Series Resistance and Meter Coil Movement
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Questions and Answers

What is the purpose of the five-position switch in the multi-range voltmeter?

  • To provide a fixed full-scale range of measurement
  • To select one resistor at a time for different full-scale ranges of measurement (correct)
  • To increase the sensitivity of the voltmeter
  • To reduce the loading error

    • What is the average value of the pulsating DC when AC is converted by a rectifier?

  • 70% of peak
  • 63.7% of peak (correct)
  • 80% of peak
  • 50% of peak

    • What is the total internal resistance of the voltmeter in the 150-V range?

  • 20 kΩ
  • 5 kΩ
  • 10 kΩ (correct)
  • 50 kΩ

    • Why is a different scale used on an AC meter?

    <p>Because the meter reacts to the average value of the AC</p> Signup and view all the answers

    What is the rating of the meter movement used in the multi-range voltmeter?

    <p>1 mA, 500 Ω</p> Signup and view all the answers

    Why is it important for a voltmeter to have a high resistance compared to the circuit being measured?

    <p>To minimize the loading effect</p> Signup and view all the answers

    What is the purpose of the labels on the meter movement's scale?

    <p>To accommodate each range of measurement</p> Signup and view all the answers

    What happens when an AC meter is used to measure DC?

    <p>It gives an incorrect reading</p> Signup and view all the answers

    What is the correct procedure when connecting or disconnecting a voltmeter from a circuit?

    <p>De-energise and discharge the circuit completely</p> Signup and view all the answers

    How are the resistor values determined for a multi-range voltmeter?

    <p>By using a known total voltage, movement full-scale deflection rating, and movement resistance</p> Signup and view all the answers

    What should be observed when using a DC voltmeter?

    <p>The proper circuit polarity</p> Signup and view all the answers

    What is the purpose of an ohmmeter?

    <p>To measure resistance</p> Signup and view all the answers

    How does a mechanical ohmmeter operate?

    <p>Through electric current</p> Signup and view all the answers

    What is the effect of connecting a voltmeter to a circuit component?

    <p>The voltage across the component decreases</p> Signup and view all the answers

    What should not be used to measure AC voltage?

    <p>A DC voltmeter</p> Signup and view all the answers

    What is the disadvantage of using a mechanical ohmmeter?

    <p>It is rarely used today</p> Signup and view all the answers

    What is the term used to describe the decrease in voltage when a voltmeter is connected to a circuit component?

    <p>Voltmeter loading</p> Signup and view all the answers

    How should a voltmeter be connected to a circuit?

    <p>In parallel with the circuit</p> Signup and view all the answers

    What is the resulting error caused by voltmeter loading?

    <p>Loading error</p> Signup and view all the answers

    What is the function of the leads in an ohmmeter?

    <p>To connect across an external resistance</p> Signup and view all the answers

    What is the purpose of the resistor R4 in the multi-range voltmeter?

    <p>To provide a full-scale range of 1 V</p> Signup and view all the answers

    What is the indication of the resistance reading in an ohmmeter?

    <p>Through a mechanical meter movement</p> Signup and view all the answers

    What determines the amount of current that flows through the meter coil?

    <p>The total resistance of resistors R1 and R2, and the resistance of the meter</p> Signup and view all the answers

    What would happen to the current flow in the moving coil if R1 or R2 were replaced with a resistor having a larger value?

    <p>The current flow would decrease further</p> Signup and view all the answers

    What is the relationship between the movement of the moving coil and the current flow?

    <p>The movement is proportional to the amount of current flow</p> Signup and view all the answers

    Why should ohmmeters never be connected to an energized circuit?

    <p>Because it would invalidate the reading</p> Signup and view all the answers

    What do the range selections on a multi-range ohmmeter indicate?

    <p>The multiplication factor for the reading</p> Signup and view all the answers

    What would be the actual resistance measurement if the pointer is set on the scale figure 20 Ω and the range switch is set at R × 100?

    <p>2 kΩ</p> Signup and view all the answers

    What happens to the pointer deflection when R1 or R2 are replaced with resistors having a larger value?

    <p>The pointer deflection decreases further</p> Signup and view all the answers

    What is the purpose of the different range settings on a multi-range ohmmeter?

    <p>To allow measurement of a wide range of resistance values</p> Signup and view all the answers

    What is the primary purpose of a static discharger?

