Combustion products detector control apparatus

Claim 2

Control apparatus for a products-of-combustion detector comprising: a source of potential having a first terminal and a common terminal; means for developing a first reference potential with respect to said common terminal; means for developing a second reference potential with respect to said common terminal; differential amplifier means having an input stage comprising a field effect transistor, said amplifier means including said means for developing a first reference potential; further amplifier means comprising second transistor means which has a plurality of electrodes including a control electrode and a first and second current carrying electrode, said first electrode being conductively connected to said first terminal and said second electrode being connected by junction means and impedance means to said second reference potential; a sensing circuit connected in controlling relation to said field effect transistor signal electrode including products-ofcombustion sensing means and resistive feedback means, said feedback means being connectEd to said junction means and normally biasing said field effect transistor signal electrode to a potential equal to said second reference potential whereby the potential existing across said feedback means remains of essentially the same magnitude as the potential existing across said impedance means so that the current flowing through said impedance means is proportional to the current flowing in said high impedance sensing circuit.

Claim 3

The apparatus of claim 1 in which said amplifier means, junction means and impedance means further comprises a potentiometer, one terminal of which is conductively connected to said second transistor means, the other terminal of which is conductively connected to said second reference potential and the adjustable wiper of which is connected to said resistive feedback means, so that when over a period of time said products-of-combustion sensing means loses its original degree of sensitivity, its effective impedance increases and said normal biasing potential tends to change, a readjustment of said adjustable wiper to restore said normal biasing potential simultaneously changes the gain of said amplifier means to compensate for the decreasing sensitivity of said products-of-combustion sensing means.

Claim 4

Control apparatus for use with a high impedance condition sensor comprising: direct coupled amplifier means having a first and a second terminal to be energized from a source of potential and further including; a field effect transistor having a pair of current carrying electrodes and a signal electrode, the signal electrode providing a potential sensitive input stage; a reference voltage of a predetermined magnitude with respect to one of said terminals; an output transistor having current carrying electrodes and a control electrode; resistive means having first and second extremities and an intermediate tap; a series circuit connected from said first terminal to said reference voltage, said circuit comprising the current carrying electrodes of said output transistor in series with said tapped resistive means, one of said electrodes being connected to said first terminal and one of said extremities being connected to said reference voltage, the other electrode and second extremity being connected together; a sensing circuit having a current flow therethrough and connected in a controlling relation to said amplifying means input stage, said circuit including a products-of-combustion sensor of the ionization chamber-type connected between said input stage and said second terminal, and resistor feedback means connected to said input stage, said current flowing through said resistor feedback means and ionization chamber biasing said signal electrode to a voltage which is equal to said predetermined potential magnitude; and conductive connecting means connecting said resistor feedback means to said intermediate tap of said resistive means so that the potential existing across said resistor feedback means changes with and remains of substantially the same magnitude as the potential existing across said resistive means portion between said tap and said reference voltage whereby the amplified current flowing through said resistive means is proportional to the current flowing in said sensing circuit.

Claim 5

Control apparatus for use with a high impedance condition sensor comprising: direct coupled amplifier means having a first and a second terminal to be energized from a source of potential and further including; a field effect transistor having a pair of current carrying electrodes and a signal electrode, the signal electrode providing a potential sensitive input stage; a reference voltage of a predetermined magnitude with respect to one of said terminals; an output transistor having current carrying electrodes and a control electrode; resistive means having first and second extremities and an intermediate tap; a series circuit connected from said first terminal to said reference voltage, said circuit comprising the current carrying electrodes of said output transistor in series with said tapped resistive means, one of said electrodes being connected to said first terminal and one of said extremities being connected to said reference voltage, the other electrode and second extremity being connected together; a sensing circuit having a current flow therethrough and connected in a controlling relation to said amplifying means input stage, said circuit including a products-of-combustion sensor of the ionization chamber-type connected between said input stage and said second terminal, and resistor feedback means connected to said input stage, said current flowing through said resistor feedback means and ionization chamber biasing said signal electrode to a voltage which is equal to said predetermined potential magnitude; and conductive connecting means connecting said resistor feedback means to said intermediate tap of said resistive means so that the potential existing across said resistor feedback means changes with and remains of substantially the same magnitude as the potential existing across said resistive means portion between said tap and said reference voltage whereby the amplified current flowing through said resistive means is proportional to the current flowing in said sensing circuit.

Claim 6

The apparatus of claim 3 in which said resistive means comprises a potentiometer, one terminal of which is connected to said output transistor, the other terminal of which is conductively connected to said reference potential and the adjustable wiper of which is connected to said resistor feedback means, so that if the sensitivity of said condition sensor decreases whereby its effective impedance increases, and the biasing of said signal electrode tends to change from said predetermined potential magnitude, a readjustment of said adjustable wiper to restore said signal electrode to said predetermined potential magnitude simultaneously increases the gain of said amplifier means to compensate the control appAratus for the decreasing sensitivity of said condition sensor.

Claim 7

The apparatus of claim 3 wherein said sensing circuit is subject to undesired leakage currents to surrounding structure, the apparatus further comprising: guard ring means energized from said reference voltage and positioned to effectively isolate said sensing circuit from the surrounding structure to eliminate said leakage currents.

Claim 8

The apparatus of claim 3 in which said reference voltage comprises: a tapped voltage divider network energized from said first and second terminal; and further transistor means having its input electrodes connected between a tap on said voltage divider network and one terminal of impedance means the other terminal of which is connected to said second terminal whereby said reference potential is maintained across said impedance means.