Absence of frequency error C. Independence of ambient temperature D. High degree of measuring accuracy. Some wire- wound resistors have bifilar winding. This type of winding is used to A.
Increase the thermal stability B. Reduce the tolerance C. Reduce the inductance of winding D. Double the power rating of the resistor.
Wien bridge is useful for measuring A. Very high frequency B. Low frequency C. Medium frequency D. High frequency. A megger is usually A. Moving iron type instrument B. Electro-static type instrument C. Hot-wire type instrument D. Moving coil type instrument. A moving iron ammeter may be compensated for frequency errors by A.
Ryall crest voltmeter is used for measurement of A. AC voltage of any form B. Low frequency voltage C. High DC voltage D. High AC voltage. Jewels are used in instruments for the purpose of A. Damping B. Torque control C. Suppressing noise D. The thermocouple instrument will measure A. Current B. Voltage C. Flux D. None of the above. A CRO can display A. AC signals B. DC signals C. Time invariant signals. The internal resistance of an ammeter should be A.
Very small B. High D. A galvanometer has A. Spring coil damping D. Eddy current damping. Electrostatic instruments are normally used for A. Low current measurements B. High current measurements C. Low voltage measurements D. High voltage measurements.
In a moving coil instrument, the deflecting torque is proportional to A. Square of the current C. Squareroot of the current D. The absolute measurement of resistance is done by A. Bridge Method C. Rayleigh method D. Lorenz method. To measure the flux, devices used are based on A. Voltaic effect B.
Piezo-electric effect C. Hall effect D. Photo-voltaic effect. The form factor in AC is the ratio of A. PMMC type instruments normally use A. Air friction damping B.
Fluid friction damping C. Eddy current damping D. In a moving iron meter, the deflecting torque is proportional to A. Current through the coil B. Square of the current through the coil C. Sine of the measurand D. Squareroot of the measurand.
In a gravity controlled instrument, the deflection angle is proportional A. Measurand B. Square of the measurand C. Ampere is one of the A. Supplementary units B. Derived units C. Base units D. Units used to measure charge. Direct method is used to measure A. Length B. Temperature C. Pressure D. Shunt resistance is 1 ohm.
Current through the meter at 0. One single phase wattmeter operating on V and 5A for 5 hours makes revolutions. Meter constant in revolutions is What is the power factor of the land? For power measurement of three phase circuit by two wattmeter method, when the value of power factor is less than 0.
When using ohmmeter, applied voltage is to be disconnected from the circuit because A. Voltage source will increase resistance B. Current will decrease resistance C.
Which wave has the least form factor? Square wave B. Rectangular wave C. Sine wave D. The called a graticule. Also on the front panel of a c. When a direct voltage is applied to the Calculate: a the approximate value of current Y plates the new position of the spot trace is neglecting the ammeter resistance , b the an indication of the magnitude of the voltage.
Determine the 25 volts. Determine the wattmeter screen as shown in Fig. The Y-plate input is left open-circuited. If not, adjust either or both of the X and Y-shift controls. The X-shift control varies the position of the spot trace in a horizontal direction whilst the Y-shift control varies its vertical position. Then the timebase control is switched to a suitable position, initially the millisecond timebase range, to ensure that the repetition rate Figure For the c.
The c. However its greatest advantage is in observing the shape of a waveform — a feature not possessed by other measuring instruments. Problem 7. Describe how a simple c. For the double-beam oscilloscope displays shown in Fig. The Figure Hence the periodic time, T D 3. A sinusoidal voltage trace displayed by a c.
This is a waveform which varies sinusoidally with time t, has a frequency f, and a maximum value Vm. Alter- nating voltages are usually assumed to have wave-shapes which are sinusoidal where only one frequency is present.
If the waveform is Figure This pulse voltage process is called harmonic analysis. The funda- [ a 0. If further odd har- monic waveforms of the appropriate amplitudes are added, a good approximation to a square wave results. In Fig. The positive and negative half cycles are seen to be dissimilar. The features mentioned relative to Figures Substituting in equation 1 gives: being initially in phase with each other.
From equation 1 , X decibels is a logarithmic ratio of two similar quantities and is not an absolute From above, the power ratio in decibels, X, is given unit of measurement.
The reference voltage V is then obtained D In general, the number P2 1 d When D D 0. The current input to a system 0. A typical decibelmeter, or dB meter, scale is shown in Fig. Problem Find its P2 output power. D P2 Hence D If the voltage gain is 27 dB, i. D lg 20 V1 Find also the overall power gain. Hence the overall decibel Thus Calculate the overall gain in decibels from which V1 D If a voltage of 15 mV is D applied to the input of the system, determine Determine the voltage at a 0 dB b 1.
Determine the decibel power ratio for each. Determine the decibel power ratio for rate and widely used method which depends on an each.
Determine the power Hence it is unnecessary for a meter sensing current loss in decibels. Examples power is 10 mW. Find its output power. Find also the overall power gain. If the voltage gain is 25 dB calculate the value Figure R1 and R2 , which have [0. E1 , the slider S is moved along the slide wire until balance is obtained i. A Figure Calculate the unknown e. E2 see Fig. Such devices may be constructed in the form of a resistive element carrying a sliding contact which is adjusted by a rotary or linear movement of the control knob.
Determine the e. A commercial or universal bridge is one which can be used to measure resistance, inductance Exercise 52 Further problems on the or capacitance. An unknown resistor Rx is connected between P and Q. Calculate the e. Equating the real parts gives: A Q-meter is described in section Determine the values of L and R assuming Equating the imaginary parts gives: the bridge is balanced.
For the a. The frequency is then varied until resonance causes voltage Vc to reach a maximum From equation 3 above, resistance, value. At resonance Vr and Vc are noted. If a variable capacitor C is L used and the oscillator is set to a given frequency, R2 D then C can be adjusted to give resonance.
Errors in measurement can exist with 1 A Q-meter measures the Q-factor of a series L- Q-meters since the coil has an effective parallel self C-R circuit to be at a resonant frequency capacitance due to capacitance between turns.
The of kHz. When connected to a Q-meter inductor. The Q-factor of the circuit is found to be and the capacitance of the Q-meter capacitor is set to pF.
Determine a the inductance, and b the resistance of the Errors are always introduced when using instru- ments to measure electrical quantities. The circuit diagram of a Q-meter is shown in Fig. Thus if a voltmeter has a f. The maximum possible error is Figure Hence the voltage, V D With linear scales the values of the sub-divisions Hence the voltage V may also be expressed are reasonably easy to determine; non-linear scale as Also, When reading a meter scale it should be which gives an indication of 6.
Neglect any loading affect that circuit to some extent. Meters require effects of the instruments. Incorrect posi- V For example, let a resistance be mea- I 6. However, in Fig. Hence the resistance of the resistor may 2. Determine the nominal value of the 5.
The arms of a Wheatstone measurement. Determine 75 V f.
0コメント