CHAPTER 2 LOGICAL SENSORS AND ACTUATORS BAKISS HIYANA

CHAPTER 2 LOGICAL SENSORS AND ACTUATORS BAKISS HIYANA BT ABU BAKAR

Objective 1. Logical Sensor – Understand Logical Sensor – Identify basic logical sensor types and their functions v v v – Contact Switches Proximity Photo optics Capacitive Inductive Ultrasonic Explain logical sensor and switches wiring (sourcing and sinking). – Develop logical sensor application based on simple logical control/automation. 2. Logical actuators – Understand solenoid, valves, cylinders and motors.

Logical Sensor • Sensors allow a PLC to detect the state of a process. • Logical sensors can only detect a state that is either true or false. Examples of physical phenomena that are typically detected are listed below : • inductive proximity - is a metal object nearby? • capacitive proximity - is a dielectric object nearby? • optical presence - is an object breaking a light beam or reflecting light? • mechanical contact - is an object touching a switch?

Types of Logical Sensor Door Contact Switches 1. Contact Switches • Contact switches are available as normally open and normally closed. • Their housings are reinforced so that they can take repeated mechanical forces. • These often have rollers and wear pads for the point of contact. • Lightweight contact switches can be purchased for less than a dollar, but heavy duty contact switches will have much higher costs. • Examples of applications include motion limit switches and part present detectors.

Types of Logical Sensor 2. Proximity • A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. • A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. • The object being sensed is often referred to as the proximity sensor's target. • Different proximity sensor targets demand different sensors. For example, a capacitive photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target.

Types of Logical Sensor 2. Proximity

Types of Logical Sensor 2. Proximity • The maximum distance that this sensor can detect is defined "nominal range". • Some sensors have adjustments of the nominal range or means to report a graduated detection distance. • Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.

Types of Logical Sensor 3. Photo Optics • • Optical sensors require both a light source (emitter) and detector. Emitters will produce light beams in the visible and invisible spectrums using LEDs and laser diodes. Detectors are typically built with photodiodes or phototransistors. The emitter and detector are positioned so that an object will block or reflect a beam when present.

Types of Logical Sensor 3. Photo Optics/ Through Beam Sensor • The emitter and detector are positioned so that an object will block or reflect a beam when present. • In the figure the light beam is generated on the left, focused through a lens. • At the detector side the beam is focused on the detector with a second lens. • If the beam is broken the detector will indicate an object is present.

Types of Logical Sensor 3. Photo Optics/ Through Beam Sensor

Types of Logical Sensor 3. Photo Optics/ Through Beam Sensor • The oscillating light wave is used so that the sensor can filter out normal light in the room. • The light from the emitter is turned on and off at a set frequency. • When the detector receives the light it checks to make sure that it is at the same frequency. • If light is being received at the right frequency then the beam is not broken.

Types of Logical Sensor 3. Photo Optics/ Through Beam Sensor • The frequency of oscillation is in the KHz range, and too fast to be noticed. • Benefit of the frequency method is that the sensors can be used with lower power at longer distances.

Types of Logical Sensor 3. Photo Optics/ Diffuse Sensor • A diffuse sensor is a single unit that does not use a reflector, but uses focused light as shown in Figure. • Diffuse sensors use light focused over a given range, and a sensitivity adjustment is used to select a distance. • These sensors are the easiest to set up, but they require well controlled conditions. • For example if it is to pick up adjacent wavelength colored objects such as red and orange, problems would result.

Types of Logical Sensor 3. Photo Optics/ Diffuse Sensor

Types of Logical Sensor 4. Capacitive • Capacitive sensors are able to detect most materials at distances up to a few centimeters. Recall the basic relationship for capacitance. • In the sensor the area of the plates and distance between them is fixed. But, the dielectric constant of the space around them will vary as different materials are brought near the sensor.

Types of Logical Sensor 4. Capacitive • An oscillating field is used to determine the capacitance of the plates. • When this changes beyond a selected sensitivity the sensor output is activated.

Types of Logical Sensor 5. Inductive � Inductive sensors use currents induced by magnetic fields to detect nearby metal objects. � The inductive sensor uses a coil (an inductor) to generate a high frequency magnetic field. � If there is a metal object near the changing magnetic field, current will flow in the object. � This resulting current flow sets up a new magnetic field that opposes the original magnetic field.

Types of Logical Sensor 5. Inductive � The next effect is that it changes the inductance of the coil in the inductive sensor. By measuring the inductance the sensor can determine when a metal have been brought nearby. � These sensors will detect any metals, when detecting multiple types of metal multiple sensors are often used.

