CA1060115A - Proximity switch - Google Patents
Proximity switchInfo
- Publication number
- CA1060115A CA1060115A CA239,202A CA239202A CA1060115A CA 1060115 A CA1060115 A CA 1060115A CA 239202 A CA239202 A CA 239202A CA 1060115 A CA1060115 A CA 1060115A
- Authority
- CA
- Canada
- Prior art keywords
- switching
- proximity switch
- source
- capacitor
- load
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
- G01V3/101—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil
- G01V3/102—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil by measuring amplitude
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
- H03K17/945—Proximity switches
- H03K17/95—Proximity switches using a magnetic detector
- H03K17/951—Measures for supplying operating voltage to the detector circuit
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
- H03K17/945—Proximity switches
- H03K17/95—Proximity switches using a magnetic detector
- H03K17/952—Proximity switches using a magnetic detector using inductive coils
- H03K17/9537—Proximity switches using a magnetic detector using inductive coils in a resonant circuit
- H03K17/9542—Proximity switches using a magnetic detector using inductive coils in a resonant circuit forming part of an oscillator
- H03K17/9547—Proximity switches using a magnetic detector using inductive coils in a resonant circuit forming part of an oscillator with variable amplitude
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Life Sciences & Earth Sciences (AREA)
- Electromagnetism (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Electronic Switches (AREA)
Abstract
PROXIMITY SWITCH
Abstract of the Disclosure A proximity switch is connected to close a circuit between a source and a load when a metal object is adjacent to a coil in the switch. The coil is part of an oscillator circuit that is selected to have its output damped below a selected amplitude when the metal object is close enough to the coil. The reduced amplitude of oscillation opens a capaci-tor shunting switch thereby permitting the capacitor to be charged. The charging of the capacitor to a selected level turns on an SCR to connect the load to the source through the SCR. A power storage circuit has a capacitor that is charged when the SCR is turned off to provide operating current for the circuits of the switch when it is not available because the SCR is turned on to shunt the current from the main power source. A circuit for controlling the proximity switch upon initial energization prevents spurious operation with a switching circuit that does not turn on until after a selected period of time after energization of the proximity switch from the main power source.
Abstract of the Disclosure A proximity switch is connected to close a circuit between a source and a load when a metal object is adjacent to a coil in the switch. The coil is part of an oscillator circuit that is selected to have its output damped below a selected amplitude when the metal object is close enough to the coil. The reduced amplitude of oscillation opens a capaci-tor shunting switch thereby permitting the capacitor to be charged. The charging of the capacitor to a selected level turns on an SCR to connect the load to the source through the SCR. A power storage circuit has a capacitor that is charged when the SCR is turned off to provide operating current for the circuits of the switch when it is not available because the SCR is turned on to shunt the current from the main power source. A circuit for controlling the proximity switch upon initial energization prevents spurious operation with a switching circuit that does not turn on until after a selected period of time after energization of the proximity switch from the main power source.
Description
0~:15 This lnvention relates to proximity switches, ~ ;
particularly to proximity switches that operate in response to metal objects adjacent to the proximity switch.
Proximity switches are devices used to sense the presence of objects, generally metallic objects, so that an output can be produced indicatingthe presence or nearness of the object. Typically they are used as position switches or ;
in a production line counting operation where objects are `~
counted. In these types of applications the proximi~y 0 SWitCil is connected in series between an el~ectrical source and a load that is typically a motor, or counter or similar device.
: . ;
l~ith this invention a proximity switch is controlled by control circuitry that effectively responds to the pre-sence of metallic objects and provides a reliable means for sensing the presence ofthe object arld connecting the load to the source with efective safeguards to ensure that accurate counting or position indication is supplied. In addition an inhibiting circuit prevents spurious operation upon initial energization and a power storage provides power when the switch is turned on to shunt current through the power source.
According to one aspect o the present invention, a proximity switch of the type connectable in series with an electrical source and an electrical load, having portions energizable from the electrical source, and operable in response to the proximity of a metallic object to shunt current from the electrical source through the proximity switch and thereby connect the source to the load, said proximity switch comprisingi a sensing means for producing a signal in response to the present of a metallic object within a selected distance from the proximlty ~witch; a switching means connected for'connection between the source ' . .
601~
and the load for disconnectiny said source from said load and connecting said source to said load by shunting the current from said source through said switching means; a switching control means responsive to the sensing means signal for controlling the switching means; an energy ~ -~
storage means for storing electrical energy received from the electrical source when said source is d:isconnected from the load by the switching means and for supplyiny electrical s energy to selected portions of the proximity switch when 10 said source current is shunted to said load through said -switching means and an operational delay means responsive to the initial connection of the proximity switch to tlle power source for turning on the control switching device to shunt ;
the switching capacitor for a preselected time after said initial energization to thereby prevent the turning on o ~ ;
the silicon controlled rectifier for said preselected time. `~
The advantages and objects of this invention will be apparent from the following description.
