Time domain capacitive field detector

Apparatus for measuring a capacitance to a ground of a plate, the plate electrically connected to the ground by a shunting conductor that is not part of the apparatus, the shunting conductor conducting electrical current pulses having durations substantially greater than a first predetermined value, the shunting conductor not conducting current pulses having durations substantially less than a second predetermined value, the apparatus comprising:

• a source of dc voltage;
• pulse generating means generating a charging pulse and a subsequent discharging pulse, at least one of the charging and the discharging pulses having a duration less than the second predetermined value;
• a charging switch having an open state and a closed state, the charging switch moving from its open to its closed state responsive to the charging pulse, the charging switch connecting the voltage source to the plate when in its closed state, the charging switch otherwise disconnecting the voltage source from the plate;
• a discharging switch having an open state and a closed state, the discharging switch moving from its open state to its closed state responsive to the discharging pulse, the discharging switch connecting the plate to a charge measuring means when in its closed state, the discharging switch otherwise not connecting the plate to the charge measuring means;
• whereby a quantity of charge representative of the capacitance of the plate is transferred to the charge measurement means.

A method of operating a sensor, the sensor responsive to a change in the capacitance to a ground of a plate that is connected to the ground by a shunting conductor that is not a portion of the sensor, the shunting conductor conducting electrical current pulses having durations substantially greater than a first predetermined value, the shunting conductor not conducting current pulses having durations substantially less than a second predetermined value, the method comprising the steps of:

• a) closing a charging switch to connect the plate to a source of charging voltage for a charging interval having a predetermined charging duration and thereafter opening the charging switch to disconnect the plate from the voltage source;
• b) closing a discharging switch to connect the plate to a charge measurement means having an output representative of the electrical charge transferred thereinto, the plate connected to the charge measurement means for a discharging interval having a predetermined discharging duration, and thereafter opening the discharging switch;
• and
• c) reading the output of the charge measurement means,
• wherein at least one of the charging and discharging durations is less than the second predetermined value.

Apparatus for measuring a change in capacitance between a sensing plate and an electrical ground, the change in capacitance operatively associated with the presence of a user proximate the plate, the apparatus comprising control means for controlling the actuation of an electrically-operated valve supplying water to a spout, the apparatus comprising:

• the sensing plate;
• a means of generating electrical pulses;
• a source of DC voltage;
• a charging switch intermediate the voltage source and the plate, the charging switch having a closed state electrically connecting the source to the plate and an open state electrically disconnecting the source from the plate, the charging switch switching between the closed and the open states responsive to a first pulse from the pulse generating means;
• a discharging switch intermediate the plate and a charge measuring means having an output, the discharging switch having a closed state electrically connecting the plate to the charge measuring means and an open state electrically disconnecting the plate from the charge measuring means, the discharging switch switching between the closed and the open states responsive to a second pulse from the pulse generating means;
• wherein the control means comprises means for storing a predetermined electric charge value, the control means receiving the output of the charge measuring means and controlling the valve to be open if the output from the charge measuring means is greater than the predetermined charge value, the control means otherwise controlling the valve to be closed.

A method of measuring the change of capacitance to ground of a conducting plate and of controlling the actuation of an electrically-operated valve supplying water to a spout responsive to the measured change, the method comprising the steps of:

• a) closing a charging switch and thereby connecting the plate to a source of dc voltage for a charging interval having a first predetermined duration;
• b) opening the charging switch at the conclusion of the charging interval;
• c) closing a discharging switch and thereby connecting the plate to a charge measurement means for a discharging interval having a second predetermined duration;
• d) opening the discharging switch;
• e) connecting the charge measurement means to a controller and reading from the charge measurement means a first quantity of charge transferred thereinto;
• f) comparing a first predetermined charge value stored in the controller with the first quantity of charge read from the charge measurement means;
• and
• g) controlling, by means of an electrical output from the controller, the valve to open and thereby supply water to the spout if the first quantity of charge exceeds the predetermined charge value, otherwise controlling the valve to be closed and to not supply water to the spout.

A method of operating a capacitive sensor for sensing the presence of an object proximate a sensing plate by measuring a change in a capacitance to an electrical ground, the method comprising the steps of:

• a) setting an output of a charge detector to a first predetermined voltage, the charge detector comprising filter means;
• b) charging the plate from a voltage source to a second predetermined voltage;
• c) discharging, for a predetermined discharging interval, the plate into the charge detector;
• d) repeating steps b) through c);
• and
• e) reading an output of the charge detector as a representation of the capacitance of the plate.

Apparatus for measuring a capacitance to ground of a plate, the apparatus comprising:

• a control means;
• a charging means connecting the plate to a voltage source supplying a first predetermined voltage;
• discharging means responsive to a discharging output from the control means to connect the plate to a charge measurement capacitor having a predetermined capacitance value, the charge measurement capacitor having two terminals, a first of the terminals maintained at a second predetermined voltage, the second of the terminals supplying a voltage output representative of the capacitance to ground of the plate;
• reset means for resetting the charge measurement capacitor to a second predetermined voltage.

A method of operating a capacitive sensor electrically connected between an electrical ground and a sensing plate disposed adjacent an external surface of a first object, the sensor measuring a capacitive change responsive to a second object adjacent the first object, the second object separately electrically coupled to the ground, the method comprising the steps of:

• a) charging the plate from a voltage source;
• b) connecting, for a discharging interval having a predetermined discharging duration, the plate to a charge detector having an output representative of the change of the capacitance to ground of the plate;
• and
• c) reading the output of the charge detector.