Multimeters come in all shapes and sizes

An ammeter-voltmeter-ohmmeter, later known as a multimeter, is one of the essential tools for radio amateurs, radio engineers, and many other people who work with electrical measurements.
This time, I’ll talk a little about these instruments in general and two particular examples.
There’ll also be a short bonus mini-review at the end.

Ever since people discovered electric current, there has been a need not only to find out that it exists, but also to measure its value.
And so began the development of instruments for measuring it.
The first measuring instrument with an electromagnetic system was invented in 1881, just 134 years ago.
These instruments could measure only one thing—current or voltage—and at the beginning of the century they looked roughly like this:
The one in the photo is already an “advanced” model, made in the early 20th century. It could measure voltage on two ranges, up to 6 and 120 V. The wire at the top was the common contact, while the “legs” at the bottom were the inputs for the respective ranges.


The first domestically produced combination instrument (multimeter) was the TT-1.
Back then, nobody bothered much with names, so they simply called it the first technical tester :)


There were other models after that, with more familiar alphanumeric names. One of them was the well-known Ts-20, or “Ts-eska.”
People call all analog (and sometimes digital) multimeters “Ts-eskas,” but the original Ts-eska looked exactly like this, and that’s where the name came from.


Many people never use measuring instruments in their daily lives, but I’m sure most of them remember the voltmeter and ammeter from school. Obviously, these are extremely simple instruments, but plenty of people have seen them :)


I haven’t owned that many instruments over the years.
1. I started with the fairly well-known Ts4324, technically a Ts-eska too, since portable combination measuring instruments had the Ts prefix.
This instrument appears in two of my reviews, but it’s not the same one I owned back then.
2. After that came another well-known instrument, the V7-22A, though this one was a bench instrument. It was very convenient, and it was my introduction to digital instruments.
3. During the perestroika years, I bought a more modern, domestically produced digital instrument—the Elektronika MMTs-01. It’s less well known, although it’s built around the popular KR572PV5 chip, which is itself an equivalent of the ICL7106, probably the most popular chip for building a simple multimeter.
4. Then, as it happened, I bought the very well-known Mastech M890G. That was 18 years ago, and it cost about $20 at the time.
It’s still my main instrument to this day. As they say, I trust it.


In all those 18 years, this instrument has never let me down, despite going through just about everything.
I guess they made them a little better back then than they do now.
But I have a feeling I’ll have to send it into well-earned retirement soon, though it may still come in handy.

In this review, I’ll tell you about two “relatives” of my multimeter, made by the same company—Mastech.
The company earned its popularity thanks to two “people’s favorites”: the simple, very cheap 830 and the more advanced 890.
But in fact, the company makes quite a few measuring instruments, mostly mid-range models that are generally decent quality. I was told that these instruments usually pass calibration without any problems, but it’s worth remembering that there are also plenty of counterfeits.
Sometimes the company’s circuit boards are installed in third-party enclosures (as in my review of the clamp meter); sometimes other boards are installed in enclosures marked Mastech, which is much worse than the first option.

Part One: Mastech MS8240D

While looking for a replacement for my old M890G, I came across the more modern MS8240D and wanted to give it a try.

The multimeter arrived in a rather large box. I honestly wasn’t expecting that—I thought it would be a bit more compact.
The box got a little battered during shipping, but the contents were unaffected.


Inside the box, the meter was packed in a sturdy fabric case.




The complete package includes:
MS8240D multimeter
USM-miniUSB cable
Set of test leads
Manual
CD with software
Four AA batteries
Fabric case
Two straps, one short and one long.


Let me spend a little time on the accessories.
The case is pretty good quality. I rarely take the meter out with me these days, though, so it will probably end up living in my closet permanently. A shame, because I like it.


The supplied test leads are decent quality, but I’ll probably use the ones from my previous multimeter.
They’re about 1 m long, with very soft insulation, and come with protective caps (I’ve punctured quite a few bags with sharp probes).


