HF scientific MicroTSCM Streaming Current Monitor - Manual (Page 9)

MICROTSCM (07/09) Page 5
REV 2.4
CHEMICAL DOSAGE ppm
TURBIDITY
Figure 3: Turbidity vs Dosage
3.2 Charge Analysis
Charge analysis is the measurement of the electro kinetic charge of a solution due to the
presence of charged particles. The electro kinetic charge can be measured by a number of
different methods.
1. Applied electric field
Measurement: The relative mobility of the solid or liquid phase.
This is the first method developed for calculating the Zeta Potential. The motion of
charged particles under the influence of an electric field was observed and the potential
required to achieve a certain amount of particle mobility was measured.
A cell consisting of two flat plates separated by approximately 0.1 mm and having an
electrode at each end of the cell is filled with water containing suspended matter. When an
electrical potential is applied to the electrodes, the particles can be observed to drift
toward one of the electrodes. The Zeta Potential is calculated from the measured speed of
particle drift.
2. Induced Electrical Potential
Measurement: The potential developed as the result of forced movement of particles in the
solution.
This is the method used by the MicroTSCM. Continuous sample water is directed into an
annulus, inside which a displacement piston oscillates vertically at a fixed frequency. This
action causes the liquid to move between the two stainless steel electrodes. The suspended
particles are absorbed onto the walls under the action of Van der Waal’s and electrostatic
forces. As the sample is moved rapidly back and forth, mobile counter ions surrounding
the colloids are sheared near the surface of the walls and moved past the electrodes. The
resultant A.C. signal or Streaming Current, proportional to charge density, is electronically
processed and displayed.