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ELECTRICAL AND ELECTRONIC MEASUREMENTS

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Nguyễn Gia Hào

Academic year: 2023

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This torque is proportional to the angular velocity of the system in motion and therefore only works when the system is in motion. The De Sauty bridge is a modified form of the Wheatstone bridge with the DC source replaced by an AC source.

Figure 7.1  |     Effect of damping on deflection.
Figure 7.1  |     Effect of damping on deflection.

MEASUREMENT OF CURRENT AND VOLTAGE

Using these gauges to operate a moving coil instrument would be impractical due to the bulk and weight of the coil required. It is determined by dividing the sum of the meter resistance (R . m) and the series resistance (Rs) by the full scale reading in volts.

MEASUREMENT OF POWER AND ENERGY

One-wattmeter method: In this method, the voltage coil of the wattmeter is connected across the phase and the current coil is connected in series with the phase. The current coils of the wattmeters 1 and 2 are in series with the two phases, R and B.

Figure 7.29  |     Dynamometer type wattmeter.
Figure 7.29  |     Dynamometer type wattmeter.

INSTRUMENT TRANSFORMERS

These windings are wound over a hollow tube and the primary winding is held between the two secondary windings. On the other hand, the primary current of a CT varies over a wide range under normal operating conditions.

Figure 7.38  |    Phasor diagram for CT.
Figure 7.38  |    Phasor diagram for CT.

CATHODE RAY OSCILLOSCOPE

The basic circuit of a digital multimeter is generally a DC voltmeter, so any parameter to be measured is first converted to voltage form. The analog voltage form is then converted to digital form using the analog to digital converter and the digital data is displayed in decimal or BCD form.

DIGITAL VOLTMETERS AND MULTIMETERS

The signal to be displayed is first amplified by the vertical amplifier and then applied to the vertical deflection plates of the CRT. A portion of the signal in the vertical amplifier is also applied to the sweep trigger as a drive signal.

Figure 7.45  |      Voltage difference V between horizontal  plates as a function of time t
Figure 7.45  |     Voltage difference V between horizontal plates as a function of time t

Q-METER

The resistance of the resistor must be very small (fractional in ohms) so that it can be neglected compared to the loss resistance of the components to be measured. The circuit for output measurement must be a high input impedance circuit so that loading of the tuned circuit by the measurement circuit is prevented.

TRANSDUCERS

A strain gauge is an instrument used to measure the strain produced on a wire by a force generated by varying the electrical resistance of the wire. Sometimes it is possible to obtain a linear approximation over a limited temperature range, which can be given by

Figure 7.51 shows a typical configuration of thermocouple.
Figure 7.51 shows a typical configuration of thermocouple.

ERROR ANALYSIS

Mean value is the most probable value for a set of measurements, which can be given as, . Calibration is the process of comparing the measured value of a particular instrument with that of a standard instrument.

IMPORTANT FORMULAS

The true values ​​can also be obtained from standard lookup tables prepared for this purpose. Calibration can be re-performed from time to time to reduce the effects of instrument wear over time.

SOLVED EXAMPLES

For the given circuit, if the voltmeter reads 60 V,. the value of the unknown resistance R will be. A passage through a secondary load of 1 Ω. The flux is established in the core by a current of 80 A.

PRACTICE EXERCISES

The ratio and phase angle errors of a current transformer can be magnified as. a) the conductor of both primary and secondary winding is taken with large cross sections. A 25 Ω shunt resistor is needed to increase the range of an ammeter from 100 mA to 500 mA. The value of the internal resistance of this ammeter is .

ANSWERS TO PRACTICE EXERCISES

Find the current range of the instrument when used as an ammeter with the coil connected through a shunt resistance of 1 × 10−3Ω. b). Choose the correct choice of the item in Group II for the corresponding item in Group I from the following.

SOLVED GATE PREVIOUS YEARS’ QUESTIONS

The probe is used to measure the voltage between P and Q as shown in the following figure. The bridge circuit shown in the following figure. is used for measuring an unknown element Z. The bridge circuit is best suited when Zx a. a) low resistance (b) high resistance (c) low Q inductor (d) lossy capacitor.

MARKS DISTRIBUTION FOR GATE QUESTIONS

ANALOG ELECTRONICS

SEMICONDUCTOR PHYSICS

Such impurities make positive carriers available because they create holes that can accept electrons. the electron and hole component. The direction of the field forces the electrons in the opposite direction, since the electron has a negative charge. The negative sign in the equation indicates that the electron drift velocity is opposite to that of the applied electric field.

The direction of the field produces a force on the holes in the same direction, due to the positive charge on the holes.

Figure 8.1  |     Energy and structure (a) insulator,      (b) semiconductor and (c) metal.
Figure 8.1  |    Energy and structure (a) insulator, (b) semiconductor and (c) metal.

SEMICONDUCTOR DIODES

If the doping concentration is not changed, the increase in charge can only occur if the width W of the depletion region increases. As a result, the width of the depletion region is reduced and there is a decrease in the barrier potential across the junction. D will appear in the diode and when it is biased, one of the capacitances will be primarily present.

The equivalent circuit of a diode (or other device) is the combination of elements that make up the device in the correct order.

