GB1592759A - Control circuits in orfor washing drying and the like machines or other apparatus - Google Patents

Description

(54) IMPROVEMENTS RELATING TO CONTROL CIRCUITS IN OR FOR WASHING, DRYING AND THE LIKE MACHINES OR OTHER APPARATUS (71) We, SERVIS DOMESTIC APPLIANCES LIMITED, a British Company of, Darlaston Road, Kings Hill, Wednesbury, West Midlands, WS10 7TE, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to control circuits for controlling the supply of current from a source to an apparatus including a plurality of functional devices energised for operation by such current.

To provide safety in operation of such apparatus it is important to ensure that the current is interrupted at least to those of the functional devices whereof continued operation, whether faulty or not, could produce a hazardous condition for the user or persons in proximity to the apparatus.

The principal obJect of the present invention is to provide a control circuit which meets this requirement.

According to the first aspect of the present invention there is provided a control circuit adapted to controll the supply of current from a source to an apparatus, the apparatus including a plurality of functional means required to be brought into operation in a sequence in accordance with at least one programme, said control circuit comprising a first switch means adapted to control the supply of current to at least some of said functional means, a control means (herein called the main control means) adapted to furnish signals to control operation of the functional means in accordance with said programme and to set the first switch means in a closed or open condition in accordance with demand requirements of said programme applicable to the apparatus, one or more monitoring means each for association with a respective one of said functional means and being adapted to generate respective fault signals when a fault condition occurs in the associated functional means and each associated ope-ratively with the main control means to cause the latter to generate an output (reset) signal in response to said fault signal to set the first switch means to an open condition, a second switch means connected through a back-up circuit means with said monitoring means, said second switch means being adapted to cause current to be interrupted to those of said functional means brought into operation in said programme, in response to the occurence of a fault condition and irrespective of response of the main control means to generation of said fault signal or signals.

Preferably, the first switch means comprises main switch contacts movable relatively between open and closed positions, and one of the functional means comprises electrically energised operating means for the main switch contacts, and which is controlled by the second switch means, the latter being responsive to either the generation of an output (reset) signal from the main control means, or to operation of the back-up circuit means in response to generation of a fault signal.

Preferably the back-up circuit means includes latch means for maintaining the second switch means in its open condition when it has been opened through generation of a fault signal and operation of the back-up circuit means. The latch means may continue to establish the first switch means in its open condition responded properly to the fault signal by generating an output (reset) signal itself to opening of the first switch means.

Thus, for current to continue to be supplied to one of said functional means after the associated monitoring means has responded to a fault condition, there would have to be a fault both in the main control means and in the back-up circuit means and associated second switch means.

The main control means may include an electronic programming means for determining the sequence, and/or duration, and/or mode of operation of said functional means and is settable to generate said output (reset) signal in response to generation of a fault signal by said monitoring means. The second switch means may comprise a semi-conductor switch which may be connected to control the supply of current to the electrically energised operating means for the main switch contacts and is itself responsive firstly to said output (reset) signal from the programming means and secondly through the back-up circuit means to said fault signal in a manner such that either of these two last said signals is operative to cause the semi-conductor switch to interrupt current supply to the electrically energised operating means for the main switch contacts.

The latch means previously mentioned may comprise a comparator means having first and seconnd input terminals, the former being connected to a sub-circuit providing an input changing in value in accordance with the incidence or not of a fault signal, and the latter being connected to a sub-circuit providing an input changing in value in accordance with a combination of the output (reset) signal and opening and closing of the first switch means, the output of the comparator means having one or the other of values which respectively maintain the second switch means closed or cause it to open, the latter value being maintained permanent upon incidence of a fault signal if an output (reset) signal is not generated by the main control means.

Whilst it would be within the scope of the invention for the monitoring means to take any of a number of forms, a preferred form of monitoring means comprises one or more monitoring circuits each of which includes a comparator means, such as an integrated circuit element connected in a comparator mode, and having at least two input terminals and an output terminal, one of the two input terminals being connected to a sub-circuit providing an input of reference level and the other terminal being connected to a sub-circuit containing a sensing means and providing an input which varies according to the parameter being sensed in the associated functional means, the output terminal providing an output the value of which changes from a normal value to a fault value according to whether the functional means associated with such monitoring circuit is operating normally or has become abnormal.

