Husnen Rupani:
Measuring resistance is one of the most fundamental tasks in electrical and electronics industry, and the instrument used for this is called an ohmmeter, which is named after the measurement unit of resistance, ohms. In this video, I’ll show you how to measure the resistance of three different types of components, a power resistor, a color-coded resistor, and the resistance of a transformer winding. I’ll do this using three different types of meters, an analog multimeter, a digital non-auto ranging multimeter, and a digital auto ranging multimeter. Before we get started, you need to remember two main things when using an ohmmeter. First, isolate the supply. Since an ohmmeter has its own battery, connecting it to another power source can, at the very least, give you incorrect reading or worse, damage the meter. And second, connection should be across the component. Let’s get started.

Let’s use an analog multimeter to measure resistances of the three components we talked about earlier. Before we get started, we need to set our multimeter to ohms scale, so I’m going to do that. Right now, my multimeter is set to times one scale. First step always is to test the tester, and to do that simply for an ohmmeter, you just connect the two probes together and read the scale.

Now, my scale is very close to zero, so that’s okay. So to measure the resistance of this component, which clearly mentions that it’s 20 R or 20 ohm resistor, we’re going to connect one probe on one side and the other probe on the other side, and we can see that our needle is pointing at 20, so it seems quite accurate there.

Now we’re going to measure the resistance of this color-coded resistor here. And then when we connect the probes to each side of this component, we get a reading that’s just around 500. So to be able to measure it more accurately, I’m going to change my setting to times 10 scale. By reconnecting these two probes, I can see that the value is just around 400, 450 ohms.

Now, let’s measure the center-tap winding of this transformer by connecting our probes to these two terminals, and we can see how the resistance value is 500 or just around that, so 50 times 10, so that’s 500 ohms resistance.

Let’s measure those three resistances using a non-auto-ranging digital multimeter. Same as before, because it’s a multimeter, we need to change the setting to ohms scale, which is on this side. So I’m going to go to 200 ohms. As usual, our first step is to testing the tester. Connecting these two, we should get roughly zero. We’re getting one, so there is a small margin of error here.

Okay, let’s measure our first resistor, the power resistor, and we’re getting approximately 21.5, and there was an error of 1 ohm. So if you deduct that, then you get about 20 ohms of resistance. Now, let’s measure the resistance of this color-coded resistor, which was clearly around 450. As you can see how it’s still showing open line, that’s because my manually ranging meter is at 200 ohms, and that resistance there is clearly more than 200, so we’ll change our setting to higher than 200. As soon as we do that, we get a reading, 0.45 kilo ohms or 450 ohms.

Now, let’s measure the winding of this transformer. So by connecting it to those two terminals, I can see that the resistance of that winding is 0.58 kilo ohms or 580 or 570 ohms. Let’s use a digital auto-ranging multimeter this time to measure these resistances. Now, since it’s an auto-ranging meter, it doesn’t have a lot of options. All it has is ohms and the meter will automatically adjust its range. So let’s set it to ohm scale first.

As usual, our first step is to test the tester. By connecting these two terminals together, I’m getting approximately 1 ohms. Okay, let’s measure our first resistor here, and the resistance is 21.3 ohms. Let’s measure our color-coded resistor, 0.466 kilo ohms or 466 ohms. Let’s measure our transformers winding, 0.588 kilo ohms or 588 ohms.

In the electrical electronics industry, there are many occasions when you would need to measure resistance. Here are some examples: correct circuit connection and polarity tests, resistance of an unknown or a variable resistor, earth resistance test, resistance of transformer or motor windings, contactor or relay coil resistance, and many more.

There you have it, how to use an ohmmeter, basic safety and its application. If you found this video informative, please like it. Thanks for watching.