Oscilloscopes Meet Most Measurement Needs
A general-purpose instrument, the scope measures analog and digital signals.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 10/1/1998
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In August-September 1999, Test & Measurement Europe |
| As an engineering student, I had my first lesson in test equipment on an oscilloscope. An old borrowed scope made with vacuum tubes helped me complete my senior project—and heated the cold basement where I worked. That heavy box with its 500-kHz bandwidth was all I needed to measure the outputs of several sensors, comparators, and logic gates.
Today’s analog scopes having bandwidths as high as 500 MHz with digital sampling oscilloscopes (DSOs) have bandwidths exceeding 2 GHz. Every engineering lab, production floor, and service shop has at least one scope. Scopes take many forms. The traditional bench scope resides not only on benches, but in ATE systems, too. Handheld scopes find use in field service and plant applications. PC plug-in cards may reside in an engineer’s lab computer or in a production test system. External PC-connected scopes reside on lab benches, on production floors, and in field applications. Benchtop Scopes Most DSOs have 8-bit resolution, which works well for displaying most digital signals and many analog signals. Some measurements require finer resolution, though. Scopes from Gould and Nicolet provide 12-bit resolution. Scope cards from Gage Applied Sciences (12 and 16 bit), Nicolet (12 bit), and PC Instruments (10 bit) also measure smaller voltage changes than 8-bit scopes. Typically, engineers use high-resolution bench and PC-based scopes for scientific measurements and for physical measurements such as sound and vibration. DSOs, with their IEEE 488 ports, find their way into many custom ATE systems, too. Many test-system builders like having a bench scope in their test systems so they can take advantage of the scope’s user panel. When something goes wrong with the UUT or the test system, test engineers want manual control over the scope for troubleshooting either the system or a UUT. In production test systems, technicians can connect probes to bench scopes and use them without removing the scope from the test system. PC-Based Scopes You also can use a VXIbus scope module or a PC plug-in scope—either an internal or external type—in an ATE system. Often, a test-system builder will use VXIbus scopes only when the customer specifies them. As I explained above, system builders like scopes with physical front panels. Although VXIbus scopes have soft front panels, the manufacturers designed those programs to help with system integration. Soft front panels tell you that the scope is working, but they may not give you access to enough scope functions for troubleshooting the UUT or the test system. Internal and external PC-based scopes often come with application software that lets you control all of the scope’s functions from your PC. You often get software drivers that let you control the scope from a test application program. Internal scopes operate through either the ISA bus or the PCI bus. External scopes connect to a host PC through a serial, parallel, Ethernet, or USB cable or to a notebook PC through a PC-Card slot. You can, of course, use a bench DSO as a PC external scope, but unless the scope has a serial port, you need an IEEE 488 interface card in your PC. Manufacturers such as Gould, Hewlett-Packard, and LeCroy offer software for remote control of their benchtop scopes. Handheld Scopes In the survey charts in this article, we’ve grouped scopes within each form factor by manufacturer and listed scope families and price categories. (The price category reflects only a general price range for each scope.) Because VXIbus and CompactPCI/PXI scopes can’t reside in a desktop PC or connect to a PC through a cable, we’ve included them in the PC External category. Hitachi has scopes that resemble notebook PCs in size; we placed these in the "handheld" category. For those companies that offer just a few models, we’ve listed specific model numbers. The specs we’ve listed reflect the maximum available for each scope family. T&MW FOR FURTHER READING Strassberg, Dan, "Digital Oscilloscopes: For Best Results, Know How They Work," EDN, Newton, MA. www.ednmag.com. July 4, 1996. Strassberg, Dan, "Digital Scopes Mimic Analogs’ Live Displays," EDN, Newton, MA. June 18, 1998, p. 44. |
