How to choose a multimeter?

[ericmar]

how to choose a multimeter

As above.

Normally, we just simply get a multimeter and use it. But what are the criteria to choose a suitable multimeter? What do we need to look at when purchasing a multimeter? Measuring range? Accuracy?

Thanks,
Eric

 

[the_edge]

fluke 19 multimeter

It depends on what do you need it for...
Usualy it is all about price, as more expensive it gets the better it is...
You have those cheap for 10$, or those expensive >500$

Measuring range? Accuracy? this also goes with price...

There are multimeters that can measure temperature, capacity, beta of transistors, etc...

It all depends on what you need them for...

 

[nguyennam]

how to choose multimeter

Choose what based on your need, experience and money.

In my opinion, you should buy now a DMM (digital multimeter), not a analog (with handle) multimeter. The best is DMM with analog bargraph.

If you agree, so we will talk about what you need pay attentions to a DMM:

1. Accuracy: if you are not a metrology engineer, so a standard accuracy is good enough, as most of DMMs now have the accuracy of 1% or better for DC ranges 2% or better for AC ranges. You should know that the analog multimeter usually has the accuracy of 2.5% or worse. So accuracy for DMM is not the problem.

2. Input impedance: most of DMMs now have 10Mohm or higher for DC voltage ranges, 1Mohm or higher for AC voltage ranges. That is quite good, so this parameter is not a problem either.

3. Measurement features: most of DMMs can measure: AC voltage, DC voltage, DC current, AC current, resistance, continuity, diode check.
You may want some more features: capacitance, frequency, temperature, humidity, pressure, transistor hFE measurement

4. Automatic switching ranges: cheap DMMs have no this feature, while it is very useful and safe, especially, when you need to measure the unknown high value of voltage, current. On the other hand, DMMs with this feature also have good enough input protection, that is the most important.

5. Measuring ranges: most DMMs have good enough wide ranges: DC voltage of 100mV to 700...1000V, AC voltage of 400mV to 600...1000V, DC and AC current up to 10A, resistance from tens to 30...40Mohm.
You may want the lower ranges of DC or AC voltage ranges, so check carefully with the DMM's manufacturer documents. In general, the DMM itself cannot have higher ranges of measurement due to unstability. If you want higher ranges, you should look for the auxiliary attachments.

6. The other features, you should take into accounts:
- fast display rate. Most cheap DMM are bad in this feature: they response to the change of measured value very slow, and sometimes you cannot be more patient to wait the display changes.
- big digit.
- with backlight.
- "Hold" function, to freeze the display.
- Auxiliary resistor divider for measuring the high voltage.
- Auxiliary clamp for measuring the high current.
- Output open-circuit voltage at the diode check: should be at least 3V. Be aware: some DMMs use 2 x AA batteries, but this voltage is only 1.5V and practically useless. With higher voltage, you can easily test diodes, LEDs, darlington transistors, MOSFETs, ...
- Ruggedness: cheap DMMs are fragile, and have no rubber holsters.

7. The last word: the best DMM I ever love is of Fluke USA. However, they are expensive, and the accuracy is much higher than I need. A few years ago, it also made the cheap Fluke 17, Fluke 19 for China and other low-end markets, but it never informed on its website, and discontinued very soon after. The other brandnames are HP/Agilent, Wavetek, Yokogawa, Sanwa, Kyoritsu, ...

Just to discuss with you.
nguyennam

 

[ericmar]

choosing multimeter

Thanks a lot! You guys really teach me something useful.

 

[flatulent]

how to choose digital multimeter

Another thing to consider is your expected future needs. One example of this is one company that "saved" money by buying a 500 W load. They soon needed a 1 kW load and had to buy that. Had they looked ahead they could have initially bought the kW load.

 

[xaccto]

$10 DMM is a good knock-about meter, good for ad-hoc voltage measurement, and like fixing things around the car...
if it breaks, just buy another.
more expensive and sub $100 ones are actually very good, you can be quite confident in their accuracy.

in any case, if your doing electronics for a bit more than a dabble, you will end up with more than 1, or 2 or 3 etc.....


Final word on the analog meter scale type - they do have a special charm to using them, especially the big one with handle etc,
and 100,000Ohm impedance - yes an important parameter in choosing a meter then, now DMM are all 1MOhm or greater across the board.
And who keeps a stock of 9V batteries for when the DMM fails....the analog only uses a battery for the resistance range.

 

[dick_freebird]

I have 8 cheapo DMMs from Harbor Freight. You can never
have enough "cannon fodder". They are currently giving
them away with a coupon (for you USA folks). I bought
mine at $3.99. The primary complaint I have is with the
current scales, the shunt resistance is what they vary
for range selection and it is large on the lower scales,
a significant error term that kicks the result around if
I have to switch ranges (no autorange).

The cheap meters also start to act funny at low battery
but before they warn you about that.

Anything fancy I use other meters for. I have some
decent handhelds and some scavenged Fluke bench
meters with really good low current / low voltage
range.

Most DMMs will inject sampling noise back into the test
setup, is my experience from noise probing. I have to
turn them off to take the noise measurements.

If you so not work for a company that takes care of
calibration regularly, knowing your DMM is right falls on
you. I just look for agreement against a common input
and assume that any drift / degradation would be
random, and show.