Re: MMC accessories

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Marc,

On 16 Aug 00, at 8:12, Tesla list wrote:

> Original poster: "Metlicka Marc" <mystuffs-at-orwell-dot-net> 
> 
> malcolm,
> can i ask you what a capacitance bridge is and if i could make one? i've
> never herd of this before and am interested. does it work kinda like a
> wheatstone bridge, but for capacitors? very interesting.
> marc

Yes. You can build or buy. There are other methods which are 
less cumbersome for measuring capacitance too. A simple 
example:

- apply a constant current to a capacitor for a set period of 
time and measure the voltage the capacitor has reached at the 
end of this time. C = i.t/V  It can be seen from the equation 
that you could alternatively use a voltage level as the 
endpoint and note the time the capacitor took to reach that 
voltage. Modern instruments use an approach like this as it is 
easy to make them autoranging. An additional advantage to 
using a DC charging current is to eliminate the need for 
taking AC losses into account which with a bridge type 
inevitably leads to the necessity for extra knobs and dials 
such as "loss balance". 

Regards,
Malcolm