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Measurement accuracy and tolerance

PRIMES measuring instruments are designed for optimal performance and accuracy under industrial conditions. However a measurand still cannot be determined to any arbitrary accuracy nominated. It is also the case that achieving higher measurement accuracy is inevitably associated with more measurement effort and higher device costs.

For this reason there are frequently multiple measuring devices in the PRIMES portfolio for a measurand, for example laser power, reflecting this principle. The class of accuracy of a measuring device is firstly a result of the repeatability of the device itself and calibration tolerances.

For every measurand that can be measured with PRIMES measuring devices, PRIMES uses so-called working standard instruments in its calibration laboratory to calibrate the devices. These working standard instruments are calibrated regularly in a chain of calibrations against so-called reference standard instruments. The reference standard instrument is then calibrated annually at the national calibration facilities. For laser power, our reference standard instrument is calibrated at the German National Metrology Institute (PTB) against its National Power Standard instruments.

We are proud of the fact that the PTB itself uses a PRIMES EC-PM adapted to its purposes as a National Standard instrument for laser power.
There are no National Standard instruments for beam dimensions and beam propagation parameters. This type of calibration at PRIMES is based on our working standard instruments, which we derive internally from SI measurands according to the redundancy principle.
In the simplest scenario, in scanning systems for example, this can involve reference to the physical dimensions of apertures or fibre ends of a known diameter, or the feed of a linear axis by a known amount. For more complex scenarios, we have working standard instruments at our disposal in the form of measurement set-ups which also allow comparison between various measurement principles (mechanical scanning versus CCD). An important aspect of our work here is the redundancy principle, in other words validation not only by one process or measurand, but validation of measurands over a whole set of independent reference values and processes. This can only be achieved by a supplier who can offer a broad range of methods for beam analysis.

Along with the measurement accuracy of the device however, the conditions under which the measurement takes place have a considerable influence on the reliability of the readings. That is why we recommend adhering as closely as possible to the optimal conditions of use described in the operating manual.

Are you unsure about what measurement accuracy you can expect for your measurement task? Than get in touch with us. Our experts will work with you to produce an ideal measuring solution.

Accuracy of power measurement

For power measurement, we offer a wide range of measuring devices and sensors which can be integrated into systems for every measurement task. The classes of accuracy stated in the table are derived from the combined effect of our chain of calibration and the respective measuring characteristics of the devices.

If you have questions regarding the measuring accuracy of our power measuring devices and your particular preferred field of use, please get in touch with us.

Accuracy of power measurement per device
 RepeatabilityMeasuring accuracy
Cube/Cube M/Cube L± 1 %± 3 %
PowerMeasuringModule PMM± 1%± 3 %
PowerMeasuringCassette PMC± 1%± 3 %
CompactPowerMonitor CPM+± 1.5 %± 3 %
PowerMonitor PM± 1%± 2 %
EC-PowerMonitor EC-PM± 1%± 2 %
Reference EC-PM @PTB± 0.3 %± 0.6 %
PocketMonitor PMT± 2%± 4 %

Accuracy of beam measurement

When calibrating measuring devices and sensors for beam measurement, in the absence of National Standard instruments we fall back on our working standard instruments. To validate our working standard instruments, these are regularly adjusted against SI-based standard instruments on our measuring machine. If you are interested in our calibration methods, please contact us.

The table shows the measuring accuracies deriving from our calibration methods. If you have questions regarding the measuring accuracy of our power measuring devices and your particular preferred field of use, please get in touch with us.

Accuracy of beam measurement per device
 RepeatabilityMeasuring accuracy
BeamMonitor BM+± 3 %± 5 % on beam diameter
LaserQualityMonitor LQM+± 2 %± 10 % on raw beam diameter
± 20 % on beam parameters of raw beam
FocusMonitor FM+ (with optimal detector)± 2 %± 5 % on beam diameter
± 10 % on beam parameter
MicroSpotMonitor MSM+± 2 %± 5 % on beam diameter
± 10 % on beam parameter
FocusParameterMonitor FPM± 4 %± 10 % on beam diameter
BeamControlSystem BCS
(with optimal detector)
± 2 %± 5 % on beam diameter
± 10 % on beam parameter

Definitions of terms

When using our measuring devices for practical applications, questions always arise as to the measuring errors and measuring accuracies to be expected. We have provided a brief explanation of the concepts used below.

Measurement accuracy
Measurement accuracy is yielded by the combined effect of repeatability, systematic measurement errors and calibration accuracy. It describes the tolerance range for a displayed reading. For measurement accuracy, many manufacturers only specify repeatability, which gives rise to apparently low figures.

Repeatability describes the divergence of a reading when the measurement is repeated under the same measuring conditions. The influence of statistically distributed disturbances on the measurement becomes evident here. In particular, repeatability does not contain the comparison with a conceived true value, but only the alteration of the indication from measurement to measurement.

Systematic measuring errors
Systematic measuring errors arise, e.g. through environmental influences, non-linear behaviour of detectors or background effects. These measurement errors can frequently be compensated for in the basic set-up of the measuring device, so that the measurement result is then largely free of systematic measurement error.

Calibration accuracy
The calibration accuracy derives when transferring of the measurement accuracy of a standard to another measuring device first of all from the measurement unreliability of the standard used, and secondly from the testing method used, the associated environmental conditions and the repeatability of the test object under the selected measuring conditions. This means that the measurement unreliability of a measuring device compared with a standard instrument, is always higher than the measuring unreliability of the standard instrument employed.