Smart Capacitive Coupling Test System Design And Realization

With the rapid development of communication technology and network, the network capacitance is larger and larger. The cable manufactures continually produce new cables, so the net cable test instrument has developed too. More and more net cable testers appear in the market. But as the main force of the audio frequency communication line, the telephone cable tester is no longer the hotspot in test instrument industry, for the telephone cable has little change in recent years. In China, the situation is more serious. People don't regard it as an important thing, so the research is in a low level.Classical telephone cable tester is based on AC bridge theory. Onside of the bridge is standard capacitance; on the other side is the test cable. By choosing the suitable standard capacitance, the bridge will balance. Then the value of the standard capacitance is just the value of the testing cable. The theory is sample, but the circuit will be not very practical because of too many adjustable components.This article aims at the telephone cable test' technology performance in China, and introduces the design procedure of Smart Instruments. First, provide a new test method which can test the capacitance directly, without adjusting bridge balance. Second, put the GB and ASTM in one system. Third, design new structure and new interface for the system, and also discuss the EMC problem. At the end of the article, make a test by a simulate cable. The result of the experiment indicates that this testing system has high measurement precision, easy-operation and many useful functions. Generally speaking, the system in this article is completely accord with the need of intelligent measurement.