Control AC Motor PLC Implementation Add Indicator Light PLC Implementation Add Limit Switch PLC Implementation Magnetic Contactor For handling large current and voltage. Can be used for interlock to prevent false and dangerous operations. Magnetic Contactor Circuit Manual Operated Switches Controlled by hand Include toggle switch, push button, selector switch, etc. Selector Switch Circuit Switches DIP Switch Limit Switch Limit Switch Circuit For Starting and stopping a motor in forward and reverse with limit switch providing over-travel protection For Starting and stopping a motor in forward and reverse with limit switch providing over-travel protection Limit Switch Symbols A typical limit switch consists of a switch body and an operating head. The switch body includes electrical contacts to energize and de-energize a circuit. The operating head incorporates some type of lever arm or plunger, referred to as an actuator. Principle of Operation The free position is the position of the actuator when no external force is applied. Pre-travel is the distance or angle travelled in moving the actuator from the free position to the operating position. The operating position is where contacts in the limit switch change from their normal state (NO or NC) to their operated state. Over-travel is the distance the actuator can travel safely beyond the operating point. Differential travel is the distance travelled between the operating position and the release position. The release position is where the contacts change from their operated state to their normal state. Release travel is the distance travelled from the release position to the free position. Momentary Operation One type of actuator operation is momentary. When the target comes in contact with the actuator, it rotates the actuator from the free position, through the pre-travel area, to the operating position. At this point the electrical contacts in the switch body change state. A spring returns the actuator lever and electrical contacts to their free position when the actuator is no longer in contact with the target. Maintained Operation In many applications it is desirable to have the actuator lever and electrical contacts remain in their operated state after the actuator is no longer in contact with the target. This is referred to as maintained operation. With maintained operation the actuator lever and contacts return to their free position when a force is applied to the actuator in the opposite direction. A fork style actuator is typically used for this application. Mounting Considerations Limit switches should be mounted in locations which will prevent false operations by normal movements of machine components and machine operators. An important aspect of limit switch mounting is cam design. Improper cam design can lead to premature switch failure. For lever arm actuators it is always desirable to have the cam force perpendicular to the lever arm. For applications in which the cam is traveling at speeds less than 100 feet per minute a cam lever angle of 30 degrees is recommended. Overriding and Non overriding Cam In overriding cam applications it is necessary to angle the trailing edge of the cam in order to prevent the lever arm from snapping back. Snapping back of the lever arm can cause shock loads on the switch which will reduce the life of the switch. Non-Overriding cams are cams which will not over-travel the actuating mechanism. Flexible Loop and Spring Rod Flexible loop and spring rod actuators can be actuated from all directions, making them suitable for applications in which the direction of approach is constantly changing. Example Application Temperature Switches Or called Thermostat, to sense temperature changes, actuated by some specific temperature change Or called Thermostat, to sense temperature changes, actuated by some specific temperature change Pressure Switch Since many machine systems use pneumatic (air) pressure, vacuum, or hydraulic pressure to perform certain tasks, it is necessary to be able to sense the presence of pressure or vacuum Pressure Switch To control pressure of liquid and gas To control pressure of liquid and gas Actuated when a specified pressure is reached. Actuated when a specified pressure is reached. Bellow Switch The bellows switch is a relatively simple device that provides a discrete (on or off) signal based on pressure. Notice that the bellows (which is made of a flexible material, usually rubber) is sealed to the end of a pipe from which the pressure is to be sensed. When the pressure in the pipe increases, the bellows pushes on the actuator of a switch. Strain Gage Pressure Sensor The strain gage pressure sensor is the most popular method of making analog measurements of pressure. It is relatively simple, reliable, and accurate. It operates on the principle that whenever fluid pressure is applied to any solid material, the material deforms (strains). Strain Gage Pressure Sensor The basic components of a pressure switch are illustrated below. Electrical contacts are operated by the movement of a