Vaisala K-PATENTS PR-23 Series, Instruction Manual, Page: 18 / 246

8 PR-23 instruction manual
2.2.3 Check list for pipe mounting
Most PR-23 refractometer models are mounted in a pipe. The recommended mini-
mum flow velocity of 1.5 m/s (5 ft/s). The diameter and form of the pipe and the
process temperature all affect the measurement and need to be taken into account.
1. If the process pipe diameter varies, select the position with the smallest diameter
(and accordingly highest velocity). Then the prism keeps better clean.
2. If the refractometer is used in a feed-back control loop, make the time lag short . E.g.
when a dilution valve is controlled, mount the refractometer close to the dilution
point. However, make sure complete mixing has occurred at mounting location.
3. 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.
4. Often the position with the highest process pressure (= after pump + before valve)
has favorable flow conditions without sedimentation or air trapping risks.
5. The sensor should be conveniently accessible for service.
2.2.4 Check list for mounting in a tank, a vessel or a large pipe
A probe sensor PR-23-AP or PR-23-GP can be inserted with a flange or clamp into
tanks and vessels which either don’t have a scraper or where the mixer doesn’t touch
the vessel wall. A probe sensor can also be flush mounted in a cooker where the
scraper touches the wall.
1. The inserted probe sensor is mounted close to a stirrer to ensure representative
sample of the process liquid and to keep the prism clean.
2. The sensor should be conveniently accessible for service.