Pharos University
EE212_ELECTRICAL MEASUREMENT & Interface Prepared By: Dr. Sahar Abd El Moneim Moussa

Dr. Sahar Abd El Moneim Moussa

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CH1_ ERRORS IN MEASUREMENTS

Dr. Sahar Abd El Moneim Moussa

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INTRODUCTION
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Measurement involves using an instrument as a physical means of determining a quantity or variable.

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A measuring device: a device used for obtaining a value which nearly represents an unknown variable or quantity.

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The advancement of science and technology leads to the progress in the measuring techniques.

Dr. Sahar Abd El Moneim Moussa

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 Classification

of Measuring Instruments:

1- Mechanical Instruments:
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These are the first type of measuring instruments.
Since they have moving parts then they are useful for stable operation but due the inertia of the moving elements are slow then they are not suitable for measuring dynamic variables and transient operations.

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Dr. Sahar Abd El Moneim Moussa

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 Classification

of Measuring Instruments: ( cont.)

2- Electrical Instruments:
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Since 1801. By discovering electricity, the electrical measuring instruments appear. Electrical instruments have in general electric circuit consisting of some resistors and a magnetic circuit consisting of either a permanent or a coil with an iron core. It depends upon the interaction between the electric circuit and the magnetic circuit.

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Dr. Sahar Abd El Moneim Moussa

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 Classification

of Measuring Instruments: ( cont.)

3- Electronic Instruments:
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Then the electronic measuring instruments appear which depends upon electronic components such as diodes and transistors.
They are fast and can be used in transient measurements.

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Dr. Sahar Abd El Moneim Moussa

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 Methods

of Measurements:

1- Direct Method:
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The unknown quantity is directly compared