By: Engr. Irfan Ahmed Halepoto Assistant Professor, Deptt: Electronics Engg. LECTURE#02 Basics of instrumentation & Measurement systems AUTOMATION & ROBOTICS

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.variableprocess 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 non- standardized 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 deviceanalogdigital –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, electro- mechanical, 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 Pneumatics: use of pressurized gas to affect mechanical motion Hydraulics: mechanical properties of liquids.

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 micro- controller). –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 valveRelays solenoidscircuit 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

24 Instrumentation Process Control