diaphragm against the force of a spring. The contacts may be normally open (NO) or normally closed (NC). The spring setting determines how much fluid pressure is required to operate the contacts. Pressure Switch Circuit Level Switch To sense the height of a liquid. To sense the height of a liquid. A float is attached A float is attached The rising and lowering of the float trips the level switch The rising and lowering of the float trips the level switch Transducers and Sensors Transducer convert energy from one form to another. Transducer convert energy from one form to another. Sensors are transducer for detecting and measuring. Sensors are transducer for detecting and measuring. Sensor One type of feedback frequently needed by industrial-control systems is the position of one or more components of the operation being controlled. Sensors are devices used to provide information on the presence or absence of an object. Sensors Sensors include limit switches, photoelectric, inductive, capacitive, and ultrasonic sensors. These products are packaged in various configurations to meet virtually any requirement found in commercial and industrial applications. Sensors Load cells A field device that measures a varying value is typically connected to a transducer. A load cell is a device that takes a varying value and converts it to a variable voltage or current output. In this example the load cell is converting a value of weight into a VDC output. This load cell outputs VDC for a Lbs input. The VDC load cell output is connected to the input of an analog expansion module. Sensors used in Manufacturing Limit Switch Vs Sensors Limit switches use a mechanical actuator input, requiring the sensor to change its output when an object is physically touching the switch. Sensors, such as photoelectric, inductive, capacitive, and ultrasonic, change their output when an object is present, but not touching the sensor. No Touch Sensors There are four types of no touch sensors: inductive, capacitive, ultrasonic, and photoelectric. 1) Inductive proximity sensors use an electromagnetic field to detect the presence of metal objects. 2) Capacitive proximity sensors use an electrostatic field to detect the presence of any object. No Touch Sensors 3) Ultrasonic proximity sensors use sound waves to detect the presence of objects. 4) Photoelectric sensors react on changes in the received quantity of light. Some photoelectric sensors can even detect a specific color No Touch Sensors Inductive Proximity Sensors The sensor incorporates an electromagnetic coil which is used to detect the presence of a conductive metal object. The sensor will ignore the presence of an object if it is not metal. Inductive Sensors This type of sensor consists of four elements: coil, oscillator, trigger circuit, and an output. The oscillator is an inductive capacitive tuned circuit that creates a radio frequency. The electromagnetic field produced by the oscillator is emitted from the coil away from the face of the sensor. The circuit has just enough feedback from the field to keep the oscillator going. When a metal target enters the field, eddy currents circulate within the target. This causes a load on the sensor, decreasing the amplitude of the electromagnetic field. Cont. As the target approaches the sensor the eddy currents increase, increasing the load on the oscillator and further decreasing the amplitude of the field. The trigger circuit monitors the oscillators amplitude and at a predetermined level switches the output state of the sensor from its normal condition (on or off). As the target moves away from the sensor, the oscillators amplitude increases. At a predetermined level the trigger switches the output state of the sensor back to its normal condition (on or off). Proximity Sensor To detect the presence of an object without physical contact. To detect the presence of an object without physical contact. Inductive is actuated by metal object Inductive is actuated by metal object Proximity Sensor Inductive Proximity Sensor Proximity Sensors Connections Hysteresis Shield Proximity Sensor The ferrite core concentrates the radiated field in the direction of use. A shielded proximity sensor has a metal ring placed around the core to restrict the lateral radiation of the field. Shielded proximity sensors can be flush mounted in metal. A metal-free space is recommended above and around the sensors sensing surface. Refer to the sensor catalog for this specification. If there is a metal surface opposite the proximity sensor it must be at least three times the rated sensing distance of the sensor from the sensing surface. Unshield Proximity Sensor An unshielded proximity sensor does not have a metal ring around the core to restrict lateral radiation of the field. Unshielded sensors cannot be flush mounted in metal. There must be an area around the sensing surface that is metal free. An area of at least three times the diameter of the sensing surface must be cleared around the sensing surface of the sensor. In addition, the sensor must be mounted so that