Agilent 5991-1707EN Language of Specifications - White Paper c20140804 [5] free download

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Keysight Technologies Language of Specifications White Paper 02 | Keysight | Language of Specifications - White Paper What do Specifications Mean? Hitting the Mark Specifications describe a product's capability but some basic terms are often misunderstood. Has this dart been thrown accurately, or precisely? Is there a difference? This article explains some of the arcane language used in describing a product's characteristics. Thumb through any instrument specification and you are presented with a whole host of technical terms describing the product's capability. There are some basic ones which are often misunderstood, though --accuracy, precision, resolution and sensitivity spring to mind. Basic Terminology Experience has shown that some basic metrological terms are often confused. What is the difference between accurate and precise, resolution and sensitivity, instability and noise? We'll use some graphics to illustrate. Firstly, there are some archery or shooting targets. Four marksmen were aiming for the center "bulls-eye". This is analogous to making a perfect measurement with the "bull" being the conventional, "true value". So, take aim and fire five rounds... Looking at the first target (above left), the shots are widely distributed and mostly off-target -- this guy's obviously a beginner, both inaccurate and unrepeatable. However, is the second marksman (above right) much better? These shots are closely grouped but they've all missed the target completely! He's precise but inaccurate. On to the third (below left) and our man has reliably hit the target but the shots are dispersed -- so we have accuracy (two in the "bull") but imprecision. Of course, the final target shows the way it should be done -- an Olympic champion's performance perhaps -- little deviation from "true" every time, showing both accuracy and precision. As far as calibration is concerned, the attribute accurate often also implies precise but it's worth remembering it may not be the case. Conversely, the supplier that claims his product is precise may not be making any claim at all for its correctness (relationship to national standards) -- be warned! The degree of accuracy and precision results from the combined effect of measuring equipment, technique, environmental conditions and the characteristics of the item being tested. If a series of repeated measurements were made and the data plotted as a histogram (bar graph), the shape described by the bar-heights represents the distribution. 03 | Keysight | Language of Specifications - White Paper 4 2 3 1 Increasing error Increasing error "TRUE VALUE" The plots show the performance of our marksmen whe