The figure is a schematic of the circuitry of a ;~
2G proximity switch according to this invention.
Rererring to the figure, a load 10 is connected to a suitable alternating current source 11 through a proximity switch 15. I~he proximity switch is of any generally known physical structure that typically comprises a mounting assembly for the electronic circuitry all of which is typically enclosed in a plastic casing with a sensing coil mounted in ~ outward location suitable for sensing the presence of a metallic object.
The proximity switch is of a type that is connectable in series with a source and a load and is energized from the source through the load, and that upon sensing the presence of a metallic object shunts the source current through the :, ~60~L15 `.'~ .
proximity switch to thereby connect the source to the load.
~ .
Proximity switch 15 comprises a rectifying means 20 ~or rectifying the alternating current :Erom the source connected in series with the load and power source a switching means 30 for connecting the source to ~he ~ ~ .
load through the rectifying means; a switching control ~ ~ :
means 40 f~r controlling switching means 30; a sensing means 50 comprising an oscillator circuit responsive to a metallic object in a selected location for producing an out~
put indicating the presence of a metallic object within a .` :
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1 selected distance; an operational delay means Go ~or controlling
particularly to proximity switches that operate in response to metal objects adjacent to the proximity switch.
Proximity switches are devices used to sense the presence of objects, generally metallic objects, so that an output can be produced indicatingthe presence or nearness of the object. Typically they are used as position switches or ;
in a production line counting operation where objects are `~
counted. In these types of applications the proximi~y 0 SWitCil is connected in series between an el~ectrical source and a load that is typically a motor, or counter or similar device.
: . ;
l~ith this invention a proximity switch is controlled by control circuitry that effectively responds to the pre-sence of metallic objects and provides a reliable means for sensing the presence ofthe object arld connecting the load to the source with efective safeguards to ensure that accurate counting or position indication is supplied. In addition an inhibiting circuit prevents spurious operation upon initial energization and a power storage provides power when the switch is turned on to shunt current through the power source.
According to one aspect o the present invention, a proximity switch of the type connectable in series with an electrical source and an electrical load, having portions energizable from the electrical source, and operable in response to the proximity of a metallic object to shunt current from the electrical source through the proximity switch and thereby connect the source to the load, said proximity switch comprisingi a sensing means for producing a signal in response to the present of a metallic object within a selected distance from the proximlty ~witch; a switching means connected for'connection between the source ' . .
601~
and the load for disconnectiny said source from said load and connecting said source to said load by shunting the current from said source through said switching means; a switching control means responsive to the sensing means signal for controlling the switching means; an energy ~ -~
storage means for storing electrical energy received from the electrical source when said source is d:isconnected from the load by the switching means and for supplyiny electrical s energy to selected portions of the proximity switch when 10 said source current is shunted to said load through said -switching means and an operational delay means responsive to the initial connection of the proximity switch to tlle power source for turning on the control switching device to shunt ;
the switching capacitor for a preselected time after said initial energization to thereby prevent the turning on o ~ ;
the silicon controlled rectifier for said preselected time. `~
The advantages and objects of this invention will be apparent from the following description.
The figure is a schematic of the circuitry of a ;~
2G proximity switch according to this invention.
Rererring to the figure, a load 10 is connected to a suitable alternating current source 11 through a proximity switch 15. I~he proximity switch is of any generally known physical structure that typically comprises a mounting assembly for the electronic circuitry all of which is typically enclosed in a plastic casing with a sensing coil mounted in ~ outward location suitable for sensing the presence of a metallic object.
The proximity switch is of a type that is connectable in series with a source and a load and is energized from the source through the load, and that upon sensing the presence of a metallic object shunts the source current through the :, ~60~L15 `.'~ .
proximity switch to thereby connect the source to the load.
~ .
Proximity switch 15 comprises a rectifying means 20 ~or rectifying the alternating current :Erom the source connected in series with the load and power source a switching means 30 for connecting the source to ~he ~ ~ .
load through the rectifying means; a switching control ~ ~ :
means 40 f~r controlling switching means 30; a sensing means 50 comprising an oscillator circuit responsive to a metallic object in a selected location for producing an out~
put indicating the presence of a metallic object within a .` :
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1 selected distance; an operational delay means Go ~or controlling
2 the switchlng control means to allow sta~lization o~ the circuit
3 conditions upon initial energization before permitting operation;
4 an energy stora~e means 70 for storing electrical energy to furnish power to the circuit when power is not available from ~_ ~
6 power source 11 because of the shunting of the power source~by ~ :
7 .switching means 30; and an indicating means 80 for signalling.
