In these times of economic uncertainty and generally tough business conditions, the cost of upgrading test instrumentation can be difficult to justify. Sometimes there’s no choice. Your current gear just can’t do the job. Often, however, the choice is not so straightforward. You might be able to squeak by with current equipment, but upgrading to newer or different instruments would provide benefits.
Many factors inform upgrade decisions, and their relative importance generally depends on the situation. For example, equipment decisions for production test applications are often driven strongly by test throughput considerations. Those for R&D applications may be driven more by resolution, accuracy, noise, and related factors.
Other applications, such as those in student laboratories, will likely demand equipment that combines modest performance, low cost, and high durability and reliability. Although factors such as ease of use and flexibility influence all equipment decisions, they can be difficult to weigh against other factors.
Measuring voltage, current, capacitance, and charge with accuracy, resolution, and precision under a variety of conditions is the foundation of modern electronic test equipment. Perhaps surprisingly, today’s instruments don’t show major improvements in these areas over instruments produced 10 or more years ago. Noise quickly becomes the limiting factor for sensitive measurements. Fortunately, newer instruments do provide many tools for minimizing the impact of noise.
The latest generation of instruments also provides real improvements over earlier generations in a variety of other areas. Many of these improvements are the result of greatly increased embedded computing capability and more sophisticated digital signal processing. Many of them can even save you money.
Of course, precision measurements don’t represent the whole equipment story. Many tests also require precision sources of stimuli. Here, too, state-of-the-art sources tend to provide dramatically higher performance than older models.
Separating Signals From Noise
Measuring tiny signals in ever-present electrical noise requires a variety of strategies and techniques depending on the test environment. Fortunately, today’s instruments are significantly better at dealing with noise than those of earlier generations.
Internal instrument noise has been reduced through the use of improved power supplies and components, as well as thoughtful circuit design and layout. Digital processing offers a variety of filtering algorithms, from simple averaging to sophisticated multi-pole filters that are useful for extracting signals from noise. Improved synchronization functions can increase rejection of line frequency or other periodic noise signals.
Often, the best strategy for dealing with noise is to keep it out of the system. New connectors and cable systems are designed to minimize signal loss and maximize noise rejection in the connections between the device under test (DUT) and instrument.
Inching Closer To The Ideal
An “ideal” instrument is one that has no effect on the circuit or DUT. But real instrument inputs (and outputs) and the cables used to connect them to the DUT have non-ideal characteristics that alter DUT behavior and affect measurement accuracy.
No one has yet produced the ideal instrument, but the latest models have inched far closer to that goal than their predecessors. For example, two generations ago, 10-MΩ input resistance was typical on voltmeters’ low dc voltage ranges. Now, 10-GΩ or 100-GΩ input resistance specifications are common.