However, a meter being shown diagrammatically in Fig. When used to measure a. For the principle of operation of a moving-coil instrument, see Chapter 8, page For sinusoidal quantities the indication is An ammeter, which measures current, has a low quantities and it is assumed by the manufacturer that resistance ideally zero and must be connected in the a.
There is no difference between the basic instru- ment used to measure current and voltage since both use a milliammeter as their basic part. This is a Figure Such a diverting resistor is called a shunt. Thus for the moving-coil instrument to be used as From Fig. Thus the value of the multiplier, Problem 2. A moving-coil instrument gives a f. Calculate the value of the 0. The digital voltmeter DVM is one which provides a digital display of the voltage being mea- sured.
Advantages of a DVM over analogue instru- Now try the following exercise ments include higher accuracy and resolution, no observational or parallex errors see section Neglecting the resistance Instruments for a. With other instruments 4 mA. Determine the value of shunt resis- the indication is either scaled up from the mean tance required in order that f.
Calculate the value of the multiplier to for sine waves only. Such waveform errors can be be connected in series with the instrument so largely eliminated by using electronic instruments. Calculate the val- State the electrical resistance. A simple ohmmeter circuit mode of resistance connection in each case.
Unlike the ammeter or [ a If supplied to a load. Thus f. The milliammeter can thus be calibrated directly in ohms. When cal- An ohmme- ation on power taken from the circuit in which ter designed for measuring low values of resis- measurements are being made. Depending on the tance is called a continuity tester.
A volt- meter should have as high a resistance as possible Calculate the power dissipated voltage. If a battery is incorporated then resistance by the voltmeter and by resistor R in can also be measured. Such instruments are Fig. Assume that the voltmeter multirange instruments. Only one measurement can be performed at a time. Often such instruments can be used in a. Thus the power dissipated Problem 5. A voltmeter having a f.
In this case the higher load resistance reduced the power dissipated such that the voltmeter is using as much power as the load. An ammeter has a f. Calculate a the ammeter b The resistance of a voltmeter having a V reading expected neglecting its resistance , f. Thus the ammeter itself has caused the circuit conditions to change from 20 mA to What is the voltage across Determine the power dissipated in the load.
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Electrical measurements and measuring instruments. Electrical measurements and measuring instruments by E. Statement [by] the late E. Golding and F. A number of worked examples have been given as illustrations of points covered in the text, which is expressed in the rationalized MKS system of units.
Electrical indicating instruments — Essential features — Deflecting devices - Controlling devices — Damping devices. This book will be of interest to all students taking courses in electrical measurements as a part of a B.
Professionals in the field of electrical engineering will also find the book of use. Electrical indicating instruments — Essential features - Deflecting devices - Controlling devices — Damping devices. The instruments which are used for such measurements are called measuring instruments.
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