UNI-T UT612 LCR meter and testing ESR in circuit?

[Stoempie]

Hey guy's,

I'm new to the hobby and i'm looking for an ESR meter for measuring in circuit, i had contact with my local shop and the say that the UNI-T UT612 LCR meter cannot read a ESR in circuit.
The peak ESR meter can do that but is there a video or explanation or someone  that can confirm that because i seen a lot of movies on testing ESR but cannot find a reason why that cannot be don by the uni-T it can test the ESR at 100khz just like the peak does ? 

Thank for the forum i learn a lot here.

[mortrek]

Not an expert. You can sometimes test caps (I assume that's your main goal) in-circuit, but depending on the circuit and how they are connected within it, you can't really rely on the result. I think that false-negatives (where ESR looks good, but isn't) are less common than false-positives (where it looks bad, but isn't), so you can kind of get an idea of whether or not a cap is bad. The only surefire way to know is to desolder at least one leg before testing it. Also most ESR meters require discharging the cap first.

It also helps if the meter is low-voltage, as it keeps from interfering with a lot of components like diodes. You also don't need a full brand-name LCR meter to just test ESR. One good design is the one by Bob Parker, but it's usually pretty pricey still at ~$80 US. Also those cheap ($10-15 bare) Chinese-made open source "component testers" can be found for very little and do a passable job. Some have sockets and some have clip leads. You'd need the ones with leads to even try using them in-circuit.

[mortrek]

Also looking at the specs for the UNI-T UT612, I think it uses 0.6V for testing which is probably why it can't test in-circuit. Bob Parker's design uses something like 0.2V for testing, IIRC. Not sure about the component testers.

[Stoempie]

ok thx, i will take a look if i can find what voltage the peak use to measure.
ESR test voltage (into 40 Ohms): 40mV (typical) for the peak so ok now i can understand why the uni-t will not work.


 

[Phoyle]

Hi,

Also looking at the specs for the UNI-T UT612, I think it uses 0.6V for testing which is probably why it can't test in-circuit. Bob Parker's design uses something like 0.2V for testing, IIRC. Not sure about the component testers.

There is also the UT622c. The Technical Specifications tab shows it has test V of 0.1 Vrms, 0.3 Vrms and 1 Vrms.
https://www.uni-trend.com/meters/html/product/tyyq/ComponentTesting/UT622%20Series/UT622C.html