8 the operation of the switching means to connect the source to g the load. i`~
10 Sensing means 50.comprises an inductive de~ice such as a ~1 11 coil 51 connected to the remaining circuitry of the sensing means ~.
12 by a suitable conductor so that typically it may be placed in 13 `the casing Or the proximity switch in a posltion suitable for . j ;
,! I .
14 sensing the presence of a metallic ob~ect, that is, in a positlon .; c~_ .
where the presence of~metallic object will i.nfluence the magnetic ield of the coil operating in an oscillator circuit. Sensing 17 ~ means 50 also comprises a transistor 52J a coupling capacitor 53, 18 an ad~ustable resistor 54, capacitors 55 and 56 connected in an 19 oscillator circuit con~iguration with transistor 52 and coil 51J
a bias resistor 57, a bias resistor 58J a bias res~stor 59, and a ~l. decoupling or filtering capacitor 61. The components and ~heir 22 .values are seleoted so that transistor 52 drives a tuned ~ `
23 ,oscillator circuit having coil 51 and capacitors 55 and 56 througn.
24 ad~ustable feedback resistor 54. The circuit is appropriately ;~ !
25 biased by resistors 58l 59 and 57 and decoupling capacitor 61 j 'I ~ r ~ $i~
26 provides a steady d..c bias ~oltage regardless of any ~ a~n*s 27 that may be picked up through coil ~1. The circuit is typically 28 ;tuned to oscillate at a relatively high frequency, about 20Q
29 kilohertz, relative to the power source frequency to provide an 30 .output through couplin~ capacitor 53. Under the se:Lected biasin~
31 and feedback conditions~ as determlned b~ ad~ustable reslstor 54, 32 oscillation ln the oscillator circuit occurs but its ampl~tude 15 ~6~5 : ~
significantly damped to a preselected level whenever a metallic article o-f a selected type is with:in a selected distance from ~;
coil 51. ~.~
The output from sensing means 50, the oscillating signal ~ :
appearing at coupling capacitor 53, is applied to switching control means 40. Switching control means 40 comprises a con- ;...... .,~
trol switching device such as a transistor 41, a resistor 42, a biasing resistor 43, a biasing circuit made up of a biasing resistor 63 and a switching device such as a transistor 64 that ~ :~
also comprises part of operational delay means 60, .a switching capacitor 45, and a bidirectional threshold diode 46 having a.;- .
. . ~, selected breakdown or thresho].d voltage. Switching control means receives the output of sensing means 50 as an input to ~.
transistor 41. The component values are selected so that when transistor 64 is turned on, transistor 41 is biased to ~
turn on during a selected portion of each positive half-cycle ~ .
of the oscillator output, at the relatively high frequency . .
rate of the oscillator, to thereby shunt and discharge capa~
. ~ . . .
citor 45 and prevent it from being charged to any significant ~.
level by the power source.
When a metallic object is within ~heselected distance from coil 51 of sensing means 50, the amplitude of oscillation in the oscillator clrcuit is reduced so that insufficient positive signal appears at the base of transistor 41 and transistor 41 remains turned off. With transistor 41 turned off, capacitor 45 is charged from power source 11 through the load and rectifying means 20 at a rate selected by the values of the resistance and capacitance of resistor 4~ and capacitor 45.
When the voltage level across capacitor 45 reaches a prede- ~.
termined level the breakdown voltage of bidirectional diode ~ :
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46 is equalled and capacitor 45 discharges through diode 46, ;~
the gate-cathode junction of an SCR 31, and a light emitting ;~
diode 81 of indicating means 80~ This discharge turns on the switching means.
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1 Switching rn~ans 30 essentially comprises SCR 31 and a 2 leakage resistor 32 that provides a path for the anode-gate 3 ; lea~a~e current. Upon receiving the positive voltage at the 4 gate of SCR 31, SCR 31 is turned on and current flows through ..
SCR 31 and rectifyi.n~ means 20 through the load- The turning 6 on of SC~ 31 is enhanced by the rapid discharge of capacitor 45 7 that occurs because of the aval~nche characteristics of bidi-8 rectional diode 46 which has a much lower conduction voltage ~ . than breakdo~m voltage.
Rectifying means 20 comprises four diodes, 20a, 20b~ 20c 11 and420d, connected in a full wave rectification bridge con-12 ~iguration and a double diode 21 connected across the power 13 ! circuit to provlde a path for transient peak voltages that may 14 occur in the circuits of load 10 or power source 11.
