01․ A high frequency AC signal is applied to a PMMC instrument. The RMS value of the AC signal is 2V, the reading of the instrument is
The permanent magnet moving coil instrument or PMMC type instrument uses two permanent magnets in order to create stationary magnetic field. These types of instruments are only used for measuring the DC quantities as if we apply AC current to these type of instruments the direction of current will be reversed during negative half cycle and hence the direction of torque will also be reversed which gives average value of torque zero. The pointer will not deflect due to high frequency from its mean position showing zero reading. However it can measure the direct current very accurately.
02․ Deflection method direct measurements are most widely used as these are
In deflection method direct measurements, the value of the unknown quality is determined with the help of measuring instruments having a calibrated scale indicating the quantity under the measurement directly, such as measurement by current by an ammeter. This process is also less time consuming.
03․ Potentiometer method of DC voltage measurement is more accurate than direct measurement using a voltmeter because
Since the circuit is not loaded, the accurate value of DC voltage is measured.
04․ In AC circuits, the connection of measuring instruments cause loading effect errors which may effect
The incapability of a system to faithfully measure, record or control the measured signal in undistorted form is known as load effect. This results in loading errors. However, under practical conditions, it has been observed that the introduction of any element of system results invariably in extraction of the energy from the system, thereby distorting the original signal. This distortion may take form of attenuation waveform distortion, phase shift, etc and consequently the ideal measurement becomes impossible.
05․ Relative error is same as
Relative error is the ratio of absolute error to the true value of the unknown quantity to be measured.
06․ When checked with an ohm meter an open resistor reads
Open resistance means that the resistance of air gap. The air gap resistance is obviously infinite. Hence, if we use an ohm meter to measure the open resistor, then it reads infinite.
07․ Which of the following is a variable displacement transducer?
A potentiometer is a device that can be used to convert a linear or angular displacement into a voltage. A potentiometer is a variable resistance whose value varies according to the angular or linear displacement of the wiper contact. The potentiometer meter is a variable displacement transducer used as error detector in control system applications. The pair of potentiometer act as a detector. The order of a potentiometer is zero.
08․ An current of is measured with a thermocouple, 5 A full scale meter. What is the meter reading?
09․ Piezoelectric effect is carried out in
In piezoelectric effect when a mechanical strain is applied to one face of a suitably cut face of a piezoelectric crystal, it causes an emf to be developed in opposite surface of that piece. Reverse is also true.
10․ A current of is measured with a thermocouple, 5 A full scale meter. What is the meter reading?