    <p>To prevent RFI by preventing sparks from jumping between the control surface and the airframe</p> Signup and view all the answers

    What is the typical range of resistance of a serviceable static discharger?

    <p>1 to 100 MΩ</p> Signup and view all the answers

    What is required to obtain a low resistance connection for the test terminal when testing a static discharger?

    <p>Removing corrosion protection from the sleeve</p> Signup and view all the answers

    What is the name given to the type of meter that combines multiple functions, such as a DC ammeter, a DC voltmeter, an AC ammeter, an AC voltmeter, and an ohmmeter?

    <p>Multi-meter</p> Signup and view all the answers

    What type of meter movement is commonly used in most multimeters?

    <p>D'Arsonval meter movement</p> Signup and view all the answers

    What is the abbreviation for a digital multimeter?

    <p>DMM</p> Signup and view all the answers

    What is the primary function of a multimeter in aircraft maintenance?

    <p>To perform various electrical measurements</p> Signup and view all the answers

    What must be re-applied to the sleeve after testing a static discharger?

    <p>Corrosion protection</p> Signup and view all the answers

    Study Notes

    Multi-range Voltmeter

    • A multi-range voltmeter can measure voltage in four different ranges: 1, 10, 100, and 1000 V
    • The meter movement's scale must be equipped with labels appropriate for each range
    • Each resistor value is determined by the same technique, using a known total voltage, movement full-scale deflection rating, and movement resistance
    • The multiplier resistances for a voltmeter with ranges of 1, 10, 100, and 1000 V are:
      • R4 = 500 Ω
      • R3 = 9.5 kΩ
      • R2 = 99.5 kΩ
      • R1 = 999.5 kΩ

    Voltmeter Loading Effects

    • When a voltmeter is used to measure the voltage across a circuit component, the voltmeter circuit itself is in parallel with the circuit component
    • The parallel combination of two resistors is less than either resistor alone, resulting in a decrease in voltage
    • This effect is called voltmeter loading, and the resulting error is called loading error
    • A voltmeter should have a high resistance compared to the circuit being measured to minimize the loading effect

    Voltmeter Safety Precautions

    • Always connect voltmeters in parallel
    • Always start with the highest range of a voltmeter
    • De-energize and discharge the circuit completely before connecting or disconnecting the voltmeter
    • In DC voltmeters, observe the proper circuit polarity to prevent damage to the meter
    • Never use a DC voltmeter to measure AC voltage
    • Observe the general safety precautions for electrical and electronic devices

    d'Arsonval Meter with Rectifiers

    • When AC is converted to pulsating DC by a rectifier, the d'Arsonval movement reacts to the average value of the pulsating DC (the average value of half of the sine wave)
    • The average value is 63.7% of peak
    • Although the meter movement reacts to the average value of the AC, the value used when working with the AC sine wave is the effective value (RMS value)

    Ohmmeters

    • An ohmmeter measures the resistance placed between its leads
    • The amount of current that flows through the meter coil depends on the total resistance of resistors R1 and R2, and the resistance of the meter
    • The inclusion of R1 and R2 raises the total series resistance, decreasing the current and thus decreasing the pointer deflection
    • Ohmmeters should never be connected to an energized circuit (that is, a circuit with its own source of voltage)

    Multi-range Ohmmeter

    • A practical ohmmeter usually has several operational ranges, typically indicated by R × 1, R × 10, R × 100, R × 1000, R × 100 000, and R × 1,000,000
    • The reading on the ohmmeter scale is multiplied by the factor indicated by the range setting

    Megohmmeter

    • A megohmmeter is used to test static dischargers
    • The resistance range between the ends of a serviceable static discharger is between 1 and 100 MΩ, which is far beyond the range of a conventional ohmmeter

    Multimeters

    • A multimeter is a device that combines the functions of a DC ammeter, a DC voltmeter, an AC ammeter, an AC voltmeter, and an ohmmeter
    • There are two categories of multimeters: analogue and digital (often abbreviated DMM or DVOM)
    • Most multimeters use a d'Arsonval meter movement and have a built-in rectifier for AC measurement

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    Description

    This quiz tests understanding of how series resistance affects current flow and meter coil movement. It involves the analysis of a circuit diagram with resistors R1 and R2 connected to a meter coil. The quiz requires knowledge of electricity and magnetism principles.

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