This invention relates to regulation and safety control devices for electric water boilers. Electric water boilers have two devices that control the temperature of the water contained in the tank.
One is a regulating thermostat (hereinafter also referred to as the heat regulator). Its task is that of adjusting the temperature by maintaining the water boiler's temperature at the t.r value set either by the manufacturer and/or by the user; of course, any regulation range made available to the user prevents that dangerous temperatures can be reached.
The other device is a thermal-protector thermostat (hereinafter referred to as the thermal-protector). Its task is that of providing thermal protection by cutting off the power supply to the electrical resistances if the monitored temperature reaches an intermediate cut-off value of t.i ranging between the temperature values that can be reached during normal operation and the maximum value of t.s envisaged by Safety Regulations. In general, this may take place only if the regulating thermostat has suffered a failure; for instance, if the setting is not correct or if its electrical contacts are welded and can no longer open. However, it is also possible that an anomalous situation such as, for instance, the lack of water in the tank, may lead to sudden increases in temperature that activate the thermal-protector even though the regulating thermostat is in perfect condition.
The accuracy of the regulating thermostat is extremely important, not so much in terms of comfort but for the purpose of limiting consumption; given the same mean temperature in the water boiler over a given period, the sharper the variations in the actual temperature owing to its inaccurate control are, the greater the loss of heat, as proven experimentally. From this point of view it is a matter of fact that the most precise electro-mechanical thermostats are those using a bulb sensor followed by a rod sensor and then by those whose sensor is composed of a bi-stable bimetallic foil. Electronic thermostats are by far the best, generally using an NTC as sensor, that not only provides for an accurate regulation which could not be otherwise reached with electro-mechanical thermostats, but they also offer many other advantages such as the ease in controlling them with a microprocessor, by means of which the operating time and temperatures as well as other functions can be programmed. While electro-mechanical thermostats cut off the power supply to the electrical resistances by physically opening an electrical contact, electronic thermostats act by stopping the passage of current through a semiconductor device (the TRIAC), which, in turn, can be arranged directly in series along the circuit of the electrical resistances if the required amperage is low enough or by commanding the opening of a relay, which, in turn, disconnects the circuit of the resistances. Nonetheless, the safety regulations do not require that the regulating thermostat physically disconnect the phases of an electric circuit.
The bipolar physical disconnection of both ends of the electrical circuit of the resistances is commanded by the thermal-protector thermostat; on the other hand, no particular degree of accuracy is required for the activation temperature, as the tolerance values of the less sensitive sensors like those with a bi-stable bimetallic foil are capable of being activated at cut-off temperatures t.i much higher than the regulation temperature t.r yet well below the maximum permissible temperatures t.s. Hitherto, the thermal-protector thermostat in water boilers has always been of the electro-mechanical type with an extremely simple mechanism; in general it is of the type containing the well-known bi-stable bimetallic disks as sensor/actuator device. When the set temperature is reached, the thermal-protector thermostat irreversibly opens the two (or three) power supply phases; the resetting of the contacts is possible in most models to restart the water boiler when the overtemperature is not the result of malfunctions affecting the regulating thermostat, but the reset device must be accessed only by a maintenance technician, thereby constituting the inconvenience that the resetting of the water boiler always requires the intervention of the technical servicing department, even if the cause of the block was absolutely accidental.
For the sake of compact and easy assembly, the electro-mechanical regulating thermostat and the thermal-protector thermostat are often lodged in the same casing; but this does not mean that they are not two independent devices, each having its own sensor, its own mechanism for opening the electrical contacts and finally its own electrical contacts. In conclusion, safety requires that the two thermostats must each have their own "electro-mechanical logic".
As for the electronic regulating thermostats, their use has been limited up to now to higher level products, considering the impossibility of eliminating the costs for the electro-mechanical thermal-protector, which, among other things, is usually quite difficult to include in the same casing with the electronic thermostat. While the most widespread type of thermal-protector is the one with bimetallic foil, it must be lodged as close as possible to the zone whose temperature must be monitored, i.e. the zone in which the operating temperature can be high enough to damage the electronic devices even in normal operating conditions.
