Closed loop control system for automatic sensitivity control of transducer

Claim 2

An automatic sensitivity control system for use with a photocell sensing system for correcting for undesired variations in the output of a photocell comprising: enabling means for periodically generating an enabling pulse of a selected time interval during exposure of the photocell to a preselected reference level of illumination which does not exceed the extreme of illumination level of information to be sensed, control means responsive to the output of the photocell and enabled by each enabling pulse from said enabling means to establish a reference level corresponding to the photocell output during the selected time interval, said control means maintains the reference level thus established and references the output of the photocell to that reference level during the succeeding sensing interval to correct for undesired variations in the photocell output, and said control means comprises means connected in the energizing circuit of said photocell to control the energization thereof during each sensing interval as a function of the reference level established during the selected time interval.

Claim 3

An automatic sensitivity control system for use with a photocell sensing system for correcting for undesired variations in the output of a photocell comprising: enabling means for periodically generating an enabling pulse of a selected time interval during exposure of the photocell to a preselected reference level of illumination, storage means, a first amplifier having an input and an output and connected at said input to said storage means and at said output to the output of said photocell, switch means connected between said storage means and said outputs of said amplifier and said photocell, said switch means being responsive to each enabling pulse from said enabling means to be switched from a normally open to a closed position, said switch means, in said closed position, connecting said storage means to said outputs of said photocell and said amplifier to charge said storage means to a reference level corresponding to the output of said photocell when exposed to said reference source of illumination and, in said open position, isolating said storage means from the said outputs, and said amplifier being responsive to said reference level of said storage means to generate a corrEsponding signal in said output thereof to which the output of said photocell is referenced for correcting for undesired variations in the output of said photocell.

Claim 4

An automatic sensitivity control system for use with a photocell sensing system for correcting for undesired variations in the output of a photocell comprising: enabling means for periodically generating an enabling pulse of a selected time interval during exposure of the photocell to a preselected reference level of illumination, storage means, a first amplifier having an input and an output and connected at said input to said storage means and at said output to the output of said photocell, switch means connected between said storage means and said outputs of said amplifier and said photocell, said switch means being responsive to each enabling pulse from said enabling means to be switched from a normally open to a closed position, said switch means, in said closed position, connecting said storage means to said outputs of said photocell and said amplifier to charge said storage means to a reference level corresponding to the output of said photocell when exposed to said reference source of illumination and, in said open position, isolating said storage means from the said outputs, and said amplifier being responsive to said reference level of said storage means to generate a corrEsponding signal in said output thereof to which the output of said photocell is referenced for correcting for undesired variations in the output of said photocell.

Claim 5

An automatic sensitivity control system as recited in claim 2 wherein: said outputs of said amplifier and said photocell are combined at a common junction to which said switch means is connected, and said switch means includes means for referencing and junction to ground potential during said enable pulse for establishing a reference level of charging of said storage means.

Claim 6

An automatic sensitivity control system as recited in claim 3 wherein: said first amplifier includes means for adjusting the amplitude of said output thereof to establish a center value of said reference level.

Claim 7

An automatic sensitivity control system as recited in claim 2 wherein: said switch means includes a second amplifier having an input and an output and being connected at said input to said outputs of said photocell and said first amplifier and at said output to said storage means, said second amplifier is rendered operative during said enable pulse to respond to the output of said photocell for establishing an output potential corresponding to said photocell output in response to exposure thereof to said reference level of illumination to control charging of said storage means to a value corresponding to the potential of the output of said second amplifier, and said second amplifier is rendered inoperative in the absence of said enabling pulse for isolating the output of said photocell from said storage means.

Claim 8

An automatic sensitivity control system as recited in claim 5 wherein: said second amplifier includes first and second power terminals at the first power terminal of which the output thereof is derived, and said switch means further includes a first switching transistor connected between a first power supply terminal and said first power terminal and a second switching transistor connected between said second power terminal and a second power supply terminal, and said first and second switching transistors are connected at said inputs thereof to said enabling means for responding to each enabling pulse to switch from a normally nonconductive to a conductive condition for rendering said second amplifier operative.

Claim 9

An automatic sensitivity control system as recited in claim 6 wherein: said storage means is connected to said first power terminal of said second amplifier to be charged by current flow from said first power supply terminal through said first switching transistor, to a reference level potential value determined by the potential of the output of said second amplifier during each enable pulse.

Claim 10

An automatic sensitivity control system as recited in claim 6 wherein: said second power supply terminal is maintained at a potential level equal to the potential drop between the input and the second power output terminal of said second amplifier to reference said junction of said outputs of said first amplifier and said photocell to ground potential during each enable pulse.

Claim 11

An automatic sensitivity control system as recited in claim 1 for use with a sensing station having a photocell for sensing information from cards which are transported in succession through said sensing system, wherein: said enabling means responds to the advancement of each such card into position for sensing by said photocell for generating an enabling pulse during exposure of the photocell to the card background prior to advancement of the information-containing portion of the card into position for sensing by the photocell.

Claim 12

An automatic sensitivity control system as recited in claim 1 for use with a sensing station having a photocell for sensing information from cards which are transported in succession through said sensing system, and which cards bear information and related timing marks displaced thereon in the direction of card travel thrOugh the sensing station, wherein: said enabling means responds to each of the timing marks on each card transported through the sensing station for generating an enabling pulse for a selected time interval during which the photocell is exposed to the background of the card preceding the next successive timing mark, whereby a plurality of periodically generated enabling pulses are produced during sensing of a given card.

