Switching Handbook A Guide to Signal Switching in Automated Test Systems Specifications are subject to change without notice. All Keithley trademarks and trade names are the property of Keithley Instruments, Inc. All other trademarks and trade names are the property of their respective companies. A G RE ATER ME A S U R E OF CO N F I D E N C E Keithley Instruments, Inc. Corporate Headquarters • 28775 Aurora Road • Cleveland, Ohio 44139 • 440-248-0400 • Fax: 440-248-6168 1-888-KEITHLEY (534-8453) www.keithley.com © Copyright 2008 Keithley Instruments, Inc. Printed in the U.S.A.

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Switching Handbook A Guide to Signal Switching in Automated Test Systems

Keithley appreciates the assistance and diligence of Dale Cigoy, Senior Applications Engineer, and Jerry Janesch, Business Development Manager—Multi-Application Products, who contributed to and reviewed the content of this edition of the handbook.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 Effects of Switching on System Performance . . . . . . . . . . . . . . 1-2 Switch Configurations and Conventions . . . . . . . . . . . . . . . . . . 1-3 Switching Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 Switching Hardware Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16 Switching Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2.1 Switching Elements . . . . . . . . . . . . . . . . . . . . . . . . . ....

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Connections, Wiring, and Cabling . . . . . . . . . . . . . . . . . . . . . . . 6-2 Shielding and Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 Hardware Verification and Troubleshooting . . . . . . . . . . . . . . . 6-8 Battery Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 Capacitor Leakage Measurements . . . . . . . . . . . . . . . . . . . . . . . 7-4 Continuity Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

S w itchi n g H a n db o o k , S i x th E diti o n A Guide to Signal S witching in Automated T est S y stems

1.1 Introduction Many electronic test systems use relay switching to connect multiple devices to sources and measurement instruments. In some cases, mul­ iple sources and t measuring instruments are connected to a single device. Switching allows automating the testing of multiple devices, thereby reducing error and costs. Designing the switching for an automated test system demands an understanding of the signals to be switched and the tests to be per­ormed. Test requirements f can change frequently, so automated test systems should provide the flexibility needed to handle a variety of sig­ als....

frame that electronically controls the opening and closing of the relays. Therefore, when calculating the overall system accuracy, the engineer must include not only the effects of the switch itself, but all the switching hardware in the system. For example, the offset current of the relays and the leakage resis­ ance of the t boards, connectors, and cables may degrade the integrity of high impedance applications. Contact potential and contact resis­ ance of the relays can reduce t the accuracy of low voltage and low resis­ ance circuits. Switches may reduce t the bandwidth of high frequency...

When more than one common terminal is used, the number of poles increases. Figure 1-1c shows a double-pole, single-throw (DPST) switch. Both poles are actuated simultaneously when the relay is ener­ ized. In this case, both poles are g either always closed or always open. Figure 1-1d shows a double-pole, doublethrow (DPDT) switch. Contact form, or simply form, is another term that relay manufac­ urers often t use to describe a relay’s contact configuration. “Form A” refers to a single-pole, normally-open switch. “Form B” indicates a single-throw, normally-closed switch, and “Form C” indicates...

Figure 1-2. Scanner – a one out of n selector switch The scanner is used to connect multiple inputs to a single output in sequential order. Only one relay is closed at any time. In its most basic form, relay closure proceeds from the first channel to the last. Some scanner systems have the capability to skip channels. illustrates an example of a scan configuration. In this diagram, the battery is connected to only one lamp at a time, such as in an elevator’s floor indicator system. Another example is a scanner for monitoring temperatures at several locations using one thermometer and multiple...

One example of a multiple closure would be to route a single device output to two instruments, such as a voltmeter and a frequency counter. Figure 1-4 illustrates another example of multiplex switching. This diagram shows measuring the insulation resistance between any one pin and all other pins on a multipin connector. To measure the insulation resistance between pin 1 and all other pins (2 and 3), close Chs. 2, 3, and 4. This will connect the ammeter to pin 1 and the voltage source to pins 2 and 3. The insulation resistance is the combination of R1-2 and R1-3 in parallel as shown. Note that...

Using a matrix switch card allows connecting any input to any output by closing the switch at the intersection (crosspoint) of a given row and column. The most common terminology to describe the matrix size is M rows by N columns (MxN). For example, a 4x10 matrix switch card, such as the Keithley Model 7012, has four rows and ten columns. Matrix switch cards generally have two or three poles As shown in Figure 1-5, a 5VDC source can be connected to any two terminals of the device under test (DUT). A function generator supplies pulses between another two terminals. Operation of the DUT can be...