US3798464A - Electronic timer - Google Patents

Electronic timer Download PDF

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Publication number
US3798464A
US3798464A US3798464DA US3798464A US 3798464 A US3798464 A US 3798464A US 3798464D A US3798464D A US 3798464DA US 3798464 A US3798464 A US 3798464A
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United States
Prior art keywords
resistor
capacitor
potential divider
transistor
wiper
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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 - Lifetime
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English (en)
Inventor
M Luursema
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US Philips Corp
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US Philips Corp
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Publication date
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/28—Modifications for introducing a time delay before switching
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B27/00—Photographic printing apparatus
    • G03B27/72—Controlling or varying light intensity, spectral composition, or exposure time in photographic printing apparatus

Definitions

  • the invention relates to an electronic timer which is provided with two input terminals intended to be connected to a direct voltage source, which input terminals are connected by means of a potential divider a tap of which is connected to the base of a transistor.
  • the main electrodes of the transistor are incorporated in a close circuit in series with a capacitor and at least one resistor, said resistor and part of the potential divider being also located in a connection from the emitter of the transistor to the tap.
  • the capacitor is coupled to a switching device and the current flowing through the closed circuit has a substantially constant value during operation of the timer.
  • a known timer of the kind mentioned above is described, for example, in Netherlands Pat No. 69101 14.
  • the said switching device is operated thereby.
  • this known timer When this known timer is to be set to a different switching time, the capacitor is to be given a different initial. voltage.
  • the discharge of the capacitor is effected with a non-variable constant current intensity during operation of thistimer.
  • a drawback thereof is that even for a range (namely between the longest switching period and the shortest switching period) of approximately :1, high initial'voltages may be present across the capacitor. In the case of still larger ranges, change-over devices have to be added to the arrangement. This is also a drawback.
  • an electronic timer is provided with two input terminals which are adapted to be connected to a direct voltage source.
  • the main electrodes of the transistor are incorporated in a closed circuit in serieswith a capacitor and at least one resistor.
  • the said resistor and part of the potential divider are alsolocated in a connection from the emitter of the transistor to the tap, while the capacitor is coupled to a switching device and the current flowing through the closed circuit has a substantially constant value during operation .of the timer.
  • a characteristic feature of the invention isethatat least part of the resistor, together with a part of the potential divider located in the connection from the emitter of the transistor to the tap, is formed as a linear potentiometer whose wiper is connected to one of the input terminals and also forms part of the closed circuit.
  • the largest ratio between the resistive value of the part of the potential divider between the wiper and the tap and that of the part of the potential divider at the other end of said tap is 1.3 at a maximum.
  • this timer is that the switching time can be adjusted in a simple manner and with a percentual accuracy which is substantially the same throughout a relatively large range. This adjustment is effected by moving the wiper along the potentiometer resistor.
  • the operation of the switching device at the end of the adjusted switching time is effected, for example, by the discharged capacitor or in more general terms: by such a discharged condition of the capacitor that only a low voltage is present across this capacitor (after the constant current discharge), or by reaching a relatively high capacitor voltage (after a constant current charge of the capacitor).
  • the typical adjustment of the switching time in a timer according to the invention is related .to the fact that simultaneously the resistance in the closed circuit (including the capacitor and the main electrodes of the transistor) and the potential divider ratio of the potential divider connected across the input terminals is varied by moving the wiper on the potentiometer. This is effected in a switching device according to the invention in such a manner that a decrease of the resistance R in the closed circuit (the emitter resistor) is accompanied'by an increase of the voltage E across this resistor (as a-result of the larger voltage due to the varied voltage division between the base of the transistor and the wiper on the potentiometer).
  • the linear potentiometer with two stopsbetween which the wiper can be moved. In that case the resistance in the closed circuit can be prevented from becoming too low and the voltage between the base and the emitter of the transistor can be prevented from becoming zero (no main electrode current).
  • connection between the emitter and the base of the transistor consists of, successively, a first resistor, the total resistor of the linear potentiometer and a second resistor, in which the first resistor and the second resistor are substantially equal and have a value of between 1/7 and 1/10 of the total resistance of the linear potentiometer.