The document
The main purpose of this invention is that of allowing the user to reset regular water boiler operation when it is blocked by the thermal-protector even avoiding dangerous situations. Another purpose of this invention is that of specifying the means by which to obtain a single control device capable of acting, at minimum, as regulating thermostat and thermal-protector in an electric water boiler.
Another purpose of this invention is that of specifying the means by which to allow the said single control device to use a single operating logic, i.e. a single hardware device and a single software device, at least for the control of the heat regulator and thermal-protector functions. Another purpose of this invention is that of assigning to the said single control device further information, programming and control functions which are not related to either the heat regulation or thermal protection.
According to the invention, these and other purposes are achieved by means of a control device including a combination of suitable electronic and electro-mechanical means which function according to appropriate methods.
The invention shall now be illustrated with regard to a number of preferred yet non-exclusive variants in the following description as well as in the drawing and attached claims, which constitute an integral part of the invention's description.
A number of preferred variants of the invention are now illustrated.
With regard to the figure, R indicates a control device which, taken as a whole, has the functions of heat regulator and thermal-protector; 1 is an electrical power circuit powering, via the connection terminals 2.1, the electrical resistances 2 that heat the water; 3 indicates a regulation relay whose opening/closing controls the power supply to the resistances 2 to maintain the water at the temperature set during regular operation; 4 indicates two safety relays (or, alternatively, a single relay with a double micro-switch) which the control device R opens should it detect any operating malfunction incompatible with the safety regulations; 5 indicates two possible fuses which are arranged in series with said relays 4 and which protect the contacts of the relays 4 against overcurrents which would lead to their sticking.
Control device R comprises one or two temperature sensors 6, preferably of the NTC type or in any case of a type fit to transmit temperature signals that can be interpreted by electronic devices; of the two sensors 6, one is dedicated to the control of the set regulation temperature t.r and the other to the control of the cut-off temperature t.i; however, consistent with the requirements of the relevant regulations and with the points in which said regulation temperature t.r and cut-off temperature t.i must or can be detected, a single sensor 6 can be used both for the information relating to the heat regulation and for the thermal protection; at least a second sensor 6 can be useful for auxiliary functions not relating to heat regulation and to thermal protection such as, for instance, and according to known methods, the estimation of the mean temperature and the energy content of the water boiler, which can be easily inferred if the water temperature in two different duly chosen zones are known.
Control device R also comprises a microprocessor 7 equipped with specific software to perform, at minimum, the following tasks:
Among other things, the operating malfunctions that can be identified by the microprocessor 7 include not only the detection of overtemperatures signalled by the sensors 6, but also the failure of said sensors owing to an interruption or short-circuit signalled by an infinite, null or absurd value of their electrical resistor, i.e. outside the range of possible values for the intact sensors 6.
The control device R comprises also a hardware circuit 8 which acts as a supervisor (commonly called and well-known as the system "watch-dog"); it monitors the proper functioning of the microprocessor 7 and it opens the relays 4 by means of the command circuits 4.2, if anomalous behaviour is detected in the microprocessor 7 or in other essential or auxiliary devices including the control device R. As regards the said watch-dog 8, which functions according to known techniques and methods, it shall not be mentioned any further below, as it is implicitly inferred that it can supervise the control of any function within the limits provided by the current state of the art.
It must be borne in mind that today's technologies for the manufacturing of electronic equipment providing for the possible redundancy of logic circuits and monitoring methods by means of hardware circuits which act as watch-dogs, at least with regard to the proper performance of the main functions, make it possible to obtain extremely reliable devices, which can be entrusted with safety functions, as is acknowledged and accepted by the relevant Regulatory Bodies.