Types of Logical Sensor 5. Inductive • The sensors can detect objects a few centimeters away from the end. • The magnetic field of the unshielded sensor covers a larger volume around the head of the coil. • By adding a shield (a metal jacket around the sides of the coil) the magnetic field becomes smaller, but also more directed. • Shields will often be available for inductive sensors to improve their directionality and accuracy.

Types of Logical Sensor 6. Ultrasonic • An ultrasonic sensor emits a sound above the normal hearing threshold of 16 KHz. The time that is required for the sound to travel to the target and reflect back is proportional to the distance to the target.

Types of Logical Sensor 6. Ultrasonic • The two common types of sensors are; • electrostatic - uses capacitive effects. It has longer ranges and wider bandwidth, but is more sensitive to factors such as humidity. • piezoelectric - based on charge displacement during strain in crystal lattices. These are rugged and inexpensive. • These sensors can be very effective for applications such as fluid levels in tanks and crude distance measurement.

Logical Sensor and Switches Wiring (sourcing and sinking)

Logical Sensor and Switches Wiring (sourcing and sinking) • The term sinking and sourcing are used in the Motion Engineering Slice I/O part description. – Voltage “Sinks” current to the ground. – Voltage “Sources” current from a voltage source.

Logical Sensor and Switches Wiring (sourcing and sinking) • Sinking/Sourcing – describes a current signal flow relationship between field input and output devices in a control system and their power supply. “Sourcing I/O modules supply (or source) current to sourcing type field devices. ” “Sinking I/O modules sink (or pull) current from sinking field devices. ”

Logical Sensor and Switches Wiring (sourcing and sinking) • In general, Sinking (NPN) and Sourcing (PNP) are terms that define the control of direct current flow in a load. • They are only pertinent with DC components and should not be associated with AC control structures. • “Sinking (NPN) provides a path to 0 VDC (-DC)” • “Sourcing (PNP) provides a path to +24 VDC (+DC).

OUTPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) • Sinking (NPN) Outputs - Are output that “Sink” or “pull” current through the load. • The common connection to the load is the 24 VDC (+DC) line. • Sinking output modules require the load to be energized by a current, which flows from +24 VDC (+DC), through the load, through the NPN output switch device to the 0 VDC (DC) line Circuit connection

OUTPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) Figure representation of the Sinking Output Module connections to “sinking” type loads.

OUTPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) • Sourcing (PNP) Outputs – Are outputs that “Source” or “push” current through the load. • The common connection to the load is the 0 VDC (-DC) line. • Sourcing output modules require the load to be energized by a current that flows from +24 VDC (+DC), through the PNP output switch device, through the load to 0 VDC (-DC) line. ** note: -ve side (0 VDC) common & +ve side (+24 VDC) switched Circuit connection

OUTPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) Figure representation of the sourcing output module connections to “sourcing” type loads

INPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) • Sinking (NPN) inputs - are input that require an external sensor device to “sink” of “pull” current from input circuitry to 0 VDC (-DC). • The external input device provides a current path to the 0 VDC (-DC) common point. Circuit connection

INPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) Notice: “common connection” is 0 VDC (-DC) Figure representation of the sinking input module connection to “sinking” type sensors.

INPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) • Sourcing (PNP) inputs - Are inputs that require an external sensor device to “ Source” or “push” current from the 24 VDC (+DC) line to the input circuitry. • The external sensor device provides a current path from the 24 VDC (+DC) common point to the input circuitry. Circuit connection

INPUT DEVICES Logical Sensor and Switches Wiring (sourcing and sinking) Notice: “common connection” is 24 VDC (+DC) Figure representation of the sourcing input module connection to “sourcing” type sensors.

LOGICAL ACTUATORS

Logical Actuators 1. SOLENOID: • Solenoid is the most common actuator component. • Solenoid is the generic term for a coil of wire used as an electromagnet. • It also refer to any device that convert electrical energy to mechanical energy using solenoid. • The device creates magnetic field from electric current and used the magnetic field to create linear motion. • Solenoid usually consists of a coil and a movable iron core called the armature. • Solenoid are inexpensive and their use is primarily limited to on-off applications such as latching, locking, and triggering. • Common applications : home appliances (washing machine valves), office equipment (copy machines), automobiles (door latches), pinball machine (plungers & bumpers) & factory automation.

