Presence detector having automatic digital tuning

Claim 2

In apparatus for determining whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including a variable frequency oscillator capable of controlling the frequency of said signal, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions; digital counting means responsive to said signal for deriving a count indicative of the frequency of said signal; digital comparator means coupled with said counting means for comparing said count with a predetermined numerical value representing said normal frequency; control means coupled with said comparator means and said variable frequency oscillator and responsive to a difference between said count and said value for varying the frequency of said oscillator at a slow rate relative to the rate of change of the frequency of said signal when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present; and means responsive to said signal and coupled with said control means for disabling the latter to prevent operation thereof when the frequency of said signal is outside of said range, whereby to prevent correction of the frequency as long as the body is present in said zone.

Claim 3

The improvement as claimed in claim 1, wherein said counting means includes a first means for producing a train of pulses having a repetition rate indicative of the frequency of said signal, a second means responsive to said pulses for deriving a series of timing signals having a time duration from the beginning to the end of said series governed by the interval between a pair of said pulses, and a counter responsive to said series of timing signals for counting the latter and delivering said count to said comparator means.

Claim 4

The improvement as claimed in claim 1, wherein said counting means repeatedly delivers said count to said comparator means at successive intervals to monitor the frequency of said signal, said comparator means producing an output in response to each count which indicates whether the count is greater than, equal to, or less than said value, and wherein said control means includes a register for storing the output information from said comparator means, tuning means for increasing or Decreasing the frequency of said oscillator, and means for actuating said tuning means in accordance with the information currently stored in said register if said information indicates that the frequency of said signal requires correction.

Claim 5

The improvement as claimed in claim 3, wherein said actuating means operates periodically to deliver said currently stored inforamtion to said tuning means whereby, whenever said information indicates that the frequency of said signal requires correction, the tuning means is periodically actuated until the frequency is corrected.

Claim 6

The improvement as claimed in claim 4, wherein the time period between successive operations of said actuating means is sufficiently long to effect said varying of the frequency of said oscillator at said slow rate.

Claim 7

The improvement as claimed in claim 5, wherein said oscillator has a circuit for controlling its frequency of operation, and wherein said tuning means includes a plurality of frequency varying components, electrically responsive switching means for operably connecting any of said components or a combination thereof with said circuit, and means responsive to said stored information and coupled with said switching means for operating the latter to connect the component or components with said circuit that will cause said signal to approach its normal frequency.

Claim 8

The improvement as claimed in claim 6, wherein said means responsive to said stored information includes an up/down counter having up and down counting inputs, and wherein said actuating means includes a pulse generator for producing time-spaced pulses defining the periodic operation of the actuating means, and an up/down control coupled between said register and said inputs and operable in response to each of said time-spaced pulses for exciting said inputs in accordance with said stored information.

Claim 9

In apparatus for determining whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including a variable frequency oscillator capable of controlling the frequency of said signal, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions, said output means including a band pass filter coupled with said detecting means and having a pass band defining said range; frequency determining means responsive to said signal for producing an output which indicates whether the frequency thereof is greater than, equal to, or less than said normal frequency; control means coupled with said frequency determining means and said variable frequency oscillator and responsive to a deviation of the frequency of said signal from said normal frequency for varying the frequency of said oscillator at a slow rate relative to the rate of change of the frequency of said signal when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present; and means coupled with the output of said filter and with said control means for disabling the control means when the frequency of said signal is outside of said pass band, whereby to prevent correction of the frequency as long as the body is present in said zone.

Claim 10

In apparatus for determining whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including a variable frequency oscillator capable of controlling the frequency of said signal, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions, said output means including a band pass filter coupled with said detecting means and having a pass band defining said range; frequency determining means responsive to said signal for producing an output which indicates whether the frequency thereof is greater than, equal to, or less than said normal frequency; control means coupled with said frequency determining means and said variable frequency oscillator and responsive to a deviation of the frequency of said signal from said normal frequency for varying the frequency of said oscillator at a slow rate relative to the rate of change of the frequency of said signal when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present; and means coupled with the output of said filter and with said control means for disabling the control means when the frequency of said signal is outside of said pass band, whereby to prevent correction of the frequency as long as the body is present in said zone.

Claim 11

In apparatus for determining whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including a variable frequency oscillator capable of controlling the frequency of said signal, wherein said oscillator has a circuit for controlling its frequency of operation, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions; frequency determining means responsive to said signal for producing an output which indicates whether the frequency thereof is greater than, equal to, or less than said normal frequency; and control means coupled with said frequency determining means and said circuit and responsive to a deviation of the frequency of said signal from said normal frequency for varying the frequency of said oscillator at a slow rate relative to the rate of change of the frequency of said signal when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present, said control means including tuning means having a plurality of frequency varying components, electrically responsive switching means for operably connecting any of said components or a combination thereof with said circuit, and means responsive to said output from the frequency determining means and coupled with said switching means for operating the latter to connect the component or components with said circuit that will cause said signal to approach its normal frequency.

