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AUTOMATION & ROBOTICS LECTURE#02 Basics of instrumentation & Measurement systems By: Engr. Irfan Ahmed Halepoto Assistant Professor, Deptt: Electronics Engg. Instrumentation • Instrumentation is defined as the science of measurement and control (process). • Instrumentation refers to handheld devices that measure some desired variables. • An instrument is a device that measures and/or regulates process variables such as flow, temperature, level, or pressure. • Instruments include many varied contrivances which can be as simple as valves and transmitters, and as complex as analyzers. • The control of processes is one of the main branches of applied instrumentation. • Instruments often comprise control systems of varied processes such as refineries, factories, vehicles etc. • successful process control requires appropriate instrumentation. INSTRUMENTION SYSTEM Measurement Systems • Measurement system: Any of the systems used in the process of associating numbers with physical quantities and phenomena. • measurement system includes factors as temperature, pressure, electric current, mass (weight), distance or length, area, and volume etc. • The aim of any measuring system is to obtain information about a physical process and to find appropriate ways of presenting that information to an observer or to other technical systems. • In order to control a dynamic variable in a process, there must be information about the variable itself.This information is obtained from a measurement of the variable. • A measurement system is any set of interconnected parts that include one or more measurement devices. • Measurement devices such as sensors, or primary elements, measure the variable Instrumentation- Measurement Parameters • • • • • • • • • • • • • • • • Pressure Flow Temperature Frequency Current Voltage Inductance Capacitance Resistivity liquid Levels Speed Flow rate Force Movement Velocity & Acceleration Stress & Strain Level Mass or Weight Density Size or Volume Instrumentation- Measurement Aspects Sensor, transmitter and transducers are the key aspects of a any measurement system • Sensor: The sensor is the primary sensing element and exists in close proximity to the process. – The sensor measures the controlled variable in the process and sends a non-standardized signal to the transmitter. • Transmitter: The transmitter contains a transducer which converts the nonstandardized signal of the sensor into a standardized form that it amplifies. – The most common standardized forms are either 4-20 milliamps or 3-15 psi. If digital signals are being used, the transmitter converts the signal to digital. – If it is a smart device , the transmitter may convert the signal into two signals, both an analog signal and a digital signal, before sending them out. – Smart devices also have the ability to superimpose a digital signal over an analog signal. • Transducers: Transducers convert one instrument signal value to another, usually a pneumatic signal to an electronic signal (pressure to current, abbreviated "P to I") or an electronic signal to a pneumatic signal (I to P). – Technically, sensors and transmitters are transducers because their basic function is to translate a signal. – However, to clarify specifically how they function the various elements are referred to individually (sensor, thermocouple, transmitter, etc.) and the term "transducer is reserved for a device that converts I to P or P to I. Instrumentation Measurement System Sensor or transducer: is an input device convert the quantity under measurement into a detectable signal form. e.g : electrical, mechanical, optical. Signal conditioning: modifies the transducer signal into a desired form. e.g. amplification, noise reduction. Output State : provides an indication of the value of the measurement (readout device or recording) SENSORS • A sensor measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. – A thermocouple converts temperature to an output voltage which can be read by a voltmeter. • Sensors may operate simple on/off switches to detect the following: – Objects (Proximity switch) – Empty or full (level switch) – Hot or cold (thermostat) – Pressure high or low (pressure switch) sensor block diagram Proximity switches : open or close an electrical circuit when they make contact with or come within a certain distance of an object. Level switch: senses the level of a liquid in a water tank. Sensors Diversity TRANSDUCER • A transducer is a device that converts one type of energy to another. • The conversion can be to/from electrical, electromechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. • Transducer commonly used as a sensor/detector. • Transducers can be found both at the input as well as at the output stage of a measuring system. Transducer Types • Transducers may be categorized by application: – Sensor (Input) – Actuator (Output) – or combination (Input & Output) . Transducer Types Sensor (Input) • Input sensor is used to detect a parameter in one form and report it in another form of energy (usually an electrical and/or digital signal). – For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electricity for display at a remote gauge. Actuator (Output) • An actuator accepts energy and produces movement (action). – The energy supplied to an actuator might be electrical or mechanical – An electric motor and a loudspeaker are both transducers, converting electrical energy into motion for different purposes. combination (Input & Output) • Combination transducers have both functions -- they both detect and create action. – For example, a typical ultrasonic transducer switches back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves. Gauge: measurement of diameter Hydraulics: mechanical properties of liquids. Pneumatics: use of pressurized gas to affect mechanical motion Classification of transducers Types of energy form Classification of transducers Modulating & self-generating transducers SENSOR TRANSDUCERS CLASSIFICATION • TEMPERATURE TRANSDUCERS – Thermocouple • RESISTANCE TYPE SENSORS – Thermistor • PRESSURE TRANSDUCERS – Mechanical Type • Bourdon Tube. • Spring and Piston. • Bellows and capsules. • Diaphragm – Electrical Type • Strain Gauge types. • Piezo electric types. • Inductive types. • Capacitive types. SPEED TRANSDUCERS Optical Types Magnetic Pickups Tachometers (Generator) FORCE SENSORS Mechanical types. Hydraulic types. Electrical strain gauge types. POSITION SENSORS Resistive Optical Inductive Measuring & Sensing System SIGNAL CONDITIONING • Signal conditioning means manipulating any signal (analogue signal) in such a way that it meets the requirements of the next stage for further processing. – Most common use is in analog-to-digital converters. • In Instrumentation & control applications, it is common to have a sensing stage (which consists of a sensor), a signal conditioning stage (where usually amplification of the signal is done) and a processing stage (normally carried out by an ADC and a microcontroller). – Operational Amplifiers (op-amps) are commonly employed to carry out the amplification of the signal in the signal conditioning stage. Signal conditioning processes • • • • • • • • Filtration Amplification Mixing Isolation Multiplexing Sampling Quantization Conversion (Analog, Digital) SIGNAL CONDITIONING & PROCESSING • The purpose of conditioning & processing is to convert the output into the standard range. • Secondary Transducers: Enables how to process the output of the transducers into the form required by the rest of the instrument system . • Primary Transducers: Can not produce these standard ranges. • Most modern equipment works on the following standard signal ranges. – Electric 4 to 20 mA – Pneumatic 0.2 to 1.0 bar (3-15 psi) – Digital standards (0 to 18V) • The advantage of having a standard range is that all equipment is sold ready calibrated. Pneumatics: use of pressurized gas to affect mechanical motion Signal Conditioning Equipments & Processing • The vast array of instrumentation & control equipment available uses many forms of signals. Here is a summary. – ELECTRICAL: Voltage, current, digital. – MECHANICAL: Force & movement. – PNEUMATIC & HYDRAULIC: Pressure & flow. – OPTICAL: High speed digital signal transmission. – RADIO: Analogue & digital transmission. – ULTRA VIOLET: Similar application to radio over short ranges • Processing may do the following things. – Change the level or value of the signal (e.g. voltage level) – Change the signal from one form to another. (e.g. current to pneumatic) – Change the operating characteristic with respect to time (Bandwidth) . – Convert analogue and digital signals from one to the other (conversion) . Instrumentation- Control • Control Instrumentation plays a significant role in both gathering information from the field and changing the field parameters. • Control instrumentation includes devices such as solenoids, valves, regulators, circuit breakers, relays etc. • These devices control a desired output variable, and provide either remote or automated control capabilities. • These are often referred to as final control elements when controlled remotely or by a control system. Instrumentation- Control Control valve solenoids Relays circuit breakers Instrumentation- Process Control • Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for controlling the output of a specific process Instrumentation Process Control 24