Sensors functions explanation and its integration in the control system

Sensors and Transducers

To make it easy when we are trying to understand and discuss the sensors or transducers (which have the same meaning and function as sensors), let us look at our human body for example as a case study.

Our human body has many sensors which we use to sense all physical phenomena and parameters around us and our brain is dealing with it accordingly. We have eyes to See, skin to feel, noses to smell, and ears to listen as well as other sensors that the human body uses. 

Our eyes are compact sensors in one item. It can sense motion, light, and color. Skin can sense heat, cool, and vibration. Ears can sense the voices and sounds. These sensors send signals to the human brain to act accordingly like looking for cooling in got days or heating in cold wither and so on. 

The existing sensors (which we can call industrial sensors to differentiate between them and humans) have become widely used and they have been developed and had many advantages compared to the old ones.

 In this article we will go through and study the definitions of the sensors, their types, how they work, their advantages, and their applications. In the next articles, we will go deeply into the sensors and submit more details about their fabrication processes and applications.

Sensors and transducers

What is the definition of Sensors?

Simply, we can define sensors as devices that are used to sense a physical phenomenon and represent it as an accurate electrical signal equivalent to that physical phenomenon. It is normally used with the industrial control system to measure the output of any process accurately to get a high performance of the system. It is sometimes called detectors or converters.

 The physical form could be heat, pressure, level, flow, weight, flame, movement, and speed. The next drawing shows the sensor at the output of the processes to measure is output. Once we convert that physical quantity to an electrical signal, I display it for monitoring and following. It can also be used to control the output of any process based on the below drawings.

Sensors - human nose and smelling

What are the types of sensors?

Types of sensors are classified based on their process output and the application used. In industrial manufacturing, we have two main types of sensors. The first one is called the digital sensor where its output is a contact and the sensor in that case is acting as a switch.  This switch is On or off when exceeds or gets down a certain predetermined value.

 For example, if we adjust the room temperature to 24 ^oC, the temperature sensor could be adjusted to work at that temperature and switch on the A/C to cool down the room if the temperature goes up more than 24 oC it starts heater if the temperature goes below 24 oC that type of sensor at any time of its operation has only two states zero or one and sometimes called it ON/OFF sensor. 

The below drawing shows an example of the on-off switch of the motor. The second type of sensor is the analogue sensor where at any time of its operation we will get an exact value that represents the physical signals.

• Digital state (ON or OFF i.e. I/O).
• Analog output signal.

Sensors in closed-loop control system

We can classify the sensors based on the application which is a huge number of applications. The list below shows the most known applications represented by the sensor. As these applications contain very important and vital applications, we will explain them in detail later.

What are the applications that use sensors?

• Temperature sensors.
• Pressure sensors.
• Level sensors.
• Flow sensors.
• Humidity sensors.
• Motion sensors.
• Speed sensors
• Tension sensors.
• Weighing sensors.
• Photo sensor.
• Ultrasonic sensors.
• Infra-red (IR sensors)

The output of the sensor could be a digital state (on or off) like a thermostat or temperature switch for example which works as a switch that changes its state when the temperature reaches a certain preset limit from on to off or from off to on.

The same expression could be used with the other physical form or state like pressure switch, level switch, flow switch, and speed switch. The other form of the sensor output is the analogue signals which show a value representing and changes with any change in the physical form along the time interval.

For weight sensing as an example, a load cell device represents the load of any object over time and increases or decreases according to the variation of that object load. In some cases, sensor output is connected to a pointer installed over a range to read and represent the physical quantities.

The sensor output signal is normally represented as volts, millivolts, amps, and milliamps. Also, the output could be represented as any changing of electrical units used in the electrical circuit like the resistance and capacitance. Sensors are normally equipped with a conditioning circuit that adapts the sensor output signal by amplifying or decaying the signal to be handled and uniform for the next step of the process.

Sensors - Applications

Where are the applications used in our daily life?

The sensors are used everywhere in our lives. At home like the iron which uses the temperature switch to determine the operation temperature suitable for each type of clothes. Also, the pressure switch is used with the potable water pump as well as the use of heat and smoke sensors or detectors in the home fire-fighting system. 

Also, mobile phones are now developed containing many sensors like temperature sensors, fingerprint detectors, and face recognition sensors as well as other important sensors. In industry, the importance of the sensors is maximized when the analog sensors are used in the open or closed loop control system to control all the operations of any process and increase its performance such as controlling of tanks and silos filling process. 

In the modern manufacturing processes as both sensor and conditioning circuits are working together they are fabricated to be in one compiled device called a transducer. Both sensors and transducer belong to the instrumentation section.