The readings will be the same as offset compensated Ohms of a DC driven ohmmeter. Its not really AC resistance, its resistance measured with a technique that uses AC excitation in the measuring process.
Why is this not AC resistance? How else would one measure AC resistance?
Remember I am machinist not an EE but I think of AC resistance as "impedance" being the sum of resistance, capacitive reactance and inductive reactance. AFAIK the DE-5000 in Rs mode is equivalent to DC resistance. It is not the sum of reactances and DC resistance. I was simply trying to convey to grumpydoc that thinking these resistance readings were somehow AC specific was not correct and would be the same readings as obtained with a DMM except more accurate in the very low ohms and milli Ohms because the AC method of obtaining the readings effectively eliminates thermal EMF issues.
Let me clarify a few points. I posted a long thread a few days ago that attempts to explain about impedance:
https://www.eevblog.com/forum/projects/impedance-lcr-esr-meters/As I explained there, impedance is the total "opposition" to the flow of AC electricity. It is indicated as an expression Z = R + jX, where the R and X quantities are values at a single frequency. They probably have different values at other frequencies, although the R quantity may be constant over a range of (usually low) frequencies for some objects being measured (such as a short piece of wire).
The real part of the impedance is represented by R, and that is the part that dissipates energy. It is the part tells you how much heat is generated when a current passes through the impedance. That is just what resistance does with DC currents, and so the R part of impedance is the AC resistance, because it also gets warm when an AC current passes through it. Its value may be nearly constant with frequency up to maybe a few megahertz, if it's a good quality resistor, designed not to vary with frequency. If the impedance measured is something other than a short piece of wire, or a good resistor, perhaps a winding on a small power transformer, for example, the value of this AC resistance will be different when measured with different frequencies. The general variable R is called Rs or Rp on LCR meters, such as the DE-5000, according to whether it was measured in series equivalent mode or parallel equivalent mode.
The DE-5000 can't directly measure Z or X (as in Z = R + jX), but it does directly measure R (Rs or Rp). It can be used to determine Z and X with a little math. For example, I measured the primary of a small 60 Hz power transformer with the impedance analyzer at 1 kHz with an excitation level of .6 volts (to try to imitate the DE-5000). Here's the result:
This shows the impedance Z, the phase angle theta, the real part of the impedance Rs and the reactance X.
The DE-5000 measurement of this transformer winding was measured two ways. First, as an inductance Ls; this measurement mode can also give the phase angle. Second, as Rs; this gives directly the real part of the impedance, which is the AC resistance. The results are Rs is 1.99 ohms, and theta is 70.4 degrees.
The impedance is obtained by dividing Rs by the cosine of the phase angle, Z = 1.99k/Cos(70.4) = 5.932k ohms. The impedance analyzer gave 5.857k ohms, and an angle theta of 71.141 degrees. The agreement with the DE-5000 is good.
The Rs resistance readings given on the DE-5000 are indeed AC specific, although as I have explained, if you're measuring a good quality resistor or a short piece of wire, not wound around a core, the measurements will probably be constant over the 100 Hz to 100 kHz frequency range of the DE-5000; this constancy could lead a person to think that the Rs measurement is not AC specific, but this is not true for all things you might measure. For many measurements on other items, Rs will vary with frequency.
But you are quite right that because the Rs measurement uses an AC stimulus, the thermal voltages are cancelled out. I often use the AC measurement capability of the impedance analyzer to get low milliohm measurements of items I know have relatively constant Rs with frequency. And, even some things that do vary with frequency can be measured with AC stimulus and obtain nearly the same value that a DC measurement would give IF the measurement frequency is low enough.
The ESR of a capacitor is the AC resistance of the capacitor at the frequency of measurement. The ESR measurement of a capacitor does not include the reactance if the measurement is made properly with sine wave stimulus (as the DE-5000 does), but, on the other hand, the dissipation factor D does involve both Rs (the AC resistance) and X (the reactance).
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