Liquid sensor systems for liquid-employing apparatus and sensors for use in such systems

A liquid sensor system for liquid-employing apparatus comprising:

• a capacitive liquid sensor adapted to have the liquid to be detected as part of the dielectric therein,
• a capacitance measuring circuit connected to the said capacitive detector and producing a first electric output when the detector is empty of liquid and a second output when it is full of liquid,
• said capacitance measuring circuit including sensitivity adjusting means operable upon start-up of the detector to adjust the sensitivity from a minimum toward a maximum and to stop and hold the sensitivity at a value at which the circuit detects the presence of the liquid in the capacitive detector,
• said sensitivity adjusting means comprising:
• a counter,
• pulse means operable to start the counter in a counting sequence,
• means operable by the counter to produce a progressively changing analogue bias voltage as the counter counts,
• means applying the changing biasing voltage to the capacitance measuring circuit to change the sensitivity thereof, and
• means operable to stop and hold the counter and the corresponding bias voltage at the values corresponding to a change of the measuring circuit from the said first electric output to the second electric output,
• motor and pump means receiving liquid to be detected from a source thereof and pumping it through the capacitive detector,
• and motor control means operative upon receipt of said first electric output of the capacitance measuring circuit to stop operation of the motor and pump means.

A liquid sensor system for liquid-employing apparatus comprising:

• a capacitive liquid sensor adapted to have the liquid to be detected as part of the dielectric therein,
• said capacitive liquid sensor comprising a pair of spaced parallel conductive plates, and a liquid-carrying structure of non-conductive material between the plates establishing a tortuous path between them for liquid which thereby constitutes part of the dielectric of the resultant capacitor,
• the said liquid-carrying structure comprising a moulded unitary body of plastic material having the tortuous elongated path established therein by internal baffles and partitions,
• a capacitance measuring circuit connected to the said capacitive detector and producing a first electric output when the detector is empty of liquid and a second output when it is full of liquid,
• motor and pump means receiving liquid to be detected from a source thereof and pumping it through the capacitive detector,
• and motor control means operative upon receipt of said first electric output of the capacitance measuring circuit to stop operation of the motor and pump means.

A liquid sensor system for liquid-employing apparatus comprising:

• a capacitive liquid sensor adapted to have the liquid to be detected as part of the dielectric therein,
• said capacitance liquid sensor comprising a pair of flat spaced parallel conductive plates, and a plurality of turns of tubing of non-conductive material establishing a tortuous elongated path and disposed between the plates in physical contact therewith, through which turns moves the liquid to be detected,
• a capacitance measuring circuit connected to the said spaced conductive plates of the capacitive detector and producing a first electric output when the detector is empty of liquid and a second output when it is full of liquid,
• motor and pump means receiving liquid to be detected from a source thereof and pumping it through the said turns of the capacitive detector,
• and motor control means operative upon receipt of said first electric output of the capacitance measuring circuit to stop operation of the motor and pump means.