If one of the relays 4 opens as a result of a detected malfunction, automatic closure by the control device cannot occur once the malfunction has been eliminated: only a manually operated resetting device 9 can command their closing. However, the said reset command is accepted by the safety system only when the microprocessor 7 ascertains that the malfunction causing the opening of the relays 4 no longer subsists. In other words, if, for instance, there is an accidental increase in the temperature, the reset command and the subsequent closing of the relays 4 is accepted, but only once the temperature is back to normal; on the contrary, if, by way of example, the malfunction consists in the irreversible failure of a sensor, it is not possible to restore normal conditions and hence the reset command continues to be rejected by the microprocessor 7. As known, electro-mechanical thermal-protectors are also provided with a reset command to reset the thermostat once the malfunction has been eliminated; it comprises a pushbutton, which, once pressed, acts directly on the electrical contacts by closing them; pressing the pushbutton, however, may force the closing of said contacts even though the malfunction is still in progress. For this reason, the said pushbutton is lodged in a place which cannot be accessed by the user and it is protected by a cover which can be opened with a special tool so that only an authorized repair technician can activate it. On the contrary, as stated above, according to this invention, since the reset command is rejected and it does not have any effect if the malfunction is still in progress, the user can nonetheless gain access to the command with the advantage that there is no need to call the technical servicing department to reset the water boiler when there has been no failure but just a temporary and reversible malfunction.
However, the control device R may also be designed to be able to take into account and memorize the number of reset commands it has accepted and limit the maximum possible number of resets to a set value beyond which it rejects any other command. Therefore, even a temporary and reversible malfunction may require the intervention of the technical servicing department if it occurs too often, hence indicating that there is a recurring problem that needs to be identified and resolved.
For this reason, too, the control device R can include the presence of a non-volatile memory 10 such as an EEPROM, i.e. a memory which is not deleted if there is no power and which saves with an appropriate code all the anomalies detected and/or the number of resets accepted; said memory 10 can also save data not relating to the heat regulation and thermal protection, but which are nonetheless useful in performing the aforementioned auxiliary functions:
In conclusion, a display 11 may also be furnished, providing the user with information on the status of the water boiler with regard to both the heat regulation and thermal protection functions and to the auxiliary functions.
Another difference not only in terms of means but also of method or, rather, of the operating logic compared to the current electro-mechanical heat regulation and thermal protection devices is, as stated above, that the latter always have two independent devices even when they are lodged in the same casing; in other words, they each follow their own mechanical logic. Instead, the control device R has a single "electronic logic", even though it is redundant for safety reasons and it includes both a software and hardware component, comprising the watch-dog 8. Said "electronic logic" is not composed of specific parts dedicated to heat regulation, thermal protection and to the auxiliary functions. Regardless of whether there is more than one temperature sensor 6, for the sake of compliance with regulations or of measuring the temperature in several points, their signals are received by a single unit which performs various functions depending on the cases: as long as the temperature levels are normal, the "electronic logic" of the control device R controls the operation of the regulation relay 3 or, in other words, it carries out the heat regulation procedure; once the cut-off temperature ti is exceeded or if there are other malfunctions, the same control device R opens both safety relays 4, namely, it starts the thermal protection procedure by blocking the water boiler; in the meantime, the "electronic logic" of the control device R can also perform other auxiliary information or programming functions, and so on.
The advantage is clearly that the control device R provides for the development of non-essential functions which are however useful for programming and other purposes with only negligible additional costs.
Other embodiments are possible for the control device R and a few non-exhaustive examples are provided below.
The safety relays 4 can be either of the Normally Closed or Normally Opened type, as they both can be safely opened or kept opened by the control device R in case of anomalous conditions.
The cut-off device 3, as in the case of current electronic regulating thermostats, may have a TRIAC instead of a relay.
As it is provided with relays that can perform a number of cycles greater than those envisaged during the life of a water boiler (for instance, 300.000 cycles at the state of the art), the regulation relay 3 can be eliminated and its function can be assigned to either one or both of the safety relays 4. In said case the safety provided by the control device R can be further improved by adding one or more of the following functions or devices:
As for the relays 4, provided that the relevant regulations consent to it, they can be replaced by a TRIAC.
In conclusion, it should be pointed out that, with the due modifications, the foregoing refers to a two-phase current and can hence be applied also to three-phase systems with the electrical resistances connected in a delta or star layout.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.