GB2091501A - 2-Wire Sensor Circuit - Google Patents

2-Wire Sensor Circuit Download PDF

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Publication number
GB2091501A
GB2091501A GB8133346A GB8133346A GB2091501A GB 2091501 A GB2091501 A GB 2091501A GB 8133346 A GB8133346 A GB 8133346A GB 8133346 A GB8133346 A GB 8133346A GB 2091501 A GB2091501 A GB 2091501A
Authority
GB
United Kingdom
Prior art keywords
circuit
load
electronic switch
resistor
current
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.)
Withdrawn
Application number
GB8133346A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Honeywell GmbH
Original Assignee
Honeywell GmbH
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Honeywell GmbH filed Critical Honeywell GmbH
Publication of GB2091501A publication Critical patent/GB2091501A/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/72—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices having more than two PN junctions; having more than three electrodes; having more than one electrode connected to the same conductivity region
    • H03K17/725—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices having more than two PN junctions; having more than three electrodes; having more than one electrode connected to the same conductivity region for ac voltages or currents
    • 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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  • Electronic Switches (AREA)

Abstract

A sensor element O changes its oscillation amplitude when a piece of metal is close, so turning on transistor QA. This fires thyristor T via firing circuit Z, and increases the load current drawn from a rectifying circuit RB1.The AC load current into RB1 therefore rises, and the voltage across resistor RG rises to fire triac SCR1. This raises the load current through load RS, so indicating that the piece of metal is near. The thyristor T therefore switches only a relatively low current, and its recovery is therefore facilitated, while the triac SCR1 carries the high current required to operate the load RS. <IMAGE>

