UNI-T UT-61E

[SeanB]

I did a quick upgrade of my one today, and added the input protection it should have had ( on the PCB but omitted for cost reasons) by adding 4 275V varistors in the required locations. I used 2 in series for each poswition, so now the input will be clamped for any voltage over 830V DC peak, as I selected the varistors for equal breakover voltage. I found a pack of RS  204-1996 275VAC varistors i had ordered long ago, and checked all 5 to see breakover voltage. 2 were 402/3V, and 2 were 425/7V, with the one being 411V, so I used the high and low in series, so each chain has a similar breakdown voltage. Did not dismantle the meter, just soldered the pretinned and precut and preformed ends into the holes in the PCB, and then joined the midpoints of the 2 strings, so that they were floating in the air inside.  Placed the varistors neatly in the space and closed it up again.Checked on resistance, and still reads open circuit, so no problems there. Was debating doing a high pot test but as they have been tested before use decided against it, they should work. I know the little green tester from Frankie can deliver 1400V as a test voltage, but I still like the meter. Ohers have tested them to destruction, and the PCB breaks down at around 1500V so I am happy enough.

[Mr Eastwood]

I did a quick upgrade of my one today, and added the input protection it should have had ( on the PCB but omitted for cost reasons) by adding 4 275V varistors in the required locations. I used 2 in series for each poswition, so now the input will be clamped for any voltage over 830V DC peak, as I selected the varistors for equal breakover voltage. I found a pack of RS  204-1996 275VAC varistors i had ordered long ago, and checked all 5 to see breakover voltage. 2 were 402/3V, and 2 were 425/7V, with the one being 411V, so I used the high and low in series, so each chain has a similar breakdown voltage. Did not dismantle the meter, just soldered the pretinned and precut and preformed ends into the holes in the PCB, and then joined the midpoints of the 2 strings, so that they were floating in the air inside.  Placed the varistors neatly in the space and closed it up again.Checked on resistance, and still reads open circuit, so no problems there. Was debating doing a high pot test but as they have been tested before use decided against it, they should work. I know the little green tester from Frankie can deliver 1400V as a test voltage, but I still like the meter. Ohers have tested them to destruction, and the PCB breaks down at around 1500V so I am happy enough.

nice mod!  any pics or can you show the mod on the original circuit diagram?

[SeanB]

When I get the chance I will post the photo. It is in the camera..........

[SeanB]

Here it is...

[Mr Eastwood]

Many thanks for posting the pic! 

It just shows how much of a beginner I am, I had to look up "varistor",  then realized it's actually a MOV.  Another really helpful thing was I didn't know the 61E used a Cyrustek chipset which is what I'm working into my DMM project, so looking at the 61E schematic is an extremely useful practical circuit, which is much better than the chipset datasheet examples.

I have a question though, in the datasheet it talks about the parasitic capacitance of the PCB; would the mod you did effect that to a point you'd need to tweak the trimmer cap on the board to compensate?   have you checked the low value cap measurements; are they working ok?

[dr_p]

Here it is...

It's interesting that on the pcb there are GDT symbols instead of MOVs. However, I think MOVs are a better choice due to the fast response.

How did you choose the 2 x 275V MOV? Simply because that's what you had and 830VDC peak seems too much for your needs anyway? I'm asking because the meter is intended to measure 1000VDC and 750VAC (1050VDC peak) so you're kind of inhibiting functionality here.

In Dave's #373, the Fluke 27 has 4 x 430V MOVs, so it clamps at 1700V, even though it only measures up to 1000V

[SeanB]

They were on hand, and were the right size to fit. They add about 50pf across the input, which will not affect the meter much. This is not going to affect the voltage divider, as it is before it. GDT tubes would probably be better as they clamp at around 90V when conducting, keeping high voltages out and making sure the PTC units will operate. Using the MOV's though will just clamp, and they have a limited power dissipation capacity of 0.2W so a long term overload will burn them out. Short term will be no problem though, it is just there for operator oopsies.

As I generally do not deal with more than 600V the value chosen is good enough for me.

[Monkeh]

I'll have to post up a fresh picture of my UT61E. GDTs fitted, as well as upgraded fuses (they were laying around).

E: Here we are.

E2: And now Farnell's back from their regular maintenance RIGHT WHEN I WANT TO USE THEM, EVERY NIGHT: http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=2118242

[SeanB]

I was looking to use some of those, but was waiting until I had an order big enough to make the postage free from RS, the VDR's were a previous order where I just needed 1 in the 5 pack, so I used them instead.

[LightAges]

Monkeh:

That is the way they should have built it in the first place!

[Monkeh]

Monkeh:

That is the way they should have built it in the first place!

That was the idea

[divemaster]

Hi can you tell me the fuse's rating that you used.......many thanks

[vrun]

RUNNING UNI SOFTWARE SIMULTANEOUSLY IN SEVERAL INSTANCES ON WIN7

Hi folks

I do not own a UT-61E yet ... thus the question.
Can I run the logging software for the UT-61E in several instances on WIN 7
iow I need to log three different values at the same time and I would like to use 3 UT-61Es

Thanks for any help

[mariush]

You should be able to... just get three serial to usb adapters/cables, they'll create 3 separate virtual COM ports in Windows, you start three instances of the application and set each one to a different COM port.  No problem at all.

See UltraDMM software, it may be able to run three at same time without having to run three applications.