My question is, what is really the use of shunt ohmmeter? Are series and shunt measuring range same but with opposite deflection?
Once you understand how the measurements of current and voltage are done, the rest is simple.
Resistance is always measured indirectly, either as a current or a voltage. It is an active measurement.
If you want to measure an unknown resistance, you have two options.
1. Apply a const voltage and measure the current current flow. As the V is constant, R will be inversely proportional to the current. So this will give you a non-linear scale, zero current corresponding to an infinite resistance. Good for measuring high resistances.
2. You can also apply a const current through a resistor and measure the voltage across it. Now the voltage drop will be linear and proportional to the resistance. Zero voltage drop now corresponds to a zero resistance. Good for measuring low resistances.
(in real life, the scales are not linear - or reciprocal - because all voltage measurements take some current and all current measurements cause some voltage drop. In other words, all meters have some finite resistance).
I hope you should be able to understand the basics now.
For measuring very high resistances, we use a very high applied voltage (say 100-500V) and measure the very small current using a sensitive meter. For measuing very low resistances, we pass a very high current and measure the voltage drop using a sensitive voltmeter (four point probes are needed).
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