CA1085495A - Control circuits in or for washing, drying and the like machines or other apparatus - Google Patents

Abstract

A B S T R A C T
A control circuit for controlling current supply to machines, such as a washing machine, the control circuit controlling the state of a first switch adapted to switch current to control means associated with the machine, functional means being monitored, such monitoring being operative to, should a fault occur, cause the first switch to open, and a back-up circuit, responsive to said monitors, including switching means operative to disconnect the current from the functional means if a fault occurs irrespective of the state of the first switch.

Description

This invention relates to control circuits for con-trolling the ~upply vr current from a source to an apparatus including a plurality of functional devices energi~ed for operation by such current.
To prov~de safety in operation o~ such apparatus it i9 important to ensure that the current be interrupted at least to those of the functional devices whereof continued operation, whether faulty or not, could produce a hazardou~ 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 for controlling the supply of current from a source to an apparatus which includes a plurality of functional means required to be brought into operation in a sequence in accordance with at least one predetermined programme, such circuit comprlsing:-a. a first switch means controlling the supply of current to at least some of said functional means, b. a main control means for furnishing signals to ~ control operation of said functional means in ; accordance with said programme and to set the first switch means in a closed or open position in accordance with demand requirements of said programme applicable to the apparatus~
c. at least one monitoring means each associated with a respective one of the functional means for , ~

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~5495 generating a fault si~lal in response to occurrence of a fault condition, d. means connecting the monitoring mean~ with the main control means to cause the latter to set the first switch means in an open condition in response to generation of said fault signal, e. a second switch means for controlling current to at least one of said functional means brought into operation in said programme, f. a back-up circuit means connecting the second switch means and the monitoring means, the second switch means being responsive to generation of said fault signal to cut off currentto said functional means to which current is controlled by said second switch means irrespective of response of the main control means to said fault signal.

Preferably, the first switch means comprises main switch contacts movable relatively between open and closed positions, and one of the functional means comprises electri-cally 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 ~V~9~i fault signal and operation of the back-up circuit means. The latch means may continue to estalblish the first switch means in its open condition responded properly to the fault ~lgnal 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 sald functional means after the associated monitoring means has responded to a fault condition, there would have to be a fault both in the maln control means and in the back-up circuit means and associated second switch means.
The main control means may include an electronic pro-gramming means for determining the sequence,and/or duration, and/or mode of operation of said functional means and i8 set_ table to generate said output (reqet) 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 itqelf responsive firstly to said output ~re-set) 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 second input terminals, the former being connected to a sub-clrcuit providing an input :

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., , changlng in value ln 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 com-bination 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 monitor means to take any of a number of form~, 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 monitor-ing circuit is operating normally or has become abnormal.

It will be understood that abnormality may in each ., .

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` ' ~, - 10~495 case result from the development of an electrical fault such a~ 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 on it from the programming means.

The invention may be applied generally, but one of is primary applications is to a control circuit for controlling machines (hereinafter referred to as being of the kind specifled) 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 programme and including means -for effecting tran~fer of the liquid to or from the chamber so that it i~ brought into contact with, or removed from, the articles, and mean~ 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 bringing the functional means into and out of operation in accordance;
with at least one, and preferably in accordance with a selected one, of a plurality of programmes to effect the particular treatment required.

i495 ~I:n this respect -the invent::iorl has been developed primarily in relat:ion to a machin~ of -the kind specified intended for washing clothes or other -tex-tile 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 in~ludes 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 .

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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 ar-ticles are supported.

In any of these f`orms 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 facilitiesfor operating the machine in accordance with a single programme or with any one of a plurality of different programmes, that any mal-functioning 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.

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i495 From a second aspect the invention re~ides in the provision in a machine of the kin,~ specified of a control circui.t including a first switch means controlling the supply of current to at least some of ~aid functional means, a main control mean~
for furnishing signals to control operation of said functlonal means in accordance with said programme and to set the first switch means in a closed or open position in accordance with demand requirements of the said programme, at leaRt one monitor-ing means each associated with the respeetive one of the function-al means ~or generating a fault signal in response to occurrence o~ a fault eondition, rneans conneeting the monitoring rneans with the main control means to eause the latter to set the first switch means in an open eondition in response to generation of said fault ~ignal, a seeond switeh means for controlling eurrent to at least one of said funetional means brought into operation in .~aid programme, a baek-up eircuit means eonneeting the seeond switeh means and the monitoring means, the seeond switeh means being responsive to generation of said fault signal to eut off eurrent to said funetional means to whieh eurrent is eontrolled by said seeond switch means irrespective of response of the main eontrol means to said fault signal.
The statistieal risk that a fault or malfunetioning of both the programming means and the baek-up eireuit means will oeeur simultaneously is very substantially less than the risk of sueh an oeeurrenee in either one of these means taken singly and this eontributes materially to reduetion of the risk that the maehine will eontinue without deteetion to operate in an unsafe manner or otherwise than in aeeordanee with the intended funetion-ing o~ the funetional means as determined by the programming means.

~0~5495 _ lC~ -Any of the optional feature~ hereinbefore de~cribed as applicable to the control circuit in accordance with the first aspect of the invention ma~ be applied to the machine and control circuit thereof in acccrdance with the ~econd aspect of the lnvention.

i 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 elevationand in vertical cross-~ection 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 i~ 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 ., ., .

~0~35d~95 ~.1 .

secon~ sw-itch means -to cause -the first switch mean.s to be opened and held open;

FIGURF 7 is a monitoring circui-t associated wi-th a therm:istor for sensing -the wa-ter -temperature in the machine.

The washing machine illus-trated in Figure 1 comprises a body which includes a stationary washing chamber l which may be of generally cylindrical form containing a washing drum 2 rotatable about a hori~ontal 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 12~ 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 .

10t~5495 as - comfort valve~ are omittccl from [~igure 1 merely for simplici-ty. The comfort valve con-trolls the flow o~ inlet water during a final rin;e -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 programme selector 11 with which is associated a number of manually operable switches such as Sl (Figure 1) for selecting the programme 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 5a operative between the door and the casing.

Referring now to Figure 2, the electrically energised 10~5495 functional unit~ are identified at 12a to 12~ (certain of these having already been mentioned) and comprise respectively an electrically energised operating means 12a for operating or controlling oper~tion of the door lock and sw~tch contacts Slà, 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 12~ 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 13~ 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 12~ in three different modes, periodically reversing (for wash)~ unidirectional low speed (for distribution of washing load), and unidirectional high speed (pin for centrifugal water extraction).

The particular outlets of the logic circuit 10 at which outlet signals are developed, and the sequence of such ., r s ~ , ~' ': :

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_ 14 -outlet signal~, ts determined by a programme selector 11 with which i~ associated a plurality of switches S1 to ~10 pertaining to differen-t programmes respectively, these switches being manually operable. The circuits 10 and 11 form the main control circ~1it or programming means previously referred to.

In the conductor 1~, which is common to the functional units, relatively movable switch contacts S1a ~the first qwitch 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 combina-tions 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~

~08~495 The operating mean~ 12a oontains an energising elernent Bl ¦Figure 6) and the current supply to this~ for operating Sla and operating or ca,ntrolling the door lock, i9 controlled by a further switch (the second 4witch means hereinbefore referred to) in the form of a solid state semi-conductor switch, namely triac Q1a contained in driver clrcuit 13a. This triac i~ rendered conducting ~y an output (set) signal from terminal 1Oa of the logic circuit 10 upon selec-tion of any programme by the programme selector 11~ and the logic circuit 10 will continue to maintain Bl 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 1~ to the input (reset) terminal 10i 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 lOa rendering triac Qla non-conducting.
~urther, a fault (reset) signal can also be delivered along the conductors 16 and 17 from a reset driver and latch circuit 19 of ~igure 5 to driver isolator circuit 14a to switch off triac Ql_ (in 13a) irrespective of whether this switching off is or i9 not accomplished by logic circuit 10.

Thus, the supply of current to each of the functional units 12b to 12~ 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 COTTOD to all of them)~ and thirdly by th: respective gate - ?

10~49~i 16.

controlled currellt supply devices 13b to 13~ (individual to units 12b to 12~ respectively) and w~ich may also comprise triacs.

Certain of the functional units have monitor circuits associated respectively with thcm, namely the heater l~f (associated moni-tor circuit 21) and the drive motor 12~
(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 lOh, to the logic circuit. If such temperature signal corresponds ~t, , to an unacceptably high water temperature then thelogic circuit generates an output (reset) signal at terminal lOa effective to open the second switch mQans 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 -thermis~r 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.

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! Referring now to Figure 3, the monitor circut 21 .
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~hown therein monitors proper operation of the heater 12f.
It comprises an integrate-1 circuit unit IC1f operating as a comparator and having two input terminals f1, f2 and an output terminal f3. The output terminal f3 provides the output from the circuit and is connected by way of conductor ~9 (Figure 2) to the reset drive and latch circuit 19 (Figure 6).
Terminal f3 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 repre~enting 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 Slf 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.

