IEEE Standard Test Procedure for Measuring Longitudinal Balance of Telephone Equipment Operating in the Voice Band

Telephone companies and equipment manufacturers have generally agreed on a definition for longitudinal balance for many years. This agreement extends also to the basic approach followed when measuring balance. Testing a device for balance involves the application of a longitudinal voltage. Then any resulting metallic voltage is measured, and the ratio of the two voltages is used to develop a balance number.Unfortunately, agreement has ended at about this point. A number of different test circuits are used by different segments of the telephone industry. Although all of the existing test circuits have some merits supporting their use, the mere existence of varied circuits leads to differences in test results.In addition to differences related to the test set, test conditions and procedures can also affect the result. When an item of equipment is to be tested, there is often a test set or procedure,or both, capable of giving any desired result.Agreement on one way of testing for longitudinal balance has been sought. This standard represents such agreement. It defines the basic requirements of a standard test circuit. Reasonable tolerances are included so that a test-set designer will find considerable latitude to make the set his own way. Besides defining the requirements for a test circuit, this standard includes test conditions and procedures that must be established and followed. As a result, all test sets designed and used in accordance with the standard will produce the same balance number for a given test specimen. Similarly, comparing balance numbers for different devices will become more meaningful when all come from tests meeting the standard.