Water treatment regeneration system incorporating alternating current

Abstract

A signal responsive circuit especially adapted for use in a water treatment system for signaling the need for regeneration of an ion exchange resin bed or the replacement of a particulate filter medium. A series of three electrodes are disposed in the water treatment medium in longitudinally spaced relation along the direction of flow and an alternating current signal drives the center-most electrode. The two outer electrodes are coupled as inputs to first and second operational amplifiers having asymmetrical gain characteristics. When the effective resistance between the center electrode and the two outer electrodes are equal, which is the condition prior to the movement of the hardness front or contamination front to the location of the electrodes, a first signal output condition exists. However, when the resin bed or filter medium becomes 'exhausted' to the point where the hardness or contamination front moves to a point between the center and upstream electrode, the signal output condition reverses state and can be used to trigger regeneration or replacement of the medium. The use of an alternating current drive signal obviates problems relating to electrode contamination or erosion. Further, an AGC circuit is utilized to ensure proper operation under variations in ambient conditions, such as temperature changes in the medium. A low pass filter also is effective to render the system less subject to short-duration transient conditions.