UNI-T UT61E Multimeter teardown photos.

[ddavidebor]

Found a son of someone who go to electronic school and has access to 6.5 digit multimeter...

[Rick Law]

... and a recently bought UNI-T UT61E ... ...friend of mine brought a Fluke 79 III...Unfortunately Fluke has not been calibrated for the last 4 years... ...Do you consider wise to “calibrate” my other multimeters according to Fluke measurements?

If your UT61E is recent, and you are considering using a (calibration-wise) 4yr old Fluke 79III to calibrate your new UT61E -- that (to me at least) means you are not trusting the UT61E being within spec.  Why not get a DMM-Check (plus) from VoltageStandard.com.  Now you have reasonably good and absolutely fresh references to go by.

I did not take a count, but based on memory: I have seen (4+) folks here posted that their UT61E (as delivered) are in spec, and only one post I can recall saying the 61E being slightly off-spec on delivery.  If you decide not to go with DMM-Check, it sounds to me a good bet to just trust the 61E to be the more accurate of the bunch.

[gatos]

At Lightages and Monkeh: I agree, but I can not explain the measurement on 1.5V battery and the difference with the 12V.
                                          Any ideas?

At T4P: Don't you think that I have to tweak up the SUMMIT, in accordance with the other three (at AC voltage-grid outlet)?

As I said before, I would like to buy a DMMcheck plus (start saving money-remember we have crisis in Greece!).

[Monkeh]

At Lightages and Monkeh: I agree, but I can not explain the measurement on 1.5V battery and the difference with the 12V.
                                          Any ideas?

Resistor network.

[Lightages]

As Monkeh said, the internal resistor network that is used to divide might be faulty. But this is getting way off topic and we are polluting this thread. Please start another thread if you want to discuss adjustment and calibration of anything other than a UT61E.

[T4P]

I don't understand what he means by "SUMMIT" and he's derailling the thread ... 

[gatos]

I don't understand what he means by "SUMMIT" and he's derailling the thread ... 

Summit=brand of multimeter. See my post at  February 24, 2013, 01:48:31 PM. I think it is obvious 

I'm not trying to derail the thread. Sorry for polluting the thread.

I understand after all that I should trust the newly bought UT-61E (and buy a DMMcheck).

Thank you for your opinions and I can assure you that I did not meant to upset anyone.
Have a nice day.

[erick]

Hello, everyone.

Although this is my first post, I've been following the forum and watched Dave's videos for quite a good time. A lot of fun and useful information.

I am a mechanical engineer, and electronics for me is just a hobby. So far, all my small projects are arduino related. So, in terms of electronics, I am a complete newbie.

Well, let's go. After watching Dave's shootout video, I decided to buy a UT61X to replace my cheaper multimeter. I could not decide between UT61D and UT61E, though, and then I came to this thread.

Although I find the backlight feature in UT61D really handy, the better specs of the UT61E model would certainly catch my favour. By reading your posts, however, I disappointedly found out about the burden voltage downside.

According to Dave's video, UT61D has surprisingly low burden voltage. Here comes my question. Since the UT61E is expected to deliver better accuracy, isn't it supposed to, at least, be as good as UT61D in terms of burden voltage? Is there a technical explanation to this fact? I mean, isn't burden voltage somehow related to accuracy?

I apologize if that is too silly a question. I just want to try to understand a bit more about multimeters specs.

[Lightages]

Burden voltage is another spec that doesn't necessarily have to be low for a meter to have other specs with high accuracy. Yes it is horrible with the UT61E. For a bit more, $90, get the Amprobe AM-270 if you can it into Brazil without high taxes. I know how hard it is to get anything in South America for normal prices.....

[mariush]

According to Dave's video, UT61D has surprisingly low burden voltage. Here comes my question. Since the UT61E is expected to deliver better accuracy, isn't it supposed to, at least, be as good as UT61D in terms of burden voltage? Is there a technical explanation to this fact? I mean, isn't burden voltage somehow related to accuracy?

I apologize if that is too silly a question. I just want to try to understand a bit more about multimeters specs.

The "brains" inside the UT61D is totally different than the one inside the UT61E, they're made by different companies, with different features and so on. So it's no surprise the burden voltage is a bit different, the meters don't have the same components inside.