  • An advantage thereof is that a linear potentiometer of lower value may be sufficient, and moreover the wiper can cover the entire potentiometer resistor tra jectory.
  • the control range is prevented from extending into extreme marginal ranges of the capacitor current adjustment.
  • the largest ratio between the part of the potential divider between the wiper and the tap and that of the potential divider at the other end of this tap is approximately one.
  • This further preferred embodiment has the advantage that a shift in equal steps of the wiper leads to a very satisfactory exponential variation of the capacitor current so that a scale along the wiper can be given a logarithmic character.
  • the percentual adjusting accuracy is the same throughout the meauring range of such a scale so that in this case the requirement referred to in the preamble is well satisfied.
  • the electronic timer is used, for example, for switching on or switching off an electric appliance after a given period, for example, an electrical kitchen range.
  • the switching device of the timer then operates, for example, a work contact in the supply of the range.
  • a further application is-in a device for feeding an exposure ligh source of a photographic enlarger.
  • This is an interesting application because in such an enlarger the exposure time must generally be varied in a large range with an adjusting accuracy which is the same throughout.
  • FIG. 1 shows an electrical principle circuit diagram of an electronic timer according to the invention
  • FIG. 2 shows a second electrical principle circuit diagram of an electronic timer according to the invention.
  • FIG. 3 shows the magnitude of the capacitor current in the timer shown in FIG. 1, plotted against the position a of the wiper on the potentiometer.
  • connection terminals 1 and 2 are connection adapted to be connected to a direct voltage source (not shown).
  • Terminal 1 is connected to the positive terminal of this source and terminal 2 is connected to its negative terminal.
  • Terminal 1 is connected to a switch 3.
  • Switch 3 is connected to a potential divider consisting at one end of resistor 4 and at the other end of the combination of a resistor 5 and a part 7 of a linear potentiometer 8 located between the wiper 6 and the resistor 5.
  • Wiper 6 is connected to the negative terminal 2.
  • the other part of the potentiometer is denoted by reference numeral 9.
  • a tap 10 between the resistors 4 and 5 is connected to the base 11 of a transistor 12. This transistor is of the npn-type.
  • the emitter of transistor 12 is connected through a resistor 13 to the part 9 of potentiometer 8.
  • a Capacitor 14 is connected, in series with a switch 15, to the collector of transistor 12. The other end of capacitor 14 is connected to the wiper 6 of potentiometer 8.
  • capacitor 14 is incorporated in a further circuit which serves to charge this capacitor.
  • This circuit consists of two connection terminals 17 and 18 which connect a two-pole switch 19 and a resistor 20 to a direct voltage source. In the closed condition of switch 19 capacitor 14 is charged through resistor 20 from the direct voltage source mentioned above.
  • a voltage-sensitive circuit represented by block 16 is connected across the series arrangement of capacitor 14 and switch 15. This voltage-sensitive circuit is formed in such a manner that when the voltage across capacitor 14 (in the closed condition of switch 15) is above a given value, an energizing winding 16a in block 16 conveys current and in which below this value of the voltage across capacitor 14 the energizing winding 16a does not convey current.
  • the contact of the relay whose energizing winding is denoted by 16a is denoted by reference numeral 21.
  • This contact is included in series with a lighting lamp of a photographic enlarger 22, namely between two input terminals 23 and 24 which are intended to be connected to an alternating voltage supply of, for example, 220 Volt 50 l-lz.
  • Part 25 represents a photographic negative and 26 is a photosensitive plate onto which the enlarged negative image is projected.
  • the voltage of the direct voltage source between terminals 1 and 2 was approximately 24 Volts.
  • the resistor 4 had a value of approximately 560kOhm.
  • the resistor 5 had a value which was approximately equal to that of resistor 13, namely approximately 58 kOhm.
  • the total resistance of potentiometer 8 was approximately 470 kOhm.
  • Transistor 12 was a silicon transistor whose voltage in the conducting state between the base and the emitter was very low.
  • the capacitor 14 had a capacitance of approximately 10 micro-Farad. This capacitor was always charged to an initial voltage of approximately 65 Volts, namely through resistor 20.
  • the threshold voltage of the arrangement 16 was approximately 15 Volts.
  • the resistive value of part 7 of the potentiometer may be varied proportionally to the resistive value of part 9 of this potentiometer.
  • the voltage between point 10 and wiper 6 was low, namely R5/R5 R4 times the supply voltage.
  • the resistance in the closed circuit 14, 15, 12, 13, 9, 6, 14 had a large value.
  • this resistance consisted of the resistor 13 plus the total resistance of potentiometer 8.
  • the said voltage between wiper 6 and tap 10 can also be considered with a satisfactory approximation as the voltage between the emitter of transistor 12 and wiper 6.
  • the ratio between the resistive part 7 of the potentiometer and the total resistor 7 9 of the potentiometer 8 will hereinafter be referred to by a.
  • FIG. 3 shows, for the situation of FIG. 1, how the constant discharge current i (in micro-amperes) of capacitor 14 varies as a function of the position a of wiper 6. on the potentiometer, represented by the solid line curve.