Figure 8.10  |     Reverse bias PN junction. (a) Circuit.
Figure 8.10  |     Reverse bias PN junction. (a) Circuit.

TRANSISTORS

As the collector-to-base junction voltage increases, the width of the collector junction depletion region increases. It refers to the change in base region width with change in collector-base voltage and is shown in Fig. The output resistance (r . o) is the reciprocal of the slope of the output characteristics in the active region.

The input characteristics of the transistor in the common emitter configuration represent the ratio of the base current I.

Figure 8.26  |     Bipolar junction transistors: (a) pnp type  and (b) npn type.
Figure 8.26  |     Bipolar junction transistors: (a) pnp type and (b) npn type.

FIELD-EFFECT TRANSISTOR (JFET AND MOSFET)

  • MOSFETS

DG, the conductive portion of the channel begins to contract more at the drain end. If the negative voltage at the gate is further increased, depletion layers meet in the center and the drain current I. The region of the curve in which the drain current ID remains fairly constant is called the pinch-off region.

It is also called the static or ohmic resistance of the channel and is defined as ratio of drain-source voltage and drain current.

Figure 8.55 |       JFET with (a) no external bias volt- volt-age and (b) small negative gate source  bias.
Figure 8.55 | JFET with (a) no external bias volt- volt-age and (b) small negative gate source bias.

SIMPLE DIODE CIRCUITS

For a shunt clipper (negative), the circuit, output waveform, and transfer curve are shown in Fig. b) output waveform and (c) transfer curve. For symmetrical clipping, the circuit, output waveform and transfer curve are depicted in the figure. The waveforms of voltage ripple and DC voltage superimposed ripple are shown in Figure b) DC voltage superimposed ripple.

8.96(a) and (b) and the input and output waveforms are shown in Figs. showed. a) Ideal circuit, (b) practical circuit and (c) input and output waveforms.

Figure 8.79  |     Shunt clipper: (a) circuit (b) diode  reverse bias and (c) diode forward bias.
Figure 8.79  |     Shunt clipper: (a) circuit (b) diode reverse bias and (c) diode forward bias.

STABILITY AND BIASING

The stability of the self-biased circuit is further improved if the input side is modified as shown in Fig. A diode is placed across the base-emitter terminals of the transistor to compensate for variation in the leakage current ICO as shown in Fig. self-bias configuration eliminates the need for two DC supplies as required in fixed-bias configuration.

GS is a function of the output current ID and is not a fixed size as in the case of a fixed bias configuration.

AMPLIFIERS

It is the ratio of the input voltage to the output voltage with the input current equal to zero. The current drawn by any of the input terminals (non-inverting and inverting) is negligible. The following analysis is performed assuming that the op-amp is an ideal one, i.e. A. The voltage of node a at inverting input terminal is grounded.

The input current can be written as I. o is proportional to the log of the input voltage.

FREQUENCY RESPONSE

It is a flat response at the upper cutoff frequency, which is determined by either the parasitic capacitances of the circuit or the frequency dependence of the gain of the active device. C is usually connected between the output of the active device and the applied load, the RC configuration that determines the low cutoff frequency due to C. In the high frequency range, the capacitive elements of importance are the internal capacitances between electrodes of the active device and the line capacitance between wires in the network.

The two poles of this circuit change the cutoff frequency and the response of the circuit.

ACTIVE FILTERS

The voltage gain magnitude equation for the second-order high-pass filter is given as. High-pass active filter is the complement of low-pass active filter and formed simply by exchanging the place of resistors and capacitors in the frequency-determining section of the filter (Fig. 8.187). A wide bandpass filter can be formed by simply cascading high-pass and low-pass sections as shown in Fig.

An all pass filter is one that passes all frequency components of the input signal without attenuation, but provides predictable phase shifts for different frequencies of the input signals.

OSCILLATORS

The circuit consists of a common-source FET amplifier followed by a three-part phase-shift RC network as shown in the figure. 180° between the amplified output voltage V. The total phase shift from the gate around the circuit and the back of the gate will be exactly zero at this frequency.

When the required phase shift of 180° is achieved, this network shifts the output voltage by a factor of 1/29.

MULTIVIBRATORS

This is for the fixed-bias type bistable multivibrator and fixed bias with commutating capacitors is shown in Fig 8.203(b). The output of the timer depends on the amplitude of the external trigger pulse applied to this pin. So either the external voltage or a pot connected to this pin determines the pulse width of the output waveform.

1 is a variable reference threshold voltage that depends on the value and polarity of the output voltage V.

SAMPLE AND HOLD CIRCUITS

The operating current is given by I=nqv A. i) Charge density of free electrons (ii) Current density. iii) Current flowing in the wire (iv) Speed ​​of electron drift Solution:. Then the drift velocity and the time it takes the electron to travel 10 mm in the crystal. Solution: In the given circuit, the germanium diode is forward biased and the output voltage is replaced by .

The data sheet for the MOSFET gives I. The circuit given in the figure below uses two.

Hình ảnh

Figure 7.18  |    Kelvin double bridge circuit.
Figure 7.23 (a) shows an arrangement for measurement  of  high  resistance  in  cables  having  metallic  sheath  by Since I
Figure 7.27  |    Ammeter with a shunt resistance.
Figure 7.29  |     Dynamometer type wattmeter.
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