I know that capacitors change there capacitance according to the frequency in the cirquit.

capacitance should change little based on frequency. its the function of temperature and other nature, but not frequency. whats changed based on frequency is impedance and phase angle. pls correct my knowledge.

Capacitance is not pure ideal capacitance! Measuring method, including frequency may affect result, even highly.

Quoted from Nichicon

"The capacitance of aluminum electrolytic capacitors

changes with temperature and frequency of measurement,

so the standard has been set to a frequency of 120Hz and.. "

Normal practice for big AlElco is 120Hz frequency for measuring "capacitance" but also this is compromize.

Different capacitor and different inductor need different measuring methid including also understanding what is frequancy meaning. (just becouse there are not ideal components in real world.)

Also it need select if use "parallel" or "series" method.

Real LCR parameter measuring equipments have many times big manuals and applicatuon notes how to do measurements. Also it is good to know how manufacturers specify component values.

Typically higher freq give too low cap values. (but there is also exptions and possible sometimes measurement may give very confusing results if frequency is near resonant freq.)

Some good LCR meter (example many Tonghui professional models) can of course change test frequency but user is responsible for make selections!

It is good to know fundamentals and principles and practices how to measure. The manufacturer may also be assumed that the measuring device used by a trained person who has sufficient knowledge and skills of the measurement technique. In this case, the manufacturer does not need to include in the basic textbook. But today it is easy, nearly all can easy find in internet.

Here some basics

NichiconCornell DubilierHere read carefully also about "Self-resonant Frequency" !

Quoted from Dubilier:

"

Self-resonant Frequency

The self-resonant frequency is the frequency at which the

capacitive reactance (1/(2?fC)) equals the inductive reactance

(2?fL). Because the capacitive reactance is 180

degrees out of phase with the inductive reactance, the two

reactances subtract out, and the remaining impedance is

purely resistive and is equal to the ESR at that frequency

Above self resonance the device is inductive.

In aluminum

electrolytic capacitors the self-resonant frequency typically

occurs at less than 100 kHz. The self-resonant frequency is

equal to 1/[2?(LC)1?2 ]. It occurs at a frequency higher than

expected based on 120 Hz capacitance because capacitance

decreases with increasing frequency, and it can decrease

with increasing temperature from capacitance increase."