Cable tester
From Wikipedia, the free encyclopedia
A cable tester is an electronic device used to verify the electrical connections in a cable or other wired assembly. Generally a cable tester consists of:
- A source of electrical current,
- A volt meter,
- A switching matrix used to connect the current source and the volt meter to all of the contact points in a cable,
In addition to these parts a cable tester may also have a microcontroller and a display to automate the testing process and display the testing results.
A cable tester is used to verify that all of the intended connections exist and that there are no unintended connections in the cable being tested. When an intended connection is missing it is said to be "open" (as in Open circuit). When an unintended connection exists it is said to be a "short" (as in Short circuit). If a connection "goes to the wrong place" it is said to be "miswired" (the connection has two faults: it is open to the correct contact and shorted to an incorrect contact).
Fully testing a cable is a very complex task. Generally, the testing is done in two phases. The first phase, called the opens test makes sure each of the intended connections is good. The second phase, called the shorts test makes sure there are no unintended connections.
There are two common ways to test a connection:
- A continuity test. You try to pass a current down the connection. If the current flows the connection is assumed to be good. This type of test can be done with a series combination of a battery (to provide the current) and a light bulb (that lights when the current is flowing).
- A resistance test. You pass a known current down the connection and measure the voltage that develops. From the voltage and current you then calculate the resistance of the connection and check to make sure the resistance is the expected value.
There are two common ways to test for a short:
- A low voltage test. You connect a low power, low voltage source between two conductors that should not be connected. Then you measure the amount of current that flows. If no current flows the conductors are assumed to be well isolated.
- A high voltage test. Again you connect a voltage source but this time you increase the voltage to several hundred volts. The increased voltage will make the test more likely to find connections that are nearly shorted.
