DMT 353/3 – Programmable Logic Controller (PLC)

1. DMT 353/3 – Programmable Logic Controller (PLC) PLC Hardware Components

2. Transducer Amplifier Output transducer (speaker) converts electric energy to sound energy Input transducer (microphone) converts sound energy to electric energy A transducer is any device that converts energy from one form to another.

3. Photoelectric sensor Sensors Sensors are input transducers used for detecting and often measuring the magnitude of something. They convert mechanical, magnetic, thermal, optical, and chemical variations into electric voltages and currents.

4. Microprocessor Optical sensor Gas sensor Microphone Probe Sensors Sensors provide the equivalent of eyes, ears, nose, and tongue to the microprocessor brain.

5. Proximity Sensor Proximity sensors or switches detect the presence of an object without making physical contact with it.

6. Proximity Sensor Applications The object being detected is too small, lightweight, or soft to operate a mechanical switch. Rapid response and high switching rates are required. An object has to be sensed through nonmetallic barriers such as glass, plastic, and paper cartons. Hostile environments conditions exist. Long life and reliable service are required. A fast electronic control system requires a bounce-free input signal.

7. As the target moves into the sensing area, the sensor switches the output ON Inductive Proximity Sensor Operation Barrel type Block diagram

8. Capacitive Proximity Sensor A capacitive proximity sensor can be actuated by both conductive and nonconductive material such as wood, plastics, liquids, sugar flour and wheat. Operation is similar to that of inductive proximity sensor. Instead of a coil, the active face of the sensor is formed by two metallic electrodes – rather like an "opened capacitor".

9. Magnet N S The switch is actuated by a magnet. Magnetic Switch (Reed Switch) A magnetic switch (also called a reed switch) is composed of flat contact tabs that are hermetically sealed (air-tight). NO NC Common

10. Reed switch Magnet Reed Switch Activation Proximity motion – movement of the switch or magnet will activate the switch Rotary motion – switch is actuated twice for every complete revolution Shielding – the shield short circuits the magnetic field; switch is activated by removal of the shield

11. Solar cell The solar cell converts light impulses directly into electrical charges which can easily be amplified to provide an input signal to a PLC. Photovoltaic Or Solar Cell The photovoltaic cell, or solar cell, is a common light-sensor device that converts light energy directly into electric energy.

12. 20 Ohms Light resistance5,000 Ohms Dark resistance Ohms Photoconductive Or Photo resistive Cell The photoconductive cell, or photo resistive cell, is another popular type of light transducer. Light energy falling on this device will cause a change in the resistance of the cell.

13. Light detector Object to be sensed Light source Photoelectric Sensor Operation Most industrial photoelectric sensors use a light-emitting diode (LED) for the light source and a phototransistor to sense the presence or absence of light. Light from the LED falls on the input of the phototransistor and the amount of conduction through the transistor changes. Analog outputs provide an output proportional to the quantity of light seen by the photo detector.

14. Diffused-reflective type Emitter/receiver Operating range Target Retro-reflective type Operating range Reflector Reflective Photoelectric Sensor Emits a light beam (visible, infrared, or laser) from its light emitting element and detects the light being reflected.

15. Emitter Receiver Operating range Target Through-Beam Type Photoelectric Sensor A through-beam photoelectric sensor is used to measure the change in light quantity caused by the target's crossing the optical axis.

16. The decoder receives the signal from the scanner and converts these data into the character data representation of the symbol's code. Diverter Decoder Scanner PLC Bar Code Systems Bar code systems can be used to enter data much more quickly than manual methods, and are highly accurate.

17. The returning echo signal is electronically converted to a 4 mA to 20 mA output, which supplies flow rate to external control devices. Ultrasonic Sensor An ultrasonic sensor operates by sending sound waves towards the target and measuring the time it takes for the pulses to bounce back.

18. Force Wire type The force applied to the gauge causes the gauge to bend. This bending action also distorts the physical size of the gauge, which in turn changes its resistance. Strain / Weight Sensors A strain gauge transducer converts a mechanical strain into an electric signal. Hopper ON/OFF Chute Control Controller Load cell The load cell provides sensor input to the controller, which displays the weight and controls the hopper chute.

