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Review and tear-down of UNI-T UT612 LCR meter
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PA4TIM:
Thanks for looking, i do not want to open my meter ( i know, the motto is " take it apart"  ;-) but that is not my motto unless it needs repair) so it looks like it is a passive guard. But in my opinion, it does not matter what kind it is, as long as it works and it must be accesible for the user. I often use farraday cups but also standards that have guard connections and then you need acces to the connection.
This is the kit I made. The lemo is for the normal probes but also to make a shieded connection to the IET. But I'm still thinking how I'm gonna do that. First I think I wil make a kelvin adapter by turning two connectors on my lath, split them and separate them by teflon make a bridge to hold them in position ( so make a connector like the double pomonas) and then to the lemo connecor. Or I maybe replace the existing croc wires with two longer ones and a lemo connector.

dark_hawk:
Thanks for the Review, was thinking about getting one and after the review I'm going for one.
dark_hawk:
Hi Wytnucls,

I got the UT612 mainly for measuring caps, I'm very new to electronics so I need some help please.

What are the typical values for ESR for a cap to be considered good:
Should I use this table from the old Bob Parker ESR Meter:
http://i1119.photobucket.com/albums/k636/mib_instruments/mib_instruments2/PreP1070439.jpg

Or should I use this table from peak atlas ESR meter:
http://dc338.4shared.com/img/kwg9wwYx/s3/esr_meter_table.jpeg

Or this chart from the Blue ESR Meter:
http://www.electronicrepairguide.com/images/blueesrmetertestchart.jpg


I also got these cables:


--- End quote ---


But the meter does not pass the calibration, are the cables too long? Any suggestions?

Thanks.
Wytnucls:
Hi,
I'm no expert on electrolytic caps, but I think that the best procedure would be to work from the datasheet, if you can find one.
Most datasheets for electrolytics will give you specs based on Tan d (D).
I would first measure capacitance at 120Hz, to find out if the cap is still within the usual 20% limit of the published rating and then compare Tan d (D) with the original max figure, to see if the ESR has increased dramatically. Tan d should be no more than 150% of the max published value.
If both capacitance and tan d are found to be out of limits, the cap is probably bad.
If you can't find datasheets, those tables should help you, if you prefer to work with ESR figures. Be aware that low ESR electrolytic caps, found mostly in power supplies, will have different parameters.

Kelvin tweezers or pincers are nice, but won't give you better measurements, as this meter is not a 4-wire instrument. To pass calibration, the test leads should be shielded and equipped with a guard connection or, if not shielded, kept as short as possible. I would recommend short test leads with small croc connectors.
dark_hawk:
Thank you for the response.

I have an assortment of caps from different manufactures and even of different series, it would take a long time to hunt every specific cap datasheet and all I need are ballpark numbers.

I don't think the leads are shielded. Will try to shorten them and see if they pass calibration.


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