Programmable Logic Controller

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

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. Photoelectric sensor

Sensors 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 Block diagram As the target moves into the sensing area, the sensor switches the output ON

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 (air-tight). The switch is actuated by a magnet. Magnet N S NO NC Common

Reed Switch Activation Magnet Reed switch 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 Photoresistive Cell The photoconductive cell, or photoresistive cell, is is another popular type of light transducer. Light energy falling on this device will cause a change in the resistance of the cell. 20 Ohms Light resistance 5,000 Ohms Dark resistance Ohms

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 photodetector. Object to be sensed Light detector Light source

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

Bar Code Systems Bar code systems can be used to enter data much more quickly than manual methods, and are highly accurate. Scanner Decoder PLC Diverter 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 mA to 20 mA output, which supplies flow rate to external control devices.

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

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 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. RTD The thermistor varies in resistance value with changes in temperature The Integrated Circuit (IC) temperature sensor produces changes in voltage or current with changes in temperature.

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. Electronic Magnetic Flow Meter 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. Flow Magnet Turbine Turbine Flow Meter Coil The turbine blades turn at a rate proportional to the fluid velocity and are magnetized to induce 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 Tach Motor M Load 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. 0 V Pickup coil Pole piece N S Magnet Sensor output 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: Pilot light Solenoid valve Control relay Alarm Heater Motor starter Small motor

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

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 When SOL A is energized, the valve spool is shifted to redirect the fluid and move the cylinder forward SOL A Forward motion of piston Directional solenoid valve FWD 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. Module Stepper-motor translator Step motor Stepper motor control system Communicates with the PLC and responds with pulse trains Enables control of the stepper motor The motor will move one step for each pulse received