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CHAPTER 10: Calibration
5. Press ESC to exit the NVP calibration mode.
10.1.3 W
HY
D
O
I N
EED TO
S
ET
C
ABLE
NVP?
In order to make accurate cable-length measurements, the correct cable
Nominal Velocity of Propagation (NVP) value must be set in the SCAN-
LAN VI. The NVP is a measure of how fast an electrical pulse travels down
a cable compared to the speed of light.
NVP is expressed as a percentage, usually between 50 and 90%. A default
NVP value is automatically set by the SCAN-LAN VI based upon the cable
test standard selected.
Using the default value, however, may result in cable-length measurement
errors of up to 7%, due to the variation in the signal propagation rate
from cable to cable. This potential length error usually will not impair
troubleshooting of a cable segment that used to work unless the length
measurement of a cable is close to the test limit (for example 100 meters
on a 10BASE-T segment).
When using the SCAN-LAN VI for cable certification, determine the true
cable NVP and save the value. This will give you the most accurate cable-
length measurements and will avoid failing cable segments that are close
to the test limit.
10.2 Remote-Unit Calibration
Remote-unit calibration should be performed on a periodic basis in order
to maintain the accuracy of attenuation measurements. Remote calibration
is most sensitive to temperature changes. Allow both main and remote
units to stabilize to their operating environment before performing the
calibration procedure.
Each SCAN-LAN VI is calibrated for remote operation at the factory. It’s
not necessary to re-calibrate the Remote unless a new SCAN-LAN VI is used
for remote operation. However, if Remote Calibration is performed, it’s
important to verify that the calibration was completed properly.
To calibrate the remote unit:
1. Connect the main unit to the CAT 3 calibration coupler, using the
Modular Plug Performance Module. (If you are using the Modular Jack
Performance Module, use the four-foot CAT 5 patch cord.)
Summary of Contents for SCAN-LAN VI
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