Bi-level condition monitor using reverse-biased control diodes

Claim 2

A circuit for monitoring a changing condition and for indicating when said condition has changed from one side of a predetermined level to the other side thereof, said circuit comprising: an astable oscillator means having a threshold level for initiation of oscillation and including a series-connected capacitor and resistor across a regulated supply voltage, said capacitor being chargeable through said resistor and said oscillator means being activated into oscillation in response to the charging of said capacitor to said threshold level, an indicator means energized in response to oscillation of said oscillator means, a current bypass path connected across said capacitor and having a diode therein, means for reverse-biasing said diode at a level less than said threshold level when said condition being monitored is on one side of said predetermined level and for reverse-biasing said diode at a level higher than said threshold level when said condition is on the other side of said predetermined level.

Claim 3

A circuit as set forth in claim 1 and further including: means for producing a condition-responsive voltage proportional to the level of said condition being monitored and variable in response to changes in said condition, and wherein said condition-responsive voltage is applied directly to said diode to provide the reverse-biasing thereof and to vary the level of said reverse bias in accordance with changes in level of said condition-responsive voltage.

Claim 4

A circuit as set forth in claim 1 and further including: means for producing a condition-responsive voltage proportional to the level of said condition being monitored and variable in response to changes in said condition, wherein said condition-responsive voltage is applied to said oscillator means to vary the threshold level thereof in accordance with changes in the level of said condition-responsive voltage, and wherein said reverse bias is maintained at a fixed level.

Claim 5

A circuit as set forth in claim 1, and further including: a test switch, means responsive to actuation of said switch for applying a reverse bias to said diode of a level greater than said threshold level.

Claim 6

A circuit for monitoring a changing condition and for indicating when said condition has changed from one side of a first predetermined level to the other side thereof and for subsequently indicating when said condition has changed from one side of a second predetermined level to the other side thereof, said circuit comprising: first and second astable oscillator means each having a threshold level for initiation of oscillation thereof and each including a series-connected capacitor and resistor across a regulated supply voltage, said capacitor being chargeable through said resistor and each oscillator means being activated into oscillation in response to the charging of its capacitor to said threshold level, first and second indicator means energized by oscillation of said first and second oscillator means respectively, first and second current bypass paths connected across capacitors of said first and second oscillator means respectively, each bypass path having a diode therein, means for reverse-biasing the diode of said first bypass path at a level less than the threshold level of said first oscillator means when said condition being monitored is on one side of said first predetermined level and for reverse-biasing said diode at a level greater than said threshold level when said condition is on the other side of said first predetermined level, means for reverse-biasing the diode of said second bypass path at a level less than the threshold level of said second oscillator means when said condition being monitored is on one side of said second predetermined level and for reverse-biasing said diode at a level greater than said threshold level when said condition is on the other side of said second predetermined level.

Claim 7

A circuit for monitoring a changing condition and for indicating when said condition has changed from one side of a first predetermined level to the other side thereof and for subsequently indicating when said condition has changed from one side of a second predetermined level to the other side thereof, said circuit comprising: first and second astable oscillator means each having a threshold level for initiation of oscillation thereof and each including a series-connected capacitor and resistor across a regulated supply voltage, said capacitor being chargeable through said resistor and each oscillator means being activated into oscillation in response to the charging of its capacitor to said threshold level, first and second indicator means energized by oscillation of said first and second oscillator means respectively, first and second current bypass paths connected across capacitors of said first and second oscillator means respectively, each bypass path having a diode therein, means for reverse-biasing the diode of said first bypass path at a level less than the threshold level of said first oscillator means when said condition being monitored is on one side of said first predetermined level and for reverse-biasing said diode at a level greater than said threshold level when said condition is on the other side of said first predetermined level, means for reverse-biasing the diode of said second bypass path at a level less than the threshold level of said second oscillator means when said condition being monitored is on one side of said second predetermined level and for reverse-biasing said diode at a level greater than said threshold level when said condition is on the other side of said second predetermined level.

Claim 8

A circuit as set forth in claim 5 and further including: means for producing first and second condition-responsive voltages, each proportional to the level of the condition being monitored and variable in response to changes in said condition, wherein said first condition-responsive voltage is applied directly to said diode of said first bypass path to provide the reverse-biasing thereof and to vary the level of said reverse bias in accordance with changes in level of said first condition-responsive voltage, wherein said reverse bias on the diode of said second bypass path is maintained at a fixed level, and wherein said second condition-responsive voltage is applied to said second oscillator means to vary the theshold level thereof in accordance with changes in level of said second condition-responsive voltage.

Claim 9

A circuit as set forth in claim 5 wherein the condition being monitored is a variable voltage, and further including: first and second potentiometers each connected across said variable voltage, wherein the wiper of said first potentiometer is connected directly to the diode of said first bypass path to provide the reverse-biasing thereof and to vary the reverse bias in accordance with changes in said variable voltage, wherein said reverse bias on the diode of said second bypass path is maintained at a fixed level, and wherein the wiper of said second potentiometer is connected to said second oscillator means to vary the theshold level thereof in accordance with changes in the level of said variable voltage.

Claim 10

A circuit as set forth in claim 5, and further including: means for producing first and second condition-responsive voltages, each proportional to the level of said condition being monitored and variable in response to changes in said condition, wherein said first condition-responsive voltage is applied directly to said diode of said first bypass path to provide the reverse-biasing thereof and to vary the level of said reverse bias in accordance with changes in level of said first condition-responsive voltage, and wherein said second condition-responsive voltage is applied directly to said diode of said second bypass path to provide the reverse-biasing thereof and to vary the level of the reverse bias in accordance with changes in level of said second condition-responsive voltage.

Claim 11

A circuit as set forth in claim 8, wherein said second oscillator means oscillates at a highEr frequency than said first oscillator means, and further including: a discharge circuit for the capacitor of said first oscillator, means responsive to oscillation of said second oscillator means for repeatedly connecting said discharge circuit across the capacitor of said first oscillator at a rate equal to the frequency of oscillation of said second oscillator means.

Claim 12

A circuit as set forth in claim 5 and further including: first and second potentiometers connected in parallel; a thermistor connected in series with said parallel connected potentiometers, said thermistor and potentiometers being connected across a regulated voltage source, wherein the wipers of said first and second potentiometers are connected directly to the diodes of said first and second bypass paths, respectively, to provide the reverse-biasing thereof and vary the reverse bias in accordance with changes in resistance of said thermistor.

Claim 13

A circuit as set forth in claim 5, and further including: a test switch, means responsive to actuation of said test switch for applying a reverse bias to both diodes of said first and second bypass path of a level greater than the threshold levels of said first and second oscillator means.