Operation Manual

Chapter 6
Structured cabling testing
67
Illustration 6.16. ACR-N (ACR) / Power Sum ACR-N (Power Sum
ACR)
6.16.1. ACR-N (ACR) Test and Power Sum ACR-N (Power Sum ACR) Test Error
A large difference between the measuring values is preferable, since this indicates a strong
signal and minor perturbations.
6.16.2. Troubleshooting ACR-N (ACR) Test and Power Sum ACR-N (Power Sum ACR)
Test Error
For information on troubleshooting, refer to the corresponding sections on NEXT and loss
test.
6.17. Headroom Test
The headroom test is a mathematical analysis of the data calculated during the preceding
test. The sum of Power Sum ACR-N (Power Sum ACR) test (i.e. corresponding value of worst
case wire pair after normalization of wire pair loss over 100 meters) and the additional
margin between the worst case Power Sum NEXT-value and the limit for Power Sum NEXT.
The headroom test is a simple way to indicate the margins available on a cable line for
faultless support of an application. This test also indicates the additional margin obtainable by
using "improved" cables and connections, as well as careful installation.
Illustration 6.17. Margin Test
6.17.1. Headroom Test Error
The headroom value indicated in dB identifies the minimum margin available for a cable line.
A high value is preferable, since it indicates a strong signal and minor perturbations. The
pass/fail limits for the margin are identical with those for Power Sum ACR-N (ACR).