Operation Manual

GMC-I Messtechnik GmbH 49
Measurements R
SL
– MΩ
ISO
@10 V/100 V – CAP Switch positions (a-b) (a-E) (b-E)
6.4 Interference-immune Capacitance Measurement
in Telecommunications Networks – CAP Function
Three jacks (a, b and E) are provided for measurements in symmetri-
cal copper cable networks with two conductors and a shield. The ro-
tary selector switch can be set to determine whether capacitance
testing will be performed between a-b, a-E or b-E.
In contrast to the capacitance measurement in selector switch
position , the measured value is only affected to a minor de-
gree by line interference and/or parallel resistance with this ca-
pacitance measurement method.
Ð Connect the measuring cables to jacks a, b and E
Ð Set the rotary switch to „a-b, a-E and b-E“, one after the other,
in order to display any interference voltage for all three conduc-
tor pairs, see also chapter 6.2.
Ð Press ZERO | ESC. The display switches from V to F. This con-
version is accompanied by a double acoustic signal.
Ð Measure the capacitance successively in the 3 selector switch
positions.
Ð Return to the interference voltage detection mode by pressing
ZERO | ESC once more.
Note
„000.0 nF“ indicates a short circuit at the jacks.
Note
If an activated DSL modem/router is connected to the cus-
tomer-side cable end emitting acoustic handshake signals,
the high level of the signals will interfere with the measure-
ment when short leads (up to approx. 500 m) are used.
These signals can be attenuated by plugging on the signa-
ture measuring adapter, thus making measurement possi-
ble. The capacitance of 100 nF of measuring adapter
SM100 must be taken into account for measurement.
6.4.1 Cable Length Measuremnemt m
In the cable length mode the instrument calculates the length as a
function of the capacitance value entered by the user:
Ð Connect the measurement cables to jacks a, b and E
Ð Set the rotary switch to „a-b, a-E and b-E“, one after the other,
in order to display any interference voltage for all three conduc-
tor pairs.
Ð Press ZERO | ESC. The display switches from V to F.
Ð Press multifunction key FUNC | ENTER. „k“ and „m“ are indicated
for km length instead of „F“ in the display.
Ð Measure the cable length successively in the 3 selector switch
positions.
Ð Return to the capacitance measuring mode by pressing
FUNC | ENTER once more.
Refer to chapter 7.4 for details on setting the scaling factor „CAP“
(capacitive linear electric constant) for cable length measurement.
Note
Please make sure that the cable parameters (e.g. cross sec-
tions) are identical when determining the cable lengths. Dif-
fering cable parameters, e.g. in the case of cables com-
posed of different cable types or cross sections, distort the
measuring results.
Length (km) =
measured capacitance (nF)
capacitance value (nF/km)