UNI-T UT61E Multimeter teardown photos.

[Hydrawerk]

Is it normal that I get 312pF when nothing is connected?? I found these UT-61E at a school lab

[Hydrawerk]

I got much better results on some old multimeters. UT70A from 2009, DT-890G from early 2000s and the M-3650D is more old, probably from mid 1990s.
(I do not know if this was discussed earlier in this thread...)

[mariush]

The capacitance is a bit on the high side.

Mine shows 84 pF with the leads connected, about 58 pF without any leads.  The manual specifies 50pF as normal/acceptable, and that you should use the REL button to zero it out.

Still, i wouldn't worry very much about it, though i would test the capacitance function with several known capacitors.

[RobertoLG]

Is it normal that I get 312pF when nothing is connected?? I found these UT-61E at a school lab

just press the Rel mode

[Hydrawerk]

Thank you for the advice. My thoughts on the meter:
The two buttons (blue and yellow) are confusing.
Why no LCD backlight? Strange on a 22000 counts DMM.
The autoranging is quite fast.
Beeper is fast.
I like the OFF position of the rotary switch. Now the DMM cannot turn on when carried in a backpack.
Well, i prefer Brymen (not owning one yet) but this UT61E is probably an OK multimeter for most needs, especially if you do not work with high energy circuits.

[MrSlack]

I've had one a few months and I have no problems with it. Gets a bit dicky if the battery goes flat. Mainly use it in manual ranging mode if I'm honest

I get ~220pF with a couple of Pomona minigrabber to 4mm leads attached to it. As someone said, use REL for capacitance measurements to deduce input circuitry and lead capacitance. The supplied component tester module is crap - I threw it away.

As for high energy I regularly use it up to ~110v DC (inside a Tek scope) and AC mains, voltage only! I make a habit of not actually probing anything high energy live and use clip probes then apply power so the meter is not making a circuit with me at all at any point and I wear eye protection when working on anything likely to go pop.

Regarding multimeter lore, I suspect more people injure themselves not from the meter blowing up but doing something stupid to start with (probe shorts, accidentally becoming part of a ground loop etc etc)

Interesting bit: I paid £40 for mine - total bargain!

[Salas]

Can high energy but low voltage as stored in a large capacitor or in a car battery damage the meter as badly as the mains or HV?

[MrSlack]

Probably not a capacitor or a car battery as the general nature of the high impedance inputs means that the capacitor can't discharge quickly enough. If you stick it on amps and short it then it'll just pop a fuse. Inductors on the other hand, when the magnetic field collapses can produce hundreds to thousands of volts which can jump around or through any protection and high impedance inputs.

[Thilo78]

I got much better results on some old multimeters.

Not sure if it helps, but I'll throw in the result from my UT71E.
No leads: 0 pF
Leads attached: 11 pF

[Salas]

My 61E shows 66pF sans leads, 85pF with Brymen leads

[Salas]

Probably not a capacitor or a car battery as the general nature of the high impedance inputs means that the capacitor can't discharge quickly enough. If you stick it on amps and short it then it'll just pop a fuse. Inductors on the other hand, when the magnetic field collapses can produce hundreds to thousands of volts which can jump around or through any protection and high impedance inputs.

A static discharge could also find its way to the main chip by jumping around If not absorbed by protection I suppose?

[MrSlack]

It could.

[Mike60]

Hello U61E users 
I received today my 61E. 49$ Ali....
I want to make some modification.
Back light. I order TP223 it is on the way. I order MCP1703 - received. I have some leds.
If everything are ok i go to next mod.
I suppose this product are old. Why ?
Please look attachment.
Regards
Mike

[SeanB]

No idea, but I would suggest as well you order some 5mm 600VAc MOV devices and put them on the board in the 2 places  SG1 and SG2 marked on the board.

RS  760-6964 or 711-8149 or 289-7109 or 178-059  would all do there, low capacitance and with a clamp voltage well above what you would normally apply to the meter in most cases, but hopefully more than enough to protect the meter from major overvoltage. First would provide most protection, but will limit maximum voltage to mains voltage only, the others will enable use at 400VAC with some care.

[Mike60]

Thank you.
I will try.
Regards
Mike

[Mike60]

SeanB
RS  760-6964 or 711-8149 or 289-7109 or 178-059 

I find all but what to buy ? And are different sizes. Please what to order ?

Regards
Mike

[SeanB]

First one is small (9mm) and will allow you to work with mains AC up to 300VAC or 400VDC, so will be fine with the meter.  So probably the best compromise as you really do not want to use these meters at higher voltage.  Lowest capacitance as well and likely the fastest acting.

You also get them in a pack of 10, so will have 8 left over just in case. Pretty cheap as well.

[Mike60]

Morning
I will order today.
Have a nice day
Mike

[hgg]

Hi,

I am thinking of adding some input protection to the UT61E. 

MOVs are fast but low current and will add capacitance.
GDTs are slower but high current and very low capacitance.

Can we use a combination of MOVs & GDPs for ever better response?

On the other hand I see that the tracks from the GDPs are very thin.
So is there any point to add the protection with such thin tracks?
Look for example the one that goes from SG1 to R28.
forget the above...

Thanks.
George.

[Fungus]

Can we use a combination of MOVs & GDPs for ever better response?

Yes. Add enough MOVs to protect you until your GDTs react. The more the better (well, two MOVs is probably enough...)

[hgg]

In series?  In Parallel?
Can you suggest a combination that will suit the UT61E?
Thanks.

[SeanB]

Slap the 3 low capacitance MOV units in, and be done with it. The limiting factor will be the PTC in any case, 1kV and it will fry itself apart in a second or so. Choose the voltage to suit your normal use, and as they mostly come from RS in packs of 10 you will have some spares. If you do blow them up the meter will not survive in any case.

In my case I just used 2 275V MOV units ( 7mm) in series, as I did have the remains of a 10 pack around, so using the 6 was easier than either placing an order and wait till I had the minimum order price in other parts, or paying the $20 courier charge RS puts on here for small orders. Still have 1 left, after replacing 3 MOV units on other equipment.

[hgg]

Hello SeanB,

Do you know if the varistors will affect the Capacitance measurements?
Did you check it on yours?

What about these GDPs?
http://www.ebay.com/itm/2PCS-2RM470L-8-470V-2R470-10KA-Ceramic-gas-discharge-tube-Mine-management-/261991644243

[SeanB]

RS ones will add 300pF to the capacitance, but as you pretty much always use REL mode in capacitance from new it does not make a difference except on the lowest values.  Might slightly drop frequency response, but as it is only specced to 1MHz in any case the slight drop off will not worry much. If you want frequency you are pretty much only measuring mains or up to 20kHz VFD values in any case, higher you want a real frequency counter, and AC will not worry at all, the RMS converter is the limiting device.

[hgg]

What about this comment from a different thread ?

https://www.eevblog.com/forum/testgear/ut61e-drift-and-recalibration/75/

"I think that MOV-s are inadequate for UT61E, because you lost the hight impedance input on mV range.
You can find GDT down to 70-100V."