Calibration - PR53 - PR53AC - PR53AP - PR53GC - PR53GP - PR53M - PR53SD - PR53W

PR53 Series User Guide

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User guide

Calibration ensures that the measurement of the refractometer is accurate.

The refractometer comes with a traceable calibration certificate which ensures that it has fulfilled the measurement criteria when sent from the factory.

There are two ways to ensure measurement accuracy: comparing online measurement with laboratory reference (field sampling), and RI calibration.

The refractometer is a very stable instrument. Calibration interval is defined according to the application, requirement of accuracy, ambient conditions, and quality system or, for example, third party requirements.

Online measurement vs. laboratory results is the primary method because it validates the complete measurement, including the effects of ambient conditions to the measurement position and, for example, possible coating of the prism. It is also a simple method because you do not need to remove the refractometer from the process.

The following circumstances affect the calibration:
  • Accuracy and repeatability of the laboratory reference
  • Traceability of the laboratory reference and its own calibrations
  • Sampling and the possible errors related to it (representativeness of the sample and changing of the sample, evaporation, for example)
  • Measurement range; the method based on the laboratory reference may not cover the whole measurement range.
Calibration is needed when the optics of the device is serviced and RI adjustment needs to be performed. Calibration is done to find out if there is measurement error in the device in the defined measurement area; RI adjustment is performed to fix the error.
RI adjustment can only be performed with Insight.

RI calibration is a secondary method which can be performed with nominal reference RI liquids. It is an offline method and requires the refractometer to be removed from the process.

RI calibration validates the whole measurement range and verifies the technical condition of the refractometer, the erosion of the prism, for example.

However, RI calibration does not acknowledge other sources of uncertainty in concentration measurement, such as ambient conditions and accuracy of the concentration curve.