I recently decided to treat myself to a new multimeter.
What prompted me to look is the fact that my current one is sub-standard (to say the least!) and can only measure DC voltages.
I had a need to carry out some mains voltage checks around my house.
I don't have much money to spare and didn't want to spend more than £100 max (Great British Pounds or GDP) and preferably much less!
I considered several options. This post will hopefully be useful if you are also looking for a quality budget multimeter.
On-line resources to help you
I like Dave Jones' EEVBlog from down under (i.e. Australia).
He did several useful videos to help people like myself make a more informed decision.
Another of my favorite electronics Vlogger is Martin Lorton.
He has some very instructive videos on multimeters.
Which DMM did I choose?
To cut to the chase, I will start by saying which DMM I selected, a Brymen BM257s.
In the UK, there are very few options to order the BM257s. I ordered mine from European distributor TME.
It cost me a total of about £86 (GDP) including tax and delivery.
The tax was charged at 23%, I assume this is the going tax rate in Poland from where it was being shipped?
UPS delivered the meter from Poland to my door in the UK within a day, I was well impressed.
Brymen is an Original Equipment Manufacturer (OEM).
The BM257 is available under brand names Elma BM257 or Greenlee DM-510A.
So why the Brymen BM257s?
Now onto the reasons of why I chose the Brymen BM257s:
- Reputable manufacturer (Brymen is a well known Taiwanese manufacturer)
- True RMS meter
- Safe design - important since I will be measuring mains voltage
- Quality - well layed out board, check out video reviews
- Reasonably fast response
- Solid build, I also like the compact design.
As for the features you get with the meter, well check out the picture below.
As they say, a picture is worth a 1000 words.
What I did not appreciate before ordering is that the BM257s has a 60mV range.
So it can measure up to 60.00 mV on its 4 digit display.
This means the smallest value it can display is therefore 00.01mV or 10 uV.
Bare in mind however that the meter accuracy is 0.4% + 5d in this range.
The "5d" translates to a +/- 00.05mV or +/- 50 uV measurement error.
Nonetheless, the meter still provides failry accurate readings for voltages of just a few mV, pretty good to me!
What about the other DMMs?
There are many DMMs to consider (and some to avoid!) but the final choice is down to your personal circumstances.
To some extent it is fair to say that you get what you pay for.
So I purposely did not consider DMMs that were under £40.
Extech EX505 (a No ! No!)
I was about to order the Extech EX505.
It comes from a reputable manufacturer, is feature packed and reasonably priced.
But then I came across Dave Jones video teardown and was simply shocked at the poor design and build quality.
It seems Extech product quality can be hit and miss. This is very dissapointing, I expected better.
It was hard to resist the temptation to buy the super-dupper cheap, feature-packed UNI-T UT61E.
This meter can be bought for under £40 on Ebay.
Even Dave Jones had a few kind words to say about the UNI-T.
He actually reviewed the UT61D but I believe the UT61E is very simliar indeed.
Several things eventually convinced me this wasn't the right DMM for me:
- No backlight
- No Temperature measurement
Dave Jones took the meter apart and revealed that the meter was obviously built to a price with lower quality components.
Also, another vlogger managed to "zap" his UT61E when he tested it with his insulation resistance tester.
Go and check out the arcing in his UT61E when he applies 5kV to the meter input.
It turned out that the input had no spark gap fitted on the PCB, possibly to reduce cost.
For me this is one step too far in the low cost direction, it is simply not fit for purpose.
This was actually Dave Jones' $100 DMM shout out winner.
It is hard to fault it, you can't go wrong with this meter.
In the end, I preferred the more rugged design and higher safety rating of the BM257s.
I must say this was a strong contender for me and pondered over it for a long time.
Quality appears to be really good.
It appears to be a well engineered DMM from Japan, check out this video review.
I also love the fact that HIOKI make their own ASIC for their DMMs, this shows a deep level of engineering.
HIOKI deserve more credits, I did not know them before starting my DMM quest.
It is available in the uk from Tester website and is very well priced at about £75.
Eventually, the lack of temperature reading option and lack of uA measurement range made me choose the Brymen DMM instead.
Fluke are considered the leader in the DMM market when it comes to design and build quality.
The 17B+ is only targeted at the "emerging" markets like China and India.
However, quality still seems on par with expectations.
It is not officially sold in the UK.
However, it can be bought from eBay for about £75.
I would have ordered the Fluke 17B+ if it wasn't for its lack of true RMS measurement capabilty.
Also, I am not sure the warranty would be valid since it is not officially sold in the UK.
What's the deal with true RMS?
To be honest, I am not quite convinced I really needed a true RMS multimeter.
So far, most of my hobbying measurements involved measuring a DC voltage level, and not an alternating (AC) signal.
So for me, this was more of a future-proof feature.
for a definition of true RMS, refer to this Agilent Application Note.
Basically cheap multimeters measure the average voltage of the absolute value of the waveform.
The multimeter then applies a scaling factor to obtain the RMS value.
The problem is that the scaling factor assumes a sinusoidal waveform.
The scaling factor is different for other waveforms such as triangular or square.
Therefore the meter will give an innacurate reading for non-sinusoidal waveforms.
True RMS meters actually make an attempt at measuring or computing the RMS value of the waveform.
For the Brymen BM257s, accurate true RMS readings are limited by the DMM bandwitdth.
Looking at the BM257s user manual, the accuracy of AC voltage range is only guarenteed for the frequency band 50 HZ to 400 Hz, see table below.
That seems quite a low bandwitdh, not sure if this is truly useful.
I am not taking apart my multimeter just yet as it is still under warranty.
However, looking at other bloggers pictures, the BM257s seems to use Analog Devices' AD737J True RMS-to-DC converter.
The AD737J datasheet specifies the 3dB bandwitdh as 490 kHz for an input signal of 200 mV rms.
So it might be possible to use the true RMS funciton of the meter at high frequencies?
Another factor that will affect the accuracy of the RMS measurement is the crest factor of the AC signal being measured.
The BM257s meter accuracy is specified for max crest factor < 3:1 at full scale and <6:1 at half scale.
I am not an expert on multimeters, so please bear this in mind.
Please feel free to leave a comment if I have said something wrong or have omitted something.
Also leave a comment if you found the post useful :-)