While simple 2-electrode sensors are inexpensive and can provide accurate data, continuous monitoring of even relatively clean water can foul the electrodes and degrade the measurement. Maintaining accuracy is made more difficult when the amount of solids dissolved in the process varies over a wide concentration range. In this case, a simple 2-electrode sensor is limited by its cell constant, which means it cannot measure the process accurately.
ATI’s Q45C4 4-Electrode Conductivity Monitor is the answer for monitoring almost any water-based process. Drinking water, plating bath solutions, cooling water, process wash water, or virtually any other aqueous system can be monitored accurately and reliably. The unique drive/control scheme used in the 4-electrode system allows a single sensor configuration to be used in conductivity ranges from 0-200 μS to as high as 0-2,000 mS (0-2 S). The “auto-ranging” feature enables the monitor to display the actual conductivity value during “overshoot” conditions. For chemical mixing applications, a concentration display can be selected for a limited number of acids and bases.
In a traditional 2-electrode sensor, each electrode performs two functions. First, the electrodes are used to generate a “drive potential” through the aqueous solution. Second, the electrodes are used to measure the level of current flow as the conductivity of the solution varies. It is this dual role that limits a 2-electrode sensor to a narrow functional conductivity range.
A 4-electrode sensor splits the two functions between two sets of electrodes. One set of electrodes is used to generate the drive potential through the aqueous solution. The other set of electrodes is used to measure the current that flows between the two drive electrodes. Because these two functions are separate, the 4-electrode sensor does not suffer the polarization effects that limit a 2-electrode sensor to a narrow functional range. This allows a single 4-electrode sensor to operate reliably over the entire 0-2 S/cm conductivity range.