1, 2. The test leads are marked CAT III 1000 V 10 A.
If the meter’s reading is to be believed, the total resistance of the leads is about 40 mΩ, or 20 mΩ per lead.
3. Since the meter can be connected to a computer, the package includes the appropriate cable. There’s not much to say about it—it’s just a cable.
It’s 1.5 m long, fairly thick, reasonably flexible, and has a ferrite filter.
4. The package also includes two straps. Attach the short one and it works as a handle; use the long one and you get a shoulder strap. But since I probably won’t use the case, the straps will go live with it.


I was surprised to find batteries included. They’re usually removed before shipping, if possible. These are probably the cheapest ones available, meant for testing the meter and getting you started until you can buy something better. Mine have lasted about two months so far.
The package included a manual and a CD with software. I don’t know what the original disc looks like, but mine was a plain CD-R.
The manual describes the meter’s functions and shows an example of the program window, but it’s all in English :(


Link to a brief description of the meter series and the manual in English.
I’d appreciate a link to a Russian version of the manual.

Specifications.


Now we’ve finally reached the meter itself.
A large, rugged body with rubberized inserts, and a very neat appearance.


Compared with my old one, it looks like a giant—the body is about twice the size. In some ways, that’s a drawback; for home use, you’d probably want to look for a meter in a more conventional “home” size.


Although measuring instruments aren’t the kind of product you should judge by appearance, I personally like the way it looks :)


Unfortunately (or perhaps fortunately), this multimeter has no flashlight, lux meter, or sound level meter, so the end panel is home to just a lonely miniUSB port.
I’ve written before that I prefer miniUSB connectors to microUSB ones.
Here, the manufacturer went a step further: the design is such that once the connector is plugged in, you can only pull it straight out. The case protects it from side loads, so it would be very difficult, if not impossible, to break it off. Nice.


There’s a kickstand on the bottom for propping the meter up at an angle.
There are also probe holders on the bottom, but no matter how many times I’ve tried using them, I still find it more convenient to wrap the leads around the meter. Maybe it’s just habit.


The bottom also has the usual markings about safety precautions, battery type, protection class, and so on. Naturally, they’re in English.


Now, a few things I didn’t like.
The stand on this meter is very inconvenient. Not only does it not lock in the open position, but it also props the meter up at a steep angle, making it less convenient to use than my familiar M890.
The manufacturer overcomplicated things here, in my opinion. They could simply have copied this part from the “classic” design instead of reinventing the wheel.


There are two screws under the stand. Remove them to access the battery compartment and fuses.
The screws go into threaded metal inserts molded into the plastic. That’s how it’s done on all reasonably well-made instruments, though; it means you don’t have to worry about stripping the threads every time you replace the batteries.


The battery polarity markings are clear and unambiguous, but a pull tab would make the batteries easier to remove.
It takes four AA batteries, which is much more practical than the familiar 9 V battery, which has a low capacity. Also, since the meter can be connected to a computer to log and display readings, the extra capacity comes in handy.
There are also markings by the fuse terminals. One fuse (250 mA) protects the lower current ranges, and the other (10 A) protects the higher range.


The package included only two fuses, both already installed. Since this type of fuse is much less common than standard miniature fuses, it would have been nice to include at least a couple of spares.
The fuse type is HC10aR, size 38 x 10 mm, rated for voltages up to 1000 V. That’s appropriate for the meter’s category.
They’re very tight to install.


I'll tell you a little about the meter—or, more precisely, its controls, modes, and indicators.
First, the indicators—
Left column
Auto-ranging mode.
Low battery
DC voltage/current
Negative voltage
AC voltage/current
Auto power-off mode. Note: when the meter is connected to a computer, this mode is disabled, and the meter will keep running until the battery is drained.