It will be understood that abnormality may in each case result from the development of an electrical fault such as an open circuit, short circuit, change of resistance or impedance value in components of the functional means such as electrical heaters, motor windings, and so forth. Alternatively, or in addition, the condition of abnormality may result when a particular functional means is operating otherwise than in accordance with the demand made to it from the programming means.

The invention may be applied generally, but one of its primary applications is as a control circuit forming part of a machine (hereinafter referred to as being a machine of the kind specified) for subjecting articles to treatment involving a liquid, each such machine comprising a body, including a chamber in which the articles can be placed for treatment, a plurality of functional means for performing respective functions during a treatment program and including means for effecting transfer of the liquid to or from the chamber so that it is brought into contact with, or removed from, the articles, and means for subjecting at least either the liquid or the articles to motion whilst both are in the chamber, said functional means being each electrically controlled or operated, said control circuit comprising a main control means for bringing the functional means into and out of operation in accordance with a programme, or in accordance with a selected one of a plurality of programmes to effect the particular treatment required.

In this respect the invention has been developed primarily in relation to a machine of the kind specified intended for washing clothes or other textile articles, and hereinafter referred to as a clothes washing machine of the kind specified. In this case the means for effecting transfer of liquid to and from the chamber includes valve means operative in supply ducts for the liquid, and includes pump means for draining the liquid from the chamber, whilst the means for subjecting either the liquid or the articles to motion may comprise either a drum defining the chamber and which is mounted for rotation by means of a drive motor, or may in some cases comprise paddle or impeller means for setting up flow patterns in the liquid whilst in the chamber. The washing machine may incorporate means for subjecting the clothes to tumble drying or not as may be desired.

It will be understood, however, that the invention may be applied to other forms of machine of the kind specified and in particular, but not exclusively, dish washing machines.

In the case of dish washing machines, the means for effecting transfer of liquid to and from the chamber may again be in the form of valve means operative in one or more inlet ducts for the liquid and may further comprise pump means for draining the liquid from the chamber, whilst the means for subjecting at least the liquid or the articles to motion may comprise a pump means operating in conjunction with a liquid delivery nozzle movable or otherwise for directing the liquid onto the articles to be washed and may further comprise means for rotating a drum, container or holder in which such articles are supported.

In any of these forms of machine of the kind specified the programming means, as mentioned, determines the sequence and/or duration, and/or mode of performance of different operations which collectively comprise the treatment and which are performed by the functional means already referred to.

It is of importance, irrespective of whether the programming means provides facilities for operating the machine in accordance with a single programme or with any one of a plurality of different programmes, that any malfunctioning of the functional means shall be detected and brought to the user's attention as early as possible after such malfunctioning has started to occur. This is partly because continuance of the malfunctioning may damage the machine and/or the articles undergoing treatment, and partly because, even if the malfunctioning is of a character such that it is not likely to cause or promote such damage, it is desirable that its occurence should be detected so that the article will not be assumed to have undergone a specified treatment for which the machine and programming means was designed without such treatment actually having been carried out.

From a second aspect of the invention resides in the provision of a machine of the kind specified wherein the control circuit includes in addition to the main control means, a first switch means for controlling the supply of current to each of the functional means brought into operation by the control means in accordance with a programme, said first switch means being settable in either an "open" state or a "closed" state respectively to establish or cut off supply current to the functional means, and two separate means for causing the first switch means to be set in its "open" state in response to a fault signal generated by operation of monitoring means monitoring proper operation of one or more of the functional means, one of which separate means comprises the main control means and the other of which comprises a back-up circuit means operating in this respect independently of the main control means.

The statistical risk that a fault or malfunctioning of both the main control means and the back-up circuit means will occur simultaneously is very substantially less than the risk of such an occurrence in either one of these means taken singly and this contributes materially to reduction of the risk that the machine will continue without detection to operate in an unsafe manner or otherwise than in accordance with the intended functioning of the functional means as determined by the programming means.

Any of the operational features hereinbefore described as applicable to the control circuit in accordance with the first aspect of the invention may be applied to the machine and control circuit thereof in accordance with the second aspect of the invention.