15 Operational delay means 60 is connected in the base circuit 1~ of ~ransistor 41 OI' the s~Jitcning concrol means to deia~ oper-17 ..ation oP the proximity switch upon initial energization. Since 18 the use of proximity switches in counting or position indicatlng 19 situations make it desirable that a count or indication not be produced erroneously upon initial energization, operational delay 21 means 60 is connected so that upon initial ener~ization of the .
! I
22 proximity switch~ transistor 64 is turned off insuring that 23 ,transistor 41 is turned on by the applied positive potential .. ~
24 through resistor 43, regardless of the output of the oscillator 25 .of sensing means 50. The turned on condition o~ transistor 41 26 keeps capacitor 45 dlscharged so that a voltage su~icient to ~7 turn on SCR 31 does not occur. Operational delay means 60 j !
28 jcomprises transistor 643 a diode 65, a capacitor 66, a bias 2~ r~sistor 67, a resistor 63J and a resistor G8.
Upon the initial energization o~ the circuit, transistor 6 31 1 i9 turned off and transistor 41 cannot turn off ln response to 32~the output of the oscillator clrcuit of sensing means 50. As the 11 -5- . j ~O~iVl~L5 . ~ ~ ~
1 energi.zation contl.nues capacitor 66 begins to charge through !
2 resistor 68 and 67 and from an energy stOrage capacitor 75 in 3 ener~y storage means 70. When the charge on capacitor-~4 reaches ~-4 a selected voltage, transistor 64 is turned on as current flows . I-through diode 65 and the base-emitter ~unction of transistor 64.
6 With transistor 64 turned on the biasing circuit of transistor 7 41 comprises resistor 43, resistor 63 and the collector-emitter ' 8 ~circuit of transistor 64 which are selected to provide the ¦~
9 ,desired bias on transistor 41 so that it will turn on during the positive half-cycles produced by the oscillator.
11 Durlng operation of the proximity switch J when SCR 31 is , 12; turned on the current is shunted through the SCR and there is .
13 insufficient current and voltage available ~rom power source 11 14 to operate the circuitry and provide the necessary biases to maintain stable operation. To enable the energy storage means " ;
16 ,~o provide power ~or ~hose periods wile~l S~n 3i i~ '~uri~e~ CA~ t1n~
17 ; characteristics of and the components in the switching control , 18 means are selected to provi.de a time delay circuit so that SCP. 31 19 does not turn on until the positive voltage in any half-cyGle of source 11, after rectification by rectifier 20~ is at or has 21 reached a minimum prese}ected level. This level results from 22 the firing delay time of SCR 31 as controlled by the character-23 i~tics of switching control means 40, particularly the breakdo~n !' .
24 voltage of bidiréctional diode 46 and the charge rate of : :
25 ,capacitor 45 through resistor 42. The level is selected to . ~;
26 insure that.sufficient electrical ener~ from source 11 is stored 27; by ~ r storage mean~ 7O at the time of eitoh~g so that 28 there is su~ficient power at a suitable voltage ror the operation 29 o~ the circuits when insufficient voltage is available because 30; of the shunting e~fect of SCR 31, ~ewe~'stora~e means 70 com-31 prises a re~istor 71, a coupling capacltor 72, a cliode 73, a , 32 diode 74J resis~or 68~ and energy storage capacitor 75. Capaci.tor ~ !
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1 75 is char~ed through resistor 68 in para.lel ~Jlth diode 74 and 2 ~the low impedance network comprising res.~stor 71 and capacitor 3 72 so that an initlal selected charge level ls achieved by 4 capacitor 75 during any period in a recti~ied half cycle of source 11 available before the firing of the SCR. Between pulses, 6 capacitor 72 discharges through resistor 71, other parts Or the 7 ;.circuit, and through d-Lode 73.
' Indicating means 80 comprises light-emitting diode 81 which .j, , . j ., .
: is turned on only when SCR 31 is turned on. Diode 81 is turned on by the discharge curi~ent from capacitor 45 through diode 46 11 , and the gate-cathode junction of SCR 31. A diode 82 is connected .
12 , to provide a path for operating current for the circult, to block ;
13 ,current in the discharge dlrection so $hat capacitor 45 discharges 14 'through dlode 81 to turn it onl and to limi~ any reverse voltages !
appearing across dlode ~
16 ; 'L'hus, in the opera~lon OI the circullry snown, upon tne 17 positloning of a metallic object: within a predetermined distance 18 from coil 51, the amplitude o~ the oscillations in the oscillator 19 circuit decrease below a selected level, This turns off transistor 41 and allows capacitor 45 to charge to a level 21 ,su~ficient to turn on SCR 31 and connect load 10 through 22 ,rectifying brldge 20 and SCR 31 to power source 11, The char~
23 acterlstics of switching control means 40 are selected so ~hat 24 SCR 31 wi.ll only turn on at some positive voltage level so that , , .