10~54~

The output at termi.nal f3 of` the comparator is dependent upon the relative magnitudes of the currents through R5 on the one hand (positive input)0 Output at f3 is low, i.e. representing a normal operative condition, when the current at terminal f2 predominates. Output at f3 goes high, representing an abnormal condition, when current at f1 predominates.

When no heater function is demanded, by reason of the settings of circuits 10 and 11, through R7, R8, current at f2 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, l D1, C1~ produces a direct voltage at the junction of D1 with j C1 of approximately + 10 volts. In this state the current representing negative input to f2 exceeds the current s representing positive input to f1 and output at f3 is low ` (normal)0 . . .

When triac Q1f is turned on, the voltage at the junction of D1, C1, falls to approximately - 1 volts, current representing positive input to f1 predominates and the comparator output terminal f3 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 ' .

0~5~95 to f2 through ~l6 would be over-ridden and would exceed that occurring at f1 maintaining f3 in the low (normal3 condition.

In the ca~e where a heater demand functlon exists, but the movable contact of the low level switch Sf1 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 f3 to the high fault signal (reset) level.

The following table summarises these various operati~e conditions.

Truth Table Heater Heater L.L. Comparator Triac Qlf Demand Switch Slf Output at f3 ... .

no demand OFF OFF X LOW (normal) . .
Heater on + no ON OFF X HIGH (fault h~ater demand reset) Heater on +
heater demand ON ON O/C LOW (normal) Heater on + low ON X S/C HIGH (fault water level reset) X = Immaterial.

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, o Referring now to Figur,e 4, thls show~ in detail one form of monitor circuit 22 for monitoring proper operation Or 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 S1~ in this monitor circuit. The spin demand signal calling for motor drive is furnished at terminal 70~ from the logic circuit 10 and fed to circuit 22 from the output side of driver/isolator 14~, the device 13~, and along conductor 25.

Output at the terminal ~3 of comparator circuit IC1~ goes high for abnormal conditions generating a fault (reset) signal, and is low for normal operative conditions.
The state of terminal ~3 is dependent on the relative values of currents through R13 to terminal $1 representing positive input on the one hand and through R14, R15, R16 to terminal ~2 representing negative input on the other hand.

If triac Q1~ is turned off, the junction of diode D2 and capacitor C2 is~ as before, approximately 10 volts and in this state the input current to ~2 exceeds input current to ~1 and output at ~3 is low.

hhen the conduction angle of Q1~ is greater than 100 (corresponding to high speed spin) the D2~ C2 junction falls below zero volts and comparator output at ~3 goes high generating a fault (reset) signal. If, however, spin _ ` ::

demand terminal lO~ is high uncler these COJIdi tions then current through T~15 and Rl6 overrides (or augments) curren-t r at I~l4, thereby inhibit:ing -the fault (reset) signal.

If however, the low level switch Sl~ is in its movable contact down position indicating the presence of water above the prede-term-ined low level (and which would pr~sent an excessive load on the motor endeavouring to execute a spin), -transistor TR2 conducts cancelling the effect of the spin demand terminal lO~ and causing g3 to go high and produce a fault (reset) signal.

The following table summarises these operational conditions.
, r Truth Table Motor Triac Spin L.L. Comparator onduction ~ Demand ~ 'witoh loutput Motor spin plus Less than X X LOW
no demand lOO

Motor spin plus Greater than OFF HIGH fault no demand lOO (reset) Motor spin plus Greater than ON Up LOW
demand lOO

Motor spin plus Greater than water high level 100 X Down HIGH fault X = Immaterial r ;

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I~`igure 5 shows a~l a:lte-r~ t:ive forrn Or circuit for use as mon.itor ci.rcuit 22. Ln this componerlts corresponding to those of l~`igure 4 bear correspond:ing re.t`erences. 'I`he input -to terminal ~rl is f~ed -throug:h R2, D2 and R5 and is deri.ved from a tacho-genera-tor 33 d:r:iven from -the motor 12~ and provi.ding arl alternatillg voltage of between 0 and 10 (positive) depend:ing upon motor speed; :lO volts output corresponds to motor operating athigh (spin) speed. The terminal ~2 is tied to -the zero vol-t line 15b through R7.
The manner of operation is as follows.

A fault (reset) signal is generated at ~3 (high) if the input to ~l from the tacho-generator via R2, D2 and R5 exceeds the reference input to ~2 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 Rl 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 Dl, generating a fault (reset) signal at ~3.

The Rl, Cl time constant allows the spin demand to rise fast enough to avoid a spurious fault detection on selecting a spin due to the input at ~2 remaining below that at gl during motor acceleration.

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When spin de111and is i11tentionalLy discontinued the 1~6, Cl, time constant holds the spin de1r1and high long enough to allow the motor to run dow11 below the trip speed level.

The slider of RVl supplies an A.C. feed-back signal rectified through 1)3, dependent upon tacho-generator output voltage, to a motor speed control unit 32. This unit includes means for generating references (demand) voltages selected to provide wash, dis-tribute, and spin speeds for the motor. The feed-back signal and the selected reference voltage are fed to an amplifier in -the unit which provides an output to the motor dependent upon the difference so as to operate the motor at a stable selected speed. If the tacho-generator goes open circuit, the voltage at the slider of RVl is then determined by the values of R3, RVl, the setting of the slider thereof, and R4, and simulates a very high tacho-generator output greater than any of the reference voltages and thereby causing the motor cvntrol circuit to shut down~the motor. The tacho-generator impedance is typically 180 ohms whilst the values of R3, RVl and R4 may be respectively 18, lO, and lO kilohms so that in substance the D.C. level at the output side of D3 in normal operation is determined only by tacho-generator outpu-t.

Referring now to Figure 7, this shows one form of circuit which may be employed for the temperature measuring circuit 24 and monitor circuit 23. These are effectively -.
-10~549'5 combined into a single circuit al1;hough f`or clarity offunction they are shown separately in the schematic diagram of 1~iguI~e 2.

Integrated circui-t element ICl~ which is a compara-tor, has one input terlllinal ~ , connec-ted via R36 to zero volt conductor 15b to establish a re~erence level. Thc other input terminal i2 has a voltage level set by a voltage follower circuit R3~, R35, TR7. The voltage on the collector of TR7 follows, and is greater than, that of the junction of R34 and thermistor Vc, which latter senses the water temperature of water in the drum.

When the ratio of voltage across thermistor Vc to voltage between the zero volt conductor l5b and the -16 volt conductor 15c, i.e. 16 volts is greater than R38~R36, i.e.
the output at terminal ~3 of ICl~ goes low, and when this ratio is below R38/R36 the output at ~3 remains high.

Conductor Z~ is connected to the TEMP INPUT terminal lOh of logic circuit lO and the latter incorporates a variable schmitt circuit which is se-t 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 lOf.

The ratio R38/R36 is selected to cause ~3 to go low when the thermistor senses a temperature of 95 C whcn 1~54~15 all component tolerances are such as to tend to increa~e the voltage level at terminal ~2.

In respect of thls func:tion the circuit acts as a temperature measuring circuit.

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

If Vc becomes open circuit, the base of TR7 i9 raised to the zero volt level, terminal i2 rises and simulates a temperature measurement of higher than 95C, 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, ~igure 2. The essential function is to generate a fault signal to the input (reset) terminal 10i 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 10~.

Referring to the circuit of Figure 6 in detail, the integrated circuit comparator element IClh is connected to ' .~

10~3549~5 , ~, the -~ero volt line 15~-througll resistor R20 to provide a refererlce a-t input -terminal hl represe}lt:illg negative :inpu-t. This ho:kls the output terminal h3 to a low value when therc is no input a-t terminal h2 (representing posi-tive input) from tllc moni-tor c:ircui-ts 21 and 22 via conductors 29, 30 and resistors R23, R2/~, connected respectively thereto. r When a fault (reset) signal is incident on ei-ther of conductors 29 and 30 the comparator circuit output terminal h3 goes high and latches in this condition through the feed-back pathR25b, R25a. The high fault signal at h3 is applied through diode D5 via conductor 16 to the CANCEL (reset) input terminal 10i of the logic circuit 10. The high faul-t 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. r . .
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 maintainence of the door lock in its operated position when it has been operated in some other manner e.g. by closing the door manually.

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io~s4~35 If the l.ogi.c circuit is functioning normally, the door lock demancl (whi.ch i~s also demand for closure of switch S1a) an~1 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) termi.nal 10l 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 X26 and R22 to be applied to input terminal hl.

The delay means included as mentioned in the operat-ing 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 S1a 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 h1 (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" con-ditions.

