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At a chemical site in northern Germany, „Novolac™“ – synthetic resins are formed through a poly condensation reaction between phenol and formaldehyde. A crucial characteristic of the end product, the resin, is its viscosity, which depends on the amount of the watery formaldehyde solution fed into the reaction vessel.
To always guarantee the specified viscosity of the end product, the dosing of the formaldehyde solution as well as its concentration must be accurate and thus has to be closely monitored.

For doing so, the plant operator decided upon installing FLEXIM's PIOX R Process Refractometer. Instead of many other Process Refractometers on the market, which work according to the critical angle reflection principle and are thus prone to build-up of media on the prism and a subsequent failure resulting out of it, FLEXIM's PIOX R employs the unique transmitted light principle. This means that it not relies on measuring at a very small interface layer between media and prism, but transmits a whole light beam through the medium. Build-up of media on the prism only leads to a slight decrease in the signal amplitude but not to a change in the measured refractive index.

PIOX R is thus completely independent of fouling on the prism and the patented system moreover allows for an accurate, stable and reliable measurement even at strong temperature and pressure variations in harsh process environments (ATEX Zone 1 certified).


  • Precise and reliable online measurement of the formaldehyde concentration
  • Permanent monitoring of the product quality
  • Independent against fouling and build-up on the prism
  • Long term stable measurement without any drift