>> How to use a digital multimeter
IAN: Hi!
This is Tony and Ian from Tektronix.
We are here in beautiful, scenic conference room three to talk about digital multimeters;
DMMs.
TONY: With the beautiful wood tables.
IAN: So what's the plan for today?
TONY: You know, like our last video, we kept it simple.
We're just going to talk about the main features [what is a digital multimeter, how to use
a digital multimeter, and digital multimeter basics] and we're going to give some examples
of how to use a digital multimeter.
IAN: Well, let's jump right into it.
TONY: OK.
IAN: At its heart, a digital multimeter is a device for measuring voltage, current and
resistance of electronic components.
They do a lot more than that, but that's really where it starts.
TONY: What you see here is an illustration that mimics what we have actually on the breadboard.
IAN: Right.
We've got a battery and two identical resistors.
IAN: We'd like to measure the voltage drop across those resistors, so we're going to
put our digital multimeter into voltage mode, and we're going to attach some probes to it,
and we're going to measure the voltage across both of those.
Let's do that now.
IAN: That's 0.809 volts... and 0.808 volts.
So the voltage drop is pretty close.
TONY: Yeah, that is pretty similar.
But it's a little bit off and it's so nice to be able to see it here.
IAN: Right.
Because back in the old days...
This is my first multimeter; an analog multimeter.
And my grandfather gave it to me about 25 years ago, by my nearest calculation.
TONY: And would this be your grandfather?
IAN: That would be my grandfather, yeah!
TONY: Well, we'll leave him on here whilst we talk about it.
IAN: Alright, so you watch the needle.
Do you want to set that down on the table here?
TONY: OK, sure.
IAN: And you watch the needle, whilst I attach the probes.
This is 15 volts here.
Each tiny tick is one volt so we want it to move about three-quarters of one of those
small ticks.
That's what we expect.
TONY: OK.
IAN: Does it look it moved about three-quarters of a tick?
TONY: Yes.
They looked like they moved the same.
IAN: Right, and they are pretty close...
TONY: Yes.
IAN: ...But I certainly couldn't tell the difference between 0.808 and 0.809 volts on
this.
TONY: Useful, but...
IAN: ...Technology has moved on!
IAN: So we found that the resistances were different by measuring the voltage but we
can actually just measure the resistance directly.
TONY: Oh, and that would require unplugging the source, right?
IAN: Right.
Pull the battery out of the equation and I'm going to put the digital multimeter into resistance
mode and so we get about 2.166 k ohms and 2.163 k ohms.
TONY: Well this screen is so convenient.
I mean, it's so easy to read.
IAN: And so these are supposed to be 2.2 k ohm resistors, and got pretty close.
Certainly within the 5% of the specification.
TONY: Let's talk about some of its main features.
Want to run through those?
IAN: This is the numeric readout - that's what you'll be watching the whole time as
an electrical engineer.
TONY: I really like how bright this one is here.
IAN: And we've got the main measurement modes where you can choose voltage, current, resistance,
and so on.
We've got the place where you attach the probes.
And we've got the ability to Range and Zero, which we'll talk about in a moment.
TONY: OK, and we're going to start with the measurements then.
That's a good place to start.
So those are down here on the bottom.
And there's five, right?
IAN: Yes, there are five.
Well, three main measurements, but when you add together the AC and the DC flavors, it
really comes out to five because you've got AC and DC voltage, you've got DC and AC current,
and you've got resistance.
This digital multimeter can also measure capacitance, it can measure power and frequency, and lots
of other things.
These are just the bread and butter types.
TONY: The ones to get started with.
IAN: Exactly - the ones to get started with.
TONY: So now we're getting to the hard stuff.
IAN: Right!
There's a lot going on in this industrial design, isn't there?!
TONY: Yes, there is.
I know it's all important right, for safety reasons?
IAN: It is, and whenever I'm confronted with a new digital multimeter, I just sort of look
for volts and ohms.
That's sort of my home base.
So I would find this and say, these are the two inputs that I'm going to be using most
often - Ground and the input for the voltage probe.
