Anyone with newbie guides/tips for using them, please post a link for us who are just beginning.
Thanks
digital multimeters are easy to use but you need to know when you would want to check voltage, when to check resistance (measured in ohms) and when to check current (measured in amps).
Voltage is the potential (power) to do work. A charged car battery sitting on the floor will have 12 volts across the posts. No current will be flowing since it is not connected up to a load. When I use my meter I am most often checking a voltage.
Lets say I have a light that isn't working. I might use my meter to see if it is getting voltage. With the light switch on and the bulb still hooked up I should read 12 volts. If I do read 12 volts I know it's getting the voltage it needs to work. Since the light isn't coming on I now suspect the bulb is bad. To double-check I can now check resistance through the bulb.
To check resistance you should always remove the component, in this case the bulb. With the bulb in hand I try to read the resistance. Resistance is measured in ohms. My meter may say it has infinite ohms. Actually my meter may not do anything as I put the leads on a bulb that is bad. I would double check to make sure I really am holding the leads on the bulb correctly. To test my meter I would then touch both my leads together. Now the meter says 0 ohms. So the bulb is bad. Okay I have a bad bulb. No electricity can go through it.
Another measurement the multimeter can read is current. It is not very often that I read current. The reason is you must break the circuit to read current. Let's say I wanted to measure the amount of current going through that bulb I suspected was bad. I would have to remove
one wire from the bulb. I would then put one lead on the wire that I removed. Put the other lead on the bulb where the wire was. Now with the lights on the current would have to go through my meter and then through the bulb. It is a pain to test a bulb this way.
It is even a bigger pain because the makers of multimeters have you plug the lead into a different spot on the meter. Notice the 3 places to plug leads into this meter.
Why do they do that? Because if you have your meter set up to read current and you accidentally try to read voltage then you will fry your meter. High current will flow through your meter. Actually the fuse in the meter will blow first. To read current they want you to take 2 steps - move the leads and turn the dial to current.
Now to put this all together with an analogy, Lets say you are at a large water tower. There is a big 12 inch pipe coming down from the water tower to ground level. There is a big cap on the pipe. The water behind that cap is under high pressure (think voltage). If you take the cap off you will be knocked across the street from the watter blast. Why? Because that big pipe has very low resistance (think ohms). You get the full power of that water pressure.
On the other hand if that was a straw coming down from the water tower there would be very little water coming out. Why? Because that little straw has high resistance. It may shoot very far from the pressure (same pressure as the big pipe). Actually that straw would probably burst. Even though it is small it would have to be a steel pipe to handle the pressure.
This tiny pipe with high pressure can be compared to an ignition wire. A spark plug needs
very high voltage - thousands of volts. But it uses very little current (amps). An ignition wire has a very small conductor in the core but it has a very thick rubber insulation. Open the hood of a car with bad ignition wires at night and you will see sparks going from the wire to the engine block or any other ground. This is comparable to that old straw coming down from the water tower with lots of leaks.
There that's it. But now I wonder: Is any one still reading my ramblings?
