OWON B35, an interesting multimeter for the careful user

A rather unusual instrument came into my hands—or, more precisely, one with an unusual feature. This multimeter can wirelessly transmit measurement results to remote devices via Bluetooth.


A coworker wanted to buy one, specifically after reading my review here. That’s why he chose this particular version. I would have picked a slightly different model, but my requirements for an instrument are usually a little different.

First, a little about the differences between the models.
There are nine different versions in the lineup. They differ in display count, whether they have Bluetooth and TrueRMS, and whether they include an offline signal logger.


An offline logger lets you record measured parameters autonomously, without connecting to any external devices. I’ve already reviewed an instrument with this feature, but it was from a different manufacturer and in a different accuracy class.

The company essentially offers a multimeter for every taste, which I think is the right approach from both a marketing perspective (you can’t ignore that) and the buyer’s perspective: everyone can choose the one that suits them best.
This review covers the version with a display up to 6000 counts and wireless connectivity, but without TrueRMS.

First, the instrument’s stated specifications.


The instrument came in a small, plain box. Nothing fancy.


The package also included a manual and a slip of paper with a QR code for downloading the software.


The manual is entirely in English. Just in case, I’ve included a PDF version in the supplementary materials.


I liked that the instrument comes with a small storage and carrying case. Unfortunately, even more expensive instruments don’t always include one :(


The case could have been just a little bigger, though. Everything fits very tightly; it feels like it’s short by barely an inch.


The package includes:
1. Multimeter
2. Test leads
3. Thermocouple
4. Adapter for testing transistors and capacitors
5. Alligator clips
6. Case
7. Manual


I definitely liked the test leads; the wires are flexible. The stated maximum current for the leads is 10 A, although the multimeter can measure up to 20 A. On the other hand, the leads don’t specify a safety category; they only say the maximum voltage is 1000 V.


For added protection and convenience, the probes have removable caps. Take them off and you get long, thin tips.
The alligator clips look a little crude, but they’re quite good from a safety standpoint. There’s a small nut on the metal part, so the clips simply screw onto the probes. The connection doesn’t look very reliable, though; to be safe, I’d solder it.


The thermocouple, on the other hand, is nothing special. I have no real complaints about the thermocouple itself, but the terminal end is awkwardly designed. A fork-style connector would be much better. The transistor test adapter lets you use a fork-style thermocouple, but the one included is the type shown in the photo.


Universal adapter
As far as I understand, it can be used to test transistors and capacitors (without probes), and to connect the thermocouple. There’s also an inductance measurement symbol, but unfortunately the meter can’t measure inductance.


That’s it for the accessories. Let’s move on to the meter itself.
I’d say it looks good. Yes, its appearance definitely catches your eye.
The outer shell is rubber, but it’s not removable; it’s part of the case. The design is very similar to the UniT UT61.


Since I’ve mentioned UniT meters, here they are alongside the one under review. Both UniT meters will serve as more accurate reference instruments for the review.


One thing I can say right away is that the Owon’s display is much easier to read, especially for people with poor eyesight: the digits are large and have good contrast. The status icons are a letdown, though; they could have made those larger too.
I once looked for a meter with large digits, good accuracy, and plenty of features. But unfortunately, you can’t have it all: you get one or the other, or a price tag like a Boeing…


The angle when standing upright is very similar to the UT61’s. I’d even say they’re twins.


But the meter under review is noticeably thinner.


I weighed them mostly out of curiosity. All the meters have batteries installed.
The weight is also very close to the UT61’s, just a little less.


Now for a more detailed look at the meter.
I have no complaints about the build. Everything fits together very tightly; nothing creaks, wobbles, or comes loose. The display has a protective shipping film, but it’s almost invisible, so I left it on—especially since the meter isn’t mine.


Display with all symbols turned on.
Strangely enough, I didn't see an inductance measurement symbol, so the meters probably can't measure inductance at all. On the other hand, there is an indication for the tachometer function.
The display updates about 3 times per second; the bar graph updates 60 times per second (according to the description).