The invention will now be described, by way of example, with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic view in side elevation and in vertical cross-section of one embodiment of washing machine in accordance with the invention; Figure 2 is a schematic circuit diagram of the control circuit of such a washing machine including the current controlling means and monitoring circuits of the present invention as hereinbefore mentioned.

Figure 3 is a circuit diagram of one of the monitoring circuits associated with the heater; Figure 4 is a circuit diagram of a further monitoring circuit associated with the drive motor for the washing machine drum; Figure 5 is a circuit diagram of an alternative form of monitoring circuit to that shown in Figure 4; Figure 6 is a circuit diagram of the reset drive and latch circuit through which output signals from the circuits of Figures 3 and 4 or 5 are fed back to the logic circuit and directly to the second switch means to cause the first switch means to be opened and held open; Figure 7 is a monitoring circuit associated with a thermistor for sensing the water temperature in the machine.

The washing machine illustrated in Figure 1 comprises a body which includes a stationary washing chamber 1 which may be of generally cylindrical form containing a washing drum 2 rotatable about a horizontal axis, the washing chamber 1 being supported in any suitable manner, as, for example, by struts 3 from a base 3a.

A casing 4 encloses the washing chamber and drive means for the drum 2 which comprises a motor 12g which drives the drum spindle 2a through the intermediary of a belt and pulley drive 9. The spindle 2a and drum is supported by a suitable bearing 8 carried by the washing chamber.

The washing chamber has a plurality of inlets, for example a hot water inlet controlled by a solenoid valve 12c, a cold water inlet controlled by a solenoid valve 12d and a drain outlet, preferably communicating with a well or sump in the washing chamber and controlled by an electrically driven pump 12e. It will be understood that other electrically energised functional units, such as a comfort valve, are omitted from Figure 1 merely for simplicity.

The comfort valve controlls the flow of inlet water during a final rinse through a reservoir containing a rinsing agent. A door lock operated by an electrically energised device preferably of the thermo-valve type may be provided as illustrated in Figure 2 hereinafter referred to.

The sequence in which the functional units are brought into operation, and the length of time, and the number of times for which these are operated, during a complete washing cycle is determined by a logic circuit 10 which is mounted in the casing. The logic circuit 10 is settable in accordance with a number of different programmes by the program selector 11 with which is associated a number of manually operable switches such as S1 (Figure 1) for selecting the program desired.

The washing chamber 1 is sealed with respect to the casing by a flexible gasket or sealing ring 6 and the entrance to the washing chamber 1 and drum 2 is controlled by a door 5 which is hingedly connected to the casing 4 about a vertical axis 7 and is movable upon release of the door lock between the closed position shown and an open position. Associated with the door is a sealing ring or gasket Sa operative between the door and the casing.

Referring now to Figure 2, the electrically energised functional units are identified at 12a to 12g (certain of these having already been mentioned) and comprise respectively an electrically energised operating means 12a for operating or controlling operation of the door lock and switch contacts Sla, a solenoid operated comfort valve 12b, a solenoid operated hot water admission valve 12c, a solenoid operated cold water admission valve 12d, a pump motor 12e for driving a pump to drain the washing chamber, a heater 12f for heating the water washing chamber, and a drive motor 12g for rotating the drum 2.

The supply of current to these units, from a 240 volt alternating current mains supply connected to line and neutral terminals L and N, is controlled respectively by gate controlled semi-conductor devices 13b to 13g in accordance with output signals (D.C.

voltage levels) developed at the outlets of a logic circuit 10, these signals being fed to the gate electrodes of the devices 13b to 13g respectively through the intermediary of output circuit means (driver/isolator circuits) 14b to 14g. The last mentioned provides for operation of the drive motor 12g in three different modes, periodically reversing (for wash), unidirectional low speed (for distribution of washing load), and undirectional high speed (spin for centrifugal water extraction).

The particular outlets of the logic circuit 10 at which outlet signals are developed, and the sequence of such outlet signals, is determined by a programme selector 11 with which is associated a plurality of switches S1 to S10 pertaining to different programmes respectively, these switches being manually operable. The circuits 10 and 11 form the main control circuit or programming means previously referred to.