All meters have burden voltage, can't really get around that, it's just that ut61e has quite a big value (about 1v for the 220mA range)
Even Fluke meters aren't so awesome when it comes to burden voltage:

http://www.fluke.com/fluke/usen/community/fluke-news-plus/ArticleCategories/Electrical/BurdenVoltage.htm

In the case of the 87V which I mentioned earlier, the burden voltage for the 400 mA range is typically 1.8 mV/mA. What that means is that if we're reading 1 ma, there will be 1.8 mV drop across the terminals of the meter, and if we're reading 300 mA, there will be roughly 0.54 volts drop across the terminals.

So if you're really trying to measure some low voltage stuff, with low power consumption, even with Fluke the 0.3-0.5v drop will be an issue.

Not much you can do about it other than possibly using clamp meters or using a device like dave's uCurrent.

[erick]

Thanks for the answers, guys.

mariush,

I didn't think there was so much difference between the models, since they belong to the same series. That explains it.

Lightages,

There is no way I can get an AM-270 for $90.00 here =/

Even the Uni-T may end up costing me about $100.00 if I get caught and have to pay taxes. Anyways, I will just look for a good price on ebay or DX.com and buy a UT61E.

In what concerns low voltage measures, I'll be probably using something like Dave's product, as mariush pointed.

[dr_p]

I doubt you'll find it cheaper than from Frakie:

https://www.eevblog.com/forum/buysellwanted/brand-new-uni-t-ut61e-for-sale/

[HKJ]

The burden voltage on auto ranging DMMs, include 61E, is a bit funny.
They usual combine two ranges on each switch position, i.e. two mA ranges when the switch is on mA and two uA ranges when the switch is on uA. These two ranges has to share the same resistors. This will give a low burden voltage on the low mA range and a high burden voltage on the high mA range (same for uA).

A good way to get a low burden voltage is to use a external resistor. With the UT61E a 0.1 ohm resistor will give a very good high mA range. At 1A the burden voltage will be 0.1 volt and at lower current you will have a resolution of 0.1mA.
With a external resistor it is also possible to connect the resistor without adding long test wires that add to the burden voltage (The test wires will only carry voltage, not current).

[JimmyMz]

What size is the ceramic capacitor on the back of the board, corresponding to the negative battery post terminal (C36)? I scorched mine, and fixed it with an electrolytic, but I want to put a SMD part back in. I don't know SMD sizes yet, so the help is definitely appreciated. Thank you 

[PedroDaGr8]

What size is the ceramic capacitor on the back of the board, corresponding to the negative battery post terminal (C36)? I scorched mine, and fixed it with an electrolytic, but I want to put a SMD part back in. I don't know SMD sizes yet, so the help is definitely appreciated. Thank you 

It is a 1206 size (metric code 3216) 10uF capacitor.

[JimmyMz]

It is a 1206 size (metric code 3216) 10uF capacitor.

I knew it was 10uF. Regardless, thank you for including the package size. 1206 is what I needed, thank you

[em132]

Parts used:

1x SIBA 10A, 1,000V, 30kA, 5AG (eBay)
1x SIBA 0.5A, 1,000V, 3AG (eBay)
2x Littelfuse CG21000L GDT's (Digi-Key)
4x Littelfuse 1/4" fuse clips (Digi-Key)

Cost: ~$27 USD (not incl. S&H)

As others have surmised in this thread, GDT's are perhaps the only way to go for the clamping devices... that is, if you want to maintain the meter's 1,000V measuring ability. The ideal MOV's in this case would've been the V10D112 (or equivalent), but they are simply too fat and tall to fit, and you just can't bend them over either because the battery compartment is in the way. (BTW, the V10D112's are the same "monsters" used in the BK2709--the ones that had Dave gushing in his $100 shootout.) The CG21000L's I used are downright tiny in comparison, but they cost ~3.5x more than the V10D112's. Also, while GDT's do have a slower response time than MOV's, they aren't as prone to "blowing up" and they don't add nearly as much capacitance to the input circuit (i.e. the residual capacitance on my 61E went from 56pF to 60 after the mod).

