Verification procedure - PR-33 - PR-33-AC

PR-33-AC User Guide

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User guide

Perform instrument verification using the web interface. On the instrument homepage, go to the Verification page. The standard liquids are placed on the prism as instructed by the instructions on the screen. Once the liquid has settled, sample is measured by clicking the New verification point button.

The liquids are automatically detected, and the quality of the measurement is constantly monitored throughout the process. If the same liquid is measured several times, the new result replaces the older one. To remove a single measurement point, click the Remove button.

The verification result displays on the page. Reloading the page removes all points. After measuring a sufficient number of points the verification can be saved by clicking the Save verification button.

In order to avoid verification errors, please make sure:

  • The temperature has settled, i.e., the refractometer is in the ambient temperature
  • The temperature of the refractometer is between 20 °C and 30 °C
  • The prism is cleaned properly before placing the sample
  • The test liquid wets the prism properly

Check the temperature of the refractometer by following the temperature measurement on the Verification page. The temperature should be constant.

Figure 1. Verification page

The sample holder keeps the sample on the prism surface and also blocks the ambient light from reaching the prism. Universal sample holder PR-1012 can be used with any Vaisala K‑PATENTS® refractometer.

The optical image displayed on the page helps determining whether the prism is wetted completely. The image should have a sharp corner as in the figure above. The position of the corner depends on the refractive index. A soft image may indicate improper cleaning of the prism. If there is not enough liquid on the prism, the image tends to flatten. If the image changes its shape during the measurement of a single liquid, redo the measurement. The most likely reason is that the liquid leaks from the sample holder.

Figure 2. Universal sample holder PR-1012

After measuring a sample, remove the sample and clean the prism and the sample holder. The prism can be cleaned by soft tissue and ethanol or other suitable solvent. Repeat the procedure (cleaning, replacing the sample, measuring) for each nD liquid. In case you perform the procedure more than once for a single sample, the latest measurement will replace earlier measurements.

The table on the verification page keeps a real time record of the points measured and the status (pass/fail) of the verification. If you have a failed point, either remove it or remeasure it.

Once all liquids have been measured, save the verification by clicking the Save verification button. The button is only available after a sufficient number of points has been measured.

The limit for acceptance is that all measurements must be within ± 0.0004 of the nominal values.

The refractometer verification concerns only the refractive index nD measurement. The calculation of concentration from nD and process temperature TEMP is not included.