# Interval for Checking Phone Line

This value controls how often the unit tests the phone line. A phone fault alarm (TFAIL) is tripped whenever this test fails.

Selecting the checkbox enables this feature. The base time and frequency work together to set the time of the test, as well as how often the test is initiated. The Catalyst firmware will look at the base time, then calculate out from that point when the tests should occur.

For example:

Base Time = 09:00 (9am)

Frequency = 04:00 (test once every four hours)

The firmware will calculate the times it needs to test the phone line. In the example above, test calls will be made every four hours on the hour, starting at the next eligible time. The firmware will not wait until 9am to make the first test. It will test at first eligible interval. Eligible intervals in this example include 0900, 1300, 1700, 2100, 0100, 0500.