IEEE 455-1985 pdf free.IEEE Standard Test Procedure for Measuring Longitudinal Balance of Telephone Equipment Operating in the Voice Band.
ANSI/IEEE Std 455-1976 was widely acceptedby organizations in the United States and Canadaas the standard method for measuring longitudi-nal balance.
Prior to the issue of the standard in 1976, tele-phone companies and equipment manufacturershad generally agreed on a definition for longitudi-nal balance for many years. This agreementextended also to the basic approach followedwhen measuring balance. Testing a device forbalance involves the application of a longitudinalvoltage. Then,any resulting metallic voltage ismeasured,and the ratio of the two voltages isused to develop a balance number.
Unfortunately，agreement ended at about thispoint. A number of different test circuits wereused by different segments of the telephoneindustry. Although all of the existing test circuitshad some merits supporting their use，the mereexistence of varied circuits led to differences intest results.
In addition to differences related to the testset,test conditions and procedures can alsoaffect the result. When an item of equipment isto be tested,there is often a test set or proce-dure,or both,capable of giving any desiredresult.
greement on one way of testing for longitudi-nal balance had been sought. The first edition ofANSI/IEEEstd455-1976，IEEEStandard TestProcedure for Measuring Longitudinal Balance ofTelephone Equipment Operating in the VoiceBand，issued september30，1976，represented such agreement. Experience gained over the pastseveral years by those who have used the stand-ard and those who have built test equipmentintended to comply with its provisions have ledto this revised edition. Idefines the basicrequirements of a standard test circuit. Reason-able tolerances are included so that a test-setdesigner will find considerable latitude to makethe set according to his design.
Besides defining the requirements for a testcircuit, this standard specifes test conditions andprocedures to be followed when longitudinal balance is measured. As a result,all test setsdesigned and used in accordance with the stand-ard will produce a consistent and repeatable bal-ance number for a given test specimen. Similarly,comparing balance numbers for different deviceswillbecome more meaningful when all comefrom tests meeting the standard.
Longitudinal balance,as defined in this stand-ard,specifically refers to longitudinal-to-metallicbalance. This differs from the FCC definition forlongitudinal balance which refers to metallic-to-longitudinal balance (see Appendix E for details).IEEE 455 pdf download.