Identification of resistor, capacitor and inductor using Ohm meter

Identification of resistor, capacitor and inductor using Ohm meter

In our previous section, we discussed about the ac and dc response of a resistor, capacitor and inductor. In this section we will discuss, how do we identify resistor, capacitor and inductor using ohmmeter.Before going to discuss, we should kept in mind the following fact.

In a circuit,

1. When voltage is maximum, current will be minimum.

2. When current is maximum , voltage will be minimum

3. If resistance is maximum, current will be minimum and voltage will be maximum

4. If resistance is minimum , current will be maximum and voltage will be minimum

5. If resistance increases with time, than, voltage will also increase with time and current will      decrease with time.

6. If resistance decreases with time, voltage will also decrease with time and current will increase  with time

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Resistor identification using ohm meter

As we know that, ohm meter is used to measure and identify resistor. The characteristic of a resistor is given below:

Fig-1: Resistor Characteristics

From the figure we see that, current is increasing with voltage. And for a particular value of voltage , we will get a particular value of current.  And if we divide the voltage by the current, we will get the resistance.

For example, if we apply 10 V and we will get 10A current, Therefore, the resistance of the resistor will  be 

R  = V/ I = 10V / 10A = 1 Ω

Again if we increase the voltage to 20V, we will get current of 0.5A, Therefore the resistance will be

R  = V/ I = 20V / 0.5A = 1 Ω.

Now if we take resistor and the two leads of ohm meter connect with the resistor lead, then the ohm meter shows a fixed value of resistance. And with time this value will be constant.  So a component among resistor, capacitor and inductor, if that component shows a fixed resistor and do not change with time, than that component will be a resistor.

Capacitor identification using ohm meter:

The characteristics and DC response is discussed in previous section:

From the graph we see that, at time t = 0, current is maximum and voltage is minimum. And with time, current decrease and voltage increase.

From the fundamental electrical knowledge, we know that, in a circuit, if current is maximum, than, voltage will be minimum and current will be maximum if resistance of the circuit is minimum. Therefore, in a circuit, if resistance is minimum, current will be maximum and voltage will be minimum and if resistance is maximum, current will be minimum and voltage will be maximum.

Now if we connect a two lead of ohmmeter with the two lead of a capacitor, then we see that, initially the ohmmeter shows low resistance and with time resistance increase. That means initially maximum current will flow through the capacitor and voltage drop will be minimum. And with time, as resistance increase, that means, current decrease through the capacitor and voltage drop will increase with time. If we see the characteristics of a capacitor, we see  that , initially current is maximum and with time it decrease and initially voltage is minimum and with time it will increase.

So if we connect a component with a ohmmeter, and initially it will show low resistance and with time resistance will increase, then this component is a capacitor.

Inductor identification using ohm meter:

The characteristics and DC response is discussed in previous section:

From the graph we see that, at time t = 0, voltage is maximum and current is minimum. And with time, current increase and voltage decrease.

From the fundamental electrical knowledge, we know that, in a circuit, if current is maximum, than, voltage will be minimum and current will be maximum if resistance of the circuit is minimum. Therefore, in a circuit, if resistance is minimum, current will be maximum and voltage will be minimum and if resistance is maximum, current will be minimum and voltage will be maximum.

Now if we connect the two lead of ohmmeter with the two lead of a inductor, then we see that, initially the ohmmeter shows high resistance and with time resistance decrease. That means initially minimum current will flow through the inductor and voltage drop will be maximum. And with time, as resistance decrease, voltage drop will decrease across the inductor and current will increase with time. If we see the characteristics of a inductor, we see that, initially current is minimum and with time it increase and initially voltage is maximum and with time it will increase.

So if we connect a component with a ohmmeter, and initially it will show high resistance and with time resistance will decrease, then this component is a inductor.