Today let's talk a little about using our multi-meter in building your home power generation project. You might be using any of the alternative energy power generation type programs. The ability to measure accurately and correctly is essential.
I have an analog meter in front of me. I really believe that if you learn not only what the measurements are but what they mean and where they come from, then you will be a better meter person.
The other day we discussed the parts of the meter. Today we will get into using the meter itself. First, let's talk about using the Ohm function to measure resistance. Machine turned on? Let's do it.
If you're not too sure what ohms or resistance means in electrical terms, stop a few minutes and look it up. It's right here in the internet. Look it up and get a basic understanding. I'll wait.
OK? Great. Pick up your machine and set the meter to Resistance or Ohms. Check to see if your meter has a separate switch for this function.
Now think about this. Electrical resistance and electrical continuity are actually exact opposites. Right? Resistance is holding back the electrons and continuity is allowing free movement.
Your meter will use ohms to measure the resistance. There is no measurement for continuity. If you have no resistance, then you have continuity. Right? Stay with me now.
The less resistance you have, the more continuity you will have. What all this means is that when you accurately measure resistance, you can make assumptions about the continuity.
Ok, look at your meter. Have your test leads sitting alone and not touching anything. Then look at your dial. The pointer (or needle) of the dial should be clear over at the left position. This shows you have an "open circuit." You would be safe in saying that there is no continuity between your red probe and your black one. Still with me?
Now look at your OHM scale. It should be the top most scale and you will note the values are highest on the left side of the dial and they gradually reduce to "0" on the right. Note now that this is the opposite of the other scales. They will have the lowest values on the left and keep increasing as you move right.
This is pretty basic stuff, but most important. If it seems somewhat hazy, go back and reread. This will be all routine in a short time, but only if you get it right now.
Ok, let's work with the meter a bit.
I have an analog meter in front of me. I really believe that if you learn not only what the measurements are but what they mean and where they come from, then you will be a better meter person.
The other day we discussed the parts of the meter. Today we will get into using the meter itself. First, let's talk about using the Ohm function to measure resistance. Machine turned on? Let's do it.
If you're not too sure what ohms or resistance means in electrical terms, stop a few minutes and look it up. It's right here in the internet. Look it up and get a basic understanding. I'll wait.
OK? Great. Pick up your machine and set the meter to Resistance or Ohms. Check to see if your meter has a separate switch for this function.
Now think about this. Electrical resistance and electrical continuity are actually exact opposites. Right? Resistance is holding back the electrons and continuity is allowing free movement.
Your meter will use ohms to measure the resistance. There is no measurement for continuity. If you have no resistance, then you have continuity. Right? Stay with me now.
The less resistance you have, the more continuity you will have. What all this means is that when you accurately measure resistance, you can make assumptions about the continuity.
Ok, look at your meter. Have your test leads sitting alone and not touching anything. Then look at your dial. The pointer (or needle) of the dial should be clear over at the left position. This shows you have an "open circuit." You would be safe in saying that there is no continuity between your red probe and your black one. Still with me?
Now look at your OHM scale. It should be the top most scale and you will note the values are highest on the left side of the dial and they gradually reduce to "0" on the right. Note now that this is the opposite of the other scales. They will have the lowest values on the left and keep increasing as you move right.
This is pretty basic stuff, but most important. If it seems somewhat hazy, go back and reread. This will be all routine in a short time, but only if you get it right now.
Ok, let's work with the meter a bit.
- First, connect the black test lead to the jack marked "common" or "-".
- Now connect the red test lead to the jack that is marked with the Omega (Omn symbol) or you might see the letter "R" near it.
- If you machine allows it, set your range to R X 100.
- Now take the test leads at the end of the probes and hold them together. Your pointer on the dial should move all the way to the right. Now find the "zero adjust" knob and rotate it so that the meter moves to "0" or as close to "0" as possible. You will be able to see that this position is what is called the "short circuit" or "zero ohms" indication for this range (R X 1) ALWAYS REMEMBER TO "ZERO" YOUR METER IMMEDIATELY AFTER CHANGING THE RESISTANCE RANGES.
- If you are unable to obtain a zero ohm indication on your meter, it could be that you need to replace weak batteries. Retry these steps after you replace the batteries.
- Now let's measure the resistance of a good lightbulb. Find the two electrical contact points on the base of the bulb. They are right on the bottom. Have someone hold the bulb by the glass only while you press the black probe against the threaded base and the red probe against the center tab on the base. Now watch the needle move from its resting place at the left and zoom quickly to the "O" over on the right.
- Now change the range of you multi-meter to R X 1. Zero the meter once more for this new range. Now repeat what you did before and note how this time the meter does not go as far to the right like it did a while ago. Why? Because the scale of resistance has been moved. The scale you select is very important. Each number on the R scale can be read directly. Try all different ranges and you will see what I mean. This is good experience. It is essential that you understand the different ranges. This is important: The values that you find on the left side are harder to read accurately than those on the right. You need to prove this to yourself. Read 5 ohms on the meter while in the R X 100 range. It looks similar to 0. Now try it at R X 1 range. Much easier. Here is an important point to remember: When you are testing resistance, try to adjust the range so that the readings you obtain will be taken from the middle of the dial, rather than the far right or left.
- One more thing and then we will quit for the day. Let's test the resistance between hands. Zero your meter when you have set it to the highest R X value that is possible. Hold one of the probes in each hand very loosely and read the meter. Now squeeze both probes very tightly. Did you note the resistance reducing? Let go of both probes and wet your hands. Pick them up again. Note the resistance is now lower. This should show you why it is so important that the probes do not touch anything than exactly what is being tested. Your fingers can provide an alternate path for the electrons when your fingers are touching the probe. An older glass automotive fuse lying on a metal surface will indicate the resistance of the metal surface. If you are not careful, each and every fuse, good or bad, will register as "good" no matter of the reality of the matter.
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