US3873893A - Fail-safe timing circuit - Google Patents

Fail-safe timing circuit Download PDF

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Publication number
US3873893A
US3873893A US446144A US44614474A US3873893A US 3873893 A US3873893 A US 3873893A US 446144 A US446144 A US 446144A US 44614474 A US44614474 A US 44614474A US 3873893 A US3873893 A US 3873893A
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United States
Prior art keywords
output
energy
energy storage
coupling
input condition
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US446144A
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English (en)
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Gianni Bianchini
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SIE FORNEY SpA A CORP OF ITALY
Ital Elettronica SpA
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Ital Elettronica SpA
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Assigned to SIE FORNEY S.P.A. reassignment SIE FORNEY S.P.A. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: S. I. E. SOCIETA ITALIANA ELETTRONICA S.P.A.
Assigned to FORNEY ENGINEERING COMPANY reassignment FORNEY ENGINEERING COMPANY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: SIE FORNEY S.P.A.
Assigned to SIE FORNEY S.P.A., A CORP. OF ITALY reassignment SIE FORNEY S.P.A., A CORP. OF ITALY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: FORNEY ENGINEERING COMPANY A CORP. OF TX
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/02—Details
    • H02H3/027—Details with automatic disconnection after a predetermined time

Definitions

  • ABSTRACT A timing circuit having an energy storage means which normally charges abruptly to a preset value and a circuit for regularly and intermittently discharging the energy storage means through an output circuit of high input impedance to provide an accurate and reliable timing interval of substantial length through the use of simple and yet reliable circuitry.
  • the identification of such danger situations occurs by specific criteria and with specific physical means which vary from case to case, and which lie outside the scope of the present description.
  • the identification is attributable to a logic type signal, which may consist, for example, in the closing or opening of an electric contact, or in switching a voltage signal between two pre-established levels.
  • the protection signal or command may, in turn, consist of a manipulation of some kind which, in general, amounts to the closing or opening of an electric contact, for example, as a result of the de-energization (or energization, as the case may be) of a relay.
  • One of the most delicate circuits is the delay circuit, or timer, which under normal conditions, after the arrival of the input signal, must prevent the output of the protection signal for a certain time, predetermined by calibration, while, as the predetermined time runs out, it must with utmost reliability cause the output of the protection signal, called end time" signal.
  • the present invention is characterized by providing a timing circuit which is well suitable for the control of long times, for example, several minutes, and generates an output signal with extremely high dependability and fail-safe reliability. This means that neither loss of insu' lation of a capacitor nor other dangerous conditions, especially all those deriving from a possible failure of any electronic component of the circuit, prevent in any way the output of the end time signal, or delay it beyond the pre-established maximum time.
  • energy storage means for example, a capacitor
  • means for modulating the power associated with the energy discharged during the time count for example, a transistor
  • means which amplify the power modulated during the time count for example, a transistor
  • Another object of the present invention is to provide a fail-safe electronic circuit adapted to command (control) delayed protections or interventions, especially with long and calibratable delays, useful in all those systems in which it is of capital importance that the inter vention to be delayed must in no way be prevented due to failures in the electronic circuit.
  • FIG.-I is a schematic diagram of a particularly simple device embodying the principles of the instant invention.
  • FIG. 2 is a schematic diagram showing a preferred realization of the timer according to the invention.
  • FIG. 3 shows waveforms which illustrate the operation of the device of FIG. 2.
  • FIG. 4 is a schematic diagram of another example of a preferred embodiment of the timer according to the invention.
  • FIGS. 5a5c show waveforms which illustrate the operation of the device of FIG. 4.
  • FIG. I shows a particularly simple form of the invention which may be described as follows:
  • the command at the input, to initiate the time count, is constituted by the actuation of the pushbutton (or release) P, provided with the contacts I1 and I2
  • the control circuit gives an end time signal by opening the contact Ul of the relay U, a certain time To after it receives said command.
  • the power supply of the circuit consists of two different sources of direct current, so that two voltage levels are available, one positive +V,, and one negative V,,
  • reference voltage 1 referred to a common line taken as reference voltage 0.
  • contact I1 is normally biased (by means not shown) to remain closed, and
  • variable resistor R having slider arm R limits thedischarge current to a value sufficient to pilot the transistor Q1, but such as to prolong the discharge time of C1.
  • the transistor Q1 is thus triggered on and off by successive current pulses.
  • the impulse current amplified by O1 is supplied through the collector of O1 to the primary P of the transformer T1 which carries out a dynamic transfer of power to the secondary S. Energization of relay U closes its contact U1.
  • the relay U remains energized as long as the capacitor C1 is not discharged below a certain value, which depends on the parameters of the components of the circuit.
  • the base of Q1 no longer receives sufficient current to allow the current operation of the circuits downstream, and the relay de-energizes reliably, causing the contact Ul to reopen, and hence giving the end time signal.
  • the time To during which the closing of the contact Ul is delayed can be calibrated by varying the value of R, and the circuit is able to control it with absolute failure-proof reliability. That is, there is no electronic component in the circuit which, by breaking down, could keep the relay U energized beyond the time To. Therefore, the circuit is particularly useful for controlling in a reliable manner the delay time of a protection intervention, causing the protection to be brought about by the opening of the contact U1.
  • the controlled time To can be varied, in a manner not shown in FIG. 1, by varying the maximum quantity of energy charged in the capacitor C], for example, by properly calibrating the value of the voltage +VA.
  • contacts I1 and Y1 stated above can be replaced by electronic switches, that is for example, transistors which alternate between the conducting state and non-conducting state, and the respective command criteria depend on the function demanded of the device.
  • FIG. 2 One preferred embodiment of the invention, for example, is the device illustrated in FIG. 2, the operation of which is diagrammatically represented. by means of the waveforms of FIG. 3 in which 0 denotes the contact open position and l indicates the contact closed" position.
  • the transistors Q2 and Q3 (in place, respectively, of the contacts 11 and Y] of FIG. 1), are controlled by an external signal Y always present, of rectangular wave shape, of a frequency equal to l KHz, whose amplitude lies in the range from 0 to 12V, which transistors act in phase opposition so that one is turned off while the other is conducting and vice versa.
  • Y always present, of rectangular wave shape, of a frequency equal to l KHz, whose amplitude lies in the range from 0 to 12V, which transistors act in phase opposition so that one is turned off while the other is conducting and vice versa.
  • the contact .I is normally maintained open, corresponding to absent input signal.
  • Q2 When Q2 conducts, it charges the capacitor 8 across the diode 9 to the voltage of about 6V. In this phase both transistors Q3 and Q4 are non conducting.
  • Q3 limits the current to a nearly constant value, dependent upon the calibration value of the variable resistor 7, and upon the voltage present across the terminals of resistor 3.
  • the capacitor 8 discharges into the base-emitter circuit of the transistor Q4 with constant (direct) current limited by Q3, so as to obtain a longer and more regular process of discharge.
  • Q4 alternates between conduction and nonconduction at the same frequency rate of the external signal Y equal to l KHz.
  • the primary P of the coupling transformer T is supplied with pulsating voltage.
  • a pulsating voltage is induced also, which is rectified by'the diode 13 and filtered by the capacitor 14, to serve to maintain the relay R energized.
  • the contact R1 is open, and the output signal across termi nals K is also absent.
  • transistor O2 when a signal is introduced at the input closing the contact ,1, transistor O2 is rendered nonconductive due to short-circuit placed across the baseemitter circuit of Q2 by closure of contact I preventing capacitor 8 'from recharging.
  • the transistor 03 continues to supply current pulses to the base of Q4 and to the circuits downstream, at the expense of the energy charged in the capacitor 8.
  • capacitor 8 When capacitor 8 is fully discharged, current can no longer flow in the output circuits, and after a time To preestablished by calibration, the relay R is deenergized, closing the contact R1 and supplying at the output the protection signal or command K; What has been described occurs when the signal I remains present at the input for a time T1 T (cf. the left part of G..- 3), Fo exampl withth u e Qf capacitor 8 of 300 ,uF a time interval To equal to three rain'utes'e'ai" be obtained. When the signal I disappears (i.e. when .I
  • FIG. 4 Another preferred embodiment of the invention, useful, for example, in self-controlled protection systems, is shown in FIG. 4, the normal operation of which is diagrammatically represented by means of the waveforms of FIGS. Sa-Sc.
  • closure on contact A represents a high level (+15V) ofa logic input signal
  • closure on contact B represents a low level (V) thereof
  • the 0 is indicated the contact R1 of the output relay R is in open position and by l is indicated the same contact in closed position.
  • the device illustrated in FIG. 4 serves to control that the logic signal X at the input carries out continuously a cycle of alternations between level A and level B.
  • the device illustrated is especially useful when TA is much greater than TB.
  • the circuit according to FIG. 4 is supplied with two continuous voltages, of opposite polarity, that is, +l5 ⁇ and -l5V, with one pole in common (OV).
  • the output relay R can remain energized across the diode 12a, since the capacitor 15 has previously been charged, as will be seen below, and at any rate it discharges, reliably supplying the output signal Z, at the end of the discharge time TB, determined by the capacitance of the capacitor 15 and by the charac-' teristic parameters of the relay R.
  • the input X switches to the level A 15 V, transistor O5 is turned off, the transistor Q6, operating alternately as circuit breaker and as current limiter by effect ofthe rectangular wave signal W ofa frequency equal to l KHz, which is always present, allows the capacitor 6 to discharge constant current pulses across the base of transistor Q7, which then switches continuously.
  • the transformer T supplied with pulsating voltage across transistor Q8, supplies the necessary power to energize the relay R across the diode l1 and further across the resistor 13 progressively charges the capaci- 6 tor 15, making it ready for the next discharge phase, as described hereinabove.
  • the capacitor 14 has much smaller capacitance than capacitor 15, and serves only to filter the voltage rectified by the diode 11.
  • the relay R can remain energized, in this phase, for the maximum time TA.
  • That time is determined by: the capacitance of the capacitor 6; the mean discharge current, limited by Q6, and the particular waveform of the signal W.
  • the possible losses in the dielectric of the capacitor 6 causes a reduction of the time TA, that is, they too act in the sense of safety.
  • Means responsive to a predetermined input condition for obtaining a delayed output signal only when said input condition persists of over the entire first delay period comprising:
  • output means having first quiescent and second active operating states
  • transfer means coupling said amplifier means to said output means
  • charging means normally coupling said energy storage means to said energy source and responsive to said input condition to decouple said energy storage means from said energy source;
  • discharge control means responsive to said input condition for coupling said energy storage means to said amplifying means in a repetitive alternating fashion
  • said transfer means comprising means for coupling only said alternating components of the output of said amplifier means to said output means;
  • said output means being operated in its active state upon occurrence of said input condition and being moved to its quiescent state only if said input condition persists after said energy storage means is fully discharged.
  • discharge con- 5 trol means comprises a vibratory relay for coupling said capacitor to said amplifier means in pulsating fashion.
  • the device of claim 3 further comprising adjustable current limiting means coupled to said relay for adjustably controlling the discharge rate of said capacitor.
  • said transfer means comprises a transformer having input and output windings respectively. coupled to said amplifying means and said output means.
  • said charging means comprises first switch means for coupling said energy source to said capacitor only during the absence of said input condition and second switch means for coupling said energy source to said vibratory relay only during the presence of said input condition.
  • said charging means comprises a first transistor for coupling said energy storage means only when said input condition is absent.
  • said discharge control means comprises a transistor coupled to said energy storage means and means coupled to the input of said transistor for operating said transistor in a pulsating fashion between its conductive and non-conductive state to thereby cause the energy stored therein to be discharged into said amplifying means in a pulsating fashion.
  • said amplifying means has a high input impedance to cause the energy stored in said energy storage means to be discharged at a low rate.
  • the device of claim 1 further comprising filter means coupled between said transfer means and said output means.
  • Means responsive to a predetermined input condition for obtaining a delayed output signal only when said input condition persists of over the entire first delay period comprising:
  • output means having first quiescent and second active operating states
  • charging means normally coupling said energy storage means to said energy source and responsive to said input condition to decouple said energy storage means from said energy source;
  • discharge control means responsive to said input condition for coupling said energy storage means to said transfer means in an alternating fashion
  • said transfer means comprising means for coupling said alternating components of the output of said amplifier means to said output means;
  • An electronic timing device which, in response to an input signal, supplies with failureproof reliability a delayed output signal, utilizable, for example, for interventions of protection, characterized by the fact that it comprises: I at least one source of energy; an energy storage device (for example, a capacitor 8 in FIG. 2, 6 in FIG. 4);
  • means for filtering the output of said amplifying means means coupling said amplifying means to said filtering means whereby only the alternate components produced by themodulation are coupled to said filtering means;
  • output means coupled to said filtering means and which, in its rest condition, that is-without any external energy supplied thereto, securely assumes a stable state unequivocally recognizable as end time signal, and which utilizes said filteredpower made available during the time count to maintain said output means in a state opposite said rest state indicating that the'end time signal has not yet occurred.
  • the device of claim 1 wherein the time count may be adjusted by varying at least one parameter which characterizes the modulation of power associated to the discharge of the stored energy 15.
  • the device of claim 1 further comprising second energy storage means coupled across said output means for storing energy transferred thereto by said transfer means to maintain said output means in the ac-

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  • Emergency Protection Circuit Devices (AREA)
  • Measurement Of Unknown Time Intervals (AREA)
  • Ignition Installations For Internal Combustion Engines (AREA)
  • Relay Circuits (AREA)
  • Electronic Switches (AREA)
US446144A 1973-05-30 1974-02-27 Fail-safe timing circuit Expired - Lifetime US3873893A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
IT24809/73A IT988790B (it) 1973-05-30 1973-05-30 Cipcuito temporizzatore a prova di guasto

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US3873893A true US3873893A (en) 1975-03-25

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US446144A Expired - Lifetime US3873893A (en) 1973-05-30 1974-02-27 Fail-safe timing circuit

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US (1) US3873893A (fr)
BE (1) BE815646A (fr)
CA (1) CA1006965A (fr)
CH (1) CH585962A5 (fr)
DE (1) DE2426318A1 (fr)
ES (1) ES426742A1 (fr)
FR (1) FR2232115B1 (fr)
GB (1) GB1470851A (fr)
IT (1) IT988790B (fr)
NL (1) NL7406813A (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4044272A (en) * 1976-08-12 1977-08-23 Westinghouse Air Brake Company Fail-safe electronic time delay circuit
US4059845A (en) * 1976-05-14 1977-11-22 Westinghouse Air Brake Company Fail-safe time delay circuit
US4150306A (en) * 1976-07-16 1979-04-17 Siemens Aktiengesellschaft Blocking converter for flash equipment
US6719388B2 (en) * 2002-01-16 2004-04-13 Xerox Corporation Fail-safe circuit for dynamic smartpower integrated circuits

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0120347B1 (fr) * 1983-03-19 1989-09-20 Joh. Vaillant GmbH u. Co. Interrupteur horaire
EP3185390A1 (fr) * 2015-12-22 2017-06-28 ABB Schweiz AG Dispositif d'installation ayant un circuit de mesure de temps et un procédé de mesure de du temps écoulé entre un premier et un second événement au moyen d'un circuit de mesure de temps

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3496389A (en) * 1967-01-25 1970-02-17 Motorola Inc Timing circuit with field effect transistor
US3573555A (en) * 1969-02-10 1971-04-06 Ite Imperial Corp Time delay extender for static relays

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3496389A (en) * 1967-01-25 1970-02-17 Motorola Inc Timing circuit with field effect transistor
US3573555A (en) * 1969-02-10 1971-04-06 Ite Imperial Corp Time delay extender for static relays

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4059845A (en) * 1976-05-14 1977-11-22 Westinghouse Air Brake Company Fail-safe time delay circuit
US4150306A (en) * 1976-07-16 1979-04-17 Siemens Aktiengesellschaft Blocking converter for flash equipment
US4044272A (en) * 1976-08-12 1977-08-23 Westinghouse Air Brake Company Fail-safe electronic time delay circuit
US6719388B2 (en) * 2002-01-16 2004-04-13 Xerox Corporation Fail-safe circuit for dynamic smartpower integrated circuits

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Publication number Publication date
DE2426318A1 (de) 1974-12-19
CA1006965A (en) 1977-03-15
NL7406813A (fr) 1974-12-03
BE815646A (fr) 1974-09-16
FR2232115A1 (fr) 1974-12-27
CH585962A5 (fr) 1977-03-15
ES426742A1 (es) 1976-07-16
GB1470851A (en) 1977-04-21
IT988790B (it) 1975-04-30
FR2232115B1 (fr) 1980-08-14

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Owner name: SIE FORNEY S.P.A.

Free format text: CHANGE OF NAME;ASSIGNOR:S. I. E. SOCIETA ITALIANA ELETTRONICA S.P.A.;REEL/FRAME:003884/0146

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