Why we have to match the frequency of LCRmeter to the frequency that DUT is tuned for

The LCR meter detects the voltage, current and phase angle of DUT. Thus, The DUT can be represented as L, C or R. But, why we have to match the frequency of LCR meter to the frequency that DUT is tuned for? When we change the test frequency, the reactance must be changed. Causes the voltage, current and phase angle change. But value of R, L, C is the specific value of the DUT, It doesn't depend on the frequency?

daffdaff said:

The LCR meter detects the voltage, current and phase angle of DUT. Thus, The DUT can be represented as L, C or R. But, why we have to match the frequency of LCR meter to the frequency that DUT is tuned for? When we change the test frequency, the reactance must be changed. Causes the voltage, current and phase angle change. But value of R, L, C is the specific value of the DUT, It doesn't depend on the frequency?

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In most cases, the R, L, C values are independent of frequency. That is the reason we can buy a 10k resistor or a 47 uF capacitor. However, for many devices the R, L, C values may depend on the frequency (second order effect) and we can therefore measure the R, L, C values at different frequencies. When these parameters are reported in the datasheet, we usually specify the applied voltage and the test frequency (and any other relevant conditions).

Hi,

I agree with c_mitra.

Just some examples:
If you have an inductance with core, then the core dissipates some power every time the polarity changes.
The often you change polarity the more power is dissipated.
You see the dissipated power in the "R" part of a RLC. Therefore (series) R increases with increasing frequency.
****

You may see a battery (or even an electrolytic capacitor) as ideal_ capacitor but it isn't.
The chemistry is slow, therefore it can't react to sudden changes in current.
Therefore with increasing frequency it seems the capacitance becomes smaller...and power dissipation increases.
Both R and C change with frequency.

***
Even worse is a loudspeaker...
It has several resonace frequencies, even the case and the reflections in a room influence RLC and all are frequency dependent..

Klaus