Logical Actuators 1. SOLENOID: Figure 1 • The basic principle of operation: – There is a moving ferrous core ( a piston ) than will move inside wire core as shown in figure 1. – Normally the piston is held outside the coil by a spring. – When voltage is applied to the coil and current flow, the coil builds up magnetic field that attracts the piston and pulls it into the center of the coil. – The piston can be used to supply a linear force. – Most industrial solenoids will be powered by 24 Vdc and draw a few hundred m. A.

Logical Actuators Figure 2 1. SOLENOID: HOW A SOLENOID WORKS? ? • When current flows through a wire, a magnetic field is set up around the wire. • If we make a coil of many turns of wire, the magnetic field becomes much stronger. Flowing around the coil and through its center doughnut shape. • When the coil of the solenoid is energized with current, the core moves to increases the flux linkage by closing the air gap between the cores.

Logical Actuators 1. SOLENOID: HOW A SOLENOID WORKS? ? • The movable core is usually spring-loaded to allow the core to retract when the current is switched off. • The force generated is approximately proportional to the square of the current and inversely proportional to the square of the length of the air gap. Figure 3

Logical Actuators 2. VALVES: What are Valves? • Valves are mechanical devices that controls the flow and pressure within a system or process. • They are essential components of piping system that conveys liquids, gases, vapors, slurries etc. • Some valves are self operated while others manually or with an actuator or pneumatic or hydraulic is operated. • Valves functions: – – – Stopping & starting flow Reduce @ increase a flow Controlling the direction @ flow Regulating a flow or process pressure Relieve a pipe system of a certain pressure/ overpressure protection.

Logical Actuators 2. VALVES: What are Valves?

Logical Actuators 2. VALVES: The types of control valve symbol

Logical Actuators 2. VALVES: • Solenoid control valve basic operation: • The solenoid is mounted on the side. When actuated, it will drive the central spool left. • The top of the valve body has two ports that will be connected to a device such as a pneumatic cylinder. • The bottom of the valve body will be connected to a pressure line. • In one position, the power flow to the right hand of cylinder port. • The left hand cylinder port is allowed to exit through an exhaust port. • In other position, the pressure is now applied to the left hand port and the right hand port can exhaust. • Valves are also available that allow the valves to be blocked when unused.

Logical Actuators 2. VALVES: Solenoid Control Valves operation. • The flow of fluids and air can be controlled with solenoid controlled valves. • The diagram to the right shows the design of a basic valve, controlling the flow of water in this example. • At the top figure is the valve in its closed state • The water under pressure enters at A. B is an elastic diaphragm and above it is a weak spring pushing it down. • The diaphragm has a pinhole through its center which allows a very small amount of water to flow through it. • This water fills the cavity C on the other side of the diaphragm so that pressure is equal on both sides of the diaphragm.

Logical Actuators 2. VALVES: Solenoid Control Valves operation. • In the previous configuration the small passage D was blocked by a pin which is the armature of the solenoid E and which is pushed down by a spring. • If the solenoid is activated by drawing the pin upwards via magnetic force from the solenoid current, the water in chamber C will flow through this passage D to the output side of the valve. • The pressure in chamber C will drop and the incoming pressure will lift the diaphragm thus opening the main valve. • Water now flows directly from A to F

Logical Actuators 2. VALVES: Solenoid Control Valves operation. • When the solenoid is again deactivated and the passage D is closed again, the spring needs very little force to push the diaphragm down again and the main valve closes. • Piloted solenoids usually need full power at all times to open and stay open, where a direct acting solenoid may only need full power for a short period of time to open it, and only low power to hold it.

Logical Actuators 2. VALVES: When selecting valves there a number of details that should be considered, as listed below: • Pipe size - inlets and outlets are typically threaded to accept NPT (national pipe thread). • Flow rate - the maximum flow rate is often provided to hydraulic valves. • Operating pressure - a maximum operating pressure will be indicated. Some valves will also require a minimum pressure to operate. • Electrical - the solenoid coil will have a fixed supply voltage (AC or DC) and current. • Response time - this is the time for the valve to fully open/close. Typical times for valves range from 5 ms to 150 ms. • Enclosure - the housing for the valve

Logical Actuators 3. Cylinders: • A cylinder uses pressurized fluid or air to create a linear force/motion as shown in Figure. • In the figure a compress air is pumped into one side of the cylinder under pressure, causing that side of the cylinder to expand, and advancing the piston. • The compress air on the other side of the piston must be allowed to escape freely.

Logical Actuators 3. Cylinders: • If the incompressible air was trapped the cylinder could not advance. • The force the cylinder can exert is proportional to the cross sectional area of the cylinder. • Single acting cylinders apply force when extending and typically use a spring to retract the cylinder. • Double acting cylinders apply force in both directions.

