Yet another DMM request... pfffff...  - Page 1
Forum section: electronics / testgear

author: 3nigm4
author_rank: Regular Contributor
timestamp: December 14, 2016, 10:41:13 am
content: Ok, I'm just looking averywhere on the web and here to try to find a goot DMM for my needsI've already watched all Dave's and other members videos and now it's the time to ask if I am missing somethingThe most use I do of a multimeter if for low voltage applications... usually I repair whats broke up in my life: notebooks, smartphones, motherboards, audio/video equipment, etc... other times I build something I have in my mindSometime I need to repair switching PSUs and those times I reach my maximum voltage: about 400V rectified (those times I use an oscilloscope)My actual equipment used in the last 20 years:- a cheap "FUKE" chinese DMM, 1999 counts, manual range, bought in an electronic trade fair- another cheap unbranded chinese rugged DMM, 1999 counts, manual range... I don't know why and when I bught it- another small repaired DMM, found broken somewhere- an old Philips dual track 50MHz oscilloscopeBoth multimeters has only one standard 250V glass fuse, and I've never broken one.Lately I started to build some embedded applications with Arduino and similar HW, and developing the firmware I found the need for an upgrade of my equipment... the last one is about 25 years oldSo, what miss and I'm looking for needs to have:- price under 200 €- not less than 100 MHz logical frequency counter- duty cycle- PC connection (USB or BT)- a good precision if preferred- temperature is also preferred- input protection is NOT needed... with both chinese cheap crap (and after inadvertently touching main) I'm still aliveEDIT: - AA or AAA batteries are preferred but an utopiaFirst option is to buy 2 DMM with different target:- general use: UT139C (Tenma 72-7780)- digital/log up to 220 MHz: UT61E (Tenma 72-10415, Gwinstek GDM-461) / Victor 86E / Owon B41TSecond option, an all-in-one a bit more expensive:- up to 200 MHz: UT71B (Tenma 72-7730A)- up to 400 MHz: UT71C (Voltcraft VC920) / UT71D (Tenma 72-7732A, Voltcraft VC960) / Voltcraft VC880- up to 100 MHz: Extech Ex542 (CEM DT-9930)The specified frequency ranges are real or only on paper? I've not found nobody testing more than 40 MHzI've looked also to known better brands (such Brymen BM829s) but are limited to 1 or 2 MHzThank you in advance for your precious help and for this great blogMoreno

author: rsjsouza
author_rank: Super Contributor
timestamp: December 14, 2016, 08:54:39 pm
content: The UT139 and UT61 are very well accepted by a number of forum members, therefore this, tied to the fact that two DMMs are a big helper in several scenarios, makes me believe the first option is the best.That said, I personally find very difficult to believe these meters can reach such high frequencies without significant losses. After all, connecting the long probe wires to circuits operating above several MHz will certainly act as very efficient antennas!

author: 3nigm4
author_rank: Regular Contributor
timestamp: December 14, 2016, 09:05:03 pm
content: Thanks for replyThe fact is that both UT139C + UT61E cost me about the same as a UT71D... and I don't know if the more functions of the last will come handy in the near futureQuote from: rsjsouza on December 14, 2016, 08:54:39 pmYes, you are true... I think to use the oscilloscope probe with the bnc->banana adapter to avoid that... ummm....

author: 3nigm4
author_rank: Regular Contributor
timestamp: December 15, 2016, 03:54:47 pm
content: Bought an UT71D on Amazon.it for 128 € including shippingHope to done the right thing for my needs... I'll report some picture

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 15, 2016, 04:43:46 pm
content: Just a heads up with the frequency counters in DMMs, at least with experience from the UT61E. They're pretty good and will hang on to about 70-80MHz fine but the resolution is low to the point it's useless for more than a few MHz (22,000 count on the UT61E), the circuit impedance is terribly variable over the entire range, they inject noise galore into the DUT and as for the amount of RF that the device chucks out if you put some power down it is anyone's guess. The killer for me though is that you can't see frequency drift easily unless you have more digits. 28.014MHz which is what the display shows is missing an entire KHz worth of resolution. Could be 10-50Hz/minute drift easily.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 15, 2016, 07:19:16 pm
content: Quote from: 3nigm4 on December 15, 2016, 03:54:47 pmCongratulations with your purchase! I hope you enjoy it and please post some pictures - we all love to see new gear.I just recalled that Dave reviewed and did a teardown of the UT71E and IMO he was expecting more than he should have. But there are some folks reporting they have been consistently improving their meters. If you are interested, take a look at:https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-%28why-uni-t-meters-suck%29/

author: 3nigm4
author_rank: Regular Contributor
timestamp: December 16, 2016, 07:54:46 am
content: Quote from: SingedFingers on December 15, 2016, 04:43:46 pmYes, that's right, but for my needs it's just enough: I need to see the rate of my little embedded projects that are below 100 MHz, just to see if my code is optimized or I need to change something... the measurement must give me an idea, not the exact HzIn the future if needed, I'll look for a bench frequency meterQuote from: rsjsouza on December 15, 2016, 07:19:16 pmThank you... I love that too... I looked all teardowns of the web till todayQuote from: rsjsouza on December 15, 2016, 07:19:16 pmYep! I know by heart all Dave's exclamations and laughterFor my usage I think it to be the best compromise