4220 Flow Meter
Section 5 Options and Accessories
The dissociation constant is a number indicating the degree of ionic dissociation for a substance after it is dissolved in water. Dissociation constants vary widely for substances depending on the nature of the substance’s chemical bonds. Ionic salts tend to have higher constants.
Each number on the pH scale between 7 and 0 equals a tenfold increase in H+ ion. Each number between 7 and 14 equals a tenfold decrease of H+ ion. pH measurements of wastewater are commonly made to monitor the effect of treatment chemicals added to raise or lower the pH.
Water that has been used for various industrial processes may deviate substantially from 7. Chemicals are often added to the water to bring the pH close to that of neutral water, which is 7. For example, if the effluent has a concentration of heavy metal ions, they must be removed before discharge. Raising the pH of solutions containing
Figure 5-3 pH Probe (with protective cap)
The pH probe is a combination of two electrochemical
The glass is of special composition, sensitive only to hydrogen ions, and is exposed to the solution to be measured. The specific sensitivity to hydrogen ions prevents interference from other ions that may be present in the solution. It is essential to prevent grease fouling of this membrane. The glass membrane produces an electrical potential proportional to hydrogen ion activity. The other electrode, called the reference electrode, completes the circuit between the glass electrode and the solution.
The Isco pH probe combines both electrodes in a single housing and also contains an amplifier to reduce the extremely high impedance of the circuit. This improves the reaction of the probe to stray capacitance and reduces interference caused by electrical noise in the vicinity.
