Length, Customizing length limits, Length test results – Microtest TSB-67 - 568A Annex E User Manual

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Length

Length can find opens, shorts, and breaks in a cable. The

PentaScanner Product Family

uses

Time Domain Reflectometry (TDR) to find the location of faults in cables. TDR is similar to ‘cable
radar’. The Scanner generates a pulse down the wire, and when the pulse encounters an impedance
change (such as an open, short, or poor connection), all or part of the pulse energy is reflected
back to the Scanner. The Scanner then measures the delay between when the pulse was sent and
when the reflection was received. Knowing the speed that the pulse travels down the cable
(Nominal Velocity of Propagation, or NVP), the Scanner can then calculate the distance to the
fault.

The Length measurement is most accurate when the NVP setting you use is set correctly.

Customizing Length Limits

To display the

LENGTH LIMITS

screen, press the

Extended Functions

key, then

select Setup

Autotest

, then highlight the Autotest to edit, then press

Edit (F2),

then select

Limits

, then select

Length

. This screen lets you change the minimum and maximum Length limits.

Press the

arrow key to select the minimum or maximum Length limit. The selected

limit will be enclosed in a box.

If your Scanner has an alphanumeric overlay on the keypad, use the keypad to enter the limits. If
your Scanner does not have an alphanumeric overlay, press

Edit (F2)

to display the edit screen.

After editing, press

Save (F1)

to store the new Length limits and exit or press the

ESCAPE

key to

exit without saving.

Length Test Results

To display the

LENGTH

screen, press

View (F1)

from the

AUTOTEST RESULTS

screen, then

press the

key until the

LENGTH

screen is displayed.

Autotest Length test results provide information for the shortest pair, displayed at the top of the
screen. The PASS/FAIL bar across the screen compares the measured Length value to the Length
limit value. Below the PASS/FAIL bar, the Length limit value is displayed. The Autotest name is
displayed after

Spec:

at the lower left of the screen.

Press

Table (F1)

to display the Length and Delay of all pairs, and the Skew between pairs (if

Propagation Delay has been selected as part of the Autotest). The Skew value is the worst-case
value of the difference in propagation delay between the wire pairs.

Press the

arrow key to display the previous or next test results screen.

Press the

ESCAPE

key to return to the

AUTOTEST RESULTS

screen.

Note: For diagnostic purposes, you can run Length and Delay continuously by pressing the

Measure Cable Performance

key and selecting

Length/Delay