Tuesday, April 8, 2008
Thursday, April 3, 2008
Process Variable - Pressure
Here we will discuss
What pressure is?
Pressure Measurement Methods
Pressure Units & Cross-Reference Chart
Terms related to pressure
Different Types of pressure
Different Laws related to pressure
Basic Methods of Pressure Measurements
Low Normal & High Pressures =>Primary + Secondary
Thermocouple Gauge
Pirani Gauge
Ionization Gauge
Accesories Related to Pressure measurement
Pressure Transmitter
Master gauge
Siphon gauge
Pressure Switch
Differential Pressure Switch
DP Transmitter
Dead Weight Tester
Air Regulator
Impulse line
+
Application Area
Accesories Related To Pressure Measurement
Pressure Transmitters
What pressure is?
Pressure Measurement Methods
Pressure Units & Cross-Reference Chart
Terms related to pressure
Different Types of pressure
Different Laws related to pressure
Basic Methods of Pressure Measurements
Low Normal & High Pressures =>Primary + Secondary
- Primary Sensors(Mechanical Type)-Tube Type-Piezometer Tube
Manometer
Elastic Type-Bourdon Tube
Diaphragm
Bellow
Capsule
Secondary Sensors(Electrical Type)-Resistive
Capacitive
Magnetic
Strain
Oscillometric
Piezometric
Thermocouple Gauge
Pirani Gauge
Ionization Gauge
Accesories Related to Pressure measurement
Pressure Transmitter
Master gauge
Siphon gauge
Pressure Switch
Differential Pressure Switch
DP Transmitter
Dead Weight Tester
Air Regulator
Impulse line
+
Application Area
Accesories Related To Pressure Measurement
Pressure Transmitters
Pressure transducers are devices that convert the mechanical force of applied pressure into electrical energy. This electrical energy becomes a signal output that is linear and proportional to the applied pressure. Pressure transducers are very similar to pressure sensors and transmitters. In fact, transducers and transmitters are nearly synonymous. The difference between them is the kind of electrical signal each sends. A transducer sends a signal in volts (V) or millivolt per volt (mV/V), and a transmitter sends signals in milliamps (mA).
Both transmitters and transducers convert energy from one form to another and give an output signal. This signal goes to any device that interprets and uses it to display, record or alter the pressure in the system. These receiving devices include computers, digital panel meters, chart recorders and programmable logic controllers. There are a wide variety of industries that use pressure transducers and transmitters for various applications. These include, but are not limited to, medical, air flow management, factory automation, HVAC and refrigeration, compressors and hydraulics, aerospace and automotive.
Both transmitters and transducers convert energy from one form to another and give an output signal. This signal goes to any device that interprets and uses it to display, record or alter the pressure in the system. These receiving devices include computers, digital panel meters, chart recorders and programmable logic controllers. There are a wide variety of industries that use pressure transducers and transmitters for various applications. These include, but are not limited to, medical, air flow management, factory automation, HVAC and refrigeration, compressors and hydraulics, aerospace and automotive.
There are important things to consider when deciding what kind of pressure transducer to choose. The first consideration is the kind of connector needed to physically connect the transducer to a system. There are many kinds of connectors for different uses, including bulletnose and submersible connectors, which have unique applications. Another important part is the internal circuitry of the transducer unit, which is housed by a "can" that provides protection and isolates the electronics. This can be made of stainless steel or a blend of composite materials and stainless steel. The various degrees of protection extend from nearly no protection (an open circuit board) to a can that is completely submersible in water. Other kinds of enclosures safeguard the unit in hazardous areas from explosions and other dangers.
The next thing to consider is the sensor, which is the actual component that does the work of converting the physical energy to electrical energy. The component that alters the signal from the sensor and makes it suitable for output is called the signal conditioning circuitry. The internal circuitry must be resistant to harmful external energy like radio frequency interference, electromagnetic interference and electrostatic discharge.These kinds of interferences can cause incorrect readings, and are generally to be avoided when doing readings. Overall, pressure transducers are well-performing and high-accuracy devices that make life easier for many industries.
to be continued.
The next thing to consider is the sensor, which is the actual component that does the work of converting the physical energy to electrical energy. The component that alters the signal from the sensor and makes it suitable for output is called the signal conditioning circuitry. The internal circuitry must be resistant to harmful external energy like radio frequency interference, electromagnetic interference and electrostatic discharge.These kinds of interferences can cause incorrect readings, and are generally to be avoided when doing readings. Overall, pressure transducers are well-performing and high-accuracy devices that make life easier for many industries.
to be continued.
