ABB ETL600 - Page 211

ETL600 1KHW001489-EN ABB Switzerland Ltd
Appreciable discrepancies between the measured results and the
nominal characteristic point to defective components and the filters
must be checked individually.
SELECTIVE LEVEL
METER SPM 32/33
Input
impedance
appr. 5 kOhm
Output
impedance
approx. 10 Ohm
GENERATOR PS 33
Return loss
measuring bridge
Rec.
Gen.
R
R
Instruments:
1.
2.
Signal generator
Selective level meter
Acterna PS 33
Acterna SPM 32/33
e.g.:
Dummy load
Nominal outpu
t
impedance:
e.g. 75 Ohm
Coaxial cable
to coupling unit
N
X
Fig. 7-1 Instruments and test circuit for measuring return loss
Phase-to-ground
CF
BT
coupling filter
balancing transformer
Z0
Z
nominal impedance
actual input impedance
Phase-to-phase or between line circuits
a = 20 log
Z0 + Z
Z0 - Z
CF CF CF
BT
Return
loss
a
Return
loss
a
r
r
r
Fig. 7-2 Test circuit for measuring return loss under practical
conditions with the transmission line as load
Commissioning November 2005 7-5