DMT 3533 Programmable Logic Controller PLC PLC Hardware

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

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

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. Photoelectric sensor

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

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

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.

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

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".

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

Reed Switch Activation Reed switch Magnet 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

Photovoltaic Or Solar Cell The photovoltaic cell, or solar cell, is a common light-sensor device that converts light energy directly into electric energy. 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.

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. Ohms 20 Ohms Light resistance 5, 000 Ohms Dark resistance

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 detector Object to be sensed Light source 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.

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

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. Emitter Operating range Target Receiver

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

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. The returning echo signal is electronically converted to a 4 m. A to 20 m. A output, which supplies flow rate to external control devices.

Strain / Weight Sensors A strain gauge transducer converts a mechanical strain into an electric signal. Hopper ON/OFF Wire type Force The load cell provides sensor input to the controller, which displays the weight and controls the hopper chute. Chute The. Controller force applied. Control 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. Load cell

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. The thermocouple consists of a pair of dissimilar conductors fused together at The detector oneresistance end to formtemperature the "hot" or measuring (RTD) varies resistance value for junction, withinthe free ends available The thermistor varies in junction. connection toin thetemperature. "cold" reference with changes The Integrated Circuit (IC) temperature A temperature between the resistancedifference value with sensor produces changes in voltage orgenerates measuring andinreference junction changes temperature current with changes in voltage. temperature. a small DC signal RTD

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. Flow Can be used with electrically conducting fluids and offers no Electronic Magnetic Turbine Flow to Meter restriction flow. A coil in the Flow Meter unit sets up a magnetic field. If a The turbine at conductive liquidblades flows turn through Coil rate proportional to theis thisamagnetic field, a voltage fluid and velocity andbyare induced sensed two Magnet electrodes. magnetized to induce Turbine voltage pulses coil.

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. Controller d a Lo M Motor 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.

Velocity/RPM Sensors The rotating speed of a shaft is often measured using a magnetic (inductive) pickup sensor. Pickup coil Pole piece Sensor output 0 V N S Magnet 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.

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

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

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

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. Stepper motor control system Module Communicates with the PLC and responds with pulse trains Stepper-motor translator Enables control of the stepper motor Step motor The motor will move one step for each pulse received

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

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)

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

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

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