PLC Sensor Types and their Selection Process
In this article we have studied different PLC sensor types and how to select the sensor depending on various industrial applications.
In PLC sensor is a device that identifies the progressions in electrical or physical or other quantities and in a way to deliver a yield as an affirmation of progress in the quantity. In simple terms, Industrial Automation Sensors are input devices which provide an output (signal) with respect to a specific physical quantity (input).
What is sensor?
A sensor is a device that detects and responds to some type of input from the physical environment. The input can be light, heat, motion, moisture, pressure or any number of other environmental phenomena.
What is a PLC sensor?
In PLC automation, a sensor is a transducer that converts a physical quantity into an electrical quantity. Programmable Logic Controllers continuously monitor input values from various input sensing devices and produce corresponding output depending on the nature of production and industry
Different type of PLC Sensor
1. Proximity sensors
A proximity sensor can easily detect nearby objects without any physical touch. It is divided into different types
- Capacitive Proximity Sensor
- Inductive Proximity Sensor
2. Pressure sensors
The Pressure Sensor is an Instrument that apprehends pressure and changes it into an electric signal where the quantity depends upon the pressure applied.
According to different uses and many more features, it is divided into different parts like, Vacuum Pressure Sensor
- Absolute Pressure Sensor
- Gauge Pressure Sensor
- Differential Pressure Sensor
Pressure sensors are used in many systems like pneumatic, hydraulic, vacuum systems, etc.
3. Photoelectric sensors
A photoelectric sensor is an optical sensor which consists of a light source, light receiver and a signal processing and control output circuitry. They can detect the presence of objects and sometimes even the surface conditions as well.
According to the application their types are
- Through-beam Sensors
- Diffuse-reflective Sensors
- Retro-reflective Sensors
- Distance-settable Sensors
- Limited-reflective Sensors
4. Temperature sensor
A temperature sensor is a device that collects information concerning the temperature from a resource and changes it to a form that can be understood by another device.
These are commonly used category of sensors which detect Temperature or Heat, and it also measures the temperature of a medium.
According to the application temperature sensor type is
- Thermometer
- Thermocouple
- Resistance Temperature Detector (RTD)
- Thermistor Temperature Sensor
- Semiconductor Temperature Sensor
- Vibrating Wire Temperature Sensor
The temperature sensor is used in a computer, refrigerator, automobile, medical device, cooking appliances, electrical motor, etc.
5. Level sensors
The main role of the level sensor is to measure the level or height of different materials like solid, liquid, and gaseous.
It is classified into different parts.Laser Level Sensor
- Float Sensor
- Capacitive Level Sensor
- Ultrasonic Level Sensor
- Hydrostatic Level Sensor
- Optical Level Sensor
- Electromagnetic Level Sensor
It is widely used in vessels, containers, water tanks, fuel tank bins, etc for water level checks.
6. Magnetic sensor
A magnetic sensor is a sensor that detects the magnitude of magnetism and geomagnetism generated by a magnet or current. There are many different types of magnetic sensors.
According to the application temperature sensor type is
- Hall Effect Sensors
- Magneto-Resistive (MR) Element Sensors
- Anisotropic Magneto-Resistive (AMR) Sensors
- Giant Magneto-Resistive (GMR) Sensors
- Tunnel Magneto-Resistive (TMR) Sensors
Selection criteria for sensors
1. Range:
Maximum and Minimum range is very important when select the sensor. value which can be sensed by the sensor. What is the minimum value you need to sense? What is the maximum value you need to sense?2. Resolution:
The smallest change which can be sensed by the sensor. High is good but not always. If it is too high, it would pickup even very minute fluctuations which would then require additional processing.3. Sensitivity:
Ratio of change in output to a unit change in the input. Again, high is good, but too high could be a problem. Also, higher the sensitivity, more will be the cost in most cases.4. Accuracy:
It is inversely proportional to Error, i.e. How close the sensor reading is to the True Value. (Should be high).5. Response Time:
Time lag between the Input and Output. (Should be Minimum)6. Cost:
How much the sensor will cost.7. Flexibility:
We check whether the sensor can adapt to changes in the product with a simple OTA.
table to use with a wide range of instruments.
Some sensors need an external power source to produce an output, so it important to provide the power source, so that additional errors aren’t introduced.
8. Size and Weight:
Sensors should be compact and lightweight.Conclusion
In PLC automation, the knowledge of input devices for sensors is a highly important use. If you have read up to this point, you now have a basic idea of the different sensor devices that are used in PLC control systems, along with a couple of examples. I believe that once you know these things, you can expand the number of designs that you can create using PLC automation systems.
