full thottle switch - how ammeters work

[txrocco at sbcglobal.net (ATS - Patrick Bureau)]

I like to have one of those, but it seems little bars on a dial is so
innaccurate, why not find one that is an actually read out in dwell/mA
whatever is the read out on those leads...

ATS - Patrick Bureau - txrocco@sbcglobal.net
----------------------------------------------
MSN:ATSGTX@hotmail.com |YAHOO:ATSGTX@yahoo.com
ICQ:32918816           |AIM:Texasscirocco
----------------------------------------------


=>-----Original Message-----
=>From: marc_scirocco Quebec [mailto:marc_scirocco@sympatico.ca]
=>Sent: Monday, September 22, 2003 5:44 PM
=>To: Patrick Bureau
=>Cc: scirocco-l@scirocco.org
=>Subject: RE: full thottle switch - how ammeters work
=>
=>
=>Even cheaper:
=>http://www.oldschoolcavy.com/Cavy%20info/DIY%20Air-Fuel%20Ratio%20
=>Monitor.ht
=>m
=>
=>http://www.oldschoolcavy.com/Cavy%20info/pictures/airfuel/diagram.jpg
=>
=>Marc
=>'83 Scirocco
=>'88 Scirocco Slegato
=>
=>-----Message d'origine-----
=>De : scirocco-l-bounces@scirocco.org
=>[mailto:scirocco-l-bounces@scirocco.org]De la part de marc_scirocco
=>Quebec
=>Envoye : lundi 22 septembre 2003 18:32
=>A : Patrick Bureau
=>Cc : scirocco-l@scirocco.org
=>Objet : RE: full thottle switch - how ammeters work
=>
=>
=>Nice goodies (permanent monitoring):
=>http://shop.store.yahoo.com/gofast/autometer4.html
=>
=>Marc
=>'83 Scirocco
=>'88 Scirocco Slegato
=>
=>-----Message d'origine-----
=>De : scirocco-l-bounces@scirocco.org
=>[mailto:scirocco-l-bounces@scirocco.org]De la part de Patrick Bureau
=>Envoye : lundi 22 septembre 2003 17:42
=>A : T. Reed; Allyn
=>Cc : L F; scirocco-l@scirocco.org; ATS - Patrick Bureau
=>Objet : Re: full thottle switch - how ammeters work
=>
=>
=>alright you guys lost me a while by I hung in there just in case
=>I would get
=>your wisdom and knowledge from reading your messages but alas I am stumped
=>again...
=>
=>in laments terms please
=>
=>I have a 2 plug connector and 2 leads from the multimeter... how
=>is putting
=>those 2 leads into the plug be a problem ?
=>
=>and if it is not the proper way of doing it, what is ?
=>
=>
=>"T. Reed" <treed2@u.washington.edu> wrote:
=>> > By the way, how can a meter NOT receive voltage if it's reading
=>> amps?????????????? i.e. one > MUST have voltage in order to
=>have amperes.
=>> Right, Toby? Allyn?
=>>
=>> > Larry
=>>
=>> ok, larry, heres how it works. its not that the meter must _receive_
=>> voltage, its that its only capable of _reading_ voltage. when reading
=>> amperes the input is ran through a *very* low internal resistance (a
=>shunt).
=>> the meter then internally reads the voltage across the shunt,
=>and displays
=>> it with a current scale instead. the lower the shunt
=>resistance, the more
=>> accurate the reading (you want the meter to look like the rest of the
=>> circuit - i.e. straight piece of wire), so the shunt resistance
=>is usually
=>> very low (0.001 ohms). so, basically, a meter set to read current is
=>similar
=>> to running around with a set of jumper cables (well, they cant
=>handle that
=>> much current, but you get the point).
=>>
=>> hth
=>> Al
=>
=>Yup, Al's right on the money. It's like measuring the flow through a dam
=>by just measuring a small portion of the flow through a fish ladder. That
=>tiny resistance diverts a portion of the current through the meter, while
=>the rest of it goes right on through.
=>
=>Which leads us to a rule of thumb: If you wouldn't connect a piece of wire
=>between two things, don't connect an ammeter between them.. because that's
=>basically what you are doing. A voltmeter is pretty much safe to connect
=>anywhere (on your car).
=>
=>To more directly answer your question, just think of the plumbing analogy
=>again. A water flow meter (ie. something like a water wheel on the back of
=>an old-fashioned riverboat) measures flow (amps) but does not cause a
=>decrease in pressure (volts), whereas a water pressure meter measures
=>pressure (volts) but does not cause a decrease in flow (it works just like
=>a tire pressure gauge).
=>
=>This actually isn't entirely true because the world is not perfect.. so:
=>You can have pressure without flow (just like you can have voltage at a
=>battery without anything connected) but in order to measure it you have to
=>have a wee bit of flow. In order to measure flow you have to have at least
=>some pressure (think of the zero pressure being zero water in the
=>plumbing).
=>
=>As far as meters go..
=>
=>Analog ammeters and analog voltmeters both use a galvanometer, which is
=>just a needle that moves a certain amount depending on how much
=>electricity goes through the coil placed next to it. Tachometers and
=>speedometers use the same thing (as do ANY electric gauges with needles).
=>
=>It's just the way the meter is designed (circuit-wise) that is different.
=>Digital meters are much more complicated (and consequently closer to
=>ideal) but the idea is the same.
=>
=>-Toby
=>
=>_______________________________________________
=>Scirocco-l mailing list
=>Scirocco-l@scirocco.org
=>http://neubayern.net/mailman/listinfo/scirocco-l
=>
=>ATS - Patrick Bureau - txrocco@sbcglobal.net
=>'85 2.0L Prowler Orange, Kamei X1 Rocco
=>'84 1.8L Silver Restoration and '83 Rocco Trailer Project
=>
=>
=>_______________________________________________
=>Scirocco-l mailing list
=>Scirocco-l@scirocco.org
=>http://neubayern.net/mailman/listinfo/scirocco-l
=>
=>
=>_______________________________________________
=>Scirocco-l mailing list
=>Scirocco-l@scirocco.org
=>http://neubayern.net/mailman/listinfo/scirocco-l