Neets Module 3 Assignment 1

Card Set Information

Author:
CVN68
ID:
165442
Filename:
Neets Module 3 Assignment 1
Updated:
2012-08-09 16:21:14
Tags:
Neets
Folders:

Description:
Neets
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user CVN68 on FreezingBlue Flashcards. What would you like to do?


  1. What are two ways that circuit measurement is used?
    Circuit measurement is used to (1) monitor the operation of a piece of electrical or electronic equipment and (2) determine the reason a piece of electrical or electronic equipment is not functioning properly.
  2. Why are in-circuit meters used?
    In-circuit meters are used to monitor the operation of electrical or electronic devices.
  3. What is one advantage of an out-of-circuit meter when it is compared with an in-circuit meter?
    Out-of-circuit meters can be used on more than one electrical or electronic device.
  4. How does a compass react when placed close to a current carrying conductor?
    The compass needle swings away from magnetic north and aligns itself with the magnetic field around the conductor.
  5. If the amount of current in the conductor changes, what happens to the magnetic field around the conductor?
    If the current increases the magnetic field increases; if the current decreases the magnetic field decreases.
  6. How does the compass needle react to a decreased magnetic field?
    The compass needle will not be deflected as far from magnetic north.
  7. What type of meter movement is the d'Arsonval meter movement?
    A permanent-magnet moving-coil meter movement used in most electrical and electronic meters.
  8. What is the effect of current flow through the coil in a d'Arsonval meter movement?
    A magnetic field is generated around the coil and the attraction of this field with the permanent magnet causes the coil to move.
  9. What are three functions of the hairsprings in a d'Arsonval meter movement?
    To return the pointer to its rest position when there is no current flow; to oppose the coil movement when there is current flow; to provide electrical connections for the coil.
  10. How would a compass react when placed close to a conductor carrying alternating current at a low frequency?
    The compass needle would swing back and forth as the current changed from positive to negative.
  11. How would the compass react if the alternating current through the conductor was a high frequency?
    The compass needle would vibrate rapidly around the zero-current point ac meter (magnetic north).
  12. What is the purpose of a rectifier in a meter?
    A rectifier changes alternating current to pulsating direct current and allows a dc meter to measure ac.
  13. How can a d'Arsonval meter movement be adapted for use as an ac meter?
    By the use of a rectifier
  14. What is damping?
    The process of "smoothing out" the oscillation in a meter movement.
  15. What are two methods used to damp a meter movement?
    As the coil moves through the field of the permanent magnet, a current is induced in the coil opposing the movement of the coil; and a vane can be attached to the coil and placed in the airtight chamber so that the movement of the vane opposes the movement of the coil.
  16. What value does a meter movement react to (actually measure) when measuring ac?
    Average value.
  17. What value is indicated on the scale of an ac meter?
    Effective value (rms).
  18. List three meter movements that can measure either ac or dc without the use of a rectifier.
    • Electrodynamic
    • Moving vane
    • Hot-wire or thermocouple.
  19. What electrical property does an ammeter measure?
    Current.
  20. How is an ammeter connected to the circuit under test?
    In series.
  21. How does an ammeter affect the circuit being measured?
    Since the ammeter is a resistor in series with the load, it increases the resistance of the circuit and lowers circuit current.
  22. How is the ammeter's effect on the circuit being measured kept to a minimum?
    The resistance of the ammeter must be much smaller than the circuit load.
  23. What is ammeter sensitivity?
    The amount of current that will cause full-scale deflection.
  24. What is used to allow an ammeter to measure different ranges?
    Shunt resistors (internal or external).
  25. Why should you use the highest range of an ammeter for the initial measurement?
    To prevent damage to the meter movement from excessive current.
  26. What range of an ammeter is selected for the final measurement?
    A range that allows a meter reading near the center of the scale.
  27. List the six safety precautions for the use of ammeters.
    • Always connect an ammeter in series.
    • Always start with the highest range.
    • In dc ammeters, observe the proper polarity.
    • Deenergize and discharge the circuit before connecting or disconnecting the ammeter.
    • Never use a dc ammeter to measure ac current.
    • Observe the general safety precautions of electric and electronic devices.
  28. Why will an ammeter be damaged if connected in parallel with the circuit to be measured?
    Since the ammeter has a small resistance compared to the load, it will have very high current if it is connected in parallel. This high current will damage the meter.
  29. What electrical quantity is measured by a voltmeter?
    Voltage.
  30. How is a voltmeter connected to the circuit to be measured?
    In parallel.
  31. What is the loading effect of a voltmeter?
    The connection of a voltmeter adds a resistance in parallel with the circuit changing the total circuit resistance, and loads the circuit.
  32. How is the loading effect of a voltmeter kept to a minimum?
    A voltmeter must have a high resistance compared to the circuit being measured.
  33. How is it possible to use a current sensitive meter movement to measure voltage?
