Transcript LECTURE 6 - Gunadarma University

PERTEMUAN 9
JEMBATAN DC&AC dan
APLIKASINYA
PENDAHULUAN
• Sirkuit jembatan biasanya digunakan untuk mengukur nilai
komponen, seperti resistansi, induktansi, kapasitansi dan
parameter sirkuit lainnya
• Keakurasiannya sangat tinggi
Wheatstone bridge
[CONTENTS]
• Photograph of the instrument
• Simplified schematic of the
bridge circuit------------------
• Operasi dasar
R x  R3
R2
R1
• Measurement errors :
– Found in the limiting errors of the three known resistors
– Insufficient sensitivity of the null detector
– Changes in resistance of the bridge arms due to the heating effect of
the current through the resistors
– Thermal emfs in the bridge circuit or the galvanometer circuit (when lowvalue resistors are being measured)
– Errors due to the resistance of leads and contacts exterior to the actual
bridge circuit
Thevenin Equivalent Circuit
• Wheatstone bridge
configuration --------------------
• Thevenin resistance looking
into terminals c and d --------
• Complete Thevenin circuit,
with the galvanometer
connected to terminals c and d
• The Thevenin, or open circuit voltage :
• The Thevenin resistance :
• The galvanometer current :
RTH 
E cd
 R1
R2

 E

R

R
R2  R4
3
 1
R1 R3
R2 R4

R1  R3 R2  R4
Ig 
ETH
RTH  R g



Kelvin Bridge
• Wheatstone bridge circuit,
showing resistance Ry of the
lead from point m to point n
Rx 
R1
R3
R2
• Basic Kelvin double bridge
circuit --------------------------
R x  R3
R1
R2
Loop Tests with The Portable Test Set
• Murray-loop test, used for
locating a ground fault (short
circuit) -----------------------------
l x  2l
B
A B
• Varley-loop test: (a) no.1; (b)
no. 2; (c) no.3, used to locate
grounds, crosses, or short
circuits in multiconductor cable
•
X1 
R2
2
(b)
Guarded Wheatstone Bridge
• Used for high resistance measurements
General Form of The AC Bridge
Z1 Z 4  Z 2 Z 3
1   4   2   3
Comparison Bridges
•
•
Capacitance comparison bridge
Equating the real terms :
R x  Rs
•
R2
R1
Equating the imaginary terms :
Cx  Cs
•
R1
R2
Inductance comparison bridge
L x  Ls
R2
R1
R x  Rs
R2
R1
•
•
Inductance comparison bridge with extended measurement range
With the switch in position 1 :
R
R x  R s  r  2
R1
•
With the switch in position 2 :
R x  Rs
R2
r
R1