just to split hairs, the link forgot one, important thing.  The coil is 
connected to a spring and the current introduced force is acting against the 
spring.  More current more force bigger deflection.  If the spring was not 
there the needle would be pegged against the end stop and 'never' come back.

Leslie.
(finally some use for my science degrees) ;-)

--------------------------------------------
On Sat, 4/4/15, Josh Muckley via CnC-List <cnc-list@cnc-list.com> wrote:

 Subject: Re: Stus-List Problem with 2 new fuel gauges...long story
 To: "C&C List" <cnc-list@cnc-list.com>, "Marek Dziedzic" 
<dziedzi...@hotmail.com>
 Date: Saturday, April 4, 2015, 9:53 PM
 
 ------------------------------------------------------------
 
 Excerpt from the following link:
 
 http://www.doityourself.com/stry/how-does-an-analog-voltmeter-work
 An analog voltmeter works by passing a current
 through a coil that is suspended between two permanent
 magnets. This coil of wire is known as a moving coil since
 it moves in relation to the permanent magnets when a voltage
 is applied. When a voltage is applied and the voltage scale
 is chosen, a resistor of known value is placed in series
 with the measurement leads. This way Ohm’s Law can be
 applied. The applied voltage through the coil creates a
 magnetic field which acts against the permanent magnets that
 the pointer pivot is placed between. This magnetic field
 causes a corresponding deflection of the pointer. This
 pointer deflection will be in direct proportion to the
 amount of voltage being applied to the moving coil wrapping
 the pointer pivot. Once pointer oscillation has stopped,
 accurate readings can be made.
 ------------------------------------------------------------
 So to summerize:  Yes Marek, basic analog
 meter movement is caused by current flow through the meter
 coil.
 I suppose in a a way that makes all anaolog
 coil meters "current" meters.  I referred to the
 fuel gage as a voltage meter so as to suggest that with the
 meter completely removed from the boat a "voltage"
 applied across the terminals from sense to ground or sense
 to vcc (+12v terminal) would cause meter deflection.  In
 order to troubleshoot one might select a common 6v lantern
 battery for this task.
 Using the attached drawing as a referance and
 understanding that R2 is the fuel level sender and
 "D" is the sender "sensing" terminal on
 the meter.  I believe that inadvertently swapping the +12v
 and sense lines or swapping the ground and +12v lines would
 cause the symptom of the fuel gage needle pegging low.
 To both our points, the attached picture
 suggests that the meter being used is a voltage meter (Vg)
 and referances the current from points D to B (Ig) as
 driving its movement.
 Josh
 On Apr 4, 2015 10:40
 PM, "Marek Dziedzic via CnC-List" <cnc-list@cnc-list.com>
 wrote:
 
 
 
 
 
 
 Josh,
 
 
 
 This is certainly not sailing related, but if i remember it
 correctly, they are all really ammeters (the current flowing
 through them creates the magnetic field that moves the
 needle). 
 
 
 
 
 Marek
 
 
 
 
 Josh Muckley via CnC-List wrote:
 
 
 
 
 
 All analog meters are just measuring the
 "voltage drop" across a resistance.  The key is
 to have the appropriate voltage input +12v.  If the +12v
 and the sensing line were reversed then the "voltage
 drop" would be "negative" driving the needle
  to the empty peg.
 Josh
 On Apr 4, 2015 7:08 PM, "Wally Bryant via
 CnC-List" <cnc-list@cnc-list.com>
 wrote:
 
 
 I thought they were Ohm meters. Anyway, I just Googled it to
 make sure, and see a ton of pages on testing marine fuel
 sender resistance.
 
 
 
 Wal
 
 
 
 you wrote:
 
 
 I agree with your diagnosis.  It's gotta be reversed
 polarity...of the
 
 sense and gnd.  Fundamentally the fuel gages are just
 voltage meters.  They
 
 respond proportionally to the voltage drop across the
 variable resistance
 
 in the sender.  I would disconnect the leads and use an ohm
 meter to
 
 measure and validate the resistance of the senders. 
 Switching the polarity
 
 of the sense and gnd monetarily probably won't break
 anything.  Before
 
 doing so validate that your wiring looks like the attached
 picture.
 
 
 
 
 
 
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