26-07-2012, 01:28 PM
Electrical Measurement and Instruments
Electrical Measurement.pdf (Size: 1,009.34 KB / Downloads: 311)
Voltmeter-ammeter method
Simple and theoretical oriented
•Requires two meter and calculations
•Subject to error: Voltage drop in ammeter
Bridge Circuit
Bridge Circuit is a null method, operates on the principle of
comparison. That is a known (standard) value is adjusted until it is
equal to the unknown value.
Sensitivity of Galvanometer
A galvanometer is use to detect an unbalance condition in
Wheatstone bridge. Its sensitivity is governed by: Current sensitivity
(currents per unit defection) and internal resistance.
consider a bridge circuit under a small unbalance condition, and apply circuit
analysis to solve the current through galvanometer
SOLUTION
Since the bridge constants have not been changed, the equivalent circuit
is again represented by a Thévenin voltage of 2.77 mV and a Thévenin resistance of
734 Ω. The new galvanometer is now connected to the output terminals, resulting a
galvanometer current.