Patent ID: 8534640

Claim:
An apparatus for switching control of one or more valves between a machine controller and an automatic controller comprising: a sensor configured to detect a signal generated by the machine controller; and a switching circuit configured to: switch control of the one or more valves from the automatic controller to the machine controller if the signal from the machine controller exceeds a predetermined threshold; and switch control of the one or more valves from the machine controller to the automatic controller if the signal from the machine controller falls below the predetermined threshold, wherein the switching circuit comprises: a resistor coupled to the sensor and configured to provide a dummy load to the machine controller; a first switch coupled between the automatic controller and the one or more valves and configured to allow a signal to pass from the automatic controller to the one or more valves when closed; a second switch coupled between the sensor and the one or more valves and configured to allow a signal to pass from the machine controller to the one or more valves when closed; and a third switch coupled to the resistor, wherein the third switch, when closed, provides a path for a signal from the machine controller through the resistor to provide the dummy load to the machine controller, wherein: the first switch and the third switch are closed and the second switch is open when the detected signal does not exceed the predetermined threshold; and the first switch and the third switch are open and the second switch is closed when the detected signal exceeds the predetermined threshold.