Fluid flow sensing device

Claim 1

A device for sensing variations in the heat exchange properties of a fluid medium as an indication of the relative velocity of the medium comprising a thermistor sensor adapted to be disposed in thermal communication with the medium, said thermistor sensor having a resistance which varies in response to variations in the heat exchange properties associated with variations in the relative velocity of the medium and being adapted to operate in a selfheating mode, calibration means coupled to said thermistor sensor and defining a junction therewith, energizing means coupled to said thermistor sensor to effect the application of sufficient electrical power to said thermistor sensor to enable operation thereof in its self-heating mode so as to establish a first preselected voltage level at said junction in response to a first relative velocity of the medium and to establish a second preselected voltage level at said junction in response to a second relative velocity of the medium less than said first relative velocity, said second preselected voltage level being associated with operation of said thermistor sensor in its self-heating mode, voltage responsive means comprising a voltage regulator diode having a threshold voltage substantially equal to said second preselected voltage level coupled to said junction for providing an electrical signal only in response to the establishment of said second preselected voltage level at said junction, and a selectively energizable switch means coupled to said voltage regulator diode and only operable in response to the generation of said electrical signal for selectively energizing a load.

Claim 2

A device for sensing variations in the heat exchange properties of a fluid medium as an indication of the relative velocity of the medium comprising a thermistor sensor adapted to be disposed in thermal communication with the medium, said thermistor sensor having a resistance which varies in response to variations in the heat exchange properties associated with variations in the relative velocity of the medium and being adapted to operate in a selfheating mode, calibration means coupled to said thermistor sensor and defining a junction therewith, energizing means coupled to said thermistor sensor to effect the application of sufficient electrical power to said thermistor sensor to enable operation thereof in its self-heating mode so as to establish a first preselected voltage level at said junction in response to a first relative velocity of the medium and to establish a second preselected voltage level at said junction in response to a second relative velocity of the medium less than said first relative velocity, said second preselected voltage level being associated with operation of said thermistor sensor in its self-heating mode, voltage responsive means comprising a voltage regulator diode having a threshold voltage substantially equal to said second preselected voltage level coupled to said junction for providing an electrical signal only in response to the establishment of said second preselected voltage level at said junction, and a selectively energizable switch means coupled to said voltage regulator diode and only operable in response to the generation of said electrical signal for selectively energizing a load.

Claim 11

A device for sensing and indicating variations in the heat exchange properties of a fluid medium comprising a thermistor sensor adapted to be disposed in thermal communication with the medium, said thermistor sensor having a resistance which increases with increasing temperature and being adapted to operate in a self-heating mode, a resistor coupled to said thermistor sensor to define a voltage divider including a junction between the resistor and the thermistor sensor, energizing means coupled to said thermistor sensor through said resistor to effect the application of sufficient electrical power to said thermistor sensor to enable operation thereof in its self-heating mode so as to establish a first preselected voltage level at said junction in response to a first condition of the heat exchange properties of the medium and to establish a second preselected voltage level at said junction associated with operation of said thermistor in its self-heating mode in response to a second condition of the heat exchange properties of the medium, said second condition representing a decrease in the heat exchange properties of the medium relative to the first condition, first switch means including a first transistor coupled to said voltage divider, said first transistor being rendered conductive in response to said first preselected voltage level and being rendered non-conductive in response to said second preselected voltage level, indicating means coupled to said first transistor, said indicating means being energized in response to conduction of said first transistor, voltage responsive means coupled to said junction for providing an electrical signal in response to the establishment of said second preselected voltage level at said junction, second switch means including a second transistor coupled to said voltage responsive means, said second transistor being rendered conductive in response to said electrical signal and shunting said first transistor so as to render said first transistor non-conductive, and selectively operable means coupled to said second transistor for providing an indication in response to conduction of said second transistor.

Claim 12

A device for sensing and indicating variations in the heat exchange properties of a fluid medium comprising a thermistor sensor adapted to be disposed in thermal communication with the medium, said thermistor sensor having a resistance which increases with increasing temperature and being adapted to operate in a self-heating mode, a resistor coupled to said thermistor sensor to define a voltage divider including a junction between the resistor and the thermistor sensor, energizing means coupled to said thermistor sensor through said resistor to effect the application of sufficient electrical power to said thermistor sensor to enable operation thereof in its self-heating mode so as to establish a first preselected voltage level at said junction in response to a first condition of the heat exchange properties of the medium and to establish a second preselected voltage level at said junction associated with operation of said thermistor in its self-heating mode in response to a second condition of the heat exchange properties of the medium, said second condition representing a decrease in the heat exchange properties of the medium relative to the first condition, first switch means including a first transistor coupled to said voltage divider, said first transistor being rendered conductive in response to said first preselected voltage level and being rendered non-conductive in response to said second preselected voltage level, indicating means coupled to said first transistor, said indicating means being energized in response to conduction of said first transistor, voltage responsive means coupled to said junction for providing an electrical signal in response to the establishment of said second preselected voltage level at said junction, second switch means including a second transistor coupled to said voltage responsive means, said second transistor being rendered conductive in response to said electrical signal and shunting said first transistor so as to render said first transistor non-conductive, and selectively operable means coupled to said second transistor for providing an indication in response to conduction of said second transistor.