What is the Difference between Sensors and Actuators?

In an embedded system, the sensor and actuator collaborate and depend on one another. They are employed to automate processes and make a system more reliable. The main difference between them is the sensor uses to monitor and measure environmental changes, whereas the environment is managed by the actuator. These both devices and their differences are described below in detail.

What is Sensor?

A sensor is a tool used to detect and measure changes in the physical environment. In other words, "A sensor is a machine, tool or module that senses changes in its surroundings and transmits the data to other electrical devices." It is used with other electronic devices.

Features of Sensor

1. A sensor is a tool for tracking and measuring environmental changes.
2. Physical values are transformed into electrical signals through it.
3. It is connected to a system's input.
4. Light, heat, temperature, and locationsensors are an example of sensors.

Classification of Sensors

1. Active sensors

Active sensors are those that generate an output signal by using an external source. The sensor's internal physical characteristics change according to the external source used. That's why it is also known as self-generating sensors.

Some information about active sensors:

1. Active sensors self-destruct during hijack attempts.
2. The active sensor generates EM energy on its own, transmits it toward the earth, and then collects EM energy reflected from the earth.
3. They have their own internal energy source for lighting.
4. Electromagnetic (EM) energy that has been collected is utilized for measurement.
5. Active sensors have the ability to take measurements at any time.
6. Examples of active sensors are LISS-1, communication satellites, and earth observation satellites.

2. Passive sensors

Sensors that generate output signals without the help of an external source are called Passive sensors. These sensors do not require extra stimulation or voltage.

Some information about passive sensors:

1. The passive sensor is defenceless against a hijack attempt.
2. When data are requested, passive sensors wait patiently.
3. Only electromagnetic energy is measured by this sensor.
4. These sensors only collect measurements in the daytime.
5. An example of a passive sensor is a Thermocouple that produces a voltage value corresponding with the heat applied. It doesn't need an additional power source.

3. Analog Sensors

The sensor that generates a continuous Analog signal as output is called an Analog sensor. The Analog output produced is proportional to the system's input.

4. Digital sensors

Digital sensors are those that convert and transmit data digitally. Continuous signals include things like temperature, stress, pressure, displacement, and other physical properties.

Example of Sensors

1. Temperature Sensors 

This sensor is utilized to determine an object's temperature. For example, if we have to measure the temperature of a cup of milk, then we can use a temperature sensor. The thermal properties of gases, liquids, and solids are measured with temperature sensors. These sensors are utilized in many industries, including AC systems, computers, aquariums, mobile phones, greenhouses, automobiles, swimming pools, boilers etc. The thermistor is utilized in this sensor. Temperature sensors come in a variety of types, including Thermistors, Thermocouples, RTDs, and Temperature sensor ICs. The LM35 is a traditional Analog temperature sensor.

2. Proximity Sensors

This is the non-contact sensor which senses the presence of an object. Optical, sound, magnetic, capacitive, and other technologies are used to develop proximity sensors. These sensors are utilized in many industries, including mobile phones, cars, and ground proximity in aircraft.

3. IR Sensor

IR sensors are light-based sensors used in a variety of applications, such as object detection and proximity. The two types of IR sensors are the transmissive type and the reflective type. IR sensors are used in various applications, such as mobile phones, robots, industrial assembly, cars, and more.

4. Pressure Sensors

Using this sensor, we can measure the pressure. These sensors are able to gauge pressure in gases, liquids, and solids.

Actuator

The actuator transforms an electrical signal into mechanical work. It receives input from a system. Actuators are connected to a system's output. The mechanical movement is produced by an actuator. An actuator's basic function is to control a machine's movement. Electric motors, comb drives, stepper motors, jackscrews, thermal bimorph, solenoids and other common devices are examples of actuators.

There are five different types of actuators

1. Pneumatic Actuator: Pneumatic actuators generate movement by applying gas pressure.
2. Manual Actuator:  This type of actuator is operated manually by using gears, levers, wheels, etc. They need human action, not a power source.
3. Electric Actuator: Electricity is required to run these actuators. It generates mobility using an electrical motor. 
4. Hydraulic Actuator: Hydraulic actuators create pressure by compressing fluid in a cylinder, which allows mechanical movement.
5. Spring Actuator: These actuators have a loaded spring that is activated and stopped to provide mechanical work.

Features of Actuator

1. An actuator is a device that transforms electrical signals into mechanical movement.
2. It accepts an electrical signal as input.
3. It is connected to a system's output.
4. The environment can be regulated with the help of an actuator using sensor readings.

Relation between Actuators & Sensors

Actuators & Sensors frequently work with each other to complete the task. Consider the example of automatic fan control to understand both working. The sensor detects the temperature and sends a signal to the system, and then the system processes the signal and sends it to the actuator. In this case, the fan will speed up or slow down, depending on the temperature. So in this way, both devices work to complete tasks.

Difference between Sensors and Actuators

Sensors	Actuators
A sensor is a tool that produces an output signal by detecting a physical phenomenon.	The actuator transforms an electrical signal into mechanical work.
A physical quantity is the sensor's input	Electrical signals are the actuator's input.
The output of a sensor is an electrical signal	The output of an actuator is mechanical work.
It is attached to a system's input.	Actuators are connected to a system's output.
A sensor may or may not need an additional power source to operate.	Actuators require an additional power source to operate.
Examples: position sensors, temperature sensors, photoelectric sensors, proximity sensors, radiation sensors, pressure sensors, particle sensors, etc.	Examples: Electric motors, comb drives, stepper motors, jackscrews, thermal bimorph, solenoids, etc.
Types: Active sensors, Passive sensors, Analog Sensors, Digital sensors	Types: Manual Actuator, Electric Actuator, Hydraulic Actuator, Pneumatic Actuator, and Spring Actuator

Conclusion

Both sensors and actuators are utilized to execute a single task. The sensor keeps track of a physical quantity and sends a system the required reading. The system then analyses the data and sends an electrical signal to the actuator. The actuator generates the required change in the physical quantity by generating movement.