Method and apparatus for detecting a dry/wet state of a dual exposed thermistor bead liquid level sensor

Apparatus for detecting a dry/wet state of a dual thermistor bead sensor over a wide operating temperature range, said apparatus comprising:

• a first circuit coupled to said sensor for conducting a first predetermined current through one of the thermistor beads of said sensor and for conducting a second predetermined current through the other of the thermistor beads of said sensor, said second predetermined current being substantially less than said first predetermined current;
• a second circuit coupled to said sensor for measuring a first voltage across said one thermistor bead in response to said first predetermined current and generating a first signal representative thereof;
• a third circuit coupled to said sensor for measuring a second voltage across said other thermistor bead in response to said second predetermined current and generating a second signal representative thereof;
• a fourth circuit coupled to said third circuit for modifying said second signal by an offset and gain to generate a third signal;
• and
• a fifth circuit for detecting the dry/wet state of said sensor over said wide operating temperature range based on said first and third signals.

Method of detecting a dry/wet state of a dual thermistor bead sensor over a wide operating temperature range, said method comprising the steps of:

• conducting a first predetermined current through one of the thermistor beads of said sensor;
• conducting a second predetermined current through the other of the thermistor beads of said sensor, said second predetermined current being substantially less than said first predetermined current;
• measuring a first voltage across said one thermistor bead in response to said first predetermined current and generating a first signal representative thereof;
• measuring a second voltage across said other thermistor bead in response to said second predetermined current and generating a second signal representative thereof;
• combining the first and second signals to generate a third signal;
• generating a reference signal;
• and
• detecting the dry/wet state of said sensor over said wide operating temperature range based on a comparison of said third signal to said reference signal.

Apparatus for detecting a dry/wet state of a dual thermistor bead sensor over a wide operating temperature range, said apparatus comprising:

• a first circuit coupled to said sensor for conducting a first predetermined current through one of the thermistor beads of said sensor and for conducting a second predetermined current through the other of the thermistor beads of said sensor, said second predetermined current being substantially less than said first predetermined current;
• a second circuit coupled to said sensor for measuring a first voltage across said one thermistor bead in response to said first predetermined current and generating a first signal representative thereof;
• a third circuit coupled to said sensor for measuring a second voltage across said other thermistor bead in response to said second predetermined current and generating a second signal representative thereof;
• a fourth circuit coupled to said second and third circuits for combining the first and second signals to generate a third signal;
• and
• a fifth circuit for detecting the dry/wet state of said sensor over said wide operating temperature range based on a comparison of said third signal with a reference signal.