It's a similar story with standard 5AG fuse clips; at ~18-19mm tall they're just too damn big to fit in the 61's. To put a 5AG fuse in the 10A spot you pretty much have no choice but to use a 3AG (1/4") clip and stretch it out (it can be done, and the results work surprisingly well, provided you do it carefully, without rushing). Another thing, the PCB holes in the mA fuse (F1) area will only support a 3AG fuse, not 5AG. Finally, if for whatever reason you want to fit a 3AG in the 10A spot instead of a 5AG, you'll need to drill an extra hole near the PCB mounting screw hole to ensure proper distance between the two clips--either that or only use one solder lug on one of the fuse clips (NOT recommended).

Anyway, here are the pics:



NOTES: Wrapped the PTC's in heatshrink, because that's the way it's done in most hi-end meters (monkey see, monkey do!). I also wrapped the GTD's in clear vinyl tubing and added some 0.5mm-thick flame-resistant insulating sheet (taken from an old PC monitor) around the fuses for increased spark-over resistance.


More pics...


Because my abode is a 100% alkaline-free zone!



Test lead kit family portrait:

UNI-T UT-C07 multi-purpose probe clips (DX)
UNI-T UT-C04 large alligator clips (NY Platform)
Mini alligator clips (Franky Tong <--  )
UNI-T UT-C08 probes (GoodLuckBuy)
Stackable short leads (DIY using parts from DX, Performance-PCs & Franky)
E-Z-Hook minigrabbers (Digi-Key)
Hook Clips (Franky)
2x pairs female banana plugs (Franky)
UNI-T UT-L14 silicone test leads (NY Platform)
UNI-T UT-D04 USB cable (409shop)



Packed to the hilt! NOTE: The case (and the USB cable) are from a UT71A I bought from 409shop over a year ago. After comparing it to another (older) 61E I couldn't get rid of it fast enough. Of course, I kept the cable and that really nice carrying case for myself. 



The end. 

[Wytnucls]

Nice job. Possibly not much of an improvement, because of trace spacing and general construction, but it looks good. Check the accuracy of the 10 amp range now, as the fuse is part of the shunt and any change in resistance will affect the original calibration. It is less of a problem on the mA side.

[Monkeh]

Nice job. Possibly not much of an improvement, because of trace spacing and construction, but it looks good. Check the accuracy of the 10 amp range now, as the fuse is part of the shunt and any change in resistance will affect the original calibration.

You want to double check that?

[c4757p]

Check the accuracy of the 10 amp range now, as the fuse is part of the shunt and any change in resistance will affect the original calibration.

Wait, really? How idiotic!

[Monkeh]

Check the accuracy of the 10 amp range now, as the fuse is part of the shunt and any change in resistance will affect the original calibration.

Wait, really? How idiotic!

No, not really.

[Wytnucls]

I checked the UT71 circuit and it does look like the measurement is also done on the shunt only. Mine went out of calibration after the fuse mod, for other reasons, obviously. Thanks Monkeh, learning everyday
No harm in checking calibration anyway... ))

[em132]

Nice job.

Thank you.

Possibly not much of an improvement

Maybe... Maybe not.

With respect, is it any worse than your 71B? How many spark-gaps has yours got?

because of trace spacing and general construction

Again, with respect, has it been determined with absolute certainty that "trace spacing" was the main factor in downgrading the "GS" models to Cat III 300V / Cat II 600V, and not, perhaps, just it being another simple case of legal "cover-your-ass-itis?"

As for the "general construction," you'd be hard-pressed to find a better solution for isolating the battery (esp. compared with the 71 series!). The 10A fuse is also essentially isolated in its own little corner of the board. The thick plastic input jack "buckets" each act as circular isolation slots, and (to my eyes) the blast protection around the case seems to be well implemented (deep U-groove and thick sidewalls).

Am I missing something?

Not looking to start anything (really!), but a little perspective would be nice.

[T4P]

I have known Wytnucls the man famous for defending his dear UT71X series DMMs

While his comes with glass fuses ours come with ceramic fuses stock  That just shows how much this DMM has to give in terms of safety (If not for cost cutting by UNi-T's beancounters)

[M0BSW]

 I got mine today and I really like it for my low powered  radio amateur projects and radio servicing , I'm really interested in the backlight hack, must loo it up.