In the conductor 15a, which is common to the functional units, relatively movable switch contacts Sla (the first switch means hereinbefore referred to) of a main switch, which is operated by the operating means 12a including a delay means for holding the switch when closed in this position for a predetermined time. The operating means may comprise thermo-motive device such as an electrically heated bimetal strip, may comprise a solenoid with means for delaying drop off, are connected. These operating means 12a for the switch contacts includes biasing means, either spring, (e.g. the bimetal strip when not heated), gravitational, or combinations of the two for maintaining the switch contacts normally open. As mentioned the operating means 12a also serves, when energised, to operate or control operation of a door lock. The contacts Sla can be caused to open by opening a manually operable mains switch connected between the mains supply terminals and the terminals L and N. The door lock would then be opened only after a delay determined by the delay means of the operating means 12a.

The operating means 12a contains an energising element B1 (Figure 6) and the current supply to this, for operating Sla and operating or controlling the door lock, is controlled by a further switch (the second switch means as hereinbefore referred to) in the form of a solid state semi-conductor switch, namely triac Qla contained in driver circuit 13a. This triac is rendered conducting by an output (set) signal from terminal 10a of the logic circuit 10 upon selection of any programe by the programme selector 11, and the logic circuit 10 will continue to maintain B1 energised until either the programme is terminated in the normal way in the logic circuit 10, or a fault (reset) signal is applied along conductor 16 to the input (reset) terminal 10j of the logic circuit 10 to change the logic circuit to the reset condition.

This causes it to generate an output (reset) signal to be present at terminal 10a rendering triac Qla non-conducting. Further, a fault (reset) signal can also be delivered along the conductors 16 and 17 from a reset driver and latch circuit 19 of Figure 6 to driver isolator circuit 14a to switch off triac Qla (in 13a) irrespective of whether this switching off is or is not accomplished by a logic circuit 10.

Thus, the supply of current to each of the functional units 12b to 12g through conductors 15a, 15b is controlled firstly by the first main switch means Sla (common to all of them), secondly by the second switch means triac Qla (also common to all of them), and thirdly by the respective gate controlled current supply devices 13b to 13g (individual to units 12b to 12g respectively) and which may also comprise triacs.

Certain of the functional units have monitor circuits associated respectively with them, namely the heater 12f (associated monitor circuit 21) and the drive motor 12g (associated monitor circuit 22) to develop fault (reset) signals in the event of abnormal operating conditions occurring. Further, a temperature sensing circuit 24 is provided, the normal operation of which is to sense the temperature of the water in the drum, and to provide a temperature input signal along conductor 20, at terminal 10h, to the logic circuit. If such temperature signal corresponds to an unacceptably high water temperature then the logic circuit generates an output (reset) signal at terminal 10a effective to open the second switch means Qla. A monitor 23 is associated with the sensor of the temperature sensing circuit to simulate a high temperature signal in the event of the sensor becoming faulty, e.g. a thermistor which goes open circuit. The temperature sensing circuit 24 is thus to be considered as one of the functional units to be monitored. It will be understood that other functional units may, if desired, have associated monitor circuits which, when detecting an abnormal condition, generate an input (reset) signal fed to the logic circuit 10.

Referring now to Figure 3, the monitor circuit 21 shown therein monitors proper operation of the heater 12f. It comprises an integrated circuit unit IClf operating as a comparator and having two input terminals fl, f 2 and an output terminal f3. The output terminal provides the output from the circuit and is connected by way of conductor 29 (Figure 2) to the reset drive and latch circuit 19 (Figure 6). Terminal can have either a high voltage level or a low voltage level, the former resulting in delivery, from circuit 19, of a fault (reset) signal along conductors 16 and 17, and the latter representing the normal operative condition allowing the selected programme to continue.

Terminal 10f is connected to the logic circuit 10 and receives a "high" signal corresponding to heater demand as part of the programme and a "low" signal when no heater function is demanded.

The monitor circuit includes a level detector switch S1f forming a sensing means. This switch is a change-over switch and is moved into the position shown, i.e. movable contact in the up position, when the water level is low i.e. below the predetermined low level, and changes over to the movable contact down position when the water level is normal i.e. at or above the predetermined low level. This monitor circuit operates in the following manner.

The output at terminal of the comparator is dependent upon the relative magnitudes of the currents through R5 on the one hand (positive input). Output at is low, i.e.

representing a normal operative condition, when the current at terminal f2 predominates.

