Electrical Measurements: Methods and Techniques
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Questions and Answers

What is the main advantage of the Direct Comparison method of measurements?

  • High accuracy with low uncertainty (correct)
  • Does not require comparison with a standard value
  • Requires minimal training and time
  • Can be carried out without a trained operator

    • Which method of measurement relies on achieving a balance in weight to determine the unknown current?

  • Indirect measurement method (correct)
  • Differential measurement method
  • Substitution method
  • Null measurement method

    • Which of the following is a characteristic of the Substitution method of measurements?

  • No need for any standard value
  • Uses digital output readings
  • Standard resistance is adjusted until a balance is reached (correct)
  • Measurement relies on continuous monitoring

    • What is a key feature of the null measurement method?

    <p>Balancing state indicated by zero current only</p> Signup and view all the answers

    In which type of measuring instruments are damping forces used to ensure stability of the pointer?

    <p>Mechanical instruments</p> Signup and view all the answers

    What distinguishes Digital instruments from Analogue instruments in terms of signal representation?

    <p>Discrete number representation</p> Signup and view all the answers

    Which type of measurement instruments have two types of scales: linear and non-linear?

    <p>Analogue instruments</p> Signup and view all the answers

    In which method can a roughly balanced state lead to pointer deflection or a change in output reading due to differences in equilibrium and actual states?

    <p>Null-Differential measurement method</p> Signup and view all the answers

    What type of force is used in Analogue instruments to prevent continuous movement of the pointer to its maximum deflection?

    <p>Controlling force</p> Signup and view all the answers

    Which method of measurements does not require standard current values for measurement?

    <p>Null measurement method</p> Signup and view all the answers

    Which type of instrument is used only for direct current measurements?

    <p>Permanent magnet moving coil (PMMC)</p> Signup and view all the answers

    What is the primary factor that causes the pointer to initially overshoot its steady-state position in an analog instrument?

    <p>The inertia of the moving parts</p> Signup and view all the answers

    Which type of control torque produces a restoring force that is proportional to the deflection angle?

    <p>Spring control</p> Signup and view all the answers

    For a gravity-controlled instrument, the current is proportional to which function of the deflection angle?

    <p>The sine of the angle</p> Signup and view all the answers

    What is the primary advantage of gravity-controlled instruments over spring-controlled instruments?

    <p>They are cheaper to manufacture</p> Signup and view all the answers

    Which equation describes the relationship between the deflecting torque and the current in an instrument?

    <p>$T = K \cdot i$</p> Signup and view all the answers

    In the equation of motion for an analog instrument during the transient period, what does the term $T_i$ represent?

    <p>The inertia torque</p> Signup and view all the answers

    Which property of the spring material is essential for ensuring accurate measurements in spring-controlled instruments?

    <p>All of the above</p> Signup and view all the answers

    What is the primary disadvantage of gravity-controlled instruments?

    <p>They have a non-uniform scale</p> Signup and view all the answers

    Which type of instrument is primarily used for alternating current measurements?

    <p>Induction type</p> Signup and view all the answers

    What is the relationship between the deflecting torque and the current in an instrument?

    <p>The deflecting torque is proportional to the square of the current.</p> Signup and view all the answers

    If the current producing a deflection angle of 90° is 2 A, what current is required to produce a deflection angle of 45° assuming spring control?

    <p>1.4142 A</p> Signup and view all the answers

    What is the purpose of damping torque in an instrument?

    <p>To stabilize the motion and prevent oscillations around the final position.</p> Signup and view all the answers

    Which type of damping is NOT effective in many situations?

    <p>Air damping</p> Signup and view all the answers

    What is the principle behind eddy current damping?

    <p>The flow of eddy currents in a conductive disc produces a damping force according to Lenz's law.</p> Signup and view all the answers

    What is the advantage of over-damped performance in an instrument?

    <p>The pointer moves slowly to its final value without oscillations.</p> Signup and view all the answers

    Which performance type is characterized by low damped behavior and high oscillations that decay with time?

    <p>Under-damped</p> Signup and view all the answers

    What is the characteristic of critical-damped performance?

    <p>The pointer moves faster than over-damped but slower than under-damped, without oscillations.</p> Signup and view all the answers

    If the damping constant is less than $4\sqrt{CJ}$, what type of performance can be expected?

    <p>Under-damped</p> Signup and view all the answers

    What is the relationship between the damping torque and the angular velocity of the pointer?

    <p>The damping torque is independent of the angular velocity.</p> Signup and view all the answers

    What is the main difference between linear and non-linear scale instruments?

    <p>Non-linear scale instruments have overcrowded graduations at the beginning of the scale, while the graduations are evenly spaced in linear scale instruments.</p> Signup and view all the answers

    Which of the following is a key characteristic of mechanical measuring instruments?

    <p>They are characterized by their heavy weight, large size and high prices.</p> Signup and view all the answers

    What is the main advantage of digital instruments over mechanical and electrical instruments?

    <p>Digital instruments provide automatic range adjustment.</p> Signup and view all the answers

    Which type of measuring instrument is suitable for measuring steady and stable operations?

    <p>Mechanical instruments</p> Signup and view all the answers

    What is the main disadvantage of electrical measuring instruments compared to electronic instruments?

    <p>Electrical instruments have a higher possibility for faults and problems.</p> Signup and view all the answers

    What is the main advantage of a graphical display over a pointer display in analogue instruments?

    <p>Graphical displays can display the magnitude and type of variation of the measured variable.</p> Signup and view all the answers

    What is the main advantage of a digital display over an analogue display?

    <p>Digital displays provide more accurate and definite readings.</p> Signup and view all the answers

    Which physical effect is utilized in ammeters and voltmeters?

    <p>Electromagnetic effect</p> Signup and view all the answers

    Which type of measuring instrument is suitable for measuring transient and dynamic applications?

    <p>Electronic instruments</p> Signup and view all the answers

    What is the main disadvantage of pointer-type analogue displays?

    <p>Pointer devices have the problem of parallax, which can cause an error in the reading.</p> Signup and view all the answers

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