The meter automatically selects the measurement range, so the mode switch has just 10 positions. They could have added an eleventh, Off, at the opposite end, though—that would have been more convenient.
The function buttons are on top:
Select — select the operating mode
Range — manually select the measurement range
Hz/Duty — measure frequency or period
Max/Min — hold the maximum and minimum readings
Backlight and hold button
Button for enabling relative measurement mode and Bluetooth.


At the bottom are the familiar probe sockets. The CAT III safety category is marked here.
But note that CAT III is specified only for voltage measurement (and even then, for DC; for AC it's 750 V), while current can only be measured in circuits with a voltage of no more than 250 V.


There's a kickstand on the back, along with four small rubber feet. Handy—I don't think I've seen that before.


The power supply is a pleasant surprise: two AA batteries, not the ubiquitous 9 V battery. A 9 V battery has its quirks, but in most cases AA cells are more convenient.
The cover is secured with a machine screw rather than a self-tapping screw, which is a plus. But the screw isn't captive, so it can go flying when you change the batteries—a minus.


The fuse for the lower current ranges is accessible without taking the case apart. Handy.


Let's take a look inside—how could I not?
The back cover is held by four self-tapping screws, with a pair of clips at the top. The screws were really tight; I could barely get them out.


To spare the more sensitive readers, I've hidden the rest of the teardown behind a spoiler :)

Before the tests, I'll take a brief detour to describe the meter's operating modes.
There are quite a few modes, and there's not much point in showing them all, so I'll hide them under a spoiler.

I completely forgot that the meter has a backlight—and a relatively “smart” one at that :)
The backlight turns on when you press and hold the button, and only switches off automatically after about a minute. Very convenient. A shorter timeout (on other meters) can sometimes be annoying.
The backlight uses three white LEDs positioned at the bottom of the display. It’s quite bright.


Now we can move on to the tests. But since this stage is almost identical to the corresponding sections in my other multimeter reviews, some of the photo descriptions will be copied from them. Naturally, with any differences taken into account.

The first test is perhaps not really a test, but just some additional information for users.
For this check, I measure a few parameters that may be useful. Here they are:
1. The meter’s input resistance is about 11 MΩ.
2. Voltage across the meter’s terminals when measuring resistance: 0.33 V
3. Voltage across the terminals in continuity mode: 0.64 V
4. Short-circuit current: 320 µA
5. Voltage across the terminals in semiconductor junction test mode: 2.81 V, enough for most LEDs.
6. Short-circuit current in this mode: 1.31 mA


Next, I tested the reference voltage source.
The board outputs 2.5, 5.0, 7.5, and 10.0 V. The measurement results are shown in the photo. In my opinion, they’re excellent.
The board doesn’t actually output exactly these voltages, but that doesn’t matter at all for this meter; it’s easier to round the values.


Another check of DC voltage measurement accuracy.
On the right are the readings from a meter with a basic accuracy almost an order of magnitude better than the one under review. Of course, using a calibrator would have been more appropriate, but I think this comparative test is more than sufficient.
The meter fully met its stated specifications, with quite a bit of margin to spare.


The meter performed well when measuring DC current. Interestingly, its accuracy was better on the 20 A range.
Finally, to test AC voltage measurement accuracy, I measured the mains voltage. The readings matched those of the reference meter.


Capacitance readings are a bit “all over the place.” At low values, the meter reads low; at high values, it reads high, though in the middle it stays within the stated measurement error.
The capacitance test reminded me somewhat of a Fluke I reviewed recently, which also didn’t always measure capacitance correctly.
The meter takes a long time to measure high-capacitance capacitors. No, let me put it this way: a loooooong time.
It couldn’t measure a 4700 µF capacitor at all.


The meter has no problems measuring resistance at all. Everything is spot on, with fluctuations limited to the last few digits—2–3 digits against a stated 2, which is a very good result.


