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 control (process).

measurement and • 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 applied instrumentation.

is one of the main branches of • Instruments often comprise control systems of varied processes such as refineries, factories, vehicles etc.

• successful process instrumentation.

control requires appropriate

INSTRUMENTION SYSTEM

Measurement Systems

•

Measurement system:

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.

Any of the systems used in the • 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 elements, measure the variable

variable

in a

process

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.

, there • Measurement devices such as sensors, or primary

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: – If it is a 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.

smart device

, the transmitter may convert the signal into two signals, both an analog signal.

analog

signal and a

digital

signal, before sending them out.

– Smart devices also have the ability to superimpose a digital signal over an 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 switches to detect the following: on/off – 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

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 amplification of the signal is done) and a usually 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:

ranges.

Can not produce these standard • 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: RADIO:

High speed digital signal transmission.

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 solenoids, valves, regulators, circuit breakers, relays etc.

as • 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

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