How to identify the measuring characteristics of ZUMBACH equipment
Quality’ and ‘precision measurement’ are arguments for all manufacturers of control and measuring systems in dimensional metrology, as they are critical to the quality of produced goods and must ultimately be considered as factors of economic success.
ZUMBACH also uses ‘quality’ and ‘precision’ as key selling points for its solutions. Nevertheless, we are convinced that offering the possibility of finding out just how accurate and precise the measured values a device can provide, for example prior to the purchase of a gauge, is only fair to our customers.
The measuring characteristics of all ZUMBACH devices are listed on the respective product data sheets using definitions recognised by a wide range of standardisation bodies and institutions. Every data sheet produced by ZUMBACH offers an overview of the device’s measuring characteristics, thereby showing what kind of information can be expected from the solution.
The measuring characteristics include:
- Error of measurement
- Measurement precision
The resolution of a device is the smallest change in a quantity being measured that can be indicated without ambiguity. A fine resolution proves the device’s capability of systematically discriminating between two distinct quantities.
Example: A device for measuring diameters with a resolution of 1μm is able to systematically indicate two different readings for two objects whose diameters differ by 1μm.
The measurement precision is the closeness of agreement between measured quantity values obtained by replicate measurements on the same object. The precision is also called repeatability when the replicate measurements are performed under the same conditions*.
Typically, the repeatability is given in terms of the standard deviation σ.
Example: A device with a repeatability of 10μm at σ indicates that about 68.27% of the obtained values lie within 10μm of the mean value.
*Same measurement procedure, same device, same measuring system, same operating conditions and same location, same object over a short period of time
In figure 2, this is equivalent of saying that, under the assumption of a distribution of the obtained values below a Gaussian bell curve, 68.27 % of the measured values fall in the blue region, while only 31.73% fall in the orange region.
If a device has instead a repeatability of 10μm at 3σ then 99.73% of the of the obtained values lie within 10 mm of the mean value (in figure 2, the Gaussian curve would be narrower and the blue region would cover 99.73% of the surface below the curve).
Error of measurement
Finally, the measurement accuracy gives the closeness of the agreement between a measured value and a true value of an object. A good accuracy means that the error of measurement, the difference between the measured values and the true value, is small, a bad accuracy means that the difference between the measured values and the true value is larger than desired.
Example: A system with a demonstrated error of measurement of 10μm indicates that the different between the measured value and the true value is smaller than 10μm.
Our devices are specified according to the above definitions. Some of the properties can be further specified for specific regions (for instance in the centre of the measurement field) or operating conditions.
ZUMBACH measuring solutions