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Instrumentasi Sistem Pengaturan - 01 1
Instrumentasi Sistem Pengaturan
Pengantar Sistem Instrumentasi
Ir. Jos Pramudijanto, M.Eng.Jurusan Teknik Elektro FTI ITS
Telp. 5947302 Fax.5931237Email: [email protected]
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Objektif
• Mengetahui konfigurasi sistem instrumentasi;• Perbedaan dari sensor dan tranduser;• Mengetahui pentingnya manfaat pengukuran;• Akurasi dari sensor;
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A Instrumentation systems includes all the components necessary for producing a measurement.
Instrumentation Systems
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Bicycle Speedometer
Sensor: A Magnet attached to one of the spokesTransducer: The Hall Effect device that produces an electrical pulse as the magnet passesSignal Conditioning: A circuit compares the pulses to a timer and determines the period. A correlation based on the measured period and wheel diameter is used to determine velocity.Output Stage: A digital signal is sent to the LCD displays and the velocity appears on the screen
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Measurement: Comparison between a standard and what we want to measure (the measurand).What is the standard?
Width of a man’s thumb =1 inchLength of a man’s foot = 1 footLength of a man’s belt = 1 yard
There is a need for an unchanging standard for physical parameters
length(m), time(s), mass(kg), temperature(K), etc.
Other parameters can be defined in terms of these standard parameters (velocity = length/time)Oversight of standards and definitions (IEEE)
What is a Measurement ?
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Sensor – converts some physical quantity into an electrical quantity
Transducer – converts one form of energy into another
What is a Sensor and Transducer ?
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Sensors and Actuators
Transducers:a sensor is an electronic transducer that converts a physical quantity into an electrical signal,an actuator is an electronic transducer that converts electrical energy into a physical quantity.They are essential to digital control systems.
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TradeGetting what you pay forGetting parts that fit
DesignDesign parameters are based on experimental measurement (ex. max. temperature = 140oC)Analysis based on measurement (Testing: Does the part fail under max load at T = 140oC?)
ControlSafety (stall sensors on an aircraft wing measure lift)Economy (fuel system controls on an automobile)
Why is Measurement so Important ?
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Strain gauge
Strain-gauge Measurement System
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Oxygen Sensor
Airflow Sensor
Water Temperature
Oil Pressure
Accelerometer
CO Sensor
Automotive Measurement System
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Ultrasound Transducer
Biomedical Measurement System
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Direct comparisonMeasure length with a rulerMeasure mass with a balanceMeasure pressure with a deadweight pressure gage
Indirect comparisonUse of a measuring systemRequires calibrationMeasure temperature with a thermometerMeasure velocity with a bicycle speedometer
How Do we Measure with Sensor ?
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There is always some uncertainty in measurementsUncertainty: A likely bound on the error
The application prescribes the required accuracySignificant consequencesCore temperature of a nuclear reactor vs. outdoor temperatureFunctionalityMeasurement of lens curvature on eyeglasses vs. curvature of a wide-angle mirror
Error Definition: Difference between the actual value and the measured valuePrecision errorBias error
How Accurate is the Sensor ?
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Precision Error
RandomCauses measurement to be randomly above or below the the average value
Estimated by statistical methodsEstimation based on standard deviation
Example: Darts
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Bias Error
SystematicConstant fractional or total error
Can not be estimated by statistical methodsEstimation based on an understanding of sources of error
Example: Darts