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Old 16th Jul 2017, 4:54 pm   #61
6AL5W-Martin
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Default Re: Cheap multimeters

keep classic

but the English version made in Gloucester is not a VTVM, it is VVM

greetings
Martin
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Old 16th Jul 2017, 5:42 pm   #62
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Default Re: Cheap multimeters

I keep trying to buy Heathkit VVMs. Absolutely no luck so I've got half way through cloning one.

Nice collection BTW.
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Old 17th Jul 2017, 7:01 am   #63
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Many thanks for the info. Im going to hold off ordering them just until after ive had chance to look for something higher spec 2nd hand at a couple of rallies (Finningley ARS rally this sunday - i'll have a small stall! [blatent plug])
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Old 17th Jul 2017, 7:01 pm   #64
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Default Re: Cheap multimeters

Quote:
Originally Posted by evingar View Post
I disagree.

White it's obviously the case that following the correct procedure minimises the risks greatly, a properly designed meter reduces the risk of dire consequences if you do something daft. Given that we all occasionally do daft things, this is a big deal !

Then there is the case of transients. Even if you are doing all the right procedural things, a transient can cause a Arc Flash. A properly designed meter reduces the risk substantially.
When I originally mentioned transients as a problem, I wasn't referring to "arc flashes". I was thinking of a fried meter. Or to be more accurate a totally dead chip inside the meter. I did investigate one such case, and I found buying a replacement chip would cost about four times more than just buying a new meter. Go figure.

And of course, I only surmise that transients were the cause of the demise of several meters. It typically happened while I had the meter hooked up to some part of a valve unit. And just after I had I flicked switch or two. The trouble with flicking switches is that the circuit configuration changes, and if that results in heavy current changes in large inductors, high voltage transients are a likely result. Valves just shrug off such transients - but modern ICs expire if they have no heavyweight protection circuits in place.

Of course the prices of the units we are discussing are extremely low. Its more the annoyance factor I was thinking of. One moment you have a working test set up - the next one or more meters has departed this world. And you are left scurrying about for another one.......

Richard
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Old 19th Jul 2017, 3:12 pm   #65
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Originally Posted by brunel View Post
Huge display, great for us oldtimers.
Philips Oldie PM2517E (I don`t like LCD)

http://www.wellenkino.de/181/25a.jpg

greetings
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Old 19th Jul 2017, 4:59 pm   #66
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Default Re: Cheap multimeters

Where the equipment has mains (or large enough batteries) red LED display takes some beating.

It's interesting how good the LCD contrast is on the toy DT830 variants. Good choice of segment size as well. Not suitable for high current or high voltage, as people have said, but on the plus side if you get one that wasn't made on a friday afternoon or in a shadow/clone factory they can be quite stable. Mine shows 2.05v on a DC source of 2.048v after 25 years use, but generally the test leads supplied should be discarded or donated to the fairies at the bottom of the garden as skipping ropes- they are no use for anything else. The LCD display really does not like a damp atmosphere, it goes crazy like a schoolboy's calculator that's been thrown across the room once too often.

One nice simple (and presumably cheap) hand-held is the DT3266L. I found mine in a skip but have yet to find any leads for it. It's more steered towards electricians than electronics engineers so is fairly basic in it's functions. I keep meaning to check if the clamp function works on DC- some of them have a hall effect sensor i think..
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Old 24th Jul 2017, 12:42 pm   #67
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Default Re: Cheap multimeters

Quote:
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Quote:
Originally Posted by MrBungle View Post
I just measured my UT61E to actually get a real reading and the 3dB point is 41KHz with a source and termination impedance of 600 ohms at the terminals. It is completely flat from about 5Hz to 20KHz. No warranty on this figure though!
That's good to know - thanks
Just a "heads up": the Uni-T UT61E is normally 40 or more, but Banggood have them on offer for 31.65

Having been procrastinating about this one for many months now, I couldn't resist at that price. I'll review it when it arrives...

Just FYI, as well as the high resolution (22,000-count), this meter does logging. I'm not sure how well that works - the manual doesn't give much away, but from what I've read previously it might be that the meter needs to be connected to the PC while logging. Normally, a logging multimeter does that on its own, with the data uploaded afterwards. There's pros and cons of each...

Based on previous experiences with Uni-T meters (badged as Tenma, as sold by Farnell), I'm frankly not expecting this one to be any safer than the Aneng meters (Joe Smith has run a series of videos investigating this meter, and there's lots on EEVBlog), but for low-energy bench use, it's a lot of functionality for not much money.
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Old 24th Jul 2017, 2:17 pm   #68
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That's not a bad price. I think I paid 35.99 for mine from ebay before the prices went up a couple of years back.

When you get it can please you post a photo of the insides so I can compare to mine. Interested to see if they are similar.

The logging is an RS232 cable with an optoisolator at the meter end. It does NOT work with cheap USB serial adapters. Any desktop PC seems to work fine though. I'm using Sigrok with mine: https://sigrok.org/wiki/UNI-T_UT61E ... the provided software is terrible!

I actually made a test rig for a huge box of germanium transistors I had a while ago that I had to test just for the hell of it. It was an Arduino with a relay attached to it connected to the USB port. The meter was connected to the serial port. All controlled by a python script. You poked a transistor in the test rig socket (a cheap textool clone), pressed enter and it read the leakage current and converted it, then read the hFe and converted it from the meter switching between two functions with the relay in the middle controlled by the arduino. This left the device in circuit until the values changing had slowed.

Would have taken me 7-8 days non stop recording otherwise - took 5 hours to get through that box.

