Most in-line refractometer models are mounted in a pipe. The recommended minimum flow velocity is 1.5 m/s (5 ft/s). The diameter and form of the pipe and the process temperature affect the measurement and need to be taken into account.
- If the process pipe diameter varies, select the position with the smallest diameter (and accordingly highest velocity). Then the prism keeps better clean.
- If the refractometer is used in a feed-back control loop, make the time lag short. When a dilution valve is controlled, for example, mount the refractometer close to the dilution point. However, make sure complete mixing has occurred at mounting location.
- If the temperature varies along the process pipe, select the position with the highest process temperature. Then the risk of prism coating is minimized, because higher temperature means higher solubility and also lower viscosity.
- Often the position with the highest process pressure (= after pump + before valve) has favorable flow conditions without sedimentation or air trapping risks.
- The sensor is accessible for service.