Output at goes high, representing an abnormal condition, when current at fl predominates.

When no heater function is demanded, by reason of the settings of circuits 10 and 11, through R7, R8 current at 2 is determined by the current through R6. If triac Q1f is turned off, resistor R1 at its upper end is virtually at 240 volts AC derived from conductor 15a. The network R1, R2, D1, C1, produces a direct voltage at the junction of D1 with C1 of approximately + 10 volts. In this state the current representing negative input tof2 exceeds the current representing positive input to fl and output at is low (normal).

When triac If is turned on, the voltage at the junction of D1, C1, falls to approximately - 1 volts, current representing positive input to fl predominates and the comparator output terminal goes high generating a fault (reset) signal.

If, however, under the last described conditions, a heater demand function were present at terminal 10f, by reason of the settings of circuits 10 and 11, the input to 12 through R6 would be over-ridden and would exceed that occurring at fl maintaining '3 in the low (normal) condition.

In the case where a heater demand function exists, but the movable contact of the low level switch Sfl is in its up position (as shown) corresponding to low water level, the base of transistor TR1 would be positively biased with respect to its emitter, TR1 would be turned on, and cancel the effect of the heater demand, thereby restoring'3 to the high fault signal (reset) level.

The following table summarises these various operative conditions.

Truth Table Heater Heater L.L. Comparator Triac Qlf Demand Switch Slf Output at f3 No heater, OFF OFF X LOW (normal) no demand Heater on + no ON OFF X HIGH (fault heater demand reset) Heater on + ON ON O/C LOW (normal) heater demand Heater on + low ON X S/C HIGH (fault water level reset) X = Immaterial.

Referring now to Figure 4, this shows in detail one form of monitor circuit 22 for monitoring proper operation of the drive motor relative to spin demand and water level in the drum. The operation of the circuit is in principle similar to that of Figure 3. The low level water switch previously mentioned has additional contacts Slg in this monitor circuit.

The spin demand signal calling for motor drive is furnished at terminal 10g from the logic circuit 10 and fed to circuit 22 from the output side of driver/isolator 14g the device 13g, and along conductor 25.

Output at the terminal g3 of comparator circuit IClg goes high for abnormal conditions generating a fault (reset) signal, and is low for normal operative conditions. The state of terminal g3 is dependent on the relative values of currents through R13 to terminal gl representing positive input on the one hand and through R14, R15, R16 to terminal g2 representing negative input on the other hand.

If triac Qlg is turned off, the junction at diode D2 and capacitor C2 is, as before, approximately 10 volts and in this state the input current to g2 exceeds input current to gl and output at g3 is low.

When the conduction angle of Qlg is greater than 100" (corresponding to high speed spin) the D2, C2 junction falls below zero volts and comparator output at g3 goes high generating a fault (reset) signal. If, however, spin demand terminal 10g is high under these conditions then current through R15 and R16 overrides (or augments) current at R14, thereby inhibiting the fault (reset) signal.

If however, the low level switch Slg is in its movable contact down position indicating the presence of water above the predetermined level (and which would present an excessive load on the motor endeavouring to execute a spin), transistor TR2 conducts cancelling the effect of the spin demand terminal 10g and causing g3 to go high and produce a fault (reset) signal.

The following table summarises these operational conditions.

Truth Table Motor Triac Spin L.L Comparator conduction Demand Switch output angle Motor spin plus Less than X X LOW no demand 100" Motor spin plus Greater than OFF X HIGH fault no demand 100" (reset) Motor spin plus Greater than ON Up LOW demand 100" Motor spin plus Greater than X Down HIGH fault water high level 100" (reset) X = Immaterial Figure 5 shows an alternative form of circuit for use as a monitor circuit 22. In this components corresponding to those of Figure 4 bear corresponding references. The input to terminal gl is fed through R2, D2 and R5 and is derived from a tacho-generator 33 driven from the motor 12g and providing an alternating voltage of between 0 and 10 (positive) depending upon motor speed; 10 volts output corresponds to motor operating at high (spin) speed. The terminal g2 is tied to the zero volt line 15b through R7. The manner of operation is as follows.

