Operation Manual
GMC-I Messtechnik GmbH 51
Measurements R
SL
– MΩ
ISO
@10 V/100 V – CAP Switch positions (a-b) (a-E) (b-E)
6.5 Galvanic Signature Recognition in Selector Switch Positions a-b
Measuring function for the recognition of a galvanic signature
which may be contained in the connection cable of a DSL
modem/router.
Electrical circuit diagram of a DSL signature
Ð Set the rotary switch to „a-b“ in order to display any interfer-
ence voltage.
Ð Select the signature recognition function „Sign“ with key
or .
Ð Start measurement with the FUNC | ENTER key.
Measurement is now conducted with a voltage below the con-
ducting-state voltage of the Zener diodes: „Lo V“ is therefore
shown in the display until the first measured value in the ±300%
range is indicated. Since the measuring voltage is smaller than the
threshold voltage of the Zener diodes of the signature, only para-
sitic influences are indicated in this case: this value is therefore
subsequently designated as influence value.
If the influence value is stable, a high measuring voltage can be
selected by pressing and holding the ZERO | ESC key. This is indi-
cated in the display with „Hi V“.
If a value between approximately +60 and +200% is shown in the
display, a signature exists, for values below +20%, however, no
signature exists. Since this value determines whether a signature
exists or not, it is subsequently designated as decision value.
The influence value last measured is taken into account for calcu-
lating the decision value: It is therefore of importance that the in-
fluence value is stable and remains within the applicable range
between –50% and +30%! The display blinks if the value is be-
yond that range.
Notes
Prerequisites for the application of the signature measurement
Parallel resistance > 200 kΩ, parallel capacitance < 1 μF,
Ripple voltage < 4 Vss 50 Hz
and exclusively high-resistance DC voltage
Passive test termination between a and b
A passive test termination leads to a deviation < 10% for both val-
ues and can thus be neglected for the signature recognition.
Signature at the output of a DSL splitter
If the signature is located at the output of a DSL splitter (operation
according to Annex B), it is not recognized due to the high-pass
filter in the splitter. If it is attached to the F jack (low-pass) by mis-
take, the signature is recognized nevertheless.
a
b
C1 U1 U2 R1U1
470n 6.8V 100k6.8V