Paul:
Remember that one time constant is the time used to go 63% of the total
voltage swing.
One time constant is equal to the resistance times the capacitance:
So,
t = RC
for 40 ohms, and 5000 microfarads, one time constant = 0.2 sec
for 40 ohms, and 10000 microfarads, one time constant = 0.4 sec
for 20 ohms, and 5000 microfarads, one time constant = 0.1 sec
for 20 ohms, and 10000 microfarads, one time constant = 0.2 sec
But notice also that:
for 10,000 ohms, and 10 microfarads, one time constant = 0.1 sec
These former are all large capacitors and fairly short time constants. The
capacitor can be reduced and resistor increased as later shown to make the
capacitor small, and small also means a better dielectric material can be
used (like tantalum) for longer life. The electrolyte in electrolytic
capacitors dries out in time and the cap becomes useless.
OR....
you can just live with it!! (My recommendation)
Kind regards,
Tim Economu phone: 360-579-2117
Design Engineer fax: 360-579-2117
Trace Engineering email: economu@whidbey.com
4131 Springwater
Clinton, WA 98236
>>Paul said:
------------------------------
Date: Fri, 20 Aug 1999 20:21:45 +0100
From: "Paul Hunt" <paul.hunt1@virgin.net>
Subject: Re: Slowing the Fuel Gauge Fluctuation on an LBC
Don't know about non-hot-wire gauges but hot-wire gauges have an impedance
of just a few tens of ohms. Haven't done any time contant calculations in a
long while but if LC = seconds then we are talking about 5,000 micro-Farads
for 1/10th sec.
PaulH.
>>
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