Top row
Semiconductor junction test mode.
Audible continuity mode
Hold function
Maximum/minimum reading display mode.
Relative measurement function.
Peak measurement mode. For example, when measuring the voltage at a standard wall outlet, the meter will show the peak values of the positive and negative half-cycles of the sine wave.

Right column
Computer mode (one-way data transfer).
Measurement function indicators.

The meter has a 5-digit display, with a 22000-count format.
At the bottom is a dynamic bar graph for roughly tracking rapidly changing signals.
While the main measurement updates about 2–3 times per second, the bar graph can update about 10 times as often.


Controls.
Buttons,
Top row
Function selection (AC/DC current/voltage, continuity modes, and auto mode)
Reading hold mode.
Relative measurements (for example, you can short the probes together, press the button, and the probe resistance will then be excluded from the measurement)
Manual measurement range selection.

Bottom row
Meter mode selector: voltage, frequency, and duty cycle measurements.
Peak measurement
Maximum/minimum measurement
Backlight (short press) and computer mode (long press)

Mode selector
Off
DC/AC voltage, 2.2 V and up.
DC/AC voltage, 220 mV range.
Resistance measurement, audible continuity mode, and semiconductor junction test mode.
Capacitance measurement
Frequency/duty cycle measurement
Current measurement up to 220 µA
Current measurement up to 220 mA
Current measurement up to 10 A

The terminals are, respectively: current up to 10 A, current up to 220 mA, common, resistance/capacitance/voltage


The display has a white backlight that turns off automatically after about a minute.
A small note about the display, by the way.
I wasn't too impressed with the viewing angles. From below, inactive segments become visible; from above, the active ones look washed out. The old meter suffers from this much less, but viewed more or less straight on, the new one has a better image, even though its characters are shorter.


The meter is quite heavy, weighing more than half a kilogram with the batteries installed. Most of the weight comes from the case.


And although the meter is large, it sits comfortably in your hand—but it's still best used on a table :)


As I mentioned above, the display shows up to 22000, but when peak recording is enabled, it shows 28000 immediately after calibration.
By the way, if you increase the voltage gradually, you can even get a reading of, say, 22.500 V.


Before starting the main round of testing, I ran a few quick tests at home.
First, I checked resistors rated for 0.1% accuracy, with values of 680 Ω and 470 kΩ. These resistors came with the transistor tester kit. I'll come back to them later.

I also checked the meter's own parasitic resistance, which is 150 mΩ.
Pressing the relative measurement button lets you “zero” the readings, so this resistance is no longer taken into account (like the Tare button on a scale).


Next, a few auxiliary tests. I run these on all the devices I review; they can sometimes be useful.

That wrapped up the testing, and I moved on to the obligatory teardown.

A few words about the software for displaying readings on a computer screen.

Part Two: Mastech MS8216

The second meter, which ended up here more or less by chance, was a small, much simpler model from the same company.
This is a pocket-sized Mastech MS8216 multimeter, costing around $12.
I'd had it lying around at home for quite a while, since last summer, but never got around to writing a review.
But since I was already reviewing one multimeter, I decided to turn this into a comparison.
This part of the review will be noticeably shorter than the previous one, roughly in proportion to the size of the multimeter :)

The multimeter came in a simple blister pack. It's small and lightweight.


The package includes:
Mastech MS8216 multimeter
Manual
Small case
Cardboard from the blister pack, listing the meter's specifications.
Batteries are also included; they were already installed in the meter.


The meter's capabilities are, of course, more limited than those of its bigger brother. The photo shows the specs claimed by the manufacturer.
The manual is in English, but the meter is simple, so I didn't see much point in reading it, although I found a Russian-language version.
The little case could come in handy, though. It's a very tight fit while new, but I think it'll stretch a little over time and fit just right.


It looks neat, is compact, and is easy to carry in your pocket—or give to someone as a small gift.


The test leads are fixed, and the cover doesn't come off either (at least not on its own).


