Electronic Ammeter and Voltmeter

Posted on Feb 7, 2014

I found that my sprite, burdened with an extra electrical load from an electric cooling fan, just barely kept the battery charged. My intended solution to this problem is an electronic voltage regulator; however, it seems obvious that, before changing the regulator, I need some way to monitor the charging. Most meters today are digital. They work by converting an analog

Electronic Ammeter and Voltmeter
Click here to download the full size of the above Circuit.

voltage to a digital number, displaying that number on a digital readout. Conventional analog meters are still in use, however, and probably will remain so. (To see why, just try to adjust something for a peak or null value with a digital meter!) Conventional meters are based on the principle that a coil of wire carrying a current experiences a torque when placed in a magnetic field. The torque rotates the coil, and a pointer connected to the coil indicates the current. Such meters respond fundamentally to current; we call them current-sensing devices. Voltmeters consist of an ammeter with a series resistance, so the voltage is measured, by Ohm`s law, as the current times the resistance. Moving-coil ammeters can be remarkably sensitive. They are usually designed to operate at very low full-scale currents, because it is straightforward to extend their ranges to higher currents but not lower. Back when all test meters were analog, the "gold standard" was a movement that required only 50 microamperes for full-scale deflection. To measure higher current, it is necessary to use a shunt, a resistor connected in parallel with the meter so that it bypasses most of the current. The shunt resistance is given by the relation, where Rs is the shunt resistance, Rm is the meter resistance, Im is the meter current for full-scale deflection, and Ifs is the desired full-scale value of the shunted meter. This relation illustrates the problem...

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    25 Watt MosFet Amplifier
    MICRO FM Bug
    Regenerative receiver for AM band
    Model rocket launcher
    Pulse generator as astable multivibrator
    89c51 ds1820 based digital thermometer
    RTD remote temperature sensing current voltage conversion circuit
    2-5-cell lithium battery charger circuit
    Adjustable thermostat controller circuit diagram created REF01E