19. The thermocouple consists of a pair of dissimilar conductors fused together at one end to form the "hot" or measuring junction, with the free ends available for connection to the "cold" reference junction. A temperature difference between the measuring and reference junction generates a small DC signal voltage. The resistance temperature detector (RTD) varies in resistance value with changes in temperature. The Integrated Circuit (IC) temperature sensor produces changes in voltage or current with changes in temperature. The thermistor varies in resistance value with changes in temperature RTD Temperature Sensors Temperature sensors convert heat into an electric signal. There are four basic types used: thermocouple, resistance temperature detector (RTD), thermistor, and IC sensor.

20. Can be used with electrically conducting fluids and offers no restriction to flow. A coil in the unit sets up a magnetic field. If a conductive liquid flows through this magnetic field, a voltage is induced and sensed by two electrodes. Turbine Flow Meter Electronic Magnetic Flow Meter The turbine blades turn at a rate proportional to the fluid velocity and are magnetized to induce voltage pulses coil. Coil Flow Magnet Turbine Flow Measurement The usual approach used in measuring fluid flow is to convert the kinetic energy that the fluid has into some other measurable form.

21. Tachometers coupled to motors are commonly used in motor speed control applications to provide a feedback voltage to the controller that is proportional to motor speed. Controller Load M Motor Tach Velocity/RPM Sensors A tachometer is a small permanent magnet DC generator which when rotated produces a voltage that is directly proportional to the speed at which it is driven.

22. The rotating speed of a shaft is often measured using a magnetic (inductive) pickup sensor. A magnet is attached to the shaft. A small coil of wire held near the magnet receives a pulse each time the magnet passes. By measuring the frequency of the pulses, the shaft speed can be determined. Pole piece Pickup coil N S Magnet Sensor output 0 V Velocity/RPM Sensors

23. Solenoid Solenoid valve Control relay Pilot light Alarm Heater Small motor Motor starter Output Control Devices A variety of output control devices can be operated by the controller output module to control traditional processes. These include:

24. Plunger The solenoid converts electric current into linear motion. Solenoid Symbol AIR Coil Actuators An actuator is any device that converts an electrical signal into mechanical movement. The principle types of actuators are relays, solenoids, and motors.

25. Forward motion of piston When SOL A is energized, the valve spool is shifted to redirect the fluid and move the cylinder forward Directional solenoid valve CR FWD SOL A SOL A CR Solenoid Valve • A solenoid valve is a combination of: • a solenoid with its core or plunger • a valve body containing an orifice in which a disc or plug is positioned to restrict or allow flow

26. Stepper motor control system Stepper-motor translator Step motor Module Communicates with the PLC and responds with pulse trains The motor will move one step for each pulse received Enables control of the stepper motor Stepper Motor A stepper motor converts electrical pulses applied to it into discrete rotor movements called steps. They are used to provide precise position control of movement.

27. 11. Sensors convert mechanical, magnetic, • thermal, optical, and chemical variations into: • electric voltages and currents. • sound • movement • all of these 12. A proximity switch can be actuated without any physical contact. (True/False)

28. 13. A thermocouple, when heated, increases Its resistance value. (True/False) 14. The force applied to a strain wire gauge causes it to bend and change resistance. (True/False) 15. A capacitive proximity sensor may be actuated by nonconductive materials. (True/False)

29. 16. When a magnetic pickup sensor is used to indicate the speed of a shaft, the speed is usually determined by measuring the: a. voltage output produced b. frequency of the pulses produced c. current output produced d. change in resistance that occurs

30. 17. A through-beam photoelectric sensor is used to measure the change in ______ caused by the target crossing the optical axis. a. resistance c. current b. voltage d. light quantity

31. 18. Which of the following devices would “not” be classified as an actuator? a. relay c. solenoid b. tachometer d. motor 19. Solenoid valves are available to control: a. oil flow c. water flow b. air flow d. all of these 20. A(n) ______ converts electrical pulses applied to it into discrete rotor movements. a. tachometer c. stepper motor b. solenoid d. electronic magnetic flowmeter