May 2002Maintenance, Test & Measurement, Calibration
The purity and the colour tone of the textiles depend on the accurate measurement of the dye pH value. By controlling the pH value, undesirable reactions may be avoided and a highly defined product obtained.
Azo-dyes are produced through several stages in a reactor which is usually rubber-coated. During the first stage the pH value is low (between pH 0 and pH 2) and the temperature less than 20°C. During the second stage the pH value is slightly raised (pH 3 to pH 5) and the temperature increases to 40-50°C. During the last reaction stage the pH value is increased to 10 and the temperature is up to 90°C.
The measuring problems are caused by precipitated dyes and azonium salts, which contaminate the junction. A variety of intermediate products may react with the reference electrolyte and compound the problem. The wide pH and temperature range of this process also puts special demands on the pH electrode, especially if repeatable accuracy at high pH and high temperature is required.
This problem has been solved by the patented pH differential technology from GLI International, which uses three measuring electrodes instead of the two in conventional pH sensors. The process electrode and the reference electrode measure the pH differentially with respect to a third ground electrode. This provides significantly enhanced accuracy, reduces reference junction fouling, and virtually eliminates ground loops. The benefit is greater reliability with less downtime and maintenance and makes these pH electrodes the preferred solution for this and other harsh pH applications.
Any GLI differential pH sensor that fails within one year from the date of shipment will be replaced free of charge. If the sensor fails for any reason, including physical damage, within 30 months, GLI will provide a replacement at a pro rata price.
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