A fault (reset) signal is generated at g3 (high) if the input to gl from the tacho-generator via R2, D2 and R5 exceeds the reference input to g2 via R7. C2 smooths the ripple from the half wave tacho-generator signal. R2 is chosen so that the fault condition occurs when the drum speed exceeds a predetermined value selected in the range approximately 150 - 200 r.p.m. If a spin demand is present on conductor 25 the input at g2 via R1 and R6 overrides any input at gl from the tacho-generator. If, however, there is water above the low level in the drum, the level switch changes over to the movable contact down position and cancels the spin demand via diode D1, generating a fault (reset) signal at g3.

The R1, C1 time constant allows the spin demand to rise fast enough to avoid a spurious fault dete output at terminal j3 of IClj goes low, and when this ratio is below R38/R36 the output at g3 remains high.

Conductor 20 is connected to the TEMP INPUT terminal 10h of logic circuit 10 and the latter incorporates a variable schmitt circuit which is set to operate at a predetermined input signal value to terminate the heating cycle, i.e. generate a "no demand" condition at logic circuit output terminal 10f.

The ratio R38/R36 is selected to cause g3 to go low when the thermistor senses a temperature of 95"C when all component tolerances are such as to tend to increase the voltage level at terminal g2.

In respect of this function the circuit acts as a temperature measuring circuit.

The monitor circuit function is to detect the possible fault of an open circuit thermistor Vc (or a thermistor of which the resistance/temperature characteristic is outside the "high" tolerance value).

If Vc becomes open circuit, the base of TR7 is raised to the zero volt level, terminal j2 rises and simulates a temperature measurement of higher than 95"C, terminating heater demand via the logic circuit 10.

Referring now to Figure 6, this shows one form of reset driver and latch circuit suitable for employment as the circuit 19, Figure 2. The essential function is to generate a fault signal to the input (reset) terminal 10j of logic circuit 10 in the event of monitor circuits 21 and 22 generating a fault (reset) signal. A further function is to switch off the second switch means Qla via conductors 16, 17, and driver isolator 14a, and to latch, i.e. prevent Qla being turned on if the logic circuit has not internally generated an output (reset) signal at terminal 10a, in response to incidence of a fault (input) signal at terminal 10j.

Referring to the circuit of Figure 6 in detail, the integrated circuit comparator element IClh is connected to the zero volt line 15b through resistor R20 to provide a reference at input terminal hl representing negative input. This holds the output terminal h3 to a low value when there is no input at terminal h2 (representing positive input) from the monitor circuits 21 and 22 via conductors 29, 30 and resistors R23, R24, connected respectively thereto. When a fault (reset) signal is incident on either of conductors 29 and 30 the comparator circuit output terminal h3 goes high and latches in this condition through the feed-back path R25b, R25a. The high fault signal at h3 is applied through diode D5 via conductor 16 to the CANCEL (reset) input terminal 10j of the logic circuit 10. The high fault signal from h3 is also applied through R29 and transistor TR5 to turn off conducting transistor TR6 and hence turn off triac Qla as already mentioned.

The main switch Sla is preferably operatively connected with a door lock mechanism which serves to hold the door 5 of the machine in its closed position when the switch Sla is closed and the door lock is in its operated position.

This may be done by mechanical connection between the door lock mechanism and the switch contacts Sla, e.g. by using the operating means 12a to operate both Sla and either move the door lock to its operated position or to establish maintenance of the door lock in its operated position when it has been operated in some other manner e.g. by closing the door manually.

If the logic circuit is functioning normally, the door lock demand (which is also demand for closure of switch Sla) and which is provided by an output (set) signal at terminal 10a is turned off due to cancellation of the programme on incidence of the fault (reset) signal at input (reset) terminal 10j via conductor 16. Transistor TR4 which was held turned on by door lock demand signal applied to its base, then turns off, and allows a further current input through R26 and R22 to be applied to input terminal hl.

The delay means included as mentioned in the operating means 12a then times out, the door lock is opened or released for opening, Sla opens, and a mains detector circuit R17, R18, D3, and D4 on the dead side of Sla undergoes a change of output at the junction D3, D4, from a positive voltage value to approximately zero volts and turns transistor TR3 on.