25,,capacitor 75 ~ill be sufficiently charged. Capacitor 75 26 provides a power source during the period that SCR 31 is turned 2'~ on to enable the opçration of the circuitr~ despite the low 28 potential across the circuit with SCR 31 conducting. Operational 29~dçlay means 60 prevents spurious operation upon initial energi-i . ~
æation o~ the circuit by preventing operation of .SCR 31 until 31 capacitor 65 has charged, A visual indicating means is provlded 3~ by li~ht-emlttlng diode 81 which provides an indication of the !
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operation of the circuit or of the count of a metalllc obJect 2 passing within the field Or coil 51.
6 power source 11 because of the shunting of the power source~by ~ :
7 .switching means 30; and an indicating means 80 for signalling.
8 the operation of the switching means to connect the source to g the load. i`~
10 Sensing means 50.comprises an inductive de~ice such as a ~1 11 coil 51 connected to the remaining circuitry of the sensing means ~.
12 by a suitable conductor so that typically it may be placed in 13 `the casing Or the proximity switch in a posltion suitable for . j ;
,! I .
14 sensing the presence of a metallic ob~ect, that is, in a positlon .; c~_ .
where the presence of~metallic object will i.nfluence the magnetic ield of the coil operating in an oscillator circuit. Sensing 17 ~ means 50 also comprises a transistor 52J a coupling capacitor 53, 18 an ad~ustable resistor 54, capacitors 55 and 56 connected in an 19 oscillator circuit con~iguration with transistor 52 and coil 51J
a bias resistor 57, a bias resistor 58J a bias res~stor 59, and a ~l. decoupling or filtering capacitor 61. The components and ~heir 22 .values are seleoted so that transistor 52 drives a tuned ~ `
23 ,oscillator circuit having coil 51 and capacitors 55 and 56 througn.
24 ad~ustable feedback resistor 54. The circuit is appropriately ;~ !
25 biased by resistors 58l 59 and 57 and decoupling capacitor 61 j 'I ~ r ~ $i~
26 provides a steady d..c bias ~oltage regardless of any ~ a~n*s 27 that may be picked up through coil ~1. The circuit is typically 28 ;tuned to oscillate at a relatively high frequency, about 20Q
29 kilohertz, relative to the power source frequency to provide an 30 .output through couplin~ capacitor 53. Under the se:Lected biasin~
31 and feedback conditions~ as determlned b~ ad~ustable reslstor 54, 32 oscillation ln the oscillator circuit occurs but its ampl~tude 15 ~6~5 : ~
significantly damped to a preselected level whenever a metallic article o-f a selected type is with:in a selected distance from ~;
coil 51. ~.~
The output from sensing means 50, the oscillating signal ~ :
appearing at coupling capacitor 53, is applied to switching control means 40. Switching control means 40 comprises a con- ;...... .,~
trol switching device such as a transistor 41, a resistor 42, a biasing resistor 43, a biasing circuit made up of a biasing resistor 63 and a switching device such as a transistor 64 that ~ :~
also comprises part of operational delay means 60, .a switching capacitor 45, and a bidirectional threshold diode 46 having a.;- .
. . ~, selected breakdown or thresho].d voltage. Switching control means receives the output of sensing means 50 as an input to ~.
transistor 41. The component values are selected so that when transistor 64 is turned on, transistor 41 is biased to ~
turn on during a selected portion of each positive half-cycle ~ .
of the oscillator output, at the relatively high frequency . .
rate of the oscillator, to thereby shunt and discharge capa~
. ~ . . .
citor 45 and prevent it from being charged to any significant ~.
level by the power source.
When a metallic object is within ~heselected distance from coil 51 of sensing means 50, the amplitude of oscillation in the oscillator clrcuit is reduced so that insufficient positive signal appears at the base of transistor 41 and transistor 41 remains turned off. With transistor 41 turned off, capacitor 45 is charged from power source 11 through the load and rectifying means 20 at a rate selected by the values of the resistance and capacitance of resistor 4~ and capacitor 45.
When the voltage level across capacitor 45 reaches a prede- ~.
termined level the breakdown voltage of bidirectional diode ~ :
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46 is equalled and capacitor 45 discharges through diode 46, ;~
the gate-cathode junction of an SCR 31, and a light emitting ;~
diode 81 of indicating means 80~ This discharge turns on the switching means.
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1 Switching rn~ans 30 essentially comprises SCR 31 and a 2 leakage resistor 32 that provides a path for the anode-gate 3 ; lea~a~e current. Upon receiving the positive voltage at the 4 gate of SCR 31, SCR 31 is turned on and current flows through ..
