Methods to accuractly measure capacitance

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Discussion Overview

The discussion centers on methods for accurately measuring capacitance, focusing on techniques that are quick, noise-tolerant, and not reliant on signal attenuation. Various approaches and technologies are explored, including specific devices and measurement principles.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant mentions the UTI technique and frequency or phase-locked loops as potential methods for measuring capacitance accurately.
  • Another participant highlights the capabilities of Agilent Impedance analyzers, noting their femto-farad accuracy and referencing older HP impedance analyzers that utilize an Auto-Balance Bridge method involving a variable power AC source and feedback loops.
  • A different participant asserts that capacitance bridges are reliable and accurate, mentioning specific brands like Andeen-Hagerling and noting the distinction between relative and absolute capacitance measurements, as well as the challenges associated with different frequency ranges.
  • One participant claims that capacitance bridges can achieve a resolution limit of 0.5 attofarad.

Areas of Agreement / Disagreement

Participants express a variety of methods and technologies for measuring capacitance, but there is no consensus on a single best approach. The discussion remains open with multiple competing views on the effectiveness and accuracy of different techniques.

Contextual Notes

Some participants mention the need for specific frequency considerations and the distinction between relative and absolute capacitance measurements, indicating that the discussion may depend on these factors.

Who May Find This Useful

Individuals interested in precision measurement techniques, electrical engineering, and those seeking to understand advanced capacitance measurement methods may find this discussion relevant.

Topher925
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I need to measure the capacitance of something as accurately and as quickly as possible. I also need the method to be very noise tolerant and not depend upon signal attenuation. I've been looking at several different methods so far on how to do this and so far I have found methods like the UTI technique, and using frequency locked or phase-locked-loops. Does anyone know how those high accuracy capacitance meters work or know of any commonly used methods to measure capacitance?
 
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Some of those Agilent Impedance analyzers are crazy. They measure capacitance with femto-farad accuracy. Check out some of their app notes on their website.

One method that was used in older HP impedance analyzers is by using an Auto-Balance Bridge.

Basically there is a variable power AC source, voltage difference amplifier between the unknown impedance, and a trans-impedance amplifier that converts current into voltage.

By using feedback loop, the CPU can set up a constant voltage source over an unknown impedance and measure current flowing into it, or a constant current source and measure voltage across the unknown impedance.

Now there are two AC voltages. One is proportional to voltage across impedance, and the other is proportional to current.

The ratio between these voltages it taken using another complicated feedback, IQ demodulator to separate the phases, and feed everything to ADCs and the CPU.

The advantage of this method is that is gets rid of any effects of ESR, and stray inductances
 
Last edited:
Yes. you need a capactance bridge.
The ones we use for routine measurement where I work are easy to use and very reliable, while still being -as far as I know- the most accurate capacitance meters you can buy.
(they are made by Andeen-Hagerling); for more accurate measurements we have other systems but they we are talking about VERY specialized equipment (which are still based on bridges).

Also, do you need to know the relative change (fairly easy) or absolute (not so easy) capacitance?
At what frequency? kHz is easy, hundreds of MHz is not so easy...
 
hi, you can use capacitance bridge, resolution limit is 0.5 attofarad.
 

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