The test lead wires are thin, and the probes themselves are pretty basic.
One downside is that they're very awkward to pack back in; they barely fit and keep trying either to break the cover or pop it open.
I'd recommend shortening the wires a little to make them easier to stow—by at least 10–15 cm.


The controls are intuitive; only the buttons might be confusing, so here's what they do.
REL — Relative measurement mode.
H/D — Frequency/duty cycle measurement mode
D-H — Reading hold mode (Hold).
The meter only has automatic measurement mode selection, an audible continuity test and a diode test, plus auto power-off after 15 minutes of inactivity.
I wasn't too keen on the function selector knob. In an effort to keep the meter thin, the manufacturer made it almost completely smooth, with hardly anything for your fingers to grip.


As with the previous multimeter, the back lists safety precautions and the meter's CAT II 600 V protection rating.
It also specifies the battery type: two LR44 cells. Not the best choice, but perfectly adequate for occasional use.


The meter weighs much less than the previous one—just 85 grams.


A few preliminary caresses tests.

Since the test results surprised me a little, I decided to take the meter apart.
Though I probably would have taken it apart anyway, but this made it more interesting :)


Part Three: Bonus Section — Reference Voltage Source

About two months ago, in my review of a reference voltage source, I wrote that I'd buy one of these boards and take it to the metrology lab to find out what it could really do.
I placed the order on September 16 here. It cost $5.88 at the time (and still does). The seller later raised the price to $9, but almost immediately dropped it back to the original price. At the time, it was the cheapest board available.
By October 2, I had the board in my hands—just over two weeks later.
It was shipped without tracking in a simple plastic mailer, but arrived intact.


Well, I said I'd go, so I did what I said I would. I hope the trip wasn't for nothing :)

The board was packaged just like the ones in my previous reviews. It also came with a label listing the measured voltages. The only difference was that those measurements were made with an Agilent 3458A multimeter, while mine were made with an HP 3458A—which is the same thing, really.


They also included battery contact tabs, though it's not clear how you're supposed to attach them.
It's small enough that, if you wanted, you could probably use a matchbox as an enclosure :)


The top of the board looks quite neat; it's made of yellow textolite.


There are terminals for connecting a measuring instrument. One drawback is that good-quality probes are usually thick and have banana plugs, so they won't fit into sockets like these on the board.
The board is also marked with the store and developer's names.


But the underside is a sorry sight, enough to make you cry :(
Sloppy soldering, flux not cleaned off.


A couple of close-up photos. It would be no big deal to just wash it off, but this is the board for a precision voltage reference (VREF), and in theory even flux could affect the readings. So cleaning it off could change the output.


Judging by the markings, the chip seems to have been made in early 1992. I haven't looked up when it was designed, but something tells me it was after 1992—though I could be wrong, and the chip really is from that era.
There is a small but noticeable dent in the chip's package; it's clearly used.
This is the K version of the chip. There's also an L version, which is noticeably more accurate, so that's the one to get.
At least this one should be no worse. Here's the datasheet for the entire AD584 voltage reference series ad584. It covers all three versions. The datasheet I found earlier covered only two, and K was the best of those, so that's the one I ordered. Turns out there are better options.


A brief digression before the tests.
Time moves much more slowly in metrology than in everyday life.
Instruments last for many years, not because everyone is trying to save money, but because developing a precision instrument takes a long time, and very few manufacturers do it.
Around the early 1990s, precision measurements were made using the Agilent 3458A. At the time, it was the most accurate multimeter in the world.
Yes, it really is a multimeter, but an extremely expensive and accurate one. There are instruments that are even more accurate, but only for a single type of measurement, such as a voltmeter or ammeter. Among multimeters, though, this was the most accurate.


This multimeter was designed using simple logic (by the standards of the time). It had a VFD display (those beautiful screens), but it was very reliable and accurate. It's still in use and respected by metrologists. The values on the certificates supplied with the voltage references were measured using these multimeters.
But around the early 2000s, Fluke set out to develop an instrument with even better specifications. The result was the Fluke 8508A, which took over as the world's most accurate multimeter.