SCR 31 and rectifyi.n~ means 20 through the load- The turning 6 on of SC~ 31 is enhanced by the rapid discharge of capacitor 45 7 that occurs because of the aval~nche characteristics of bidi-8 rectional diode 46 which has a much lower conduction voltage ~ . than breakdo~m voltage.
Rectifying means 20 comprises four diodes, 20a, 20b~ 20c 11 and420d, connected in a full wave rectification bridge con-12 ~iguration and a double diode 21 connected across the power 13 ! circuit to provlde a path for transient peak voltages that may 14 occur in the circuits of load 10 or power source 11.
15 Operational delay means 60 is connected in the base circuit 1~ of ~ransistor 41 OI' the s~Jitcning concrol means to deia~ oper-17 ..ation oP the proximity switch upon initial energization. Since 18 the use of proximity switches in counting or position indicatlng 19 situations make it desirable that a count or indication not be produced erroneously upon initial energization, operational delay 21 means 60 is connected so that upon initial ener~ization of the .
! I
22 proximity switch~ transistor 64 is turned off insuring that 23 ,transistor 41 is turned on by the applied positive potential .. ~
24 through resistor 43, regardless of the output of the oscillator 25 .of sensing means 50. The turned on condition o~ transistor 41 26 keeps capacitor 45 dlscharged so that a voltage su~icient to ~7 turn on SCR 31 does not occur. Operational delay means 60 j !
28 jcomprises transistor 643 a diode 65, a capacitor 66, a bias 2~ r~sistor 67, a resistor 63J and a resistor G8.
Upon the initial energization o~ the circuit, transistor 6 31 1 i9 turned off and transistor 41 cannot turn off ln response to 32~the output of the oscillator clrcuit of sensing means 50. As the 11 -5- . j ~O~iVl~L5 . ~ ~ ~
1 energi.zation contl.nues capacitor 66 begins to charge through !
2 resistor 68 and 67 and from an energy stOrage capacitor 75 in 3 ener~y storage means 70. When the charge on capacitor-~4 reaches ~-4 a selected voltage, transistor 64 is turned on as current flows . I-through diode 65 and the base-emitter ~unction of transistor 64.
6 With transistor 64 turned on the biasing circuit of transistor 7 41 comprises resistor 43, resistor 63 and the collector-emitter ' 8 ~circuit of transistor 64 which are selected to provide the ¦~
9 ,desired bias on transistor 41 so that it will turn on during the positive half-cycles produced by the oscillator.
11 Durlng operation of the proximity switch J when SCR 31 is , 12; turned on the current is shunted through the SCR and there is .
13 insufficient current and voltage available ~rom power source 11 14 to operate the circuitry and provide the necessary biases to maintain stable operation. To enable the energy storage means " ;
16 ,~o provide power ~or ~hose periods wile~l S~n 3i i~ '~uri~e~ CA~ t1n~
17 ; characteristics of and the components in the switching control , 18 means are selected to provi.de a time delay circuit so that SCP. 31 19 does not turn on until the positive voltage in any half-cyGle of source 11, after rectification by rectifier 20~ is at or has 21 reached a minimum prese}ected level. This level results from 22 the firing delay time of SCR 31 as controlled by the character-23 i~tics of switching control means 40, particularly the breakdo~n !' .
24 voltage of bidiréctional diode 46 and the charge rate of : :
25 ,capacitor 45 through resistor 42. The level is selected to . ~;
26 insure that.sufficient electrical ener~ from source 11 is stored 27; by ~ r storage mean~ 7O at the time of eitoh~g so that 28 there is su~ficient power at a suitable voltage ror the operation 29 o~ the circuits when insufficient voltage is available because 30; of the shunting e~fect of SCR 31, ~ewe~'stora~e means 70 com-31 prises a re~istor 71, a coupling capacltor 72, a cliode 73, a , 32 diode 74J resis~or 68~ and energy storage capacitor 75. Capaci.tor ~ !
Il -6- i ~ . ! ' ' ~
1 75 is char~ed through resistor 68 in para.lel ~Jlth diode 74 and 2 ~the low impedance network comprising res.~stor 71 and capacitor 3 72 so that an initlal selected charge level ls achieved by 4 capacitor 75 during any period in a recti~ied half cycle of source 11 available before the firing of the SCR. Between pulses, 6 capacitor 72 discharges through resistor 71, other parts Or the 7 ;.circuit, and through d-Lode 73.
' Indicating means 80 comprises light-emitting diode 81 which .j, , . j ., .
: is turned on only when SCR 31 is turned on. Diode 81 is turned on by the discharge curi~ent from capacitor 45 through diode 46 11 , and the gate-cathode junction of SCR 31. A diode 82 is connected .