The combined current input to the terminal hl (representing negative input) now exceeds the current input terminal h2 (representing positive input), and output terminal h3 reverts to its low level corresponding to "normal" conditions.

The current input through TR3, R20 and R21 to hl always overrides current input through R23 and R24 to h2 when the output terminal h3 of comparator ICIh is low (and ICIh has not latched via R25a, 25b) and if no programme is selected the additional input to hl through R26 and R22 guarantees maintenance of a low output at the output terminal h3.

In the event of a failure of the logic circuit 10 to turn off the output (set) signal at terminal 10a, i.e. demand for operating means 12a is still generate internally and appears at 10a in response to a fault (reset) signal on line 16, transistor TR4 continues to conduct, inhibiting current flow through R22 to terminal hl. When the operating means for Sla and the door lock times out, TR3 turns on as above described. However, the absence of current via R22 prevents current to hl predominating over that applied at h2 and hence prevents comparator IClh from being reset. The circuit including TR5 and TR6 acting as a driver for the operating means 12a for the switch Sla and door lock remains inhibited (i.e. TR5 on and TR6 off) resulting in a permanently safe state being maintained so long as logic circuit fails to generate an output (reset) signal at 10a. This inhibited condition can be removed only by switching off the main 240 volt supply from conductor 15a, 15b.

The following table summarises the above described operations.

Truth table Condition Heater Motor Door Door Comp.ICIh output output Lock Lock Output Mains Demand No programme ON ON OFF OFF LOW selected Waiting for Programme door lock selected but ON ON OFF ON LOW door lock off Programme selected but OFF OFF ON ON LOW no fault Heater ON OFF ON ON HIGH fault (fault) Motor OFF ON ON ON HIGH fault (fault) After Door lock ON ON OFF ON HIGH fault de-energised (fault) but logic circuit not reset.

WHAT WE CLAIM IS: 1. A control circuit adapted to control the supply of current from a source to an apparatus, the apparatus including a plurality of functional means required to be brought into operation in a sequence in accordance with at least one programme, said control circuit comprising a first switch means adapted to control the supply of current to at least some of said functional means, a control means (herein called-the main control means) adapted to furnish signals to control operation of the functional means in accordance with said programme and to set the first switch means in a closed or open condition in accordance with demand requirements of said programme applicable to the apparatus, one or more monitoring means each for association with a respective one of said functional means and being generated to generate respective fault signals when a fault condition occurs in the associated functional means and each associated operatively with the main control means to cause the latter to generate an output (reset) signal in response to said fault signal to set the first switch means to an open condition, a second switch means connected through a back-up circuit means with said monitoring means, said second switch means being adapted to cause current to be interrupted to those of said functional means brought into operation in said programme, in response to the occurrence of a fault condition and irrespective of response of the main control means to generation of said fault signal or signals.

2. A control circuit according to Claim 1 wherein the first switch means comprises main switch contacts movable relatively between open and closed positions, and one of the functional means comprises electrically energised operating means for the main switch contacts and which is controlled by the second switch means, the latter being responsive to either the generation of an output (reset) signal from the main control means, or to operation of the back-up circuit means in response to generation of a fault signal.

3. A control circuit according to Claim 2 further including latch means for maintaining

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. comparator IClh from being reset. The circuit including TR5 and TR6 acting as a driver for the operating means 12a for the switch Sla and door lock remains inhibited (i.e. TR5 on and TR6 off) resulting in a permanently safe state being maintained so long as logic circuit fails to generate an output (reset) signal at 10a. This inhibited condition can be removed only by switching off the main 240 volt supply from conductor 15a, 15b. The following table summarises the above described operations. Truth table Condition Heater Motor Door Door Comp.ICIh output output Lock Lock Output Mains Demand No programme ON ON OFF OFF LOW selected Waiting for Programme door lock selected but ON ON OFF ON LOW door lock off Programme selected but OFF OFF ON ON LOW no fault Heater ON OFF ON ON HIGH fault (fault) Motor OFF ON ON ON HIGH fault (fault) After Door lock ON ON OFF ON HIGH fault de-energised (fault) but logic circuit not reset. WHAT WE CLAIM IS:

1. A control circuit adapted to control the supply of current from a source to an apparatus, the apparatus including a plurality of functional means required to be brought into operation in a sequence in accordance with at least one programme, said control circuit comprising a first switch means adapted to control the supply of current to at least some of said functional means, a control means (herein called-the main control means) adapted to furnish signals to control operation of the functional means in accordance with said programme and to set the first switch means in a closed or open condition in accordance with demand requirements of said programme applicable to the apparatus, one or more monitoring means each for association with a respective one of said functional means and being generated to generate respective fault signals when a fault condition occurs in the associated functional means and each associated operatively with the main control means to cause the latter to generate an output (reset) signal in response to said fault signal to set the first switch means to an open condition, a second switch means connected through a back-up circuit means with said monitoring means, said second switch means being adapted to cause current to be interrupted to those of said functional means brought into operation in said programme, in response to the occurrence of a fault condition and irrespective of response of the main control means to generation of said fault signal or signals.

2. A control circuit according to Claim 1 wherein the first switch means comprises main switch contacts movable relatively between open and closed positions, and one of the functional means comprises electrically energised operating means for the main switch contacts and which is controlled by the second switch means, the latter being responsive to either the generation of an output (reset) signal from the main control means, or to operation of the back-up circuit means in response to generation of a fault signal.

3. A control circuit according to Claim 2 further including latch means for maintaining

the first switch means in its open condition when it has been opened through generation of a fault signal and operation of the back-up circuit means.

4. A control circuit according to any one of the preceding claims wherein the main control means includes an electronic programming means for determining the sequence, and/or duration, and/or mode of operation of said functional means and is settable to generate said output (reset) signal in response to generation of a fault signal by said monitoring means.

5. A control circuit according to Claim 4 wherein the second switch means comprises a semi-conductor switch which is connected to control the supply of current to the electrically energised operating means for the main switch contacts and is itself responsive firstly to said output (reset) signal from the programming means, and secondly through the back-up circuit means to said fault signal in a manner such that either of these two last said signals is operative to cause the semi-conductor switch to interrupt current supply to the electrically energised operating means for the main switch contacts.

6. A control circuit according to Claim 2 or any one of Claims 3 to 5 as appendant to Claim 2 wherein the latch means comprises a comparator means having first and second input terminals, the former being connected to a sub-circuit providing an input changing in value in accordance with the incidence or not of a fault signal, and the latter being connected to a sub-circuit providing an input changing in value in accordance with a combination of the output (reset) signal and opening and closing of the first switch means, the output of the comparator means having one or the other of values which respectively maintain the second switch means closed or cause it to open, the latter value being maintained permanently upon incidence of a fault signal in the absence of an output (reset) signal.

7. A control circuit according to any one of the preceding claims wherein the monitoring means comprises monitoring circuits each of which includes a comparator means, and having at least two input terminals and an output terminal, one of the two input terminals being connected to a sub-circuit providing an input of reference level and the other terminal being connected to a sub-circuit containing a sensing means and providing an input which varies according to the parameter being sensed in the associated functional means, the output terminal providing an output the value of which changes from a normal value to a fault value according to whether the functional means associated with such monitoring circuit is operated normally or has become faulty.

8. A machine of the kind specified wherein the control circuit is as claimed in any one of claims 1 to 7.

9. A machine of the kind specified wherein the control circuit includes, in addition to the main control means, a first switch means for controlling the supply of current to each of the functional means brought into operation by the control means in accordance with a programme, said first switch means being settable in either an "open" state or a "closed" state respectively to establish or cut off current supply to the functional means, and two separate means for causing the first switch means to be set in its "open" state in response to a fault signal generated by operation of monitoring means monitoring proper operation of one or more of the functional means, one of which separate means comprises the main control means and the other of which comprises a back-up circuit means operating in this respect independently of the main control means.

10. A control circuit substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawings.

11. A control circuit according to Claim 10 including one or more monitoring circuits substantially as hereinbefore described with reference to and as shown in any one or more of Figures 3, 4, 5 and 7 of the accompanying drawings.

12. A control circuit according to either of Claims 10 and 11 including a reset drive and latch circuits substantially as hereinbefore described with reference to and as shown in Figure 6 of the accompanying drawings.

13. A machine of the kind specified being a clothes washing machine having a control circuit as claimed in any one of Claims 10 to 12.