Claim 13

A data processing system having a photocell sensing system for sensing information from cards having plural columns of indication areas for receiving indicia representative of information and a column of timing marks, with corresponding groups of answer indication areas and timing marks aligned in rows, comprising: a sensing station including a photocell corresponding to each of the columns of timing marks and answer indication areas provided on the card, means for successively advancing said cards through said sensing station for sequential scanning of the rows of answer indication areas and timing marks, enabling means for periodically generating an enabling pulse of a selected time interval in response to advancement of each such card through said sensing station and during exposure of the photocell to a preselected portion of the background of each such card, control means associated with each of said photocells, each of said control means being responsive to the output of the corresponding photocell and being enabled by each enabling pulse from said enabling means to establish a reference level corresponding to the photocell output during the selected time interval, and each of said control means maintaining the reference level thus established with regard to the output of its associated photocell and referencing the output of that photocell to the reference level during the succeeding sensing interval to correct for undesired variations in the output of the associated photocell.

Claim 14

A data processing system having a photocell sensing system for sensing information from cards having plural columns of indication areas for receiving indicia representative of information and a column of timing marks, with corresponding groups of answer indication areas and timing marks aligned in rows, comprising: a sensing station including a photocell corresponding to each of the columns of timing marks and answer indication areas provided on the card, means for successively advancing said cards through said sensing station for sequential scanning of the rows of answer indication areas and timing marks, enabling means for periodically generating an enabling pulse of a selected time interval in response to advancement of each such card through said sensing station and during exposure of the photocell to a preselected portion of the background of each such card, control means associated with each of said photocells, each of said control means being responsive to the output of the corresponding photocell and being enabled by each enabling pulse from said enabling means to establish a reference level corresponding to the photocell output during the selected time interval, and each of said control means maintaining the reference level thus established with regard to the output of its associated photocell and referencing the output of that photocell to the reference level during the succeeding sensing interval to correct for undesired variations in the output of the associated photocell.

Claim 15

A data processing system as recited in claim 11 wherein: said enabling means responds to the advancement of a leading edge of each of said cards successively advanced into said sensing station for generating a corresponding enabling pulse when said photocell is exposed to a portion of the background of said card preceding the information containing portion of the card.

Claim 16

A data processing system as recited in claim 11 wherein: said enabling means responds to the output of the photocell of said sensing station corresponding to the column of timing marks for generating an enabling pulse in response to detection of each such timing mark during exposure of the photocell to a portion of the background following the detected timing mark preceding the following timing mark, whereby a plurality of enabling pulses are generated during advancement of each successive test card through the sensing station.

Claim 17

A data processing system as recited in claim 13 wherein: said enabling means includes delay means responsive to the output of the photocell corresponding to the column of timing marks for generating an enable pulse a predetermined time period after the detection of the trailing edge of each timing mark by the said corresponding photocell.

Claim 18

An automatic sensitivity control system as recited in claim 1 wherein said control means comprises an active element having a variable voltage-current characteristic controlled in accordance with said reference level.

Claim 19

A closed loop control system for controlling the output of a transducer which responds to a varying condition to be sensed, in accordance with a preselected reference level of that condition, comprising: storage means, first means operable during a reference setting interval for establishing a reference level indication in said storage means in response to the output of said transducer when sensing a preselected reference level of the condition, said first means being operable in a subsequent sensing interval to isolate said storage means frOm said transducer for maintaining the reference level indication established in said storage means during the sensing interval, and control means responsive to the reference level set in said storage means to control the overall response of said transducer during the sensing interval.

Claim 20

A closed loop control system for controlling the output of a transducer which responds to a varying condition to be sensed, in accordance with a preselected reference level of that condition, comprising: storage means, first means operable during a reference setting interval for establishing a reference level indication in said storage means in response to the output of said transducer when sensing a preselected reference level of the condition, said first means being operable in a subsequent sensing interval to isolate said storage means frOm said transducer for maintaining the reference level indication established in said storage means during the sensing interval, and control means responsive to the reference level set in said storage means to control the overall response of said transducer during the sensing interval.

Claim 21

A closed loop control system as recited in claim 16 wherein said control means is connected in the energizing circuit of said transducer to control the energization thereof during each sensing interval as a function of the reference level indication of said storage means.

Claim 22

A closed loop control system as recited in claim 17 wherein said control means comprises an active element having a variable voltage-current characteristic controlled in accordance with said reference level.

Claim 23

A closed loop control system as recited in claim 18 wherein: said active element comprises a Darlington circuit, said storage means comprises capacitive storage means charged to a voltage level in accordance with said reference level indication, said capacitor being connected to the input of said Darlington circuit, and said Darlington circuit is connected with its collector-emitter current conducting path in the energizing circuit of said transducer and is connected at its base to said capacitive storage means and responds to the voltage level of said reference level indication to correspondingly vary its voltage-current characteristic and thereby vary the energization of said transducer.

Claim 24

A closed loop control system as recited in claim 17 wherein: said control means and said transducer are connected to a common junction to which said first means is connected, and said first means includes means for referencing said common junction to ground potential during each reference setting interval to enable charging of said storage means to establish said reference level indication.

Claim 25

A closed loop control system as recited in claim 20 wherein: said control means includes adjustable means for adjusting the level of current flow in said energizing circuit to establish a center value of said reference level indication.

Claim 28

A method as recited in claim 22 wherein the control of the overall response characteristic of the transducer comprises controlling the energization of the transducer during the sensing interval thereby to control the output thereof in accordance with the preselected reference level.