One of the primary concerns when using an inline process analyzer for real-time liquid or gas analysis is validating the instrument is working to specification. Process photometers are often calibrated using liquid or gas calibration standards or directly to the process. These calibration methods can require considerable resources, so the preferred maintenance approach is often to validate performance as opposed to full recalibration of the instrument.
The most typical validation method is verification of instantaneous reported instrument reading against process sample measured offline. This method is limited to only one sample concentration at a time and may not provide a true indication of how the instrument will perform under changing process conditions. This paper will discuss the pros and cons of various photometer validation and verification methods and the impact photometer instrument design has on these methods.