Petroleum Instrumentation NGT 160 Basics Instrumentation Other Sensors

Petroleum Instrumentation NGT 160 Basics Instrumentation Other Sensors “This product was funded by a grant awarded by the U. S. Department of Labor’s Employment and Training Administration. The product was created by the grantee and does not necessarily reflect the official position of the U. S. Department of Labor. The Department of Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with respect to such information, including any information on linked sites and including, but not limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy, continued availability, or ownership. ” Unless otherwise specified, this work by Shale. NET U. S. is licensed under a Creative Commons Attribution 4. 0 International License.

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

Type of Sensor: 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). 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 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. 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 photodetector.

Reflective Photoelectric Sensor Emits a light beam (visible, infrared, or laser) from its light emitting element and detects the light being reflected. Diffused-reflective 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 Wire type Force The load cell provides sensor input to the controller, which displays the weight and controls the hopper chute. Controller The force applied to the gauge causes the ON/OFF gauge to bend. This bending action also Chute distorts the physical size of the gauge, Control 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 Theof resistance temperaturefused detector dissimilar conductors (RTD) variesat inone resistance with"hot" together end to value form the The. Circuit thermistor varies in The Integrated (IC) temperature changes in temperature. or measuring junction, with the free resistance value with changes sensor produces changes in voltage or to the ends available for connection in temperature current with changes in temperature. "cold" reference junction. A temperature difference between the measuring and reference junction RTD generates a small DC signal voltage.

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 Electronic Magnetic Turbine Can be. Flow used. Meter with electrically Flow conducting fluids and offers no Coil Meter restriction to flow. A coil in the The turbine blades turn at a unitrate setsproportional up a magnetic to field. the If a Magnet conductive liquidand flows fluid velocity arethrough magnetic field, a voltage is Turbine thismagnetized to induced andpulses sensed by two voltage coil. electrodes.

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 ad o L 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 0 V Sensor output Pole piece 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.