the metal surface of the mounting area is at least two times the sensing distance from the sensing face. If there is a metal surface opposite of the proximity sensor it must be at least three times the rated sensing distance of the sensor from the sensing surface. Capacitive Proximity Actuated by any dirt in their environment. Actuated by any dirt in their environment. Usually supplement to the inductive proximity sensor when there is no metal available for the actuation. Usually supplement to the inductive proximity sensor when there is no metal available for the actuation. Capacitive Sensors Capacitive sensing is a noncontact technology suitable for detecting metals, nonmetals, solids, and liquids, although it is best suited for nonmetallic targets because of its characteristics and cost relative to inductive proximity sensors. Due to their ability to detect most types of materials, capacitive sensors must be kept away from non-target materials to avoid false triggering. For this reason, if the intended target contains a ferrous material, an inductive sensor is a more reliable option. Magnetic Switch A magnetic switch also called reed switch, composed of two flat contact sealed in a glass tube. A magnetic switch also called reed switch, composed of two flat contact sealed in a glass tube. As a permanent magnet approaches, the ends of the overlapped contact tab attract one another. As a permanent magnet approaches, the ends of the overlapped contact tab attract one another. Light Sensor Photovoltaic cell converts light energy directly into electric energy. Photovoltaic cell converts light energy directly into electric energy. Photoconductive cell also called photo-resistive cell. Light energy falling on the cell will cause change in resistance Photoconductive cell also called photo-resistive cell. Light energy falling on the cell will cause change in resistance Photoelectric Sensor Use a LED for the light source and phototransistor to sense the presence of light. Use a LED for the light source and phototransistor to sense the presence of light. Two main types of photoelectric : - Reflective - Through Beam Two main types of photoelectric : - Reflective - Through Beam Reflective Type It is used to detect the light beam (visible, infrared, or laser) reflected from the target. It is used to detect the light beam (visible, infrared, or laser) reflected from the target. Through Beam It is used to measure the change of light quality caused by the target crossing the optical axis. It is used to measure the change of light quality caused by the target crossing the optical axis. Features of Photoelectric Sensor Non contact detection long service life Non contact detection long service life Almost any material based quantity of light received Almost any material based quantity of light received Long detection distance reflective(1m), through beam (10m) Long detection distance reflective(1m), through beam (10m) High response speed 50us High response speed 50us Color Discrimination based on absorption of its color Color Discrimination based on absorption of its color Highly accurate Highly accurate Barcode Technology Bar code system consists of : bar code symbol, a scanner, and a decoder. Bar code system consists of : bar code symbol, a scanner, and a decoder. Bar code symbol contains up to 30 characters encoded in a machine-readable form. Bar code symbol contains up to 30 characters encoded in a machine-readable form. Bar code system Mostly based on UPC (universal product code) Mostly based on UPC (universal product code) UPC type (1 char) Manufacturer or vendor ID (5 chars) Item number (5 chars) Check digit (1 char) Barcode Scanner A light source illuminates the bar code symbol, those bar absorb light, and spaces reflect light. A light source illuminates the bar code symbol, those bar absorb light, and spaces reflect light. A photo detector collects this light in the form of an electronics signal pattern. A photo detector collects this light in the form of an electronics signal pattern. The decoder received the signal and converts these data into character data. The decoder received the signal and converts these data into character data. Ultra sonic Sensor An ultrasonic sensor operates by sending sound waves toward the target and measuring the time it takes for the pulses to bounce back. An ultrasonic sensor operates by sending sound waves toward the target and measuring the time it takes for the pulses to bounce back. Its bounce back time proportional to the distance Its bounce back time proportional to the distance Strain/Weight Sensor A strain gauge transducer converts a mechanical strain into an electric signal. A strain gauge transducer converts a mechanical strain into an electric signal. Strain gauge are based on the principle that the resistance of a conductor varies with length and cross-sectional area. Strain gauge are based on the principle that the resistance of a conductor varies with length and cross-sectional area. Temperature Sensor Thermocouple Most commonly used for temperature measurement. Most