Self-checking fluid level indicators

Claim 2

In a fluid level detector, the combination of a reservoir for fluid, an electrical power source, an indicator circuit including an indicator device and a current-responsive device connected to the power source, the current-responsive device when energized being operative to effect energization of the indicator device by the power source, a probe circuit including a probe in series with the power source and positioned in the reservoir at a fluid level to be detected, the probe circuit being connected to the current-responsive device and operative to control the energization thereof by the power source and accordingly the energization of the indicator device in response to the immersion of the probe in the fluid, and an RC timer circuit operative after the detector commences operation for causing the currentresponsive device to effect energization of the indicator device for a predetermined time so as to provide a check of the detector operativeness.

Claim 3

In a fluid level detector, the combination of a reservoir for a conductive fluid, an electrical power source, a probe circuit including a probe for controlling current flow in the probe circuit, the probe being positioned in the reservoir so as to be immersed in the fluid when the fluid is at a certain level to be detected and being so constructed that the conductivity thereof is determined by the extent of immersion of the probe in the fluid, an indicator circuit including an indicator device and a transistor responsive to current flow in the probe circuit, the transistor being operative to control the energization of the indicator device in response to the conductivity of the probe so as to cause the indicator device to be energized when the probe is not immersed in the fluid, switch means selectively operable to connect the indicator and probe circuits to the power source so as to render the detector operative, and an RC timer circuit for rendering the transistor operative after the switch means is operated so as to energize the indicator device for a predetermined time as an indication of the detector operativeness.

Claim 4

In a fluid level detector, the combination of a reservoir for a conductive fluid, an electrical power source, a probe circuit including a probe for controlling current flow in the probe circuit, the probe being positioned in the reservoir so as to be immersed in the fluid when the fluid is at a certain level to be detected and being so constructed that the conductivity thereof is determined by the extent of immersion of the probe in the fluid, an indicator circuit including an indicator device and a transistor responsive to current flow in the probe circuit, the transistor being operative to control the energization of the indicator device in response to the conductivity of the probe so as to cause the indicator device to be energized when the probe is not immersed in the fluid, switch means selectively operable to connect the indicator and probe circuits to the power source so as to render the detector operative, and an RC timer circuit for rendering the transistor operative after the switch means is operated so as to energize the indicator device for a predetermined time as an indication of the detector operativeness.

Claim 5

In a fluid level detector, the combination of a reservoir for a conductive fluid, a probe circuit, an indicator circuit, an electrical power Source, a switch selectively operable to connect the probe and indicator circuits to the power source, the probe circuit including a probe positioned in the fluid reservoir so as to be immersed in the fluid when the fluid is at a certain fluid level to be detected, the probe being operative to control current flow in the probe circuit in response to the extent of immersion thereof in the fluid, the indicator circuit including an indicator device and a transistor responsive to current flow in the probe circuit for controlling energization of the indicator device, the transistor being placed in a certain operative condition when the probe is not immersed in the fluid so as to energize the indicator device to provide an indication that the fluid in the reservoir is below the certain level, and a timer circuit including an RC network operative after the switch is operated to supply current to the transistor for a predetermined time effective to place the transistor in the certain operative condition so as to energize the indicator device for the predetermined time, thereby providing a check of the detector operativeness.

Claim 6

In a fluid level detector, the combination of a reservoir for a conductive fluid, a probe circuit, an indicator circuit, an electrical power Source, a switch selectively operable to connect the probe and indicator circuits to the power source, the probe circuit including a probe positioned in the fluid reservoir so as to be immersed in the fluid when the fluid is at a certain fluid level to be detected, the probe being operative to control current flow in the probe circuit in response to the extent of immersion thereof in the fluid, the indicator circuit including an indicator device and a transistor responsive to current flow in the probe circuit for controlling energization of the indicator device, the transistor being placed in a certain operative condition when the probe is not immersed in the fluid so as to energize the indicator device to provide an indication that the fluid in the reservoir is below the certain level, and a timer circuit including an RC network operative after the switch is operated to supply current to the transistor for a predetermined time effective to place the transistor in the certain operative condition so as to energize the indicator device for the predetermined time, thereby providing a check of the detector operativeness.

Claim 7

In a fluid level detector, the combination of a fluid reservoir; an indicator circuit comprised of a Schmitt trigger and an indicator device, the Schmitt trigger being operative in response to a trigger signal as to control the energization of the indicator device; a probe circuit comprised of a probe positioned in the reservoir at a fluid level to be detected, the probe circuit providing the trigger signal to the Schmitt trigger in response to the immersion of the probe so as to effect energization of the indicator device and provide an indication of the fluid level in response to immersion of the probe in the fluid; and a timer circuit adapted to effect energization of the indicator device for a predetermined time when the detector commences operation, thereby providing a check of the detector operativeness.

Claim 8

In a fluid level detector, the combination of a fluid reservoir; an indicator circuit comprised of a Schmitt trigger and an indicator device, the Schmitt trigger being operative in response to a trigger signal as to control the energization of the indicator device; a probe circuit comprised of a probe positioned in the reservoir at a fluid level to be detected, the probe circuit providing the trigger signal to the Schmitt trigger in response to the immersion of the probe so as to effect energization of the indicator device and provide an indication of the fluid level in response to immersion of the probe in the fluid; and a timer circuit adapted to effect energization of the indicator device for a predetermined time when the detector commences operation, thereby providing a check of the detector operativeness.

