PUMP CONTROLLER

A method and apparatus for controlling an electric motor pump. The method includes the acts of providing an AC power signal having a positive half cycle and a negative half cycle, measuring the voltage of the AC power signal and generating a first two-state output signal that is in a logic high state when the measured voltage is on the positive half cycle and that is in a logic low state when the measured voltage is on the negative half cycle, and measuring the current of the AC power signal and generating a second two-state output signal that is in logic high state when the measured current is on the positive half cycle and that is in a logic low state when the measured current is on the negative half cycle. The method also includes determining a time difference between the first and second two-state output signals, calculating a phase difference based on the time difference, comparing the phase difference to a predetermined threshold value, opening a switch if the determined phase difference is equal to or greater that the predetermined threshold value, and, after the switch is opened, closing the switch after a predetermined amount of time has elapsed. The invention may be implemented in an apparatus that includes a voltage filter capable of being coupled to an AC power source and of generating a first two-state output signal, a current filter capable of being a coupled to an AC power source and of generating a second two-state output signal, a power supply circuit capable of producing a DC power signal, a programmable device coupled to the voltage filter, the current filter, and the power supply circuit and operable to produce a control signal based on the time difference between the first and second two-state output signals, and a switch coupled to the programmable device and operable to open in response to the control signal. Méthode et appareil pour commander une pompe à moteur électrique. La méthode consiste en premier lieu à fournir un signal d'alimentation c.a. ayant un demi-cycle positif et un demi-cycle négatif, à mesurer la tension du signal d'alimentation c.a. et à générer un premier signal de sortie à deux états qui est en état logique 1 lorsque la tension mesurée est en demi-cycle positif, et en état logique 0 lorsque la tension mesurée est en demi-cycle négatif. La méthode consiste ensuite à mesurer le courant du signal d'alimentation c.a. et à générer un deuxième signal de sortie à deux états qui, lui aussi, est en état logique 1 lorsque