes to stop a liquid or gas from expanding.


The vehicle industry: They are used to form part of the safety system of a vehicle. Pressure sensors are used to monitor the oil follow and coolant in the vehicle. They are used to regulate the power given to the engine based on the pressure applied on the accelerator and brake. The airbag safety system also uses pressure sensors. The air bags will be trigged to inflate when a high amount of pressure is applied to certain parts of the vehicle.

Chemical and nuclear plants: They are used to monitor and control the flow of gases and liquids in industrial plants. This, means that substances that are being transported in the plant, or any other chemical reactions that are carried out, are done extremely safely. This makes sure that high level of safety is maintained in the industrial plant at all times.

Aviation and marine industry: They are used to monitor and control the atmosphere within an airplane or submarine. This is to make sure the correct breathing conditions are maintained.

Touch screens: A touch screen that uses pressure sensors is built of multiple layers. When pressure is applied to the top layer of the screen it is pushed into the bottom layer of the screen, creating a connection that generates an electrical signal. This electrical signal informs the device of the location where the pressure had been applied to the screen.

Moisture and humidity sensors:

A humidity sensor is an electronic device that measures the humidity in its environment and converts its findings into a corresponding electrical signal. ​

Humidity sensors vary widely in size and functionality; some humidity sensors can be found in handheld devices (such as smartphones), while others are integrated into larger embedded systems (such as air quality monitoring systems).​


  1. Wine cellars: The humidity level in a wine cellar is very important. Too much or too little humidity can cause the wine to spoil. The humidity level needs to be kept constant and correct in order to keep the wine at its best.
  2. Meteorological stations: They are used to help monitor and predict weather conditions by measuring humidity levels.​
  3. Controlling allergies: An atmosphere that is high in humidity can encourage the growth of bacteria and mold. This can trigger allergies. ​Humidity sensors can be used to monitor and control the level of humidity in a room.
  4. Manufacturing: In the manufacturing of many products the level of moisture in the atmosphere is very important.​ If humidity is too high or too low it could adversely affect the product.​
  5. Agriculture and farming: ​Humidity and moisture sensors can be used to grow and farm crops in the best conditions possible. ​By monitoring and controlling the conditions in which the crops are grown, the most perfect conditions can be created, producing the best crops. ​The level of moisture in the soil can be kept constant to help the crops grow.​

Temperature sensors:

Temperature sensors monitor and measure the temperature of an environment.

They do this by measuring how much heat is present. Temperature sensors are used in a great number of control systems, many of them in our home appliances.


  1. Washing machine and dishwasher: ​A temperature sensor is used in a washing machine and a dishwasher to measure the temperature of the water. ​A microprocessor in the washing machine or dishwasher will receive the data sent by the temperature sensor and can trigger an action to heat up or cool down the water if necessary
  2. Dryer: A temperature sensor is used in a dryer to measure the temperature of the hot air flowing into the dryer. ​A microprocessor in the dryer will receive the data sent by the temperature sensor and can trigger an action to heat up or cool down the air if necessary.​
  3. Refrigerator and freezer: ​A temperature sensor is used in a refrigerator or freezer to measure the ambient temperature inside. ​A microprocessor in the refrigerator or freezer will receive the data sent by the temperature sensor and can trigger an action to heat up or cool down the air if necessary.​

Light sensors:

Light sensors monitor and measure light.

There are different types of light sensors and they measure light in different ways.


  • The most common type of light sensor is a photo resistor. This type of sensor will change the resistance when light shines on and is normally used to measure the intensity of light. Important in devices such as digital cameras or street lights.
  • Light sensors can also be used in many other devices including barcode scanners, display screens, automated lighting systems and smartphones.

Advantages and disadvantages of using sensors:

  • By using a sensor or a number of sensors in a monitoring or control system, multiple readings can be taken in quick succession. ​
  • The computer system will make decisions based on the data it is given. It will act logically on these decisions in the way it has been programmed. ​
  • This can be beneficial as the decisions made and actions taken will be consistent. If a human performed the same decision-making process, external factors may affect the decision they make.​
  • This could cause inconsistency in the decision-making process and actions taken.​
  • This can sometimes be a disadvantage and a computer system may not be able to react to an unexpected event that a human would be able to assess and make a decision about.
  • Sensors are also extremely beneficial for use in environments that are dangerous to humans.​
  • Also, computers can process data much more quickly and respond faster to any necessary actions than a human, so a dangerous environment can be monitored and controlled more effectively.​
  • There is always a risk involved in using computer systems in monitoring and control. ​
  • The system is electronic and if a power failure occurs, the system will not operate.