Residual chlorine monitors and indeed, ozone monitors, pH meters and chlorine dioxide analyzers have all been around a long time and it would seem unlikely that they could be improved upon greatly, but for some applications they have!

How Pi Solved A Paper Mills’ Ongoing pH Sensor Problems

CRIUS Instrument Controller with Autoflush System

Autoflush mounted on a board with a CRIUS controller.

In 2007 a paper mill approached Process Instruments (UK) Ltd (Pi) with a problem. They had a de-inked stock that they measured pH in to control a chemical addition. The problem was that their pH sensor was coating with ink that set hard on the glass. The pH sensors were unreliable a short time after replacement and the cost of replacing the sensors monthly was prohibitive. Following a detailed survey and discussion with the customer Pi proposed an auto-flushing device that would flush the pH sensor with warm, soapy water regularly enough to prevent rather than remove build up of ink.

Two years after installation the same pH sensor continues to give reliable results with the CRIUS 100 analyser not only controlling the pH sensor, but providing the PID control for the chemical addition.

The CRIUS Autoflush is controlled by the analyser where user variables adjust the flush time, frequency and signal hold time.

Fortunately not all cleaning requirements are so tough and via a ‘customer consultation’ exercise (we asked them!) Pi discovered that the need to keep sensors clean is far greater than previously imagined. Since 2006 Pi has shipped approximately 50 autoflush units all using potable water to keep various sensors clean under varying conditions. Some of the applications that have benefitted from a CRIUS Autoflush are:

  • pH sensor in a de-inking plant
  • free chlorine sensor in white water in a paper plant
  • chlorine dioxide sensor in a food plant
  • pH sensor in an industrial chemical plant

If you have an application where your sensors require excessive maintenance or where the sensors need to be replaced too often, visit our website!

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