capacitance limit

[Gi4CZW]

My 4170 has a lowest frequency of 0.1 MHz. I assume that will limit the value of capacitance it will detect, I did a hunt but was not able to find that value. Can somebody give me a guide. Thanks in advance. Cliff.

[Bob]

The min value of capacitance is primarily a function of the reactance of the capacitor. At 100KHz, the min capacitance would be around 100 pf. By testing at a higher frequency, you can measure smaller values, down to the pf range. In general the reactance should be less than 10K ohms. Lower reactance is better as long as other attributes of the capacitor, such as the lead inductance do not become significant.

With the latest program (845B and up), you can scan the capacitor over a frequency range and see how it varies versus frequency.

--73/Bob

[Gi4CZW]

Hello Bob, thank you for the quick reply. 100pF !. I had been reading up on " testing ESR (Equivalent Series Resistance) of electrolytic capacitors " and had dug out an old electrolitic to see if 4170 could read the leakage. When 50uF failed to show, I wondered what the limit is. I always seem to have more to learn. Thanks again. Cliff.

[kc0ws]

Bob replied with what the MINIMUM capacitance limit is, but I think you are looking for the MAXIMUM capacitance is that can be measured. I don't know what it is, but yes, you will measure the lowest capacitance at the lowest frequency the AIM will measure. The newer units that go down to 5KHz should be able to measure much larger capaciatances.

A large capacitor looks like a short to the AIM, so it has to have enough reactance to distinguish it from a short. A quick punchup on an online calculator says that 1000uf capacitors have about 1.5 ohms of reactance at 0.1MHz, so I would guess that would be about your limit.

By the way, ESR is not leakage. AIM can measure ESR (if it is bad enough to measure up toward an ohm), but AIM cannot measure leakage, which is a DC phenomenon. Also, it isn't fair to grab an old eletrolytic off the shelf and measure it for leakage (or much of anything else). Put it under DC voltage to "form" it before you test it. It can make a lot of difference (for some capacitors).