Description

SPECIFICATION 2-Wire Sensor Circuit The present invention relates to 2-wire sensor circuits, and more particularly to such circuits in which a rectifying circuit is connected, on its AC side, in series with a load circuit to an AC supply and, on its DC side, to a sensor element, such that the sensor element obtains its DC power from the rectifying circuit and, when the condition which it senses increases, it causes additional current to be drawn to energize the load.
Various such circuits are known. One such circuit has a zener diode and an electronic switch connected in series across the DC side of the rectifying circuit, with a high voltage resistor connected in parallel with the electronic switch.
When the sensor element senses the relevant condition, it fires the electronic switch to produce a sharp increase in load current.
This circuit has the disadvantage of a substantial voltage loss across the zener diode.
This can be overcome by omitting the zener diode, but the resulting circuit has the disadvantage that the turning off of the electronic switch is uncertain, particularly at high currents, in view of the relatively long recovery time that is then required.
Another circuit has the electronic switch placed instead on the AC side of the rectifying circuit. This however has the disadvantage that a transformer coupling from the sensor element, on the DC side, to the control electrode of the electronic switch, on the AC side, is required.
The object of the present invention is to provide a 2-wire sensor circuit in which the disadvantages of the known circuits are alleviated or overcome.
Accordingly the present invention provides a 2wire sensor circuit comprising an AC load and an electronic switch connected in series, an actuating resistor and a rectifying circuit connected in series across the electronic switch, the junction of the rectifier circuit and the actuating resistor being coupled to the control electrode of the electronic switch, and a seriesconnected sensing element connected to the DC side of the rectifying circuit.
A 2-wire sensor circuit in accordance with the present invention operating as a proximity switch will now be described, by way of example, with reference to the drawing, which is a simplified circuit diagram.
The actual proximity switch comprises an oscillator 0 the oscillation condition of which controls an output transistor Q of a switching amplifier (not further shown). If the output transistor 0A is turned on, it switches on a thyristor T by means of a firing circuit Z. The thyristor T is connected across a rectifier bridge RB 1. The DC output of the rectifier bridge RB1 also charges a capacitor C over a charging circuit L, so that the voltage on the capacitor C forms the supply voltage for the oscillator 0 and the switching amplifier as well as for other circuit components not shown, for example a demodulator, a hysteresis circuit, an inverter stage, etc.
At its AC side the rectifier bridge RB1 is fed from a series arrangement comprising a firing.
resistor R,, a load R,, and an AC voltage source 0.
A triac SCR1 is connected across the series arrangement of the load Rs and the AC voltage source Q. The ignition electrode of the triac SCR1 is connected to the ignition resistor RG.
Assuming that the proximity switch is working as a normally open switch contact, if a metal piece is brought near to it-the oscillator 0 has its amplitude attenuated and the output transitor 0A is turned on. Hence by means of the ignition circuit Z the thyristor T is fired, so that a current flows from the AC voltage source 0 through the load R9, the ignition resistor RG, the rectifier bridge RB1, and the thyristor T. Independently of the switching condition of the proximity switch, the charging capacitor C is charged from the rectifier bridge RB 1 over the charging circuit L in order to provide the supply voltage required for operation of the proximity switch.
The firing of thyristor T causes the load current to attain a high value in relation to the given value of the voltage of the AC voltage source Q and an accordingly low resistive load R5. This load current also flows through the ignition resistor RG, and due to the increased voltage drop over the ignition resistor R0 the triac SCR1 is fired and substantially takes over the load current flowing through the load Rs.
The value of the current at which the triac SCR 1 takes over the load current may be adjusted within certain limits by the value of the ignition resistor RG. Hence the value at which the triac SCR1 takes over the load current may be chosen in such a manner that the recovery times of the thyristor T, which initially at low values conducts the load current, is of no importance.
A proximity switch has been described whose components as the oscillator, the trigger stage, etc., require a current supply. Instead of a proximity switch, another sensor element requiring a current supply, as for instance an optical sensor, a temperature sensor, etc., may be operated together with the circuitry shown.
Claims
1. A 2-wire sensor circuit comprising an AC load and an electronic switch connected in series, an actuating resistor and a rectifying circuit connected in series across the electonic switch, the junction of the rectifier circuit and the actuating resistor being coupled to the control electrode of the electronic switch, and a seriesconnected sensing element connected to the DC side of the rectifying circuit.
2. A sensor circuit according to Claim 1, wherein the electronic switch is a triac.
3. A sensor circuit according to either previous claim including a further electronic switch connected across the DC side of the rectifying
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION 2-Wire Sensor Circuit The present invention relates to 2-wire sensor circuits, and more particularly to such circuits in which a rectifying circuit is connected, on its AC side, in series with a load circuit to an AC supply and, on its DC side, to a sensor element, such that the sensor element obtains its DC power from the rectifying circuit and, when the condition which it senses increases, it causes additional current to be drawn to energize the load. Various such circuits are known. One such circuit has a zener diode and an electronic switch connected in series across the DC side of the rectifying circuit, with a high voltage resistor connected in parallel with the electronic switch. When the sensor element senses the relevant condition, it fires the electronic switch to produce a sharp increase in load current. This circuit has the disadvantage of a substantial voltage loss across the zener diode. This can be overcome by omitting the zener diode, but the resulting circuit has the disadvantage that the turning off of the electronic switch is uncertain, particularly at high currents, in view of the relatively long recovery time that is then required. Another circuit has the electronic switch placed instead on the AC side of the rectifying circuit. This however has the disadvantage that a transformer coupling from the sensor element, on the DC side, to the control electrode of the electronic switch, on the AC side, is required. The object of the present invention is to provide a 2-wire sensor circuit in which the disadvantages of the known circuits are alleviated or overcome. Accordingly the present invention provides a 2wire sensor circuit comprising an AC load and an electronic switch connected in series, an actuating resistor and a rectifying circuit connected in series across the electronic switch, the junction of the rectifier circuit and the actuating resistor being coupled to the control electrode of the electronic switch, and a seriesconnected sensing element connected to the DC side of the rectifying circuit. A 2-wire sensor circuit in accordance with the present invention operating as a proximity switch will now be described, by way of example, with reference to the drawing, which is a simplified circuit diagram. The actual proximity switch comprises an oscillator 0 the oscillation condition of which controls an output transistor Q of a switching amplifier (not further shown). If the output transistor 0A is turned on, it switches on a thyristor T by means of a firing circuit Z. The thyristor T is connected across a rectifier bridge RB 1. The DC output of the rectifier bridge RB1 also charges a capacitor C over a charging circuit L, so that the voltage on the capacitor C forms the supply voltage for the oscillator 0 and the switching amplifier as well as for other circuit components not shown, for example a demodulator, a hysteresis circuit, an inverter stage, etc. At its AC side the rectifier bridge RB1 is fed from a series arrangement comprising a firing. resistor R,, a load R,, and an AC voltage source 0. A triac SCR1 is connected across the series arrangement of the load Rs and the AC voltage source Q. The ignition electrode of the triac SCR1 is connected to the ignition resistor RG. Assuming that the proximity switch is working as a normally open switch contact, if a metal piece is brought near to it-the oscillator 0 has its amplitude attenuated and the output transitor 0A is turned on. Hence by means of the ignition circuit Z the thyristor T is fired, so that a current flows from the AC voltage source 0 through the load R9, the ignition resistor RG, the rectifier bridge RB1, and the thyristor T. Independently of the switching condition of the proximity switch, the charging capacitor C is charged from the rectifier bridge RB 1 over the charging circuit L in order to provide the supply voltage required for operation of the proximity switch. The firing of thyristor T causes the load current to attain a high value in relation to the given value of the voltage of the AC voltage source Q and an accordingly low resistive load R5. This load current also flows through the ignition resistor RG, and due to the increased voltage drop over the ignition resistor R0 the triac SCR1 is fired and substantially takes over the load current flowing through the load Rs. The value of the current at which the triac SCR 1 takes over the load current may be adjusted within certain limits by the value of the ignition resistor RG. Hence the value at which the triac SCR1 takes over the load current may be chosen in such a manner that the recovery times of the thyristor T, which initially at low values conducts the load current, is of no importance. A proximity switch has been described whose components as the oscillator, the trigger stage, etc., require a current supply. Instead of a proximity switch, another sensor element requiring a current supply, as for instance an optical sensor, a temperature sensor, etc., may be operated together with the circuitry shown. Claims
1. A 2-wire sensor circuit comprising an AC load and an electronic switch connected in series, an actuating resistor and a rectifying circuit connected in series across the electonic switch, the junction of the rectifier circuit and the actuating resistor being coupled to the control electrode of the electronic switch, and a seriesconnected sensing element connected to the DC side of the rectifying circuit.
2. A sensor circuit according to Claim 1, wherein the electronic switch is a triac.
3. A sensor circuit according to either previous claim including a further electronic switch connected across the DC side of the rectifying circuit and actuated by the sensor element to increase the current drawn to a value which turns on the first electronic switch.
4. A sensor circuit according to Ciaim 3, wherein the second electronic switch is a thyristor.
5. A 2-wire sensor circuit substantially as herein described and illustrated.
GB8133346A 1980-11-06 1981-11-05 2-Wire Sensor Circuit Withdrawn GB2091501A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19803041808 DE3041808A1 (en) 1980-11-06 1980-11-06 TWO-WIRE SWITCHING ARRANGEMENT

