Voltech AT3600 User Manual page 314

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RANSFORMER ESTS
1.17. GBAL – G
W
The general longitudinal balance test is intended to measure what is effectively the
Common Mode Rejection Ratio of a transformer designed to connect to a balanced
line. Two measurements are performed each by applying a voltage to the transformer
and measuring the resulting voltage to calculate the CMRR. To overcome the
differences of three standard methods of measuring the CMRR the GBAL dialogue
box has a separate group of terminals X and Y for the first and second measurements
respectively. The preferred method of measurement is the LBAL test for which
Voltech provide a separate test specifically for this measurement.
This test is suitable for audio & telecommunication transformers and checks the
effective common mode rejection ratio of the transformer.
M
Unfortunately, there are several published specifications for measuring longitudinal
balance. These are all different, and potentially give different results for the same
transformer.
To allow each user the freedom to test to his preferred method, the GBAL test has
been configured with the greatest flexibility. It therefore consists of two separate
measurements which the user can program, and the result is the ratio between the two
expressed in dB.
O
PERATION
For the reasons outlined above, the test consists of two separate user programmed
measurements, each with its own 'energised' and 'measured' terminals. This
approach is illustrated below with reference to three standard methods
P 7.1.34.
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