MONITORING DEVICE FOR A SAFETY ELEMENT OF A DOMESTIC ELECTRICAL APPLIANCE OR OF A GAS APPLIANCE

The present invention relates to a monitoring device for a safety element of an electrical appliance for domestic use or of a gas appliance in accordance with the introduction to the main claim.

Each safety element present in an electrical appliance (for example a washing machine, a dishwasher, a refrigerator, an oven or the like) or a gas appliance (for example the gas valve in the case of a boiler) must be subjected to adequate control to prevent its malfunction or undesirable operation which could also have problematic consequences (gas leakage, explosion, fire, etc.). The control devices usually comprise a change-over switch or a series of change-over switches provided in an electrical supply line to said safety element, the opening and closure of which results in the operation of said element. Although these devices operate in accordance with current regulations, problems could arise in the powering of the safety element with consequent opening or closure errors, such problems being currently difficult to identify, or identifiable only by using complex solutions of some cost. An object of the present invention is to provide an improved monitoring device able to monitor correct operation of a safety element of an electrical or gas appliance.

A particular object of the invention is to provide a device of the stated type which is able to effectively identify all problems in the electrical supply to the safety element, such as to prevent its inopportune activation. Another object is to provide a device of the stated type which is able to identify any risk conditions (for example risk of gas leakage) if the monitored element is the gas valve and if abnormalities exist in its electrical supply. A further object is to provide a device of the stated type which enables effective

control of the safety element and enables its timed operation (if provided) to be monitored as required for safety standard purposes.

These and other objects which will be apparent to the expert of the art are attained by a monitoring device in accordance with the accompanying claims. The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which the single figure shows the essential parts of an electrical circuit diagram for a device according to the invention. With reference to said figure, a device of the invention comprises an electric circuit 1 connected to a power supply mains, for example of an environment in which a gas appliance is installed. The circuit 1 is used to monitor the operation and power supply of a safety element of said appliance, such as a gas solenoid valve 2 presenting electrical connectors or terminals 2A and 2B which connect it to the circuit 1. This solenoid valve can present a dispersion towards earth 34 indicated for example by 33 in the figure. The connector 2A is connected to a first branch 3 of a power supply line 4 of the circuit 1, whereas the connector 2B is connected to the branch 5 of this line. Each of the two branches 3 and 5 of the line 4 comprises a corresponding change-over switch 7 A and 7B controlled in any manner by a control element, for example external to the device of the invention such as a usual electronic control unit of the burner flame control type. Each change-over switch 7A and 7B is hence able to close onto its own electrical branch 3 or 5 to power the valve 2 when necessary, to hence operate the boiler. Two parallel electrical branches 10 and 11 are connected between the branches 3 and 5. These parallel branches are connected to the corresponding line branches 3 and 5 at nodes 1OA, 10B and nodes 11A and 11B respectively. The change-over switches 7A and 7B are connected between the nodes 10A, 11A and 10B, 11 B.

Each branch 10, 11 comprises a first portion 1OC, 11C positioned between the node 1OA, 11A and an intermediate node 10D, 11 D to which an electrical branch 13 comprising a resistor 14 is connected. In parallel with this latter there is a branch 15 comprising an optoisolated device such as an optoisolator 16, of known type, arranged to generate electrical signals across its terminals 16A, 16B at the moment in which an electrical signal is present in the branch 15. The signals generated at the terminals 16A and 16B are fed to an appliance control unit (not shown) operating as stated hereinafter. Between the node 10A, 11A and the intermediate node 10D, 11 D, each portion 10C, 11C comprises a resistor 18A, 18B and an electrical unidirectional device or diode 19A, 19B (which can also be of electronic type, i.e. a transistor). Each branch also comprises, between the intermediate node 10D, 11 D and the node 10B, 11 B, a further branch portion 10E, 11E comprising a resistor 2OA, 2OB and another unidirectional electrical device or diode 21 A, 21 B; the latter opposes the diode 19A, 19B connected into the said branch 10, 11. It should also be noted that the diode 19A opposes the diode 19B and the diode 2OA opposes the diode 2OB (i.e. the diodes 19A, 2OB are disposed in the same direction in the respective branch portions 10, 11 , as are the diodes 19B, 21A) to hence enable an electrical signal to transit along the portions 3, 10C, 13, 15, 11 E, 5 or, vice versa (depending on the polarity), 5, 10E, 13, 15, 11C and 3 as a result of the closure of only one of the change-over switches in the respective branch in the case of a fault.