    Since the resistance of a meter movement remains the same as the pointer is deflected, the amount of current through the movement is proportional to the voltage applied. Therefore, only the scale of the movement must be changed.
  34. What is voltmeter sensitivity?
    It is an indication of the resistance of the meter expressed in ohms per volt. The total resistance of the meter is the sensitivity multiplied by the full-scale voltage.
  35. What method is used to allow a voltmeter to have several ranges?
    The use of resistors in series with the meter movement.
  36. Why should you always use the highest range when connecting a voltmeter to a circuit?
    To prevent excess current through the meter movement.
  37. What type of meter movement reacts to voltage rather than current?
    Electrostatic.
  38. What is the only use for the voltage sensitive meter movement?
    High-voltage measurement.
  39. List the six safety precautions for the use of voltmeters.
    • Always connect a voltmeter in parallel.
    • Always start with the highest range.
    • Deenergize and discharge the circuit before connecting or disconnecting the voltmeter.
    • In a dc voltmeter, observe the proper polarity.
    • Never use a dc voltmeter to measure ac voltage.
    • Observe the general safety precautions of electric and electronic devices.
  40. What electrical quantity is measured by an ohmmeter?
    Resistance.
  41. What other measurement can an ohmmeter make?
    Circuit continuity.
  42. How is a series-type ohmmeter connected to the circuit being measured?
    The ohmmeter is connected in series with the resistance to be measured.
  43. What is used to provide the ohmmeter with several ranges?
    An ohmmeter has several internal range resistors and a switch or a series of jacks to select the proper range.
  44. What area of an ohmmeter scale should be used when measuring circuits?
    The middle of the scale.
  45. What are the two types of ohmmeters?
    Series and shunt.
  46. What is the most obvious difference between the two types of ohmmeters?
    Series ohmmeters have 0 on the right end of the scale and � on the left end of the scale. Shunt ohmmeters are the opposite.
  47. List the four safety precautions observed when using ohmmeters.
    • Deenergize and discharge the circuit before connecting an ohmmeter.
    • Do not apply power to a circuit while measuring resistance.
    • Switch ohmmeters to the OFF position, if provided, or to highest range and remove meter leads from the meter when finished measuring resistance.
    • Adjust the ohmmeter after changing resistance range and before measuring reading indicates the resistance.
  48. What is the primary use of a megger?
    To measure high resistance.
  49. What is the procedure for using a megger to check the insulation of a conductor?
    Connect one lead to the insulation and one lead to the conductor. Turn the handcrank until it starts to slip. Note the reading.
  50. What is a normal indication on a megger when checking insulation?
    Infinity.
  51. List the four safety precautions observed when using a megger.
    • Use meggers for high-resistance measurement only.
    • Never touch the test leads when the handle is being cranked.
    • Deenergize and discharge the circuit completely before connecting a megger.
    • Disconnect the item being checked from other circuitry, if possible, before using a megger.
  52. What is a multimeter?
    A single measuring device capable of performing the functions of a dc voltmeter and ammeter, an ac voltmeter and ammeter, and an ohmmeter.
  53. Why is a multimeter preferred over separate meters?
    It is much more convenient to have one meter with several functions than several meters each with a single function.
  54. How is a multimeter changed from a voltage measuring device to a resistance measuring device?
    By changing the position of the function switch.
  55. Why is the dc scale on a multimeter different than the ac scale?
    The meter movement reacts to average ac voltage and current and the effective value is desired.
  56. What is the reason for having a mirror on the scale of a multimeter?
    To stop parallax error
  57. How is the mirror on a multimeter used?
    Make sure no image of the pointer is visible in the mirror when reading the meter.
  58. List the 11 safety precautions for multimeters.
    • Deenergize and discharge the circuit completely before connecting or disconnecting a multimeter.
    • Never apply power to the circuit while measuring resistance with a multimeter.
    • Connect the multimeter in series with the circuit for current measurements, and in parallel for voltage measurements.
    • Be certain the multimeter is switched to ac before attempting to measure ac circuits.
    • Observe proper dc polarity when measuring dc.
    • When you are finished with a multimeter, switch it to the OFF position, if available. If there is no OFF position, switch the multimeter to the highest ac voltage position.
    • Always start with the highest voltage or current range.
    • Select a final range that allows a reading near the middle of the scale.
    • Adjust the "0 ohms" reading after changing resistance ranges and before making a resistance measurement.
    • Be certain to read ac measurements on the ac scale of a multimeter.
    • Observe the general safety precautions for electrical and electronic devices.
  59. Why would you use a hook-on voltameter instead of a multimeter?
    To measure current safely and easily (with no need to disconnect the wiring of the circuit).
  60. What electrical quantity is measured by a wattmeter?
    Power.
  61. What electrical quantity is measured by a watt-hour meter?
    Energy.
  62. What are two types of frequency meters?
    • Vibrating reed
    • Moving disk.

What would you like to do?

Home > Flashcards > Print Preview