In terms of frequency measurement, the meter reminded me somewhat of my UniT UT181, which also consistently reads low.
That’s actually why I ran this test with the Unit UT61E: using the UT181 wouldn’t have been fair.
The meter won’t measure frequencies above 6 MHz, despite its stated limit of 9.999 MHz.


For a clearer picture, I’ve put the test results in a table. This isn’t a metrology lab test, of course, but it’s more than enough to give you a general idea of the accuracy.


And of course, I have to talk about the meter’s main “feature”—the reason it costs about $10 more than a similar model without Bluetooth.
Incidentally, you can add the same feature to the popular UT61E, but that will cost you an extra $30.

This meter can display readings on a tablet or smartphone. And it doesn’t just display them—it can also log measurement results.
The photo shows several different modes; I’ll take a closer look at them later.
Connecting it to a phone takes just a few seconds. Here’s what you need to do:
Turn on Bluetooth on the multimeter (press and hold the relative measurement button)
Turn on Bluetooth on your phone
Launch the software
Tap the top of the screen in the software to open a menu showing the multimeter’s Bluetooth connection.
Tap the line with the multimeter’s name, and that’s it.

After that, you can view measurement results, control all the meter’s additional functions within the selected range, display the logger’s results, and save and review previous measurements.
The connection range is at least 6 meters—I tested it.


Of course, you might ask: how can you log measurements if the meter runs on batteries?
Here’s the explanation. After reading the datasheet, I concluded that it should be easy to modify the meter to run from a 3.7 V lithium battery.
You just need to add a diode in series with the battery, since the battery voltage is higher than the voltage of two cells.
The ADC datasheet specifies the operating voltage range and the battery-low indicator voltage.
In this case, the lithium battery voltage ranges from 3 to 4.2 V. With a diode (something like a 1N4148) in series, the voltage will be 2.4–3.6 V.
Let’s check the datasheet: it all adds up, and even the low-battery indicator will work—

I’ll tuck screenshots of the different modes under a spoiler, since they’re quite large.

As a bonus, here are a few videos about this meter that I found online.



And here's what the multimeter looks like in your hand :)


That seems to cover everything. I've checked what I could and shown what I wanted to, so it's time to draw some conclusions.
Pros
Excellent accuracy when measuring everything except capacitance.
Very high-quality construction
Good set of accessories.
Can connect wirelessly to a smartphone or tablet.
Can log and save readings (only when connected to a tablet/smartphone).
Relatively easy to modify for battery power.

Cons
Poor protection for the meter.
Large measurement error when measuring capacitance on some ranges.
The maximum frequency and capacitance measurement values don't match the specifications.

My take: what can I say? It's a good meter, a very good one. On its own, it doesn't stand out much from the competition in terms of accuracy or features. But wireless connectivity, along with software that can work with several meters at once, makes it much more versatile than similar models. Sure, you could say it's a bit pricey, but as I mentioned in the review, the Bluetooth adapter for UniT multimeters alone costs around $30, while this meter with the same feature costs less than $50.
I expected better results when measuring capacitance, but what disappointed me more was the poor protection. I don't know how the manufacturer overlooked this. I'm not saying the meter will burn out at the slightest sneeze—not at all—but probing blindly can have consequences. The one reassuring thing is that the ADC chip can be bought separately. It's not exactly cheap, but it can actually be replaced, after which you can recalibrate the meter.

The usual question: would I buy this meter for myself?
Not now, since I have a meter in a higher class with more features.
About six months to a year ago, probably yes, though I might have chosen a different model, one with TrueRMS and a standalone logger.

As a bonus, I've uploaded an archive for download containing the manual, software, and a multilingual voice pack (the software can read measurement results aloud) — link.

I asked for a discount on this meter for the review. Use coupon GB94B to get it for $46.59. I didn't think to ask for discounts on the other meters in this series at the time, but I'll try on Monday.

That seems to be everything; I tried to show it all. As always, feel free to ask questions in the comments. I hope you found the review useful.