The Transistortester's ESR measurement method delivers a suprisingly good approximation, but it will never be as good as a proper LCR meter. And it's optimized for the ATmega MCU family.
I will add one important addition to madires post - this is true for
POLAR ELECTROLYTIC capacitors!
If you want to check the ESR of non-polar capacitors, especially those with ratings less than 1µf, be prepared that the results may differ from those measured on an LCR bridge meter by a factor of 10-100. The serviceability of such capacitors on the transistor tester can be checked, as it is correctly stated in the author's manual, only by comparison with a previously known serviceable capacitor of the same type!
For example, comparing the TT DTU-1701 with the LCR DE-5000 which I made relatively recently at the request of a forum member.
DTU-1701 is equipped with the author's firmware 1.13k. By hardware update - LDO MCP1702-5.0 and ION LM4040-2.5 are installed.
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
The test capacitors are not used or soldered (except the last bad one for clarity) in the photo below.
In order from left to right:
1. Hinano 4.7µFx50V 105°;
2. Hitano 47µFx160V 105°;
3. Hitano 220µFx50V 105°;
4. Hitano 470µFx100V 105°;
5. Hitano 1000µFx50V 105°;
6. Jamicon 2200µFx10V 105°;
7. Hitano 3300µFx25V 105°;
8. KZG 3300μFx6.3V 105° (defective, removed from computer motherboard).
Measurement results and comparison in the photo below:
From left to right - DE-5000 capacitance and ESR measurements at 100Hz,at 10kHz(or Rs if capacitance measurement is not available),at 100kHz(or Rs if capacitance measurement is not available),DTU-1701 test.
I'll explain the results a little bit:
Low ESR values of 0.00 ohms, especially near 0 on TT "float" plus or minus 1-2 units of the lowest digit, which is understandable and acceptable for this circuitry.
The capacitance of the faulty capacitor is overestimated compared to the DE-5000, but the high losses and ESR already show that it is unusable.
In principle, as I wrote before, you can trust the transistor tester readings if the
AUTHOR'S OSHW firmware is loaded,
the device is in good working order and properly calibrated!