This technical write-up will deal with the primary sensing elements used in an Industrial Control System – (1) Sensors and (2) Actuators – the output control devices. These are the TWO Basic primary sensing elements of any control systems. We will learn technicalities of industrial control systems after having some basic knowledge of sensors and actuators.
What is a Sensor?
Sensors are normally electro-mechanical devices that measure physical parameters like temperature, pressure, force, acceleration etc. and convert these into an electrical signal. This electrical signal is proportional to the parameters and can be quantified, displayed, stored or may be used to control some other parameters in an automatic process control. It can also provide simple binary signal output like a simple limit switch whose output is either ON or OFF. The power source of all active sensors is either DC or AC Voltage or current (however, if potential free switch contacts are used as sensors, these do not require any power source).
Function of a Sensor in an Automatic Process Controller:
Look at the basic block diagram at Fig—1 below-
The automatic process controller is shown as a simple block with an error detector and amplifier, the actual controller is micro-controller based and much more complicated (which we will discuss in some other technical blog).
Sensors used in an automatic process controller will measure some output physical parameters of the process equipment in a plant that is required to be controlled. The output of the sensor is normally either an electrical signal (voltage or current) or just potential free ON/OFF Signal.
This signal from the sensor is fed to the error detector. The error detector will compare the sensor output signal with respect to a pre-set reference signal and provide an output to the amplifier for further processing. The reference signal is generated from the set-point of the controller. The set-point can be manual or auto controlled depending on the type of automatic controller.
Here is an example of the most frequently used PIR Motion Sensor. These Sensors are mostly used for Automatic Sliding Doors and Security Systems.
See the operation of this sensor in Fig-2 below:
Fig-2 – Operation of a PIR Motion Sensor
PIR Motion Sensor or Passive Infrared Sensor is an electronic sensor that measures infrared (IR) light radiating from its field of view and detects presence of people by their body temperature. The output of this sensor is used to open an automatic sliding door when anyone approaches the door.
An electronic engineer should have comprehensive knowledge about sensors used in industries. We’ll treat this subject as the most important and include wide ranging texts and images on sensors in various technical blogs in electronics15.com.