Between the line branches 3 and 5 there is also present a further branch 30 comprising a fan 31 (to provide combustion air in the case of a gas appliance) and a controlled change-over switch 32A. This latter can be part of a two-pole member with a single control, said member also comprising the change-over switch 7B or 7A.

It will now be assumed that the device of the invention is in the rest state and

the change-over switches 7A and 7B are open. In this (rest) state there is no signal along the branch 15 comprising the optoisolator 16, hence there is no signal across its terminals 16A, 16B. The boiler control unit hence senses that the solenoid valve 2 is not powered and is closed. When the switch 7B positioned in the line branch 5 (which powers the fan in the typical gas appliance configuration) is closed, a signal appears at the optoisolator 16 with a frequency equal to mains frequency (i.e. 50 Hz or 60 Hz), said signal corresponding to the positive half-wave of the mains signal. This signal passes through the branches 3, 10C, 13, 15, 11E and 5. On closure of the other switch 7A positioned in the line branch 3, the (current) signal with the other half-wave (opposite the first) is added to that already circulating through the device circuit 1. In both cases, the optoisolator 16 senses the current circulation through the circuit 1 (of frequency double the mains frequency, i.e. 100 Hz or 120 Hz), this current enabling operation of the safety element 2. This is therefore also recognized by the appliance control unit; this latter, depending on the frequency of the electrical signal or current circulating through the optoisolator 16, can control the safety element (valve 2) to which the circuit 1 is connected. Said unit can also verify operation timing of the safety element 2, necessary for safety regulation purposes. If a fault appears in the circuit 1 , this can be immediately identified. In this respect, if when in the rest state a signal is present through the optoisolator 16, it is possible that at least one of the switches 7A or 7B is closed, in spite of the fact that it should be open. This error situation is then detected by the signal generated by the optoisolator 16, and an alarm signal or other fault indication can be generated to prevent starting of the (known) control sequence leading to activation of the safety element, because of the presence of a system fault or malfunction. By virtue of the device 1 , both the regular operation of the safety element and

that the situation of a fault therein or in its piloting circuit can be identified rapidly even in the rest state, with consequent possible immediate intervention by the user (or by any electronic control member of the appliance) aimed at preventing further problems in the use of the appliance itself or for the environment in which it is positioned. The monitoring device also enables the safety element to be actively controlled by monitoring the electrical signal generated by the optoisolator 16.

The invention also enables the presence of earth dispersions (for example winding insulation deficiency) of the safety element (for example if it comprises a coil) to be verified, even in the rest state. In this case the potential difference between the branches 3 and the earth 34 (to which the element 2 is "virtually" connected as already described) generates a current flow through the branches 3, 10C, 13, 15, 11 E, 33 or 5, 10E, 13, 15, 11 C, 33, the control member then being able to act in the aforedescribed manner by monitoring the output of the optoisolator 16.

A preferred embodiment of the invention represented simplified in its main aspects has been described. The invention has been described in particular with reference to a gas appliance, but can also be used for other electrical appliances such as washing machines, dishwashers etc. Moreover, the invention has been described as comprising an optoisolator device which is usually necessary when separation is required between the electrical supply mains and the control unit for the safety element, which operates at low safety voltage. However, if this separation/isolation is not necessary (for example if the control unit is not isolated from the electrical supply mains), said optoisolator device can be omitted and, for the purpose of detecting the electrical signal transiting towards the safety element, direct use can be made of a signal withdrawn, in any known manner, from across the resistor 14 or another electrical component able to determine a passage of current through

the branch 13 (such as a shunt or equivalent). Consequently other solutions are obtainable in the light of the aforegoing, and are to be considered as falling within the scope of the following claims.