Topic: Measuring Instrument , Most expected Questions From the selected topic.
Q1. Resolution of an instrument may be defined as:
(a) the maximum quantity it can measure.
(b) the minimum quantity in can measure.
(c) the minimum non-linearity of instrument.
(d) the maximum non-linearity of instrument.
Q2. Torque/weight ratio of an instrument indicates
Q3. The error introduced by an instrument is categorized in:
(a) Random Errors
(b) Gross Errors
(c) Systematic Errors
(d) Environmental Errors.
Q4. In a moving iron instrument, the hysteresis error may be reduced by using:
(a) High speed steel
(b) stainless steel.
(c) silver coating.
(d) Mumetal or Permalloy.
Q5. The deflecting torque of moving iron instrument is:
(b) 1/2 I²dL/dθ
(c) I dL/dθ
(d) 1/2 I dL/dθ
Q6. AC signal with RMS value 2√2 V, is applied to a PMMC instrument, then the reading of the instrument will be:
(a) 2√2 V
(b) 4 V
(d) 1/√2 V
Q7. The value of Resistance Rs to be added in series with ammeter whose full-scale defection is of 0.1 mA and internal resistance is of 500Ω, to make it suitable to measure (0-10) V is.
(a) 99.5 K Ω
(b) 0.04 K Ω
(c) 96.5 K Ω
(d) 199.5 K Ω
Q8. The minimum number of watt-meter(s) required to measure 3-phase 3-wire balanced or unbalanced power is:
Q9. If an energy meter disc makes 10 revolutions in 100 seconds when a load of 450 W is connected to it, the meter constant (in rev/kWh) is
Q10. Megger is an instrument used for measuring:
(a) A very high voltage
(b) A very high Resistances
(c) A very low voltage
(d) A very low Resistances
Sol. Resolution can be defined as the minimum quantity in can measure.
Sol. Systematic error
Sol. Mumetal or Permalloy.
Sol. 1/2 I²dL/dθ
Sol. With high frequency signal the PMMC will reflect the average value which will be Zero.
Sol. Resistances Required to connect in series:
R series = V/I_m -R_m
= 10/(0.1×10^(-3) )-500
= 99.5 KΩ
Sol. Minimum Two watt-meter are required.
Sol. Energy consumed in 100 second.
Given load= 450 W
Meter constant in revolution per kWh
= (Revolution by meter)/(Energy consumed)
= 10/0.0125 rev/kWh
Sol. Megger is used to measure very high resistance.