Publications (1)

Publication Number Publication Date
GB2091501A true GB2091501A (en) 1982-07-28

Family

ID=6116052

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8133346A Withdrawn GB2091501A (en) 1980-11-06 1981-11-05 2-Wire Sensor Circuit

Country Status (3)

Country Link
DE (1) DE3041808A1 (en)
FR (1) FR2493638A1 (en)
GB (1) GB2091501A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2262998A (en) * 1991-12-31 1993-07-07 Square D Co Power supply for proximity switch integrated circuit
GB2330704A (en) * 1997-10-21 1999-04-28 Timeguard Limited Semiconductor AC switch units

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3615052A1 (en) * 1986-05-03 1987-11-05 Balluff Gebhard Feinmech TWO-WIRE SWITCH
FR3040107B1 (en) * 2015-07-10 2018-06-22 Open App CONTACTLESS SWITCH FOR REPLACING A VISIBLE CONTACT SWITCH

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2262998A (en) * 1991-12-31 1993-07-07 Square D Co Power supply for proximity switch integrated circuit
GB2262998B (en) * 1991-12-31 1995-10-25 Square D Co Improvements in and relating to proximity switches
GB2330704A (en) * 1997-10-21 1999-04-28 Timeguard Limited Semiconductor AC switch units

Also Published As

Publication number Publication date
FR2493638A1 (en) 1982-05-07
DE3041808A1 (en) 1982-06-03

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)