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The use of Automatic test system switching test equipment allows for high-speed testing of a device or devices in a test situation, where strict sequences and combinations of switching must be observed. By automating the process in this way, the possibility of test errors and inaccuracies is minimized, and only systematic errors would generally be encountered due to such as an incorrect programmed test condition. This eliminates error due to human factors and allows the application of a standard test sequence repetitively. The design of a test system’s switching configuration is governed by the test specification, which is derived from the functional tests to be performed. A typical test system would involve the connection of input and outputs of the device under test to the test equipment, which is usually controlled by an electronic program generated by a computer or a Programmable Logic Controller. ==Switch Relays== The simplest definition of a switch is “a device that opens or closes a circuit.” 〔“Switch,” The Penguin dictionary of Electronics, 2nd ed, London, UK: Penguin Books, 1998.〕 A relay is an electronically operated switch. Three relay types are commonly used in automated test system switching: * Electromechanical relays are the most-often-used type because they have the largest signal range capability of the three. They also have the slowest actuation time and the shortest useful life. Electromechanical relays are ideal for high-voltage, high-current, and RF applications. A latching feature makes the latching relay type very appropriate for low-voltage applications where contact potential can interfere with the measurement. * Reed relays have actuation times of 0.5 ms to 2 ms and long life. By design, reed relays can only handle a portion of the signal range that electromechanical relays can offer. But they do provide a useful trade-off between increasing speed and maintaining signal integrity. * Solid-state relays can switch the fastest and have essentially infinite life. However, they can only handle small signal ranges and suffer from high on-resistance and high offset currents in the nanoamp range compared to picoamps of offset current for the other two types. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Automatic test switching」の詳細全文を読む スポンサード リンク
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