Ayrton shunt or universal shunt is a high-resistance shunt used in

galvanometer A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. A galvanom ...

s to increase their range without changing the

damping Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples incl ...

. The circuit is named after its inventor

William E. Ayrton William Edward Ayrton, FRS (14 September 18478 November 1908) was an English physicist and electrical engineer. Life Early life and education Ayrton was born in London, the son of Edward Nugent Ayrton, a barrister, and educated at University ...

. Multirange ammeters that use this technique are more accurate than those using a make-before-break switch. Also it will eliminate the possibility of having a meter without a shunt which is a serious concern in make-before-break switches. The selector switch changes the amount of resistance in parallel with R_m (meter resistance). The voltage drop across parallel branches is always equal. When all resistances are placed in parallel with R_m maximum sensitivity of ammeter is reached. Ayrton shunt is rarely used for currents above 10

amperes The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...

. ''m1 = I1/Im , m2 = I2/Im, m3 = I3/Im''

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