Logical Actuators 3. Cylinders: • If the incompressible air was trapped the cylinder could not advance. • The force the cylinder can exert is proportional to the cross sectional area of the cylinder. • Single acting cylinders apply force when extending and typically use a spring to retract the cylinder. • Double acting cylinders apply force in both directions.

Logical Actuators 3. Cylinders:

Logical Actuators 4. Motors: DC motors

Logical Actuators 4. Motors: Basic Principle of DC Motor Creation of flux at the rotor. • Accomplish by commutator which is produces the alternating current from dc supply. Alternating current is used to create flux.

Logical Actuators 4. Motors: Basic principle of single phase ac motor. • Single phase AC motor is different from three phase because resulting field did not rotate. • The resulting field only alternate between electromagnet. • It is possible to obtain a single phase squirrel cage induction motor using an electromagnet connected to a single phase AC power. Stator Windings for Three Phase Motor

Logical Actuators 4. Motors: Basic principle of single phase ac motor. • However, when the rotor is turned manually, a torque acts in the direction of rotation is produced. Motor continues to turn as long as ac power is supplied to the stator electromagnet. This torque due to rotating magnetic field that results from interaction of the magnetic field produced by the stator and rotor (current induced). • Motor continues to turn as long as ac power is supplied to the stator electromagnet. • This torque due to rotating magnetic field that results from interaction of the magnetic field produced by the stator and rotor (current induced).

Logical Actuators 5. Electro-hydraulics: Hydraulic: • Use incompressible fluids to supply very large forces at slower speeds & limited ranges of motion. • If the fluid rate is kept low enough, many of the effects may be avoided. • The system used hydraulic fluid ( normally oil) pressurized by a pump & passes through hoses & valves to drive cylinders. • At the heart of the system is a pump that will give pressures up to hundreds/ thousand of PSI. • These are delivered to a cylinder that convert it to a linear force and displacement.

Logical Actuators 5. Electro-hydraulics: • The word electro-hydraulic has two meanings for two highly different operations. • It can stand for an electrical control device that makes precise adjustments in a hydraulic system. • Also, it can mean a chemical reaction that is created by firing short, powerful electrical impulses into or directly beneath the surface of a body of liquid. Hydraulic system components: • Hydraulic fluid • Oil reservoir • A pump to move oil & apply pressure • Pressure line • Control valve- to regulate fluid flow • Piston & cylinder – to actuate external mechanisms. • Perhaps the most well-known electrohydraulic device is an automobile's power steering unit — also called an electro-hydraulic actuator.

Logical Actuators 5. Electro-hydraulics: • The unit combines high power with a high degree of accuracy to adjust for the minute movements of the steering wheel in a vehicle. • This type of technology, where electrical components are used to increase the accuracy of hydraulic movements, can be applied to almost any situation where hydraulics is used.

Logical Actuators 5. Electro-pneumatics: Pneumatics: • Pneumatic system respond very quickly & are commonly use for low force applications in many locations on the factory floor. • Pneumatic have much in common with hydraulic systems with few differences. • The reservoir is eliminate as there is no need to collect and store the air between uses in the system. • Also, because air is a gas, it is compressible & regulator are not needed to re-circulate flow. • But the compressibility also means that the systems are not a stiff / strong.

Logical Actuators 5. Electro-pneumatics: Pneumatics: Basic characteristics of pneumatic system: 1. Stroke – from a few mm to meters in length ( longer stroke have > springiness) 2. Pressure – up to 85 psi above normal atmosphere. 3. Weight of the cylinders can be quite low. 4. Additional equipment may required for a pressurized air supply – linear rotator actuator are available. 5. Dampers can be used to cushion impact at the ends of cylinders travel

Logical Actuators 5. Electro-pneumatics: • The electro-pneumatic action is a control system for pipe organs, whereby air pressure, controlled by an electric current and operated by the keys of an organ console, opens and closes valves within wind chests, allowing the pipes to speak. • This system also allows the console to be physically detached from the organ itself. • The only connection was via an electrical cable from the console to the relay, with some early organ consoles utilizing a separate wind supply to operate combination pistons.

Logical Actuators 5. Electro-pneumatics: • The basic operation of the system is as follows: 1. when the organist selects a stop and depresses a key, an electric circuit is completed, causing a low-voltage current to flow from depressed key, through the stop-tab switch, and on through the cable to the electropneumatic relay. 2. The relay interprets the command from the console and sends an electric current to the appropriate solenoid. 3. The solenoid is energized, causing the pipe valve connected to it to open, which emits compressed air into the pipe, allowing the pipe to speak.