As I understand the “hierarchy,” the chain of precision measurements, calibrations, and so on looks roughly like the diagram below.
Primary standard — Primary standards for quantities such as voltage, current, resistance, capacitance, and so on.
As I understand it, nothing is more accurate than these.
They are also verified, but the verification methods are completely different from the usual ones.
Secondary standard — There are actually many types of secondary standards, but their main purpose is to replicate the primary standard. Reference multimeters can serve as secondary standards.
Calibrator — An instrument that generates various voltage, current, capacitance, and other values to verify other instruments. There are different kinds of calibrators, but they are usually verified against a secondary standard. You wouldn't want to haul this whole pile to the primary standard every time.
Instrument under test — All the other instruments whose readings are verified in a metrology lab.


When I checked the voltage reference I bought, it was measured with a reference multimeter that had, of course, been calibrated. The results are in the photo.


Now let's compare that with the values listed on the certificate.
You can see that as the voltage increases, the difference between the lowest voltage and the others gets larger. But it's worth noting that in every case the voltage reading was rock steady—the last digit didn't change either.



Now for the conclusions.
Each instrument has its pros and cons. I'll try to highlight the key points, along with the pros and cons of each one.
Mastech MS8240D
Pros.
Good, reliable construction
5-digit display
Good accuracy on most ranges.
True RMS measurements
Can be connected to a computer.
Quite a few measurement modes
Backlight
Batteries included (though it's hard to say whether that's a pro or a con), and the battery type itself.
Good set of accessories

Cons
Accuracy issues on two ranges. The second issue (measurements with the second calibrator) is still uncertain, though; I'll look into it.
The mounting for the computer interface board wasn't thought through well enough; it definitely needs modification.

Mastech MS8216
Pros
Excellent accuracy
Compact size
Comes with a case

Cons
Capacitance measurement problems on the highest range.
It's very awkward to stow the probes in their designated slots, and the case design isn't very convenient.

I won't say anything about the reference voltage source board; everything is clear from the mini-review.

My take: as they say, different instruments are needed, and different instruments matter :) The review showed that even a small, inexpensive multimeter can have high measurement accuracy.
A high digit count doesn't always improve absolute measurement accuracy, but it definitely helps when tracking slow processes or when relative accuracy matters.
I was a little surprised by the oversight in the way the interface board is mounted in the large multimeter. How they managed to mess that up is beyond me.
After testing the small multimeter, I came away with a mostly positive impression, spoiled only by the case design itself. It's harder to say the same about the large one.
Overall, it's not bad, and I liked some of its interesting features, but the measurement accuracy was disappointing; I expected more.
Most likely, the person who calibrated it initially set the reference voltage a little off, then adjusted everything else to match. It can be fixed, although I'm fine with it as is for now.
The reference voltage source module impressed me with its fairly good accuracy, especially for the price, but disappointed me with its poor build quality. Even so, I think it could be useful to radio amateurs and professionals alike. I plan to expand its functionality a bit and turn it into a stable current source as well. I may write a review about that, since it's just as useful as a reference voltage source.
My visit to the metrology lab also showed that my preparation was pretty weak. Next time, I'll prepare my own test plan for the instrument first and simply follow it to the letter. On the other hand, I now know what can be tested and how; I just need to brush up on the testing methods themselves.
For example, these tests should have included the large multimeter's 220 µA and 10 A ranges, and I should have paid more attention to the True RMS tests. The small multimeter should have been tested around the 4000-count range, not 1000. I'll fix that in the future; we'll learn from our mistakes :)
At least I got a little perk and saw an instrument I definitely want, but the $300–600 price tag is still a bit off-putting :(

I hope you found the review useful and interesting. I tried to trim some parts, but somehow the review grew on its own.
I'd be very glad to hear your suggestions and questions, which, as always, I'm looking forward to in the comments.


The product was provided by the store for review.