12 , to provide a path for operating current for the circult, to block ;
13 ,current in the discharge dlrection so $hat capacitor 45 discharges 14 'through dlode 81 to turn it onl and to limi~ any reverse voltages !
appearing across dlode ~
16 ; 'L'hus, in the opera~lon OI the circullry snown, upon tne 17 positloning of a metallic object: within a predetermined distance 18 from coil 51, the amplitude o~ the oscillations in the oscillator 19 circuit decrease below a selected level, This turns off transistor 41 and allows capacitor 45 to charge to a level 21 ,su~ficient to turn on SCR 31 and connect load 10 through 22 ,rectifying brldge 20 and SCR 31 to power source 11, The char~
23 acterlstics of switching control means 40 are selected so ~hat 24 SCR 31 wi.ll only turn on at some positive voltage level so that , , .
25,,capacitor 75 ~ill be sufficiently charged. Capacitor 75 26 provides a power source during the period that SCR 31 is turned 2'~ on to enable the opçration of the circuitr~ despite the low 28 potential across the circuit with SCR 31 conducting. Operational 29~dçlay means 60 prevents spurious operation upon initial energi-i . ~
æation o~ the circuit by preventing operation of .SCR 31 until 31 capacitor 65 has charged, A visual indicating means is provlded 3~ by li~ht-emlttlng diode 81 which provides an indication of the !
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operation of the circuit or of the count of a metalllc obJect 2 passing within the field Or coil 51.
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23 ~ ~ :
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27 j -29`~
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i 3l .1 . ~ ,.q .. ~ ~ - ' 1 ~
g', ' ' . I ~-10''. ' . ' ' ~ I ' 11 , 12,i ' ' ~ ; I, .
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Claims (18)
1. A proximity switch of the type connectable in series with an electrical source and an electrical load, having portions energizable from the electrical source, and operable in response to the proximity of a metallic object to shunt current from the electrical source through the proximity switch and thereby connect the source to the load, said proximity switch comprising:
a sensing means for producing a signal in response to the presence of a metallic object within a selected distance from the proximity switch;
a switching means connected for connection between the source and the load for disconnecting said source from said load and connecting said source to said load by shunting the current from said source through said switching means;
a switching control means responsive to the sensing means signal for controlling the switching means;
an energy storage means for storing electrical energy received from the electrical source when said source is disconnected from the load by the switching means and for supplying electrical energy to selected portions of the proximity switch when said source current is shunted to said load through said switching means; and an operational delay means responsive to the initial connection of the proximity switch to the power source for turning on the control switching device to shunt the switching capacitor for a preselected time after said initial energization to thereby prevent the turning on of the silicon controlled rectifier for said preselected time.
a sensing means for producing a signal in response to the presence of a metallic object within a selected distance from the proximity switch;
a switching means connected for connection between the source and the load for disconnecting said source from said load and connecting said source to said load by shunting the current from said source through said switching means;
a switching control means responsive to the sensing means signal for controlling the switching means;
an energy storage means for storing electrical energy received from the electrical source when said source is disconnected from the load by the switching means and for supplying electrical energy to selected portions of the proximity switch when said source current is shunted to said load through said switching means; and an operational delay means responsive to the initial connection of the proximity switch to the power source for turning on the control switching device to shunt the switching capacitor for a preselected time after said initial energization to thereby prevent the turning on of the silicon controlled rectifier for said preselected time.
2. A proximity switch according to claim 1 wherein said sensing means comprises an oscillator circuit having an inductive device positioned as a sensing device for the proximity switch and adjusted to produce an oscillating output that decreases in amplitude to produce the signal for the switching control means upon presence of a metallic object within said selected distance from said inductive device.
3. A proximity switch according to claim 2 wherein said switching control means comprises a switching capacitor shunted by a control switching device with said control switching device connected to be turned on by the oscillating signal from the sensing means to thereby discharge said switching capacitor.
4. A proximity switch according to claim 1 wherein said operational delay means comprises a delay circuit connected to control the control switching device, said delay circuit having a switching device responsive to the initial energization of the proximity switch to turn on said control switching device to continuously shunt the switching capacitor for the preselected time after said initial energization.
5. A proximity switch according to claim 3 wherein said switching means comprises a semiconductor switching device connected to be connected between the source and the load having a gate electrode responsive to the application of a selected voltage to said gate electrode to turn on and thereby connect said source to said load.
6. A proximity switch according to claim 5 wherein said switching capacitor is connected to the gate electrode of the semiconductor switching device to turn on said semiconductor switching device when said switching capacitor reaches a preselected charge voltage.
