Multimeters considered helpful


#1

[Permalink]


#2

When I was 8 or 9 this was the bets present my dad ever gave me. It was a 30k to the volt moving coil multimeter. Best toy a kid could have and the only present I can clearly remember now, 30 years later.


#3

Splendid!

When teaching garage physics, I make sure that each kid uses a multimeter.

Yes, start with the continuity beeper. Perhaps the most handy part of the meter.

Now, pass around a few resistors: 10 ohms, 50 ohms, a hundred, etc. A few are little half-watters, a 5 and 10 watter, maybe a honking 25 or 50 watt resistors. Measure their resistance -- does the meter agree with the resistor's markings? Does the physical size of the resistor say anything about its resistance?

Now set up a battery - what's its voltage? Clip it to a resistor and measure the current. Did Ohm get it right?

For icing on the cake, get the kids to hook a few resistors in series or parallel. Is Kirchoff smiling?

One joyous occasion, I scribbled a complex series/parallel circuit for my 8th graders; one girl thought about it, and went ahead and simplified the circuit - after numerous calculations, determined that the total resistance should be 15.7 ohms. Three other kids took up her challenge. They got a handful of clipleads and built the circuit. After 15 minutes of connecting and arguing, they measured the resistance of the network. To everyone's amazement, the multimeter read 15.7 ohms. One of those classroom experiences that the teacher never forgets...

At the end of the class, each student keeps her multimeter ($10 at Al Lasher's in Berkeley).


#4

I going to file that headline in the same place as the one I wanted to see when the Queen Mother died

One hundred and one year old woman dies of natural causes.


#5

LOVED!!! This was so cool - and so nice to see Lady Ada too! Strangely enough lots of computer nerds venture to electronics but have only read and touched and not had another's explanation. Wonderfully captured!!!


#6

It's a basic tool that everyone should learn how to use. It only looks complicated to the uninitiated, but will save you a lot of time -- and sometimes money -- in the long run.


#7

Is it just me, or wouldn't it be reasonable to expect that makers would own a multimeter before they own a breadboard?


#8

A multimeter transforms electronics from tinkering to science, via numbers. That's a big step. Its not surprising that the breadboard would come first, then the multimeter to help understand what's going on.


#9

And extra points for Lady Ada's Electric Giraffe Project t-shirt - you'll see it around Maker Faire, Burning Man, and other kinds usual suspect places where a large robotic giraffe might show up. (And cool tie, Colin!)


#10

Well, from personal experience, it would seem to me that if you're curious enough about electronics to consider making something using a breadboard, you would be curious enough to learn from electronics near at hand.

Y'know, take older non-functioning stuff apart (say, a toaster) to see how it works or doesn't. At some point, you might realize that you need a multimeter (as you hazily recall using one in high school physics).

Edited to add: "Multimeters considered helpful"? Ahem: Multimeters are considered essential!

Also, really, really, really good analogue meters are such beautiful pieces of equipment. I've handled that Simpson meter in the video - quality manufacturing. Mind you, give me a modern digital ultra-high impedance meter over them, any day.


#11

Multimeters have been a major tool for me for nearly 50 years. I started building a kit Heathkit VTVM (Vacuum Tube Volt Meter) that took a big chunk of my savings to purchase in 1968 but it was mine no more borrowing form others. Today I use a digital multimeter for everything but audio measurements (audio requires a higher impedance input and a real meter movement for accuracy IMHO I use an FET voltmeter). The one piece of advice I have is to get the best test leads you can afford they make all the difference. Meter probes need to be as sharp as a hypodermic injection needles to cut thru the thin layer of oxide on pc boards and component leads to get accurate measurement and to make it easier to get an accurate measurement. The other advantage of sharp probes is the bite into the contact and don't slip around causing shorts. Back in the day test probes were made that used steel phonograph needles as replaceable tips. Today there are some great probes, I prefer the type that have insulated telescoping tips that allow you to get into tight places with ease. If you don't have good probes you will likely have a lot of bad measurements. For the other connection a good alligator clip connected to ground if possible since making measurement with 2 probes is clumsy and should be avoided if possible (besides if the device under test is powered up one of your hands should be in your pocket for safety). Today a decent digital multimeter is dirt cheap and everyone should have one of their own.


#12

I'd like to know more about measuring resistance while a component is in a circuit...

If an adult is learning this I can see how it'd all come at the same time, breadboard, components, meter, soldering, ect.. As a child I had a basic meter even before I had a soldering iron. There's a lot to tinker on that doesn't have circuit boards that a meter is extremely helpful for.


#13

Measuring resistance in circuit is a bit tricky. The reading will be affected by all possible electrical paths possible i.e. other resistors and even semiconductors (if there is sufficient current to turn them on). Even pro electronic techs lift one end of the resistor for accurate measurements. It is possible with experience to check resistors based on the voltage across them when the power is on. The good news is that resistors usually are either good or when bad are an open circuit (burned out) they rarely change resistance or cause problems like intermittent faults (old carbon comps can shift value but they are not used much except by guitar amp and FX manufacturers). In my many years of repair the most common fault I found is bad connections (cold solder joints, bad grounds, dirty connectors, bad tube sockets etc.) followed by bad semiconductors. But back to measuring resistance I do voltage readings around the circuit while it is operating and find the bad component by analyzing the various voltage drops. Again experience is the most necessary tool in the toolbox. Of course sometimes it is not possible to just run the circuit if it is drawing excessive current but there are some tricks that I use to get around that problem. The best thing to do is keep trying, study schematics and most of all studying electronics. Sorry for the long answer.


#14

I certainly don't doubt that the decent-to-excellent seats are all occupied by digital units these days; but for certain applications (if you are stuck using a cheap unit of one sort or the other) the analog meters have their virtues: Both cheapie analogs and cheapie digitals have annoyingly long 'settle' times; but at least the analogs twitch visibly while attempting to settle. If you are trying to pick up transient voltage changes, or the rapidly changing resistance as you jiggle a failing connector, or similar situations, some cheap digitals will simply sit there and fail to display anything too fast for them to settle on, while the analogs always show you that something is up.

Once things get classy, of course, the analog multimeters can do little more than upgrade the bearings and add higher-spec passives, while the digitals get all kinds of neat features (Especially when juggling more than one meter, Serial logging is my friend...)


#15

Incidentally, a cheap DIY method of ensuring that your meter probes are that sharp is to use needles. Depending on the brand, you may need to snip away some plastic; but the sampling lancets used for diabetes care are crazy sharp and comparatively inexpensive in boxes of 100 or so. A touch of soldering to connect the needle to the wire, and you've got something that will bite right through oxide, conformal coating, etc. and plenty of backups for when the first becomes dull or snaps.


#16

My dream non-bench/portable multimeter has multiple displays:
You could show DC voltage on one display and AC on the other, so you could see if there's any ripple in the DC voltage without reaching over to the meter and switching it. Some time ago, I found a Brunelle Instruments meter that had four displays. Nifty.

Back in university, I had to measure voltages for a physics class lab. All of the other students had to use cheap-but-tough analog instruments whose impedance, if I recall, was something like 1,000 ohms. You could tell when the VOM was measuring: the circuit's power supply transformer's hum would change pitch, under the VOM's load. Me, I brought my own tools. Heh.

However, I agree with you, being able to watch the needle's behaviour on a good VOM can give you valuable information.


#17

This topic was automatically closed after 5 days. New replies are no longer allowed.