Ammeter:
The ammeter measures electric current. It might be calibrated in amperes, milliamperes, or microamperes. In sequence to measure current and the ammeter must be placed in series with the circuit to be tested that was display in above figure.
Figure: Ammeter
Whenever an ammeter is placed in series along with a circuit, it will increase the resistance of in which circuit by an amount equal to the internal resistance of the meter Rm. Equation (14-3) is the mathematical representation of the current without the meter installed.
Io =V/ Ro (14-3)
The given Equation (14-4) is the mathematical representation of the current along with the meter installed within the circuit.
Iw =V/Ro +Rm (14-4)
The accuracy of the ammeter KA is the ratio of the current while the meter is in the circuit, Iw, to the current along with the meter out of the circuit, Io. Given Equation (14-5) is the mathematical representation for solving for the accuracy of the ammeter (KA).
KA = Iw/ Io (14-5)
Through substitution laws, the Equation (14-6) is a mathematical representation of the accuracy by using circuit resistance.
K A = (V/Ro +Rm) (Ro/V) = Ro/Ro +Rm (14-6)
The percent loading error is that % of error due to loading effects in which result from the added resistance of the meter. Given Equation (14-7) is a mathematical representation of the percent loading error.
% loading error = (1 - KA)(100 %) (14-7)
A second error that occurs in an ammeter is alibration error. A Calibration error is an error which occurs due to inaccurately marked meter faces. Classically values of calibration error within terms of full scale current are about 3 %.