Operation; Design - Teledyne TIENet 301 Installation And Operation Manual

TIENet® 301 pH/Temperature Device
Section 1 Introduction

1.1 Operation

1.2 Design

1-2
For greater distances, external connection via conduit, and con-
nection of additional TIENet devices, the TIENet Expansion Box
is available. Bulk TIENet cable may also be used for greater dis-
tances.
The maximum distance between the 301 and the flow meter is
1,000 ft. (304.8 m).
The pH probe measures the acidity or alkalinity of an aqueous
solution by determining the relative quantity of dissociated
+
hydrogen ions, H (actually H
+
quantity of H ions indicates acidity, while a smaller quantity of
+
H ions indicates alkalinity. The H in pH stands for Hydrogen
and the p stands for power.
The normal scale for pH runs from 0 to 14, with 0 being most
acidic and 14 being most alkaline. Distilled water at 25° C is
neutral at 7, based on the fact that the dissociation constant
and OH - [hydroxyl] ions present) for pure water
+
(number of H
at that temperature is 10
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
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 transition-metal ions will cause them to pre-
cipitate, where they can easily be removed as sludge. The
resultant solution will be high in pH and will require acid to neu-
tralize it.
The pH probe is a combination of two electrochemical half-cells.
Together they provide a low-voltage signal that corresponds to
the hydrogen-ion concentration of a solution. The bulb at the end
of the probe is called the glass mono electrode.
The glass is of special composition, sensitive only to hydrogen
ions, and is exposed to the solution to be measured. The specific
sensitivity to the hydrogen ion prevents interference from other
ions that may be present in the solution. It is essential to prevent
grease from fouling this membrane. The glass membrane pro-
duces 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.
+
O ) in the solution. A larger
3
-7
.
ion. pH measurements of wastewater are