Abstract: A monitor and indicating circuit for use with a reverse osmosis filter for signaling the need for servicing of the filter comprises first and second conductivity cells respectively located in the water inlet and outlet pipes of the filter. An AC signal of a predetermined frequency and amplitude is used to drive an op amp whose input resistance comprises the outlet conductivity cell and whose feedback impedance comprises the inlet conductivity cell. Normally, the resistivity of the outlet conductivity cell is substantially larger than the resistivity of the inlet conductivity cell, assuming that the filter is functioning properly. As the ROF fails, the resistivity at the outlet approaches that at the inlet thereby increasing the gain of the variable gain amplifier. The output from the variable gain amplifier is then peak detected and applied to a comparator where it is compared to a predetermined reference voltage.

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.

Abstract: A temperature controller for monitoring the temperature of a rotating heating system and regulating the temperature relative to a desired temperature. A transmitter within the rotating system coupled to a remote stationary controller via slip rings produces a magnitude varying current control signal within a calibrated range at a magnitude proportional to the sensed temperature. A pair of voltage dividers within the transmitter establish the level and range of current magnitude relative to a constant current source. The remote stationary controller compares the current control signal to a set-point and synchronously supplies power to the heater elements of the rotating system, so long as the sensed temperature is below the desired temperature.

Abstract: An electronic interface circuit for coupling a source of analog signals to a measuring and/or recording device whereby the time varying component of the analog signal can be separated from any steady-state component, such as a DC bias, which may be present, allowing further signal processing on the time varying component only. The interface circuit comprises a servo control device having both a digital feedback loop and an analog feedback loop. Upon closure of a manually operable switch, a timer is initiated which first actuates the digital feedback loop wherein a digital number is generated which is proportional to the deviation of the signal output from a summing amplifier from a zero volt level. This digital number is applied through a digital-to-analog converter to the summing amplifier along with a second feedback signal obtained by sampling the output from the summing amplifier at a time subsequent to the digital correction operation.

Abstract: A method and apparatus for initiating the regeneration cycle of an ion exchange resin type water softener based upon the movement of the "hardness front" through the resin bed as water being treated is passed therethrough. Electrical probes are provided at predetermined longitudinally spaced locations and the difference in potential between the probes is measured, as is the rate of change of this potential with respect to time. It is found that as the hardness front passes between the probes, a detectable change in potential occurs which may be applied to an electronic circuit for generating a control signal which may initiate the regeneration cycle of the water softener subsequent to the arrival of the hardness front in the zone between the probes.

Abstract: A heater roll in which a resistor-type heater mounted in the roll is controlled by use of a temperature sensing element also located in the roll. Electrical power, particularly AC power, is provided through slip rings and the set point for the temperature control is determined by a signal from a current source applied through the slip rings. The set point transmitter is designed to provide a constant current signal to the temperature regulator, irrespective of resistance variations which may be introduced by changes in the slip ring characteristics. As such, the temperature regulator maintains a predetermined temperature in the rotating roll, irrespective of slip-ring resistance variations.