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. _______________________________________________ Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com _______________________________________________ Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com -----Inline Attachment Follows----- _______________________________________________ Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com _______________________________________________ Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
