EP1300503A1 - Steam generator with a water level display - Google Patents

Abstract

The steam generator includes a water container (1) which to produce steam. An electronic circuit (30) determines and displays the level of water remaining. This is calculated as a function of the temperature graph during the initial heating up stage and subsequent loss of water to steam. The result is displayed on the electronic circuit box. <??>The steam generator comprises a water container (1) which is filled with water, and heated in order to produce steam at a pressure greater than atmospheric pressure. Steam is driven along a pipe to the iron (20) where a switch (21) is provided to control an electro-valve (13) on the container, regulating the flow of steam. An electronic circuit (30) is provided for determining and displaying the level of water. The initial level of water is calculated as a function of the temperature graph during the initial heating up stage. By subsequently subtracting the quantity of water which has been converted to steam, it is possible to calculate the quantity of water remaining in the container, and thus the working time remaining for the steam iron. A display (32) on the electronic control indicates this.

Description

The present invention relates to steam generators comprising a tank previously filled with water and then heated to produce steam at a pressure higher than atmospheric pressure.

Such generators, economical because they are manual filling, are used to supply irons or other appliances with steam household.

The generally metallic tank has a filling opening provided a plug, a vapor withdrawal orifice usually provided with a solenoid valve, a heating element, one or more temperature sensors or pressure regulator, and safety devices.

Sensors, which can be associated with the regulation, are able to detect the absence of water in the tank and consequently to light an indicator.

This useful device for the user confirms the origin of a pressure drop, in inviting him to recharge his generator with water. She must then interrupt her work, allow the device to cool to reduce the residual pressure, open the cap, reload the tank with water and wait for a new temperature.

The timing of this work disruption is sufficient unpredictable to make this obligation unpleasant. Furthermore, even for short ironing sessions, the user is encouraged to complete the tank as completely as possible to avoid interruption of work. This leads to heating up a useless body of water and lengthens the warm-up time, especially as the manufacturers increase the size of the tank, as much as possible economically and for use easy, so as to increase the autonomy of the generator between two refills.

Reading the water level in the tank would allow the user to anticipate the remaining time of ironing and make arrangements accordingly. However, it is not possible to read the level through the opaque wall of the tank.

A vertical or oblique transparent tube connected to the tank allows to visualize the level, but in addition to being a technically delicate device for a household appliance, it builds up and quickly becomes illegible. So you need a device comprising an indirect determination of the level and a display, for solve this problem.

Determining the level of hot water under variable pressure and temperature can be done by plunger devices such as that described in the patent US3992941. But these devices require delicate moving parts and little compatible with household appliances.

There are also known level measurement devices using ultrasound such than that described in patent US4229798. But these devices mounted in boilers require numerous corrections and are disturbed by boiling.

More simply, we know a level measurement, in a refill boiler automatic water from a tank, described in patent EP0843039. This document describes how to determine the water level in the boiler tank and we control the filling pump according to the slope of the curve temperature of this tank. This device is sophisticated and takes into account successive heating and sampling. Precision is good because this type of generator has a small volume automatic filling tank. Through As a result, instant withdrawals are significant relative to the volume of the tank, which is not the case for the application envisaged on a large tank manual periodic filling capacity.

The object of the following invention is an economical steam generator, the tank is manual filling and which includes a device for determining and display of the water level not having the disadvantages mentioned. Level of water can be expressed in height of water in the tank, in remaining volume, or in mass of water remaining in the tank, these values being physically linked.

The object of the invention is achieved by a steam generator comprising a tank intended to be filled with water and then heated to produce a steam at a pressure higher than atmospheric pressure, a device remarkable electronic water level determination and display in that the device for determining the water level comