Transcript Instrumentation Measurement System

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
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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.
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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
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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
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