Leak detector comprising a self-heated thermistor control circuit

A method for detecting fluid leaks in an instrument, said method comprising:

• a) driving a fluid leak detector circuit in a manner so as to provide constant power dissipation in both a first thermistor device adapted to detect a fluid leak upon contact with a liquid and a second thermistor device functioning as a reference device, said first and second thermistor devices adapted to being driven with a current to operate in self-heated mode at a temperature above an ambient temperature;
• b) receiving a first voltage Vs′ at a reference point in said fluid leak detector circuit that connects said first reference thermistor device and a first resistor device connected in series, and receiving a second voltage Vs at a reference point in said fluid leak detector circuit that connects said second reference thermistor device and a second resistor device connected in series;
• and,
• c) comparing said first Vs′ and second Vs voltages;
• and,
• d) determining a fluid leak condition on the basis of a comparison result irregardless of said ambient temperature.

A control circuit for a detector device comprising a sensing circuit including a first thermistor device adapted to detect an environmental condition, and, a second thermistor device functioning as a reference device, said control circuit comprising:

• means for driving said first and second thermistor devices with a current such that both manner such that said first and second thermistor devices operate in self-heated mode at a temperature above an ambient temperature;
• and,
• means for monitoring a voltage Vs at a reference point in a portion of said sensing circuit connecting said second thermistor device with a sense resistor;
• a control system for controlling said driving means so as to maintain a constant application of power through both said first and second thermistor devices in response to said voltage Vs, said means additionally monitoring a voltage Vs′ at a reference point in a portion of said sensing circuit including said first thermistor device;
• and,
• a comparing means for comparing the voltage Vs′ at a reference point in said sensing circuit including said first thermistor device with the voltage Vs at a reference point in said sensing circuit including said second thermistor device and detecting said environmental condition on the basis of a comparison result irregardless of said ambient temperature.