List of Formulae in Electrical and Electronic Measurements

Electrical measurements formulae:

An error is defined as the deviation of the measured quantity from the true value.

E = Am -  At

Error = measured value - true value

The value which we are adding or subtracting from measured quantity in order to get the true value.

                                    Correction factor ±  Am =  At

Relative static error:

It is defined as the ratio of the error to the true value.

This error decides the quality of the instrument.

Sensitivity:

Sensitivity = 1 / Ifsd

Current in Full scale deflection - Ifsd

Resolution = Full scale value / No of divisions

Equivalent circuits of voltmeter:

Equivalent circuit of an ammeter:

Permanent magnet moving coil instrument:

Td/coil (deflection torque)   = BiAN

 θ = BiAN / Kc

 θ ∝ i

Moving iron instrument:

Extension of Ammeter:

Extension of Voltmeter:

Electromagnet moving Coil instrument:

The deflection torque is,

The deflection angle is,

Two different currents without phase difference in two different coils are,

Two different currents with phase differences in two different coils are,

Electronic Measurements formulae:

Cathode Ray Oscilloscope:

Deflection sensitivity:

Deflection sensitivity is defined as the amount of deflection produced per unit deflecting signal voltage.

The deflection factor is the reciprocal of deflection sensitivity.

DF = 1 /  Sv

Sv (vertical sensitivity) = y/Vy

SH (horizontal sensitivity) = x/Vx

Sv = LD / 2sVa

Sv is the vertical deflection sensitivity

s is the distance between two VDPs

L is the length of each VDP

D is the distance between the center of the VDP and the screen

Va is the accelerating anode voltage.

Q-Meter:

For Cd measurement, L , R and Qtrue measurement:

Digital Voltmeter:

Resolution = voltage range of operation / total steps

Sensitivity:

S = lowest voltage range / total steps

Condition to reject noise in Dual slope integrating digital voltmeter:

T1 = n Ts

V1 * T1 = Vref * T2