To be able to guarantee that the reading of a process photometer is still correct even after years of operation in a sometimes rough environment, a reference measurement should periodically be carried out for quality assurance. Measurement of the primary standard is often unsuitable in the field. Hence, SIGRIST measuring instruments are delivered together with a solid reference allowing the photometer to be verified. The solid reference is manually inserted into the flow cell. Some SIGRIST measuring instruments are designed to carry out an autonomous reference measurement by automatically inserting the solid reference into the flow cell. In both cases, the measuring instrument can compare the actual reading of the reference measurement with the stored value of the solid reference. In case a considerable difference is determined, the instrument will issue an error message. Using this reference measurement, the reading can be validated at any time.
Fig. 38: Schematic illustration of a flow cell with a solid reference. The measuring instrument can automatically move the solid reference into the optical path and carry out a reference measurement.