Claim 12

In apparatus for determining whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including a variable frequency oscillator capable of controlling the frequency of said signal, wherein said oscillator has a circuit for controlling its frequency of operation, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions; frequency determining means responsive to said signal for producing an output which indicates whether the frequency thereof is greater than, equal to, or less than said normal frequency; and control means coupled with said frequency determining means and said circuit and responsive to a deviation of the frequency of said signal from said normal frequency for varying the frequency of said oscillator at a slow rate relative to the rate of change of the frequency of said signal when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present, said control means including tuning means having a plurality of frequency varying components, electrically responsive switching means for operably connecting any of said components or a combination thereof with said circuit, and means responsive to said output from the frequency determining means and coupled with said switching means for operating the latter to connect the component or components with said circuit that will cause said signal to approach its normal frequency.

Claim 13

The improvement as claimed in claim 9, wherein said control means further includes a register for storing the output information from said frequency determining means, and means for periodically actuating said tuning means in accordance with the information currently stored in said register if said information indicates that the frequency of said signal requires correction.

Claim 14

The improvement as claimed in claim 10, wherein said means for operating the switching means includes an up/down counter having up and down counting inputs, and wherein said actuating means includes a pulse generator for producing time-spaced pulses defining the periodic operation of the actuating means, and an up/down control coupled between said register and said inputs and operable in response to each of said time-spaced pulses for exciting said inputs in accordance with said stored information.

Claim 15

The improvement as claimed in claim 10, wherein the time period between successive operations of said actuating means is sufficiently long to effect said varying of the frequency of said oscillator at said slow rate.

Claim 16

The improvement as claimed in claim 10, further comprising means responsive to said signal and coupled with said actuating means for disabling the latter to prevent operation of said tuning means when the frequency of said signal is outside of said range, whereby to prevent correction of the frequncy as long as the body is present in said zone.

Claim 17

In apparatus for determing whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including variable frequency circuit means capable of controlling the frequency of said signal, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions; frequency determining means responsive to said signal for producing an output which indicates whether the frequency thereof is greater than, equal to, or less than said normal frequency; and control means coupled with said frequency determining means and said circuit means and responsive to a deviation of the frequency of said signal from said normal frequency for causing said circuit means to vary the signal frequency at a slow rate relative to the rate of change thereof when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present, said control means including a plurality of frequency varying components, electrically responsive switching means for operably connecting any of said components of a combination thereof with said circuit means, and means responsive to said output from the frequency determining means and coupled with said switching means for operating the latter to connect the component or components with said circuit means that will cause said signal to approach its normal frequency.

Claim 18

In apparatus for determing whether a movable metallic body is present in a preselected zone of interest along a path of travel thereof, where a sensing element is adapted for disposition adjacent said zone and detecting means is employed which is coupled with said element for generating an oscillatory electrical signal having a frequency subject to relatively slow variation in accordance with changing environmental conditions in said zone and sudden variation as said body passes through said zone, said detecting means including variable frequency circuit means capable of controlling the frequency of said signal, the improvement comprising: output means responsive to said signal and having an output condition indicating that said body is present in said zone when the frequency of said signal is outside of a predetermined range within which the signal is permitted to vary from a normal frequency in response to changing environmental conditions; frequency determining means responsive to said signal for producing an output which indicates whether the frequency thereof is greater than, equal to, or less than said normal frequency; and control means coupled with said frequency determining means and said circuit means and responsive to a deviation of the frequency of said signal from said normal frequency for causing said circuit means to vary the signal frequency at a slow rate relative to the rate of change thereof when said body passes through said zone, whereby to correct the frequency of said signal in response to changing environmental conditions to prevent a false indication of the presence of the body, without preventing said output means from responding when the body is actually present, said control means including a plurality of frequency varying components, electrically responsive switching means for operably connecting any of said components of a combination thereof with said circuit means, and means responsive to said output from the frequency determining means and coupled with said switching means for operating the latter to connect the component or components with said circuit means that will cause said signal to approach its normal frequency.

Claim 19

The improvement as claimed in claim 14, wherein said means for operating the switching means includes a plurality of digital control connections operably coupled with said switching means, and a counter whose output comprises said digital control connections and which has input means receiving the output information from said frequency determining means.

Claim 20

The improvement as claimed in claim 15, wherein said control means further includes means for periodically delivering said output information to said input means of the counter at time intervals of sufficient length to provide said slow rate of variation of the signal frequency.