Wednesday, April 2, 2008
Basic Instrumentation
Instrumentation deals with measuring & controlling the variables like pressure, temperature, flow, level &quality ( pH,humidity,viscosity,conductivity,position ).When instruments are used to measure & control industrial process variables,we use the term process instrumentation.The aim of instrumentation in industry is maximum output with minimum usage of raw-materials,time,energy & manpower.The technology of using instruments to measure & control the physical & chemical properties of materials is called instrumentation & if it is used in a process,its process instrumentation.
Instruments used in industry are of 5 major classes:indicating,transmitting,controlling,final control & alarming type.Same instrument can have more than one functions like indicating,alarming,recording& transmitting.
1.Indicating:Meters of all sort,LED
2.Transmitting:DP Transmitter
3.Controlling:Controllers,micro computer
4.Final Control:control valve,damper,fan,motor,pumps
5.Alarm:smoke detectors,home security system,buffers,LED
Process Instrumentation is broadly classified as field instrumentation & control instrumentation.Field instrumentation mainly deals with instruments to indicate,transmit,alarm &final controlling.Improvement occur continously in this field .Control instrumentation deals with control systems like DCS( Distributed Control System ),SCADA( Supervisory Control And Data Acquisition ),PLC( Programmable Logic Control ),SIS( Safety Instrumented System ).
Actually there are 2 types of process industries:continous & batch type.Continous type of process industries include chemical,water treatment,power,oil & gas industry.In continous process industries the process variables ( Pressure,Temperature,Flow,Level etc) tend to approach a desired set value(Set Point).Batch type process industries include pharmaceutical,food & beverages industry.In batch type industries together with the process value approaching the set point value,all physical events are synchronized with sequence of events in process reciepe.
DCS is mainly used in plants of process industries where closed loop control is prominent like refinery & is interested in process trends.It is also process oriented & hardwired system which is always connected to data source.SCADA is mainly used in plants of process industries where long distance material transfer is prominent like oil & gas transmission,water supply & distribution,raiways,power transmission & distribution.It is also a data gathering oriented & process event driven system.PLC is used in plants where sequential control & motion control is prominent like machine control,packaging & material handling.SIS is the result of guidelines for safe operations of industrial installations in the petrochemical,oil and gas production devoloped by industrial groups,safety certifying agencies and insurance companies for more stingent regulation and legislation.
Before moving into the details of each process variable,process control & Control instrumentation,we will first go through functional(operation) & characteristics(performance) features of an instrument with some of the basic terms used in instrumentation field.
One of the main function of instrumentation is measurement without which no control is possible.Measurements have got to be one of the most important equipment in any processing plant. Any decision made on what the plant should do is based on what the measurements tell us. Measurement is actually the process of comparison between a predefined quantity( standard) & the quantity to be measured(measurand).Standard of measurement is the physical representation of a unit of measurement.The various standards of measurement are
1.International : at International Bereau Of Standards
2.Primary : at National labs
3.Secondary :Basic reference standard used in industrial labs
4.Working standard : Used commercially
The various measurement units doesnt require special mention like
1.Fundamental
2.Supplementary
3.Derived
Measurement system application are
1.used to regulate trade
2.used in monitoring function
3.caliberation of instruments
4.used as automatic feedback control system
FUNCTIONAL ELEMENTS OF AN INSTRUMENT/INSTRUMENT SYSTEM
Fuctional element of an instrument system provide how an instrument operates.
1.Primary Sensing Element => Sensor + Transducer
Sensor: sense the various physical variables related to measurement like force,length,temp,acceleration,velocity,pressure,frequency,capacitance,resistance & time
Transducer: convert one form of energy into another mainly electrical.
2.Signal Conditioning Element =>Variable Conversion & Variable Manipulation
Variable Conversion: Ex:Analog to Digital Convertor
Variable Manipulation: Ex:Amplifier,Filter,Isolation
Transmitter => Primary Sensing Element & Signal Conditioning Element
O/P of Transmitter =>4-20 mA,3-15 psi,0-10 V
3.Data Transmission Element => Telemetry system,Fiber Optic Cables
O/P of a transmitter corresponding to process variable measured value is transmitted via data transmission element to monitoring,recording,storage or controlling instrument.