Claim 9

In a fluid level detector, the combination of a fluid reservoir; an indicator circuit comprised of a Schmitt trigger and an indicator device, the Schmitt trigger being operative in response to a voltage signal effective to control the energization of the indicator device; a probe circuit comprised of a probe positioned in the reservoir at a fluid level to be detected for generating the voltage signal; means connecting the probe circuit to the Schmitt trigger effective to control the energization of the indicator device in response to the immersion of the probe; a timer circuit including an RC network and operative in response to the detector commencing operation effective to energize the indicator device for a predetermined time when the detector commences operation, thereby providing a check of the detector operativeness; and a shunt resistor in parallel with the probe so as to provide a charging path to the RC network when the probe is not in the fluid whereby the Schmitt trigger is caused to intermittently effect energization of the indicator device so as to provide a periodic indication when the probe is not immersed in the fluid.

Claim 10

In a fluid level detector, the combination of a fluid reservoir; an indicator circuit comprised of a Schmitt trigger and an indicator device, the Schmitt trigger being operative in response to a voltage signal effective to control the energization of the indicator device; a probe circuit comprised of a probe positioned in the reservoir at a fluid level to be detected for generating the voltage signal; means connecting the probe circuit to the Schmitt trigger effective to control the energization of the indicator device in response to the immersion of the probe; a timer circuit including an RC network and operative in response to the detector commencing operation effective to energize the indicator device for a predetermined time when the detector commences operation, thereby providing a check of the detector operativeness; and a shunt resistor in parallel with the probe so as to provide a charging path to the RC network when the probe is not in the fluid whereby the Schmitt trigger is caused to intermittently effect energization of the indicator device so as to provide a periodic indication when the probe is not immersed in the fluid.

Claim 11

In a fluid level detector, the combination of a fluid reservoir; a probe circuit comprised of a thermistor probe positioned in the reservoir so as to be immersed in the fluid at a fluid level to be detected, the probe circuit providing a signal determined by the immersion of the probe in the fluid; an indicator circuit that is responsive to the signal provided by the probe circuit for providing an indication of the fluid level as determined by immersion of the probe in the fluid; and a timer circuit adapted to energize the indicator circuit for a predetermined time when the detector commences operation so as to provide a check of the detector operativeness.

Claim 12

In a fluid level detector, the combination of a fluid reservoir; a probe circuit comprised of a thermistor probe positioned in the reservoir so as to be immersed in the fluid at a fluid level to be detected, the probe circuit providing a signal determined by the immersion of the probe in the fluid; an indicator circuit that is responsive to the signal provided by the probe circuit for providing an indication of the fluid level as determined by immersion of the probe in the fluid; and a timer circuit adapted to energize the indicator circuit for a predetermined time when the detector commences operation so as to provide a check of the detector operativeness.

Claim 13

In a fluid level detector, the combination of a fluid reservoir; a probe circuit comprised of a thermistor probe positioned in the reservoir so as to be immersed in the fluid at a fluid level to be detected, the probe cirCuit providing a signal determined by the immersion of the probe in the fluid; an indicator circuit responsive to the signal provided by the probe circuit so as to provide an indication of the fluid level in response to the immersion of the probe; regenerative feedback means combined with the indicator circuit so as to increase the sensitivity of the indicator circuit to the signal provided by the probe circuit; and a timer circuit adapted to energize the indicator circuit for a predetermined time when the detector commences operation, thereby providing a check of the detector operativeness.

Claim 14

In a fluid level detector, the combination of a fluid reservoir; a probe circuit comprised of a thermistor probe positioned in the reservoir so as to be immersed in the fluid at a fluid level to be detected, the probe cirCuit providing a signal determined by the immersion of the probe in the fluid; an indicator circuit responsive to the signal provided by the probe circuit so as to provide an indication of the fluid level in response to the immersion of the probe; regenerative feedback means combined with the indicator circuit so as to increase the sensitivity of the indicator circuit to the signal provided by the probe circuit; and a timer circuit adapted to energize the indicator circuit for a predetermined time when the detector commences operation, thereby providing a check of the detector operativeness.

Claim 15

In a fluid level detector, the combination of a fluid reservoir; a probe circuit comprised of a thermistor probe positioned in the reservoir so as to be immersed in the fluid at a fluid level to be detected, the probe circuit providing a signal determined by the immersion of the probe in the fluid; an indicator circuit including an indicator device and responsive to the signal provided by the probe circuit so as to provide an indication of the fluid level in response to the immersion of the probe; a feedback impedance adapted to combine a regenerative feedback signal from the indicator device with the signal provided by the probe circuit so as to increase the sensitivity of the indicator circuit; and a timer circuit adapted to energize the indicator circuit for a predetermined time when the detector commences operation so as to provide a check of the detector operativeness.

Claim 16

In a fluid level detector, the combination of a fluid reservoir; a probe circuit comprised of a thermistor probe positioned in the reservoir so as to be immersed in the fluid at a fluid level to be detected, the probe circuit providing a signal determined by the immersion of the probe in the fluid; an indicator circuit including an indicator device and responsive to the signal provided by the probe circuit so as to provide an indication of the fluid level in response to the immersion of the probe; a feedback impedance adapted to combine a regenerative feedback signal from the indicator device with the signal provided by the probe circuit so as to increase the sensitivity of the indicator circuit; and a timer circuit adapted to energize the indicator circuit for a predetermined time when the detector commences operation so as to provide a check of the detector operativeness.