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17 August 2017

Back to Basics: Metrology

Some sciences are more obscure than others; these may be of interest and importance to relatively few. The term “metrology” may leave even some science geeks scratching their heads, but for those in the test and measurement arena, metrology is an extremely critical area of scientific endeavor.

Metrology is the science of studying the errors in measurements. Test equipment, such as the oscilloscopes we manufacture here at Teledyne LeCroy, are only as good as long as their measurements are consistently precise and accurate. So for us, metrology is a science that is central to our mission.

At the root of our practice of metrology are international standards of measurement for quantities such as currents, voltages, frequency, time, resistance, impedance, and power. These standards are defined by bodies such as the National Institute of Standards and Technology (NIST) in the United States, or the International System of Quantities as represented by the ISO/IEC 80000-1 standard.

An oscilloscope, like any other electronic system, is the sum of its parts. We design the instruments so as to maximize measurement accuracy, and specify the components built into them to deliver that accuracy. These components have themselves been characterized by their respective manufacturers, and their characterization process has some amount of error associated with it. Thus, the overall accuracy of our instruments incorporates that error as well.

Bear in mind that an instrument can be very precise and not accurate at all – or very accurate but not very precise. “Precise” means the measurement has many significant digits. “Accurate” means the digits are the correct ones.

It’s important to note that the objective of metrology is not to ensure that a given instrument is tweaked for perfect accuracy, but rather at determining how accurate the instrument actually is as measured against NIST or ISO/IEC standards. The metrologist documents that comparison so that the instrument’s end user knows exactly what he or she is getting. Unless specified otherwise, measurements are reported quoting an error of two “sigma”, which indicates a >95% chance that estimated errors are not exceeded. Another rule of good metrology is that the instrument is measured, when possible, against a standard that is 4X more accurate than the unit under test.

The Deeper Dive of Metrology

Of course, all Teledyne LeCroy oscilloscopes are subjected to quality control inspections. But metrology takes a deeper dive into how the parts come together to form the whole. It tells the customer, and our own staff, how close each instrument is to ever-elusive perfection.

All of our oscilloscopes come with a calibration certificate, and that calibration must be traceable to the definitions of quantities emanating from one or more international standard. The errors found through metrology reduce the margin of effort you can afford in your system. When the certificate states that an instrument is precise in measuring a given quantity to within ±1%, it typically means that we must measure the quantity to a fraction of 1% error. Thus, the instrument’s specifications are demonstrably met.

Calibration certificates spell out what equipment was used in the calibration of the instrument, and what the results of the testing showed. For example, a datasheet might show that a particular oscilloscope model is specified for DC measurement accuracy to within 1% ± some number of millivolts. The calibration certificate might show that a specific instrument is accurate to within 0.75% ± some smaller number of millivolts. It tells you the maximum amount of uncertainty in the instrument’s measurements.

To the oscilloscope’s owner, the calibration certificate represents a certificate of trust. It tells them how close the instrument is to the center of the range called for in the specification. It’s a matter of confidence in the owner’s measurements over time.

Metrology gives you a firm handle on your measurement margin for error. But with the advent of high-speed communications standards such as PCIe, that margin of error has been squeezed such that it becomes very difficult to ensure that everything works as it should. As a result, all oscilloscope makers have been pushed for greater measurement accuracy across ever-growing instrument bandwidths.

When instruments arrive at Teledyne LeCroy’s service department for calibration, some owners want the oscilloscope returned exactly as it was. They want only to learn how aging has affected the instrument. Did its measurement accuracy change, and if so, by how much? Other customers want their instrument restored to like-new condition, complete with software updates.

With the advent of high-speed communications standards such as PCIe, the margin for measurement error is minimal, making it extremely difficult to make sure everything is working correctly. Thus, the oscilloscope industry strives for more precision across the instruments’ wide frequency range. It could almost be said that Teledyne LeCroy’s LabMaster 10 Zi-A oscilloscope is akin to a 100-GHz voltmeter. There is an overriding need for high precision at every frequency. Thus, metrology will remain an integral part of the engineering effort for all instrument manufacturers.

27 July 2017

The Periodic Table of Oscilloscope Tools: Document

Teledyne LeCroy's Document toolset for its oscilloscopes
Oscilloscope users can find themselves managing a lot of detail in the course of driving their instruments. They need to keep track of instrument setups. They have to know standards-based compliance test routines backward and forward. Often, the need arises to remotely control the oscilloscope, interface it with other applications, and export/import acquisition data. And, importantly, the oscilloscope has to aid, and not hinder, collaboration with other members of the engineering team(s).

26 July 2017

The Periodic Table of Oscilloscope Tools: Analyze (Part III)

We're nearing the end of our tour of the Periodic Table of Oscilloscope Tools, our way of presenting our broad palette of oscilloscope tools in a concise, clear fashion. In this installment, we'll finish up the Analyze grouping, by far the largest on the Periodic Table.

20 July 2017

The Periodic Table of Oscilloscope Tools: Analyze (Part II)

The Analysis tools in an oscilloscope lend it debug power
Figure 1: The Analysis
tools in an oscilloscope
lend it debug power
Oscilloscopes are central to many engineering tasks, but perhaps to none more so than debugging. Something is going on with your design but you don't know what it is. However, armed with an oscilloscope with the sort of sophisticated analysis tools found in Teledyne LeCroy's instruments, even Mr. Jones can get to the bottom of the problem. Let's continue our survey of the Periodic Table of Oscilloscope Tools with more on analysis tools.

18 July 2017

The Periodic Table of Oscilloscope Tools: Analyze (Part I)

Analysis tools deepen insight into waveform behavior and relationships
Figure 1: Analysis tools deepen
insight into waveform behavior
and relationships
The path from problem to solution via oscilloscope moves through a number of stages. Doing so involves capture of a signal, determining how it's to be viewed, taking measurements of various parameters, and possibly applying math functions to the waveform. All of these stages depend on the roster of tools that the oscilloscope brings to bear on the process. Teledyne LeCroy's Periodic Table of Oscilloscope Tools represents our view of the world of such tools.

14 July 2017

The Periodic Table of Oscilloscope Tools: Math

DSP-based Math functions can reveal deep insights hidden in waveforms
Figure 1: DSP-based
Math functions can
reveal deep insights
hidden in waveforms
The usefulness of oscilloscopes skyrocketed once digital signal processing began to be applied to acquired waveforms. By applying DSP, oscilloscopes could now perform complex processing in the time, frequency, statistical, and other domains, all while imposing no restrictions on acquisition length. Here at Teledyne LeCroy, we collectively refer to these DSP-based processes as Math functions. We've presented those functions, along with all of the other functions our instruments perform, in chart form in our Periodic Table of Oscilloscope Tools.

12 July 2017

The Periodic Table of Oscilloscope Tools: Measure

Measure tools are at the heart of an oscilloscope's utility
Figure 1: Measure
tools are at the heart
of an oscilloscope's
An oscilloscope is only as good as the tools it provides to users for acquiring, viewing, measuring, analyzing, and documenting waveforms. We present an overview of our deep collection of oscilloscope tools in our Periodic Table of Oscilloscope Tools, and in prior Test Happens posts, we've surveyed the Capture and View categories. Today we'll break down the Measure section of the Table.