  • FIG. 3 The vertical axis of FIG. 3 is a logarithmic axis.
  • the upper horizontal axis of this Figure is a linear axis.
  • FIG. 3 furthermore shows by means of a broken line an ideal logarithmic variation between i and a. This broken line is of course a straight line.
  • FIG. 3 shows that the deviation of the true curve relative to the straight line is relatively very small. The deviation is in the order of 15 percent.
  • the t-sca'le in FIG. 3 having a logarithmic character "shows enlarged the time scale which is presentalongside the potentiometer 8 of FIG. 1.
  • the Figures are expressed in a unit of time not further shown. A small a of course corresponds to a low discharge current i of capacitor 14 and hence to a long exposure time t.
  • a constant discharge of capacitor 14 took place using a transistor of the npn-type. It is likewise possible to use a transistor of the pnp-type in such a capacitor discharge. Alternatively it is possible that in a switching device according to the invention a constant current charge of the capaciator is used instead of the constant current discharge of the capacitor.
  • FIG. 2 shows an arrangement in which a constant capacitor current charge is used and in which a transistor of the pnp-type is used.
  • the circuit of FIG.2 operates roughly the same as that of FIG.
  • Input terminals 50 and 51 are intended to be connected to a direct voltage source in which terminal 50 is connected to the positive terminal.
  • a switch 52 is connected to terminal 50.
  • Switch 52 is furthermore connected to a wiper 53 on a linear potentiometer 54.
  • One end of this potentiometer 54 is connected to a series arrangement of a resistor 55 and a resistor 56.
  • the other end of resistor 56 is connected to the negative terminal 51.
  • a tap 57 between resistors 55 and 56 is connected to the base 58 of a transistor 59.
  • potentiometer 54 is connected through a resistor 55a to the emitter of transistor 59.
  • the collector of transistor 59 is connected to a capacitor 60.
  • the other end of capacitor 60 is connected to terminal 51.
  • a series arrangement of a threshold element 61 and an energizing winding 62 of a switching device is connected in parallel across the capacitor 60.
  • the switching device is not shown in further detail.
  • the capacitor 60 is also shunted by a series arrangement of a resistor 63 and a switch 64.
  • the operation of the circuit of FIG. 2 resembles that of FIG. 1. One difference is, however, that first the switch 64 is closed so that any possible charge on capacitor 60 is depleted. Then switch 64 is opened again and switch 52 is closed.
  • the described switching devices according to the invention are simple and produce an adjustable discharge current (charge current) when using a linear-potentiometer (see 8 and 54), or an adjustable exposure time with which the relation between the shift of the wiper on the potentiometer relative to the variation in expo-v sure time has a logarithmic character so that substantially the same percentual accuracy is present throughout the adjusting range.
  • FIG. 3 shows the range between the maximum capacitor current intensity and the minimum current intensity, or between the maximum exposure time and the minimum exposure time, is more than 40 in the described case. This is a relatively large range.
  • An electronic timer comprising two input terminals adapted to be connected to a direct voltage source, a potential divider, a transistor, a capacitor, means connecting the input terminals to said potential divider, means connecting a tap of the potential divider to the. base of the transistor, means connecting the transistor main electrodes in a closed circuit in series with the capacitor and at least one resistor, said resistor and a part of the potential divider being located in a connection between the emitter of the transistor and the potential divider tap, the capacitor being'coupled to a switching device and the current flowing through the closed circuit having a substantially constant value during operation of the timer, and wherein at least a part of the resistor together with a part of the potential divider located in the connection between the emitter of the transistor and the tap comprises a linear potentiometer having a wiper connected to one of the input terminals and as a part of the closed circuit, the largest ratio between the resistive value of the part of the potential divider between the wiper and the tap and that of the part of the potential divider
  • connection between the emitter and the base of the transistor includes, successively, a first resistor, the total resistor of the linear potentiometer and a second resistor, the first resistor and the second resistor having substantially the same resistance value which lies between one-seventh and one-tenth of the total resistance of the linear potentiometer.
  • An electronic timer as claimed in claim 1 further comprising an exposure lamp for a photographic enlarger, voltage responsive means connected across the capacitor and including means for selectively applying a source of voltage to said lamp as a function of the capacitor voltage.
  • An electronic timer as claimed in claim 1 further comprising means connecting the potentiometer wiper to one electrode of the capacitor.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • General Physics & Mathematics (AREA)
  • Electronic Switches (AREA)
  • Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
  • Control Of Exposure In Printing And Copying (AREA)
  • Electric Ovens (AREA)
  • Relay Circuits (AREA)
  • Measurement Of Predetermined Time Intervals (AREA)
US3798464D 1971-09-11 1972-09-11 Electronic timer Expired - Lifetime US3798464A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL7112528A NL7112528A (fr) 1971-09-11 1971-09-11

Publications (1)

Publication Number Publication Date
US3798464A true US3798464A (en) 1974-03-19

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Application Number Title Priority Date Filing Date
US3798464D Expired - Lifetime US3798464A (en) 1971-09-11 1972-09-11 Electronic timer

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US (1) US3798464A (fr)
JP (1) JPS4837669A (fr)
BE (1) BE788668A (fr)
CA (1) CA969645A (fr)
DE (1) DE2243630A1 (fr)
FR (1) FR2152841B1 (fr)
GB (1) GB1347187A (fr)
NL (1) NL7112528A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6249328B1 (en) 1997-09-10 2001-06-19 International Business Machines Corporation Liquid crystal display device having red, green, and blue fluorescent lamps having a particular phosphor composition or a double tube lamp
WO2014147626A1 (fr) * 2013-03-21 2014-09-25 Basson Yinon Interrupteur marche-arrêt

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4491828A (en) * 1978-10-16 1985-01-01 American District Telegraph Company Two-wire multi-zone alarm system
US4423410A (en) 1978-10-16 1983-12-27 American District Telegraph Company Two-wire multi-zone alarm system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2434157A (en) * 1948-01-06 heppeard
US2818532A (en) * 1955-11-01 1957-12-31 Rca Corp Single action timing circuit

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2434157A (en) * 1948-01-06 heppeard
US2818532A (en) * 1955-11-01 1957-12-31 Rca Corp Single action timing circuit

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6249328B1 (en) 1997-09-10 2001-06-19 International Business Machines Corporation Liquid crystal display device having red, green, and blue fluorescent lamps having a particular phosphor composition or a double tube lamp
WO2014147626A1 (fr) * 2013-03-21 2014-09-25 Basson Yinon Interrupteur marche-arrêt

Also Published As

Publication number Publication date
JPS4837669A (fr) 1973-06-02
BE788668A (fr) 1973-03-12
FR2152841A1 (fr) 1973-04-27
CA969645A (en) 1975-06-17
NL7112528A (fr) 1973-03-13
GB1347187A (en) 1974-02-27
FR2152841B1 (fr) 1976-05-21
DE2243630A1 (de) 1973-03-15

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