4.Data Presentation Element =>Pointer moving on a scale,recording of a pen moving on chart.
5.Data Storage Element =>Printer,Digital Memory
If its a automatic feedback control system,The transmitter value is passed to a control system too.
.....to be continued.
Instruments used in industry are of 5 major classes:indicating,transmitting,controlling,final control & alarming type.Same instrument can have more than one functions like indicating,alarming,recording& transmitting.
1.Indicating:Meters of all sort,LED
2.Transmitting:DP Transmitter
3.Controlling:Controllers,micro computer
4.Final Control:control valve,damper,fan,motor,pumps
5.Alarm:smoke detectors,home security system,buffers,LED
Process Instrumentation is broadly classified as field instrumentation & control instrumentation.Field instrumentation mainly deals with instruments to indicate,transmit,alarm &final controlling.Improvement occur continously in this field .Control instrumentation deals with control systems like DCS( Distributed Control System ),SCADA( Supervisory Control And Data Acquisition ),PLC( Programmable Logic Control ),SIS( Safety Instrumented System ).
Actually there are 2 types of process industries:continous & batch type.Continous type of process industries include chemical,water treatment,power,oil & gas industry.In continous process industries the process variables ( Pressure,Temperature,Flow,Level etc) tend to approach a desired set value(Set Point).Batch type process industries include pharmaceutical,food & beverages industry.In batch type industries together with the process value approaching the set point value,all physical events are synchronized with sequence of events in process reciepe.
DCS is mainly used in plants of process industries where closed loop control is prominent like refinery & is interested in process trends.It is also process oriented & hardwired system which is always connected to data source.SCADA is mainly used in plants of process industries where long distance material transfer is prominent like oil & gas transmission,water supply & distribution,raiways,power transmission & distribution.It is also a data gathering oriented & process event driven system.PLC is used in plants where sequential control & motion control is prominent like machine control,packaging & material handling.SIS is the result of guidelines for safe operations of industrial installations in the petrochemical,oil and gas production devoloped by industrial groups,safety certifying agencies and insurance companies for more stingent regulation and legislation.
Before moving into the details of each process variable,process control & Control instrumentation,we will first go through functional(operation) & characteristics(performance) features of an instrument with some of the basic terms used in instrumentation field.
One of the main function of instrumentation is measurement without which no control is possible.Measurements have got to be one of the most important equipment in any processing plant. Any decision made on what the plant should do is based on what the measurements tell us. Measurement is actually the process of comparison between a predefined quantity( standard) & the quantity to be measured(measurand).Standard of measurement is the physical representation of a unit of measurement.The various standards of measurement are
1.International : at International Bereau Of Standards
2.Primary : at National labs
3.Secondary :Basic reference standard used in industrial labs
4.Working standard : Used commercially
The various measurement units doesnt require special mention like
1.Fundamental
2.Supplementary
3.Derived
Measurement system application are
1.used to regulate trade
2.used in monitoring function
3.caliberation of instruments
4.used as automatic feedback control system
FUNCTIONAL ELEMENTS OF AN INSTRUMENT/INSTRUMENT SYSTEM
Fuctional element of an instrument system provide how an instrument operates.
1.Primary Sensing Element => Sensor + Transducer
Sensor: sense the various physical variables related to measurement like force,length,temp,acceleration,velocity,pressure,frequency,capacitance,resistance & time
Transducer: convert one form of energy into another mainly electrical.
2.Signal Conditioning Element =>Variable Conversion & Variable Manipulation
Variable Conversion: Ex:Analog to Digital Convertor
Variable Manipulation: Ex:Amplifier,Filter,Isolation
Transmitter => Primary Sensing Element & Signal Conditioning Element
O/P of Transmitter =>4-20 mA,3-15 psi,0-10 V
3.Data Transmission Element => Telemetry system,Fiber Optic Cables
O/P of a transmitter corresponding to process variable measured value is transmitted via data transmission element to monitoring,recording,storage or controlling instrument.
4.Data Presentation Element =>Pointer moving on a scale,recording of a pen moving on chart.
5.Data Storage Element =>Printer,Digital Memory
If its a automatic feedback control system,The transmitter value is passed to a control system too.
.....to be continued.
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