And, if I'm measuring current, then I will still use this for the ground but now I will
hook my red probe up to either the 400 milliamps or the 10 amps.
And this little caution sign and the fused indicates that if we overload these inputs,
we can damage our equipment.
TONY: So it's important to really realize what you're doing, and what you're hooking
up to?
IAN: Yes.
And then these last two inputs are for something called four wire resistance, which is a more
accurate resistance measurement.
IAN: A topic for a future video, maybe?
TONY: Yeah, great idea.
And that's a good point.
If you guys have comments or ideas of different videos and what you'd like to see, then let
us know.
TONY: So now we're moving into Ranges.
IAN: Right.
So as we said, if the digital multimeter is in voltage mode, it can measure up to 1,000
volts.
But you're usually measuring different kinds of things.
If you're at 1,000 volts, you might be measuring some batteries in an electric car all chained
together.
If you're at the 1 volt level, you might be measuring something really small like a solar
cell.
When you're measuring a really large voltage, you probably don't care about accuracy down
to the micro-volts.
But when you're measuring something that is just a few tenths of a volt on a circuit board,
you probably do.
TONY: So things like we just did here.
IAN: Exactly.
And so, you want the digital multimeter to be in the right range for what you're measuring.
Basically, the right ballpark.
TONY: And for all you people who like visuals, I've actually included this here so we can
actually visualize this.
IAN: Excellent.
So let's look at the next slide to show how to do that.
IAN: If you're in a certain mode like 10 volts and you need to measure something larger than
10 volts, then you would hit the up arrow and that would take you to the 100 volt range,
and now you can measure something that was dozens of volts.
And the other button here, if you hit the Range button and put it into Auto mode, then
the digital multimeter will do that for you.
And the disadvantage is that it takes slightly longer to do that because it's got to look
at what you're measuring first before you get to see it.
But the advantage is you don't have to mess around with manually choosing a range.
TONY: OK, so depending on what you're doing, you can decide between the two.
IAN: Exactly.
TONY: And this is more efficient, is it not?
IAN: Right.
It's faster to use manual because you're not waiting for the Auto Ranges to make up its
mind.
TONY: OK.
And now I know this is another important feature - all the instruments have them - is Zeroing
out.
What is that exactly?
IAN: The digital multimeter is full of electronic components, and for all electronic components,
their performance changes over time.
And so if we were to put this in volts mode and apply a voltage of zero volts.
And again, making sure that we're not in current mode and that we are not connected to the
current inputs before I do this.
But I'm going to touch the two inputs together and apply a voltage of zero volts.
Now, before we set this up, do you remember what it showed on the screen when I did this?
TONY: Yeah, it was like 0.03 or something.
It actually showed something in there.
IAN: So some signal that wasn't exactly zero.
And so we touched the two probes together (you can also use a shorting plug for this)
and then we pressed the Zero button - basically telling the digital multimeter, "No, that's
zero volts".
And so now, it's zero all the way across the board.
TONY: I know we've been talking through this the whole time - you've mentioned the safety
and making sure you're plugged into the correct place, and what you're probing.
Do you want to talk a little more about other safety issues?
IAN: I think that would be good just to get one final mention in.
It's important to use the right connectors for the signal you are measuring, especially
between current and voltage, but also at the right level of current.
If you pipe a 10 amp current through the connector that is marked maximum 400 milliamps, you're
probably going to blow a fuse.
You could damage your equipment.
But the other thing to remember is, if you're dealing with something that is up to 1,000
volts or if you're dealing with something that is up to 10 amps, you've got to worry
about yourself too.
TONY: The whole environment around you.
IAN: Exactly.
And so, be aware of your environment, be aware of your surroundings, be safe with the signals
and the equipment that you're working with.
And make sure whatever model digital multimeter you are using, give its safety section a quick
read, or a thorough read.
Ours is at this address here...
TONY: www.tektronix.com/learning/digital-multimeter-tutorial
IAN: So that will get you the manuals, that will give you information on other types of
measurements to do with the digital multimeter, and safety information.
IAN: Alright, well I think that's a good place for us to sign off.
So bye for now.
TONY: Yeah, and don't forget to write in comments if you have any.