The current input through TR3, R20 and R21 to h1 always overrides current input through R23 and R24 to h2 when the output terminal h3 of comparator IClh is low (and IClh has not latched via R25a, R25b) and if no programme ~' .
, 10~54C~5 _ ~8 -is selected the additional input to hl through R26 and R2Z
guarantees maintenance of a low output at the output terminal _3. In the event of a failure of the logic circuit lO to turn off the output (set) signal at terminal 10a~ i.e. demand for operating means 12a is still generated internally and appears at terminal 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. T~5 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.

..

, 10859~9'~
, ,~,, .

The following table surnmarises the above described operations.

Truth table Condi-tion ~leater Motor Door Door Comp.IClh output outputLock Lock Output M~i~ ~and i No .
prograrnme ON ON OFF OFF LOW
selected I
Waiting for Programme door lock selected but ON ON OFF ON LOW
door lock off _ . ~.
Programme selected-but OFF OFFON ON LOW
no fault _ _ _ . Hfauletr ON OFF ON ON ~ault) .
r Motor OFF ON ON ON HIGH
fau].t ~ault) _ ., After Door lock ON ON OFF ON HIGH
fault de-energised (fault) : -but logic circuit not reset. .

.~, . .

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:-

1. A control circuit for controlling the supply of current from a source to an apparatus which includes a plurality of functional means required to be brought into operation in a sequence in accordance with at least one predetermined programme, such circuit comprising:-a. a first switch means controlling the supply of current to at least some of said functional means, b. a main control means for furnishing signals to control operation of said functional means in accordance with said programme and to set the first switch means in a closed or open position in accordance with demand requirements of said programme applicable to the apparatus, c. at least one monitoring means each associated with a respective one of the functional means for generating a fault signal in response to occurrence of a fault condition, d. means connecting the monitoring means with the main control means to cause the latter to set the first switch means in an open condition in response to generation of said fault signal, e. a second switch means for controlling current to at least one of said functional means brought into operation in said programme, f. a back-up circuit means connecting the second switch means and the monitoring means, the second switch means being responsive to generation of said fault signal to cut off current to said functional means to which current is controlled by said second switch means irrespective of response of the main control means to said fault signal.

2. A control circuit according to claim 1 wherein the back-up circuit means includes 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.

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

4. A control circuit according to claim 1 wherein the main control means includes an electronic programming means for determining the sequence, duration, 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 3 wherein:-a. said second switch means comprises a semi-conductor switch, b. conductor means are provided connecting said semi-conductor switch in a circuit controlling the supply of current to said electrically energised operating means for the main switch contacts, c. said semi-conductor switch is itself responsive i. to said output (reset) signal from the programming means and ii. 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 said semi-conductor switch to interrupt current supply to the operating means for the main switch contacts.

6. A control circuit according to claim 2 wherein:-a. said latch means comprises a comparator means having first and second input terminals, b. said first input terminal is connected to a sub-circuit providing an input changing in value in accordance with the incidence or not of a fault signal, c. said second terminal is connected to a sub-circuit providing an input changing in value in accordance with a combination of an output (reset) signal from the main control means and the opening and closing of the first switch means, d. the comparator means has an output presenting one or other of different 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 from the main control means.

7. A control circuit according to claim 1 wherein the monitoring means comprises one or more monitoring circuits each of which comprises:-a. a comparator means having at least two input terminals and an output terminal, b. one of the two input terminals being connected to a sub-circuit providing an input of reference level, c. at least one other of the input terminals 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, d. 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 the monitoring circuit is operating normally or has become abnormal.

8. In a machine for subjecting articles to treatment involving a liquid, 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 the treatment programme and including means for effecting transfer of the liquid to and from the chamber so that it is brought into contact with, or removed from, the articles, and means for subjecting either the liquid or the articles to motion while both are in the chamber, said functional means being each electrically controlled or operated, a control circuit for bringing the functional means into and out of operation in accordance with one or more selected programmes to effect the particular treatment required, the improvement wherein the control circuit comprises:-a. a first switch means controlling the supply of current to at least some of said functional means, b. a main control means for furnishing signals to control operation of said functional means in accordance with said programme and to set the first switch means in a closed or open position in accordance with demand requirements of the said programme, c. at least one monitoring means each associated with the respective one of the functional means for generating a fault signal in response to occurrence of a fault condition, d. means connecting the monitoring means with the main control means to cause the latter to set the first switch means in an open condition in response to generation of said fault signal, e. a second switch means for controlling current to at least one of said functional means brought into operation in said programme, f. a back-up circuit means connecting the second switch means and the monitoring means, the second switch means being responsive to generation of said fault signal to cut off current to said functional means to which current is controlled by said second switch means irrespective of response of the main control means to said fault signal.