Electrochemical Ratio
Mathematical relationships between the change in electrical potential and the change in ph value define the sensitivity of a measuring electrode. A perfect sensor exhibits a nernstian slope efficiency of one hundred percent, which corresponds to a change of 59.16 millivolts per ph unit at 25 degrees Celsius. In practical textile mill environments, this value usually falls between 95 and 102 percent.
Deviations from the theoretical ideal indicate that the glass membrane is aging or becoming contaminated.
Sensor Validation
Calibration routines use two or more buffer solutions to calculate the actual slope of the electrode. If the nernstian slope efficiency drops below a certain threshold, typically 92 percent, the meter will no longer provide reliable data for process control. Low efficiency leads to compressed readings where the difference between ph 7 and ph 8 appears smaller than it actually is.
This error causes problems in dyeing operations where small shifts in acidity affect the color yield. Technicians must record these values during every calibration to track the health of the equipment. A sudden drop in performance often points to physical damage or deep fouling of the glass surface.
Temperature Dependency
Theoretical slope values increase as the temperature of the sample rises according to the laws of thermodynamics. Automated systems must adjust the nernstian slope efficiency calculation to account for the heat of the dye bath.
Replacement Criterion
Electrodes eventually lose their ability to respond linearly due to the leaching of alkali ions from the glass. When the nernstian slope efficiency can no longer be maintained through cleaning or reconditioning, the sensor is at the end of its functional life.