commonly used for temperature measurement. It is a pair of dissimilar conductors welded or fused together at one end to form the hot, junction with the free ends available for connection to the cold or reference junction. It is a pair of dissimilar conductors welded or fused together at one end to form the hot, junction with the free ends available for connection to the cold or reference junction. When temperature difference occurs, a small dc voltage is generated. When temperature difference occurs, a small dc voltage is generated. Non contact Temperature Sensor Infrared radiation from the object surface generates hot spot on the thermocouple Infrared radiation from the object surface generates hot spot on the thermocouple Flow Measurement Converts the kinetic energy that the fluid has into some other measurable form. Converts the kinetic energy that the fluid has into some other measurable form. Turbine flow meters blades turn at a rate proportional to the fluid velocity. Turbine flow meters blades turn at a rate proportional to the fluid velocity. Magnetic flow meter offers no restriction to flow. A coil set up a magnetic field, if a conductive liquid flows through this magnetic field, a voltage is induced Magnetic flow meter offers no restriction to flow. A coil set up a magnetic field, if a conductive liquid flows through this magnetic field, a voltage is induced Flow The flow, Q, of a fluid in a pipe is directly proportional to the velocity of the fluid, V, and the cross sectional area of the pipe, A. Therefore, we can say Q = V x A. Therefore, we may conclude that if we wish to increase the flow of a fluid in a pipe, we have two choices - we can increase the fluids velocity, or install a larger diameter pipe. Fluid flow is measured in many different ways. Drag Disk Flow Switch This unit consists of a case containing a snap- action switch, a switch lever arm extending from the bottom of the case, and a circular disk attached to the end of the lever arm. In this case, the device is threaded into a T connector installed in the pipe and oriented such that the drag disk is perpendicular to the direction of flow. As flow rate increases it increases the force on the drag disk. At a predetermined high flow rate the force on the drag disk is sufficient to push the lever arm to the right and actuate the switch. Inline Flow Meter This device has its drag disk mounted inside a plastic or glass tube with an internal spring to counteract the force applied to the disk by fluid flow. A toroidal permanent magnet is mounted on the downstream side of the drag disk and is held in place by the spring force. A magnetic reed switch is mounted on the outside of the tube with its vertical position on the tube being set by an adjustment screw. As fluid flow increases the disk and piggy-back magnet will rise in the tube. When the magnet aligns with the reed switch the switch will actuate. Thermal Dispersion Flow Switch A method to indirectly measure flow is by measuring the amount of heat that the flow carries away from a heater element that is inserted into the flow. By setting a trip point, we can have an electronic temperature switch actuate when the temperature of the heated probe drops below a predetermined level Cont. One problem associated with this technique is that, since we may not know the temperature of the fluid in the pipe, it is difficult to determine the flow based simply on the temperature of the heated probe. Paddlewheel Flow Sensor One method to directly measure flow velocity is to simply insert a paddlewheel into the fluid flow and measure the speed that the paddlewheel rotates. Cont. It provides an output of pulses, with the pulse rate being proportional to flow velocity. Some of the more elaborate models will also convert the pulse rate to a DC voltage (an analog output). Keep in mind that as with many types of flow sensors, the device actually measures fluid speed, not flow rate. However, flow rate can be calculated if the pipe diameter is also known. Turbine type flowmeter. Cont. Turbine-type flowmeters are a popular means of measurement and control of liquid products in industrial, chemical, and petroleum operations. Turbine flowmeters, like windmills, utilize their angular velocity (rotation speed) to indicate the flow velocity. The bladed rotor rotates on its axis in proportion to the rate of the liquid flow through the tube.Fluid passing through the flow tube causes the rotor to rotate, which generates pulses in the pickup coil. Velocity/RPM Sensor The output of a generator varies with the speed at which the generator is driven. The output of a generator varies with the speed at which the generator is driven. Tachometer Generator Tachometer generators provide a convenient means of converting rotational speed into an analog voltage signal that can be used for motor speed indication and control applications. Optical Encoder An encoder is used to convert linear or rotary motion into a binary digital signal. Encoders are used in applications where positions have to be precisely determined.