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    Industrial Instrumentation

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    Nhân Phạm Đình
    This document discusses methods for measuring fundamental electrical quantities such as resistance, capacitance, inductance, and frequency. It focuses on resistance measurement using various sensor types that rely on a change in electrical resistance in response to a measured variable. Common resistance sensor types are described along with basic resistance measurement methods like voltage dividers, Wheatstone bridges, and deflection techniques. Requirements for sensor signal conditioners are outlined. An example is provided of designing a voltage divider circuit to measure carbon monoxide concentration using a gas sensor.

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    Industrial Instrumentation

    Uploaded by

    Nhân Phạm Đình
    24 views21 pages
    This document discusses methods for measuring fundamental electrical quantities such as resistance, capacitance, inductance, and frequency. It focuses on resistance measurement using various sensor types that rely on a change in electrical resistance in response to a measured variable. Common resistance sensor types are described along with basic resistance measurement methods like voltage dividers, Wheatstone bridges, and deflection techniques. Requirements for sensor signal conditioners are outlined. An example is provided of designing a voltage divider circuit to measure carbon monoxide concentration using a gas sensor.

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    C5_1

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    This document discusses methods for measuring fundamental electrical quantities such as resistance, capacitance, inductance, and frequency. It focuses on resistance measurement using various sensor types that rely on a change in electrical resistance in response to a measured variable. Common resistance sensor types are described along with basic resistance measurement methods like voltage dividers, Wheatstone bridges, and deflection techniques. Requirements for sensor signal conditioners are outlined. An example is provided of designing a voltage divider circuit to measure carbon monoxide concentration using a gas sensor.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    24 views21 pages

    Industrial Instrumentation

    Uploaded by

    Nhân Phạm Đình
    This document discusses methods for measuring fundamental electrical quantities such as resistance, capacitance, inductance, and frequency. It focuses on resistance measurement using various sensor types that rely on a change in electrical resistance in response to a measured variable. Common resistance sensor types are described along with basic resistance measurement methods like voltage dividers, Wheatstone bridges, and deflection techniques. Requirements for sensor signal conditioners are outlined. An example is provided of designing a voltage divider circuit to measure carbon monoxide concentration using a gas sensor.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 21

    INDUSTRIAL

    INSTRUMENTATION
    Lecturer: Nguyen Duc Hoang
    Department of Control & Automation
    Faculty of Electrical & Electronics Engineering
    Ho Chi Minh City University of Technology
    Email: ndhoang@hcmut.edu.vn
    Chapter 5: Methods to measure
    fundamental quantities
    • Measurement of resistance
    • Measurement of capacitance
    • Measurement of inductance
    • Measurement of frequency
    Measurement of resistance
    • Sensors based on the variation of the electric resistance of a device
    are very common:
    • POTENTIOMETERS
    • STRAIN GAGES
    • THERMISTORS, RTD
    • MAGNETORESISTORS
    • LIGHT-DEPENDENT RESISTORS
    • RESISTIVE HYGROMETERS
    • RESISTIVE GAS SENSORS
    • LIQUID CONDUCTIVITY SENSORS
    Measurement of resistance
    • The general equation for a sensor whose resistance changes by a
    fraction x in response to a measurand is :

    Assuming :
    • For linear sensors we have:

    • The range of values for x depends strongly on the type of sensor and
    on the measurand span
    Measurement of resistance
    • There are two requirements for all conditioners for
    resistive sensors:
    • they must drive the sensor with an electric voltage or current in
    order to obtain an output signal,
    • this supply, whose magnitude affects that of the output signal,
    is limited by sensor self-heating,
    Measurement of resistance
    • Some sensors require particular circuits.
    • Thermistors require linearization.
    • Strain gages require interference cancellation.
    • Sensors that yield small outputs require large gains in order for
    the dynamic range of the output signal to match the input
    range of the ADC .
    • Conditioners for remote sensors must be insensitive to
    connecting lead resistance or compensate for it.
    Measurement of resistance

    remote sensors
    Measurement of resistance
    • Methods for resistance measurement can be
    classified into:
    • Deflection methods sense the drop in voltage across the
    resistance to be measured or the current through it or
    both.
    • Null methods are based on measurement bridges.
    Measurement of resistance
    • Deflection method (1)

    𝑉𝑟
    𝑉 0= 𝑅0 ( 1+ 𝑥 )
    𝑅𝑟
    Measurement of resistance
    • Deflection method (2)

    𝑉0
    𝑅=𝑅𝑟
    𝑉𝑟
    Measurement of resistance
    • Voltage dividers :
    • commonly used to measure high-value resistances.
    Measurement of resistance

    Example: The MGS1100 CO gas sensor (Motorola) has 1000 kΩ in air,


    from 30 k Ω to 300 k Ω (150 k Ω typical) for CO concentration of 60ppm
    (R60) , and a ratio R60/R400 = 2,5 (typical). If the allowable voltage across
    the sensing resistor and power dissipation in it are 5 V and 1mW, design a
    voltage divider for such a sensor if the expected CO concentration range
    is from 0 to 400ppm.
    Measurement of resistance
    • Wheatstone bridge : balance measurements
    Measurement of resistance
    • Wheatstone bridge: deflection measurements
    Problems
    • A given Pt100 has R = 100 and  = 6 mW/K when immersed in air and  = 100 mW/K when
    immersed in still water. Calculate the maximal current through the sensor to keep the self-heating
    error below 0.10C.
    A bridge circuit has R1 = R2 = R3 = R4 = 120Ohm resistances and a 10.0-V supply. Suppose a 3-1/2
    digit DVM on a 200-mV scale will be used for the null detector. Find the resistance resolution for
    measurements of R4.
    BT5

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