I was going to wire it up to a label printer as well but I ran out of serial ports by then
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Old 24th Jul 2017, 2:37 pm   #69
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I wondered about USB-RS232 adaptors. Usually they are OK with devices that use genuine RS232, but other applications that use the serial port in a non-standard way (like the JDM PIC programmer) are fussy because of the latency in the USB chip. It's hard to tell from the pictures what's in the optical "dongle", so perhaps it contains something that is fussy about timings. We'll see
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Old 24th Jul 2017, 2:44 pm   #70
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It's got a IR photodiode or phototransistor in it I think. Probably does use one of those horrible JDM style RS232 derived power supplies for itself. I remember spending literally 3 hours trying to get one of those working in the late 1990s!

I've got an industrial grade USB/serial box now with own power source.

Let me know if you win against it
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Old 5th Aug 2017, 3:11 pm   #71
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Default Re: Cheap multimeters

Quick update from the UT61E department. I decided to try and solve the serial adapter being useless with USB/serial converters. I found the schematic online for the UT61E that covers this:

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I think they are a little optimistic to get +/-12v out of a cheap USB/serial adapter, or are they? Hooked it up to my DMM, hooked up a small electrolytic cap and watched the voltage climb to a not too shabby +/-12v on the mark. Hmm. So I knocked up a quick RS232 male/female patch and plugged the adapter in and we're down to +5v/-3v under load which isn't enough to bias the transistors in this into anything usable. Which is why they don't work!

I snipped the RTS and DTS lines on the patch and hooked up my bench supply to provide +/-12v and it now works.

Modified schematic of interface:

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Now it's a bit much to drag 9Kg of bench power supply around with this so I'm knocking up a small inline adapter with a couple of MC34063 ICs and a generic wall wart socket in it which will do the job.

I suspect the root cause of this is the USB/serial adapter being rubbish (it was only 2!) more than anything else.
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Old 5th Aug 2017, 4:05 pm   #72
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Default Re: Cheap multimeters

Assuming you've got +5V at a sensible current available on another USB port, you can easily knock up a little circuit using a MAX860-series chip

https://www.maximintegrated.com/en/p...ps/MAX680.html

to get your 'proper' RS232 supply-voltages.

I've done this in the past when needing to use a laptop-and-USB-to-RS232 for programming commercial two-way radios. Also had to do it back in the days when plenty of laptops used custom low-power serial-port driver chips which didn't give you a proper RS232/V.24 voltage-swing.
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Old 5th Aug 2017, 4:15 pm   #73
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Yeah that and the MAX232 as well.

I'm only using the MC34063 because that's all I have floating around that is legitimately close to the job at hand. You can do the same with a 555 and a couple of diodes and caps as well if you really want but it can't source as much current.
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Old 5th Aug 2017, 5:14 pm   #74
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Interesting. So it's definitely voltage and not timings?

A lot of RS232 ports only give +/-5V rather than the "official" 12V, but as the input sensitivity is quite low (+/-3V IIRC), that usually works.

As for the circuit (thank for posting!) if the lack of voltage is the problem, surely the resistors can be changed to help it work at 5V? It doesn't look as if it's biased up as a linear amplifier as such. I'll definitely investigate this when mine arrives.
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Old 5th Aug 2017, 5:28 pm   #75
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Definitely voltage for mine at least. My USB to serial has a hooky fake FTDi in it I think. They probably can be replaced but I didn't want to open it or do any mathematics today. Figured it was easy enough to fix via the black box abstraction.
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Old 7th Aug 2017, 2:30 pm   #76
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Had a more detailed look at this today while "tidying the bench" (not). The electronics are in the head end that plugs into the meter rather than the DB9 shell. This is glued together and all surface mount by the looks so i won't be taking it to bits
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Old 7th Aug 2017, 3:10 pm   #77
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Quote:
"tidying the bench"
Ah pushing just enough carp around to give a bit of room.
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Old 7th Aug 2017, 3:12 pm   #78
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That's the one

Actually bought an arbitrary waveform generator but realised it was such a mess I had nowhere to put it!
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Old 7th Aug 2017, 6:39 pm   #79
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Well, my UT61E still hasn't arrived, but in the meantime I've been writing up my multimeter reviews on my website, bringing together lots of information that was previously spread across several forums.

In addition to those covered earlier in this thread, there are some other meters, including the Fluke 101, and the BSIDE ADM08A. The latter might be interest to those who prefer manual ranging meters. This unit is 6,000-count, has true RMS, capacitance, frequency/duty cycle, and also has no-contact voltage detection - all for less than 20 delivered. Also, I've done a write-up on my UNI-T UT210E, which is an AC/DC current clamp with 1mA resolution.

I've also written a brief article on the subject of multimeter safety. It doesn't pretend to be exhaustive, but it does attempt to be balanced. Personally, I don't care if you use a 10 Chinese special or a 500 Fluke, but what does matter to me is that everyone has been able to make an informed choice in full knowledge of the possible problems and limitations of cheap multimeters.

Constructive feedback welcome. Also, suggestions for other meters to review will be considered, although please note that I've spent quite a lot of my beer reserves on the meters I have already bought for this project. Please go easy on me in the typo department - there's a lot of text in these reviews, and it is impossible to proof-read your own work, especially on a screen. I'll have another go at proof-reading later on.

https://www.markhennessy.co.uk/budget_multimeters/

Mark
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Old 7th Aug 2017, 7:10 pm   #80
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Very nice. I will read through this when I get a few minutes.

I ordered an AN8008 about a month ago. Nothing arrived yet.
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