Re: Capacitance Meter or LCR

From: Winfield Hill (hill_a_at_t_rowland-dotties-harvard-dot.s-edu)
Date: 02/26/05 

Date: 26 Feb 2005 04:42:01 -0800

shayan wrote...
>
> Hello every one, Can i measure the continuous variation(with frequency
> above 10 kHz) in the capacitance and dielectric constant of a fine
> capacitor with capacitance meters or LCR's? Please introduce me a web
> link for these instruments.

 I have an hp 4275A LCR meter, which measures from 10kHz to 10MHz with
 5.5-digit resolution. You will find, as I have, that most capacitors
 will not have a significant capacitance variation over most of that
 frequency range. If you have in mind a specific part or type of
 capacitor, I would be happy to measure it for you.

 OTH, there is the issue of dielectric absorption, which affects the
 observed value of capacitors at lower frequencies. If the polarizing
 voltage is present long enough, "remnant polarization trapped on
 dielectric interfaces" adds to the capacitor's value, see AoE pages
 220-221. The hp 4274A 5.5-digit LCR meter measures from 100Hz to
 100kHz, and is a good instrument to observe this effect.

 Both of these hp instruments appear on eBay from time to time, e.g.
 http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3875144082
 http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3872211489

 For frequencies below 100kHz, capacitance bridges are better suited
 for high resolution measurements. For example, the General Radio
 1615-A and 1616 bridges have 6 and 12-digit! readout, respectively.
 They can be used down to 10Hz, but the maximum bridge-excitation
 voltage must be reduced, lowering the achievable resolution. I have
 both of these fine, elegant instruments. :<>) A google search will
 turn up used-instrument dealers, and they're supposedly still being
 produced by IET, http://www.ietlabs.com/Genrad/GenRadtestInstr.html
 At least the old GR datasheets are available there for you to read.
 Search on 1620 and 1621 precision capacitance-measurement systems. 

-- 
 Thanks,
    - Win
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