7. A proximity switch according to claim 6 wherein said semiconductor switching device is a silicon controlled rectifier with the switching capacitor connected between the gate electrode and the cathode electrode of said silicon controlled rectifier and said switching means also comprises a threshold switching device connected between the switching capacitor and the gate electrode whereby said silicon controlled rectifier is turned on when the switching capacitor charge provides a voltage across said threshold device that equals or exceeds the threshold level of said threshold device.
8. A proximity switch according to claim 2 wherein said switching means comprises a semiconductor switching device connected between the source the load having a gate electrode responsive to the application of a selected potential to said gate electrode to turn on and thereby connect the source to the load.
9. A proximity switch according to claim 8 wherein said switching control means comprises a time delay circuit responsive to the decrease in amplitude of the oscillating output from the sensing means to operate a preselected time after said decrease to produce the selected potential at the gate electrode of the semiconductor switching device.
10. A proximity switch according to claim 9 wherein said switching control means comprises a switching capacitor shunted by a control switching device with said semiconductor switching device connected to be turned off by the decrease in amplitude of the signal from the sensing means to thereby remove the shunt from said switching capacitor.
11. A proximity switch according to claim 10 wherein said semiconductor switching device is a silicon controlled rectifier with the switching capacitor connected between the gate electrode and the cathode electrode of said silicon controlled rectifier and said switching means also comprises a threshold switching device connected between the switching capacitor and the gate electrode whereby said silicon controlled rectifier is turned on when the switching capacitor charge provides a voltage across said threshold device that equals or exceeds the threshold level of said threshold device.
12. A proximity switch according to claim 10 also comprising a light-emitting diode connected in the discharge circuit of the switching capacitor to be energized by the discharge of said switching capacitor through the gate electrode of the semiconductor switching device.
13. A proximity switch according to claim 1 also compris-ing an indicating means for indicating the turning on of the switching means.
14. A proximity switch according to claim 13 wherein said sensing means comprises an oscillator circuit having an induc-tive device positioned as a sensing device for the proximity switch and adjusted to produce an oscillating output that decreases in amplitude to produce the signal for the switching control means upon presence of a metallic object within said selected distance from said inductive device.
15. A proximity switch according to claim 14 wherein said switching means comprises a semiconductor switching device connected to be connected between the source and load having a gate electrode responsive to the application of a selected voltage to said gate electrode to turn on and connect said source to said load.
16. A proximity switch according to claim 15 wherein said switching control means comprises a switching capacitor shunted by a control switching device with said control switching device connected to be turned on by the oscillating signal from the sensing means to thereby discharge said switching capacitor.
17. A proximity switch according to claim 16 wherein said indicating means comprises a light-emitting diode connected in the discharge circuit of the switching capacitor to be energized by the discharge of said switching capacitor through the gate electrode of the semiconductor switching device.
18. A proximity switch according to claim 1 also compris-ing an operational delay means responsive to the initial connec-tion of the proximity switch to the power source for controlling the switching control means to control the switching means to prevent connection of the source to the load for a preselected time after said initial energization irrespective of the sensing means output.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB50629/74A GB1531217A (en) | 1974-11-22 | 1974-11-22 | Proximity switch |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1060115A true CA1060115A (en) | 1979-08-07 |
Family
ID=10456687
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA239,202A Expired CA1060115A (en) | 1974-11-22 | 1975-11-03 | Proximity switch |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA1060115A (en) |
| FR (1) | FR2292242A1 (en) |
| GB (1) | GB1531217A (en) |
| IT (1) | IT1051270B (en) |
| ZA (1) | ZA756924B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3041840C2 (en) * | 1980-11-06 | 1989-01-12 | Honeywell Gmbh, 6050 Offenbach | Two-wire feed circuit |
| GB2180938B (en) * | 1985-09-24 | 1990-02-28 | Square D Co | Low leakage, a c proximity switch circuit |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1924279C3 (en) * | 1969-05-13 | 1975-06-12 | Hans 4330 Muelheim Turck | Two-pole thyristor switching device for AC circuits |
| FR2148789A5 (en) * | 1971-08-02 | 1973-03-23 | Crouzet Sa |
-
1974
- 1974-11-22 GB GB50629/74A patent/GB1531217A/en not_active Expired
-
1975
- 1975-11-03 CA CA239,202A patent/CA1060115A/en not_active Expired
- 1975-11-04 ZA ZA00756924A patent/ZA756924B/en unknown
- 1975-11-21 FR FR7535599A patent/FR2292242A1/en active Granted
- 1975-11-21 IT IT69884/75A patent/IT1051270B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| GB1531217A (en) | 1978-11-08 |
| IT1051270B (en) | 1981-04-21 |
| FR2292242B1 (en) | 1982-07-09 |
| FR2292242A1 (en) | 1976-06-18 |
| ZA756924B (en) | 1976-10-27 |
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