Presentation by ICA on limit switches and proximity sensors.pptx

1. Limit switches/Proximity sensors

2. Limit and proximity switches

3. Introduction:
• Instrumentation is the regulation of industrial process using a set of instruments working in a loop.
• A control Loop starts from a sensor through a transmitter to a controller and back to final control element.
• Sensors ar called the primary elements because it is the beginning of a process control system,there are different
types of sensors but for the purposes of this presentation we will limit our scope to position sensors and limit
switches.

4. Position sensors:
• Position sensors are devices that sense the presence or absence of objects. The sensors gather information
and convert it into a signal that can be read and/or seen by an observer or a logic controller,the controller MUST
understand the sensors position at any time or it will generate an error signal and cause a trip.
• Examples of position sensors are limit switches, proximity sensor,IR sensors. Photo electric sensors etc
• Sensors are used in everyday applications such as cars ( crankshaft,camshaft,flywheel,speed etc), machines,
manufacturing and robotics, and perform several functions.

5. Types of Position sensors:
We will look at the two most common types of position sensors in details
• Limit switches
• Proximity switches
1.Limit switches;
A limit switch is an electromechanical device operated by a physical force applied to it by an object.
Limit switches are used to detect the presence or absence of an object like in elevators and valve travels,these switches were
originally used to define the limit of travel of an object, and as a result, they were named Limit Switch.
•

6. Limit switches continued
Types of limit switches:
There are 4 general types of limit switches:
• 1. Whisker
• 2. Roller
• 3. Lever
• 4. Plunger
Depending on the application, a limit switch may be a combination of 2 of the general types such as roller-lever.

8. Limit switch Applications
• When you open the fridge door, a light comes on inside. How does that happen? Yes…. you guessed it! A limit switch is used to detect if the fridge door is open or closed.
• On many overhead garage doors/automated gates, there is a limit switch that stops the movement of the door when it reaches its fully opened position.
• Marshalling cabinets lights are switched on or off by the use of limit switches
• At the the various lact units, the valve position feedback on the HMI is made possible by the use of limit switches.
How limit switches work:
Alright….now that we’ve looked at a couple of limit switch applications where you might see them in action at home, let’s have a closer look at the device itself.
• Limit switches are electromechanical devices consisting of an actuator mechanically linked to an electrical switch.
• When an object contacts the actuator, the switch will operate causing an electrical connection to make or break.

9. Configurations of limit switches
• Limit switches are available in several switch configurations: Normally Open, Normally closed,or one of
each.
Proximity sensor vs. limit switch
Limit switches are slowly starting to disappear from many industrial applications. They are being replaced by proximity
sensors.
Unlike a limit switch, a proximity sensor has no mechanical moving parts.
A proximity sensor performs the switching action with electronic switches.

10. Types of Position sensors:
2. Proximity sensors:
• Proximity sensors are sensors that detect the movement/presence of objects without physical contact and relay that
information captured into an electrical signal. It can also be defined as a proximity switch, a definition given by the
Japanese Industrial Standards (JIS) to all contactless detecting sensors

11. Where are proximity sensors used
• Proximity Sensors are widely used in industrial and manufacturing applications, especially for safety and inventory
management applications. In an automated production line, for example, it is used for object detection, positioning,
inspection and counting. It is also used for part detection in an industrial conveyor system.
• It is used in oil and gas industries to detect valve misalignment, position error or discrepancies, often times the start up
sequence is aborted by the PLC or DCS when any of these errors are detected
• Proximity sensors can also be found in consumer devices. In smartphones, proximity sensors are used to detect if a user is
holding their phone near their face. They are also used as capacitive touch switches on consumer electronics products.
• It is also used for many other different applications such as a diffuse sensor in a public washrooms or a collision detection
sensor for robots!

12. Features of proximity sensors
• To further understand what proximity sensor is all about, we’ll take a look at its features. The following is its features, with some
uniquely seen as compared to traditional optical/contact sensors:
• Contactless sensing
• Contactless proximity sensing allows for detection without touching the object, ensuring object stays well-conditioned
• Unaffected by surface conditions
• Proximity sensors are nearly unaffected by surface colors of objects since it mainly detects physical changes
• Suitability for wide range of applications
• Proximity sensors are suitable for damp conditions and wide temperature range usage, unlike your traditional optical detection.
• Proximity sensors are also applicable in phones as well, be it your Andriod or IOS devices. It consists of simple IR technology that
switches on and off display accordingly to your usage. For example, it turns off your display when a phone call is ongoing such that
you wouldn’t accidentally activate something while placing it near your cheeks!
• Longer service life
• Since a proximity sensor uses semiconductor outputs, there are no moving parts dependent on the operating cycle. Thus, its
service life tends to be longer as compared to other sensors!
• High speed response rate
• Compared to switches where contact is required for sensing, proximity sensors offer a higher-speed response rate.

13. Types of proximity sensors
1. INDUCTIVE PROXIMITY SENSOR
• Inductive proximity sensors are contactless sensors used to only detect metal objects. It’s based on the law of induction, driving a
coil with an oscillator once a metallic object approaches it.
• It has two versions and comprises of 4 main components:
• Versions:
• Unshielded: Electromagnetic field generated by the coil is unrestricted, allowing for wider and greater sensing distances
• Shielded: Electromagnetic field generated is concentrated in the front, where sides of the sensor coil are covered up
• Components:
• It comprises of 4 main components as seen in the picture; Coil, Oscillator, Schmitt Trigger, and output switching ciircut

14. Types of inductive proximity sensors
How do Inductive Proximity Sensors work?
1. An alternating current is supplied to the coil, generating an electromagnetic detection field
2. When a metal object comes closer into the magnetic field, eddy currents build-up, and result in coil inductance changes
3. When coil inductance changes, the circuit that has been continuously monitoring, will trigger the sensor’s output switch
• *Note: Even when a target is not present, inductive sensors continue to oscillate. The switch is only triggered when an object is present.
• Common applications:
• Industrial usages
• Production automation machines that count products, product transfers
• Security usages
• Detection of metal objects, armoury, land mines, etc.

15. Types of proximity sensors
• Advantages of inductive proximity sensors
• Contactless detection
• Environment adaptability; resistant to common conditions seen in industrial areas such as dust and dirt
• Capable and versatile in metal sensing
• Considerably cheap when it comes to price
• No moving parts, ensuring a longer service life
• Disadvantages of inductive proximity sensors
• Lack in detection range, averaging a max range of up to 80mm
• Can only detect metal objects
• Performance can be affected by external conditions; extreme temperatures,
cutting fluids or chemicals

16. Types of proximity
CAPACITIVE PROXIMITY SENSOR:
• Capacitive proximity sensors are contactless sensors that detect both metallic and non-metallic objects, including liquid, powders, and granular. It operates by
detecting a change in capacitance.
• Similarly to inductive sensors, it consists of an oscillator, Schmitt trigger and output switching circuit. The only difference is it comprises of 2 charging plates (1
internal, 1 external) for capacitation:
• Internal plate connected to the oscillator
• External plate (sensor electrodes) used as the sensing surface
How do capacitive proximity sensors work?
1. Capacitive proximity sensor produces an electrostatic field
2. When an object (conductive/non-conductive) approaches the sensing area, the capacitance of both plates increases, resulting in oscillator amplitude gain
3. The resulted amplitude gain triggers sensor output switch
• *Note: Capacitive sensors only oscillate when the target object is present
Common applications:
• Industrial usages
• Production automation machines that count products, product transfers
• Filling processes, pipelines, inks, etc.
• Fluid level, composition, and pressure
• Moisture control
• Non-invasive content detection
• Touch applications

17. Types of proximity
• How do capacitive proximity sensors work?
1. Capacitive proximity sensor produces an electrostatic field
2. When an object (conductive/non-conductive) approaches the sensing area, the capacitance of both plates increases, resulting in oscillator
amplitude gain
3. The resulted amplitude gain triggers sensor output switch
• *Note: Capacitive sensors only oscillate when the target object is present
• Common applications:
• Industrial usages
• Production automation machines that count products, product transfers
• Filling processes, pipelines, inks, etc.
• Fluid level, composition, and pressure
• Moisture control
• Non-invasive content detection
• Touch applications

18. Capacitive proximity sensors
Advantages of Capacitive proximity sensors
• Contactless detection
• A wide array of materials able to be detected
• Able to detect objects through non-metallic walls with its wide sensitivity band
• Well-suited to be used in an industrial environment
• Contains potentiometer that allows users to adjust sensor sensitivity, such that only wanted objects will be sensed
• No moving parts, ensuring a longer service life
• Disadvantages of Capacitive proximity sensors
• Relative low range, though incremental increase from inductive sensors
• Higher price as compared to inductive sensors

19. Types of proximity sensors continued
Other types just for mention are:
-Ultrasonic and IR proximity sensor.
Troubleshooting Position Sensors:
Troubleshooting is done on limit switches by measuring continuity,resistance or output voltage but for proximity switches,output
voltage is measured with target metal on the face of the switches,voltages less than 8VDC indicates a faulty proximity switch.
Thank you.