METREL MI 2014, Инструкция по эксплуатации, Страница: 24 / 32

MI 2014 Cable Scanner Section III Cable Scanner operation
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12.1 Cable Length Calibrations
The accuracy of the length measurement is calculated from the time it takes the pulse to
travel along the cable and reflect back to the instrument. For this reason the cable NVP
(nominal velocity of pulse propagation) must be known. Cable NVP factors differs
between different cable types and are further influenced by ageing and temperature. By
using the Length Calibration this errors are eliminated and very precize length
measurements can be performed.
Two calibration types are available with Cable Scanner:
- Calibrations based on known NVP. Use this calibration when the exact NVP factor is
known from the manufacturer data sheet or others.
- Calibration based on known cable length. In this mode the NVP is calculated from a
cable sample of known length. Best results can be obtained this way especially if
performing the calibration on the same cable or cable of the same type.
Setting a new (known) NVP factor manually
1. After selecting Length&Reflections with
rotary switch press
twice . The 'NVP
Calibration' screen is displayed.
NVP calibration display
2. Select new NVP factor with
/
key.
displayed NVP factor
3. Press . After that the new NVP is
displayed for about 1 second together
with the
sign.
Checking the set NVP factor (without changing it)
1. After selecting Length&Reflections with rotary switch press twice to enter the 'NVP
Calibration' screen.
2. Press
or key once. The currently set NVP is displayed.
3. Press
to return to basic screen without changing the settings.
Setting a new NVP on base of a known cable length
Best results are obtained when performing a calibration on the same cable or cable type
on a known length.