Microtest TSB-67 - 568A Annex E - Manual (Page 26)

Customizing ACR Limits
To display the ACR LIMITS screen, press the Extended Functions key, then select Setup Auto-
test , then highlight the Autotest to edit, then press Edit (F2), then select Limits , then select ACR .
This screen lets you set the Limit Function and edit the Fixed Minimum ACR limit. Use the ž or ¬
arrow keys to select the field to change. The selected field will be enclosed in a box.
If your Scanner has an alphanumeric overlay on the keypad, use the keypad to enter the limit. If
your Scanner does not have an alphanumeric overlay, press
Edit (F2) to display the edit screen.
When Limit Function is selected, press Change (F2) to toggle between Fixed , Derived and
(ISO) Class D :
•
When Fixed is selected, the minimum ACR limit that you specify is applied across the full
frequency range measured.
•
When Derived is selected, the ACR limit applied is derived from the equation:
NEXT limit - Attenuation limit.
•
When Class D is selected, the ACR limit applied is as specified for ISO Class D links.
•
When Fixed Minimum is selected, the value you enter can range from 0 to 60 dB.
ACR Test Results
When using the 2-Way Injector+ (or the 2-Way Injector ), the top line of the screen indicates if
ACR is being reported for the Scanner ( Penta ) or Injector ( Inj ) end of the link.
At the upper left of the screen, the pair combination is shown. The ACR, in decibels (dB), is
shown to the right of the pair combination. The PASS/FAIL bar across the screen compares the
measured ACR value to the ACR limit value. Below the PASS/FAIL bar, the ACR limit value is
displayed. The Autotest name is displayed after
Spec: at the lower left of the screen.
Press Pair (F3) to toggle through the ACR test results for each pair combination.
When using the 2-Way Injector+ (or 2-Way Injector ), press F4 to toggle between NEXT results
for the Scanner or Injector end of the link.
Press the
Ò
or
Ñ
arrow key to display the previous or next test results screen.
Press the ESCAPE key to return to the AUTOTEST RESULTS screen.
Impedance
Impedance is a measure of the opposition to the flow of current in a cable. Unshielded Twisted
Pair (UTP) is commonly rated at either 100 or 120 ohms. This value must be constant over the
operating bandwidth of the cable.
Impedance measurements, useful for finding mismatches, include the effects of resistance,
inductance and capacitance. An Impedance mismatch will cause a signal reflection in the cable,
which in turn absorbs signal energy. This creates excessive loss, shorter distances that data can travel
reliably, and data errors. The
PentaScanner Product Family uses Time Domain Reflectometry
(TDR) to measure Impedance.
The Impedance function measures the characteristic impedance of the cable at a fixed propagation
delay down the cable. Depending on the NVP of the cable, this sample point is between 25 and 40