GB2160733A

GB2160733A - Monostable relay control

Info

Publication number: GB2160733A
Application number: GB08511792A
Authority: GB
Inventors: Erwin Potthof; Hans Graber; Tilmann Kruger
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1984-05-09
Filing date: 1985-05-09
Publication date: 1985-12-24
Also published as: DE3417102A1; GB2160733B; GB8511792D0; FR2564237A1

Abstract

The energy-saving control of a monostable relay (1) involves a first monostable circuit (7) feeding to the relay an attraction (pull up) impulse of defined, preferably supply-voltage-independent duration, which is adequate to switch the relay over. A second monostable circuit (10) driven by an oscillator (9) then feeds a train of holding impulses to the relay. The holding impulses are preferably varied in their energy content as a function of the supply voltage, in which respect the respective energy content ensures that the relay remains in the switched-over position. In addition, after expiry of specific timespans, additional attraction impulses may be generated to produce once more the correct switching state of the relay after disturbances or the like. <IMAGE>

Description

SPECIFICATION A method of controlling a relay and an arrangement for carrying out the method The present invention relates to a method of, and an arrangement for, controlling a monostable relay.

German Patent No. 28 09905 shows a circuit arrangement for holding a relay in which two separate sources of current are provided for the attaction (pull up) and the holding ofthe relay. The attraction of the relay is achieved by connection to the first source of current. The current flowing through th relay triggers a control signal which serparates or disconnects the relay from the first source of current and connects it to the second source of current. The second source of current is such that the power consumption of the relay is less than in the case of operation with the first source of current, i.e. the relay can still be held, but not attract again after release.In the event of disturbances in the voltage supply, which could lead to the (attracted) relay being released, by a regulator circuit, which senses the flow of current through the relay, the first source of current is switched at least partially in parallel with the second source of current, so that the flow of current through the relay does not fall below a predetermined minimum value.

The expenditure for such a circuit arrangement is relatively high, and more especially so since analogue regulating technology is used.

Furthermore, two sources of current which are basd on sources of voltage having different values are necessary for the operation of the aforedescribed relay. As a result of the partial connection of the first souce of current, in the event of supply voltage disturbances fairly high power losses can occur. Futhermore, it is necessary for the current to be sensed by the relay, which similarly leads to losses.

An object of the present invention is to provide a method of, and arrangement for, controlling a monostable relay which may alleviate the power consumptioin for the operation of the relay.

According to the present invention there is provided a method of controlling a monostable relay during the active phase, such that during attraction or pull-up of the relay a higher electrical power is supplied than during a holding phase, in which method a supply voltage is fed as an attraction or pull-up impulse to the relay during a time period which is predetermined by the electrical properties of the relay, and following said time period a timed supply voltage is fed as holding impulses to the relay.

Further according to the present invention there is provided an arrangement for carrying out the method according to the immediately preceding paragraph.

More especially, the relay may be such that it is operable only with a single current supply, i.e. with a single source of voltage.

Futhermore, the control of the relay, preferably also in the event of disturbances to the current supply, may be such that it is effected in a purely digital manner. Furthermore, an arrangement designed for carrying out the method may be easy to integrate.

This method has the particular advantage that it is not restricted to use of electromagnetically-driven relays, but it also allows control of other types of drive, such as for example in the case of piezoelectrical drives.

Furthermore, this method can be applied in a simple manner by means of an appropriatelyprogrammed microcomputer, in which respect the relay is advantageously controlled directly, or, in the event of inadequate output loading capacity of the microcomputer, by way of a controllable switch or by way of a driver or exciter stage.

Thus, the attraction impulse can be repeated in each case after a specific period of time or a predeterminable number of holding impulses. As a result of this measure the relay can be prevented from remaining in the released state for longer than for a maximum permissible timespan.

In the event of fluctuating supply voltage, in an advantageous manner the duration of the attraction impulse can be varied in such a way that within a specific fluctuation range a reliable attraction of the relay with seemingly minimum power consumption is made possible.

In a similar way, in the vent of fluctuating supply voltage the number or duration of the holding impulses can be varied. Thus, the power loss of the relay in the attracted (pulled up) state can seemingly be restricted to a minimum, without it leading, upon a decline of the supply voltage, immediately to a release of the relay.

An arrangement for carrying out the method is realisable in a simple manner with conventional electronic components. To generate the attraction impulse, in this respect for example a flank-triggered monoflop with a suitable time constant can be used as the timing member. Serving as holding impulse in this respect are preferably output impulses from a simple timing generation circuit. If a timing generation circuit having an output frequency which is dependent upon the voltage is used, which is given a flank-triggered monoflop with a suitable time constant, then the holding impulses are generated in a simple manner as impulses having a constant length and a variable repetition frequency.

An appropriate arrangement works in a particularly precise manner if counters with a subsequently-connected comparator stage are used as the timing members, in which respect the respective counter state upon response of the comparator stage corresponds to the duration of attraction of holding impulses, or respectively to the repetition duration of the attraction impulses.

Further advantages can be gathered from the drawings and from the description.

Embodiments of a method of, and an arrangement for, controlling a monostable relay in accordance with the present invention wili now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows several voltage/time diagrams to illustrate embodiments of the method in accordance with the invention; Figure 2 is a circuit diagram for the first embodiment of the arrangement for carrying out the method; and Figure 3 is a further circuit diagram for the second embodiment of the arrangement for carrying out the method.

Fig. 1 consists of four voltage/time diagrams a to d, and the horizontal time axis t is valid for all these diagrams.

Diagram a shows a voltage course (control voltage signal) for conventional control of a monostable direct-current relay which at the point of time t, is acted upon with a supply voltage U and thus the state of the relay is switched over.

Diagram b shows a voltage course for the control, in accordance with the present invention, of such a relay, which relay is also arranged to be switched over at the point in time t,.

To switch the state of the relay, the supply voltage U is fed as an attraction (pull up) impulse A to the relay as from the point in time t1 during a predetermined minimum time TA. The minimum time TA is governed by the electromechanical properties of the relay; electromechanical properties mean or relate to the attraction (pull up) or switching speed of the relay with the particular supply voltage U. The minimum time TA for the attraction impuls A lies, in the case of conventional relays, in the order of magnitude of between one and one hundred milliseconds.

It is, of course, possible to lengthen the attraction impulse A-for example for safety reasons beyond the minimum time TA.

At the end of the attraction impulse A at a point in time t2, the supply voltage U is applied to the relay in timed form as a holding impulse H with a period duration tH. The period duration tH is in turn dependent upon the electromechanical properties of the relay and lies, in the case of conventional relays, in the region below about twenty milliseconds (corresponds to a control frequency of about 50 Hz), preferably in the range between 10 milliseconds and 50 microseconds (corresponds to a control frequency of about 100 Hz up to 20 kHz).

The pulse/interval ratio of the holding impulses lies in the range from about 2:1 up to about 1:2, preferably at about 1:1 and is also a function of the respective electromechanical properties of the relay. The period duration tH of the holding impulse H is preferably so selected that it does not lead to resonance phenomena in parts of the relay.

Furthermore, diagram b shows that the relay can be acted upon, after a predeterminable number of holding impulses H, at a point in time t3 with a further attraction impulse A of length TA. Thi further impulse ends at the point in time t4 and serves for switching the relay once again when the relay has inadvertently been released as a result of electrical or mechanical disturbances. Through this preferred measure the relay may remain in the "false" switching state only for a restricted period of time limited by the number of the predetermined holding impulses H.

Shown in diagrams c and d are the voltage courses corresponding to two different methods for controlling relays which methods are, preferably, used when the supply voltage U is likely to fluctuate. With both of these voltage course it is assumed that the supply voltage U drops by an amount of about 20% during the control of the relay as compared with a regular supply voltage U, and then remains constant.

The two methods illustrated with reference to these voltage courses can, of course, be used with other kinds of fluctuation of the supply voltage U. The two examples in diagrams C and d have been selected for reasons of clarity of representation.

As may be gathered from diagrams C and d, a relay is acted upon with an attraction impulse 1 as from the point in time t,. The duration TA of this attraction impulse A is equal to the duration in diagram b, since the supply voltage U is here equal to the regular supply voltage Ur. The attraction impulse A ends at the point in time t2, then the supply voltage U is applied in timed form as holding impulse H with a period duraction tH. If, now, the actual supply voltage U drops to a value below the regular supply voltage U,, then the relay is acted upon with modified holding impulses H' with a period duration tH,.

In diagram c, now the period duration tH is equal to the period duration tH., i.e. the period duration is independent of the level of the supply voltage U; however, the pulse/interval ratio of the holding impulses H' is varied as a function of the level of the supply voltage U, namely in such a way that the pulse/interval ratio increases with decreasing supply voltage and vice versa, i.e. the duration TH, of the holding impulses H' becomes longer with decreasing supply voltage U and shorter with increasing supply voltage U.

In daigram d, the period duration tH is smaller than the period duration tH; the dura tion TH, of the holding impulses H' is, how ever, equal to the duration TH of the holding impulses H. This means that the number of the holding impulses acting on the relay rises with decreasing supply voltage U per unit of time, or vice versa.

Thus, in the two control methods described by way of example in diagrams C and d, either the pulse/interval ratio of the holding impulses H or respectively H' or else the frequency of the holding impulses H or respectively H' in the case of constant duration TH or respectively TH,, is in each case varied as a function of the supply voltage U. This variation is, preferably, carried out in such a way thath time integral over the holding impulses H, H' for a specific period of time T which is greater than the period duration tH or respectively tH. is to be approximately equal to or greater than U,.T/3, preferably U, . T/2, i.e.

the temporal mean value of the holding impulses H or respectively H' is to be in each case the same and constant over a specific period of time.

Furthermore, it can be gathered from diagram C that a renewed attraction impulse A' is fed to the relay-in turn at the point in time t3. This attraction impulse A' ends at the point in time t4, and has the duration TA,. Since, as described in the foregoing, the supply voltage U is lower than the regular supply voltage U,, the attraction impulse A' has a greater duration TAT than the original attraction impulse A.

The energy content (U . TA,) of the renewed attraction impulse A' is equal to the energy content (U,. TA) of the original attraction impulse A, i.e. a possibly released relay is, even with a low supply voltage U, in the appropriate circumstances to be able to attract (pull up). If, on the other hand, the supply voltage U is higher than the regular supply voltage U,, then the duration TA, of the attraction impulses A' can be shortened for the purpose of saving energy in the same way.

In diagram d representation of a further attraction impulse A' has been dispensed with. If here too the attraction impulses A' are designed to be dependent on the supply voltage U, for the duration TA, of the further attraction impulse A' similar results would emerge as in the case of the method in accordance with diagram c, since in the case of both examples the supply voltage U deviates in the same way from the regular supply voltage U,.

However, also a method may be used in which only the holding impulses H or respectively H' are varied as a function of the supply voltage U, whilst the duration TA of the attraction impulses A is from the very start so selected that the relay still reliably switches over even with the lowest permissible supply voltage U.

The further Figures show two circuit diagrams for the control of a relay in accordance with one of the above-described methods. The circuits are in this respect, preferably, so designed that they can be used in a simple way to replace a conventional monostable relay without electronic control.

Fig. 2 shows a particularly simple circuit arrangement in which the duration TA of the attraction impulse A is constant and independent of the voltage. The holding impulses H can-with use of appropriate components in the circuit arrangement cither be independent of voltage with respect to the duration TH and their period duration tH, or else be dependent upon the voltage with respect to their period duration tH in the case of constant duration TH (as in the method in accordance with diagram d).

In Fig. 2 a monostable relay 1 has one of its exciter connections 2 directly connected to a supply voltage input Eu. The other exciter connection 3 of the relay 1 is connected to a controllable switch 4, for example an appropriately dimensioned grounded-emitter transistor 5, and the relay 1 lies in the collector line of the transistor.

The controllable switch 4 is controlled by way of an OR-gate 6 with the output signals (A and H) of a timing member 7 for the generation of the attraction impulses A, for example by a flank-triggered (step-pulse triggered) monoflop and a holding-impulse generating circuit 8.

The timing member 7 is connected directly to the supply voltage input Eu and generates, upon the application of the supply voltage U, an attraction (pull up) impulse A with a fixed duration TA.

The holding-impulse generating circuit 8 consists of an oscillator 9 and a flank-tiggered monoflop 1 0. The oscillator 9 is connected to th suply voltage input Eu and generates timing impulses so long as the supply voltage U is applied. The monoflop 10 is controlled directly by the timing impulses generated by the oscillator 9, and generates, upon each timing impulse, a holding impulse H of a fixed duration TH. The frequency or respectively period duration tH of the holding impulses H is thus predetermined by the frequency of the oscillator 9, whist the duration TH of the holding impulss H is fixed by the delay duration of the monoflop 1 0.

If the oscillator is used at a fixed (indpendent of the supply voltage) frequency then the monoflop 10 is controlled bin a completely voltage-independent manner, i.e. the period duration tH and the duration TH of the holding impulses H are in each case constant and independent of fluctuations in the supply voltage U.

If, on the other hand, a voltage-controlled oscillator 9 with a suitable voltage/frequency characteristic curve is used, then the period duration tH or respectively tH of the holding impulses H or respectively H' becomes depen dent upon the level of the supply voltage U, as explained at the beginning of the description with regard to Fig. 2, whilst the duration TH or respectively THR determined by the monoflop 10, of the holding impulses H, H' remains constant.

The voltage/frequency characteristic curve of the oscillator 9 must in this respect so appear that the frequency decreases with rising supply voltage U in accordance with the electromechanical properties of the relay 1, i.e. less holding impulses H with constant duration TH per unit of the time are generated or vice versa.

Fig. 3 shows a circuit arrangement for controlling a monostable relay 11, in which a particularly precise adjustment of the duration TA,TH of the attraction impulses A and of the holding impulses H to the supply voltage is possible. Preferably flank-triggered logic elements are used for this circuit arrangement.

The relay 11-as in the case of Fig. 2 is applied with one of its exciter connections 1 2 directly to a supply voltage Eu. The other exciter connection 1 3 of the relay 11 is connected to a controllable switch 14, for example to an appropriately dimensioned grounded-emitter transistor 1 5 and the relay 11 lies in the transistor collector line.

The controllable switch 14 is controlled by way of an OR-gate 1 6 with the output signals (A and H) of a first timing member 1 7 for the generation of the attraction impulses A and with a holding-impulse generating circuit 1 8 for the generation of the holding impulses H.

The first timing member 1 7 consists of a first resettable counter 21, and a first ANDgate 23 is connected prior to the counting input 22 of counter 21. The outputs 24 of the counter 21 are connected to a first comparator 25, which, with a predetermined counter state, switches its output signal over from logic 0 to 1. Furthermore, connected subsequent to the first comparator 25 is a first inverter 26, the output 27 of which is connected firstly to the OR-gate 1 6 and secondly to an imput 28 of the first AND-gate 23.

The holding-impulse generating circuit 18 consists of a second resettable counter 31, and connected prior to the counting input 32 of counter 31 is a second AND-gate 33. The outputs 34 of the second counter 31 are connected to a second comparator 35, which, in the case of a predetermined state of the second counter 31, switches its output signal over from logic 0 to 1. Connected subsequent to the second comparator 35 is a second inverter 36, the output 37 of which is connected to the OR-gate 1 6.

Furthermore, a second timing member 1 9 is provided, which consists of a third resettable counter 41, and connected prior to the counting input 42 of counter 41 is a third AND-gate 43. An input 48 of the AND-gate 43 is acted upon with the (non-inverted) output signal of the first comparator 25 of the first timing member 17.

The outputs 44 of the third counter 41 are connected to a third comparator 45, which, as from a predetermined state of the third counter 41 switches its output signal over from logic 0 to 1. A reset input 49 of the third counter 41 as well as a reset input 29 of the first counter 21 is acted upon with this output signal.

The first and second timing members 17, 1 9 as well as the holding-impulse generating circuit 1 8 are controlled by a voltage-controlled oscillator 51 and by a timing oscillator 52 having a fixed frequency. For this, the two oscillators 51, 52 are connected directly to the supply voltage input Eu and thus begin to oscillate as soon as the supply voltage U is applied to the entire arrangement.

The timing oscillator 52 determines, through its fixed output frequency, both the period duration tH of the holding impulses H, (which is thus here constant and independent of the voltage) and the constant repetition frequency of the attraction impulses. The timing oscillator 52 therefore controls the holding-impulse generating circuit 1 8 by way of a reset input 39 of the second counter 31 and the second timing member 1 9 by way of a second imput 50 of the third AND-gate 43.

The oscillator 51, controlled by the supply voltage U, has an opposite voltage/frequency characteristic curve to that described in the case of Fig. 2, i.e. its timing frequency rises with the supply voltage U and vice versa. The oscillator 51 determines the duration TA or respectively TH both of the attraction impulses A and of the holding impuses H. For this purpose, the oscillator 51 controls the first timing member 1 7 by way of a second input 30 of the first AND-gate 23 and the holdingimpulse generating circuit 1 8 by way of a second inpulse input 40 of the second ANDgate 43.

The mean frequency generated by the voltage-controlled oscillator 51 must clearly exceed the fixed frequency generated by the timing oscillator 52, for example in the case of a fixed frequency of 200 Hz a mean frequency of 5 kHz is selected for the oscillator 51.

The operation of the arrangement in accordance with Fig. 3 will now be explained in more detail: As soon as a supply voltage U is applied to the supply voltage input Eu, the two oscillators 51, 52 begin to generate their respective timing frequencies. The first counter 21 of the first timing member 1 7 is set at zero and begins to count the timing frequency, which is dependent upon the supply voltage, of the oscillator 51, until a predetermined value is reached. At this value the first comparator 25 changes its output state from logic 0 to 1.

With this inverted output signal (logic 0) the input 28 of the first AND-gate 23 is controlled and thus the first counter 21 blocked. The duration of this counting procedure is now dependent upon the timing frequency of the voltage-controlled oscillator 51. In accordance with the above-described voltage/frequency characteristic curve of the oscillator 51, the timing frequency in the case of lower supply voltage U becomes less and the counting duration of the first counter 21 thus greater or vice versa. The thus obtained inverted output signal of the first comparator 25 then forms the attraction in pulse A which is dependent in its duration TA upon the supply voltage U.

At the same time, after the end of the counting procedure of the first counter 21 with the non-inverted output signal (logic 1) of the comparator 25 the first inputs 38, 48 of the second AND-gates 33,43 of the holding-impulse generating circuit 1 8 and of the second AND-gate 43 of the second timing member 1 9 are controlled. In this way the second counter 31 and the third counter 41 are freed and begin to count.

The fixed frequency generated by the timing oscillator 52 is applied to the second input 50 of the third AND-gate 43 in the second timing member 1 9. After release of the third counter 41, this counts the fixedfrequency timing impulses up to a counter state predetermined by the third comparator 45. Upon reaching this counter state, the third comparator 45 switches its output signal from logic 0 to 1. With this output signal the first counter 21 of the first timing member 1 7 as well as the third counter 41 are reset. In this way, in the first timing member 1 7 a renewed counting procedure is triggered, i.e.

the attraction impulse A is repeated. However, up until the end of the attraction impulse A-as described above 'hue third counter 41 is blocked. Since the third counter 41 is already reset, the second timing member 1 9 can, after the end of the attraction impulse A, begin a renewed counting period, i.e. the attraction impulse is in each case repeated after a predetermined time.

Simultaneously with the beginning of the counting period of the second timing member 19, also the second counter 31 of the holding-impulse generating circuit 1 8 is freed and counts the timing generated by the oscillator 51 which is controlled by the supply voltage.

As from a specific counter state of the second counter 31, the second comparator 35 switches its output signal from logic 0 to 1. This output signal is inverted in the second inverter 36 and then forms the holding impulse H which is dependent upon the supply voltage U. The duration TH of the holding impulse H is accordingly dependent upon the counting duration of the second counter 31 and thus upon the respective timing frequency of the supply-voltage-controlled oscillator 51. As emerges from the above-described voltage/ frequency characteristic curve of the oscillator 51, accordingly the duration TH of the holding impulses H is shortened with rising supply voltage U and vice versa. The period duration tH of the holding impulses H is determined by the timing frequency of the timing oscillator 52.In this respect, the timing oscillator 52 is connected to the reset input 39 of the second counter 31 and thus resets the counter 31 upon each timing impulse. The period duration tH of the holding impulses H is accordingly equal to the period duration of the timing generated by the timing oscillator 52, i.e. the period duration tH of the holding impulses H is independent of the supply voltage and constant.

After the reset procedure of the second counter 31. the supply-voltage-dependent timing of the oscillator 52 is counted afresh. This process is repeated until an attraction impulse A is triggered afresh by the second timing member 19.

The attraction impulses A generated by the first timing member 1 7 and the holding impulses H generated by the holding-impulse generating circuit 1 8 are brought together by way of the OR-gate 1 6 and act upon the controllable switch 14, which then switches the relay 11 in accordance with the method in accordance with the present invention onto the supply voltage U.

Also a purposefully programmed and appropriately wired up microcomputer may be used to control a monostable relay in accordance with the method of the invention. In similar manner to the circuit diagram in accordance with Fig. 3, for example an appropriately programmed microcomputer with a voltagecontrolled oscillator could be wired up and act with a single output on a controllable switch.

Then an internal system timing of the microcomputer can be used as the voltage-independent timing frequency.

Claims

1. A method of controlling a monostable relay during the active phase, such that during attraction of pull up of the relay a higher electrical power is supplied than during a holding phase, in which method a supply voltage is fed as an attraction or pull up impulse to the relay during a time period which is predetermined by the electrical properties of the relay, and following said time period a timed supply voltage is fed as holding impulses to the relay.

2. A method as claimed in Claim 1, in which after a predeterminable time or after a predeterminable number of holding impulses an attraction impulse is fed afresh to the relay.

3. A method as claimed in Claim 1 or 2, in which the duration of the attraction impulses is varied as a function of the level of the supply voltage.

4. A method as claimed in any one of Claims 1 to 3, in which the pulse/interval ratio of the holding impulses is varied as a function of the level of the supply voltage.

5. A method as claimed in Claims 1 to 3, in which the frequency of the holding impulses with constant duration of the holding impulses is varied as a function of the level of the supply voltage.

6. A method as claimed in Claim 4 or 5, in which the time integral over the holding impulses for a specific period of time is approximately equal to or greater than Ur . T/3 (preferably Ur . T/2) in which respect Ur is the regular supply voltage.

7. An arrangement for carrying out the method as claimed in any one of Claims 1 to 6.

8. An arrangement as claimed in Claim 7 in which the supply voltage is fed to the relay by way of a controllable switch, and in which the controllable switch is controlled by way of a first timing member and a holding-impulse generating circuit, and by way of the first timing member the duration of the attraction impulses are predetermined, and by way of the holding-impulse generating circuit the period duration of the holding impulses are predetermined.

9. An arrangement as claimed in Claim 8, in which a second timing member is provided through which the first timing member can be triggered afresh after a predetermined time and/or after a predetermined number of holding impulses.

10. An arrangement as claimed in Claim 8 or 9, in which the first timing member is controlled by the supply voltage in such a way that the duration of the attraction impulses is dependent upon the level of the supply voltage.

11. An arrangement as claimed in any one of Claims 8 to 10, in which the holdingimpulse generating circuit is controlled by the supply voltage in such a way that the duration or the period duration of the holding impulses is dependent upon the level of the supply voltage.

1 2. An arrangement as claimed in any one of Claims 8 to 10, in which a supplyvoltage-controlled oscillator and a supply-voltage-independent timing oscillator are provided, and the period duration of the holding impulses is determined by the supply-voltageindependent timing oscillator and the duration of the holding impulses is determined by the supply-voltage-controlled oscillator.

1 3. An arrangement as claimed in any one of Claims 8 to 12, in which provided as timing members for the holding-impulse generating circuit are counters, by means of which, in the case of a predeterminable counter state, control signals (e.g. attraction impulses A, A' holding impulses H, H') can be generated.

14. A method as claimed in Claim 1 and substantially as herein described with reference to Fig. 1 b, or Fig. 1 C, or Fig. 1 d of the accompanying drawings.

1 5. An arrangement for controlling a monostable relay substantially as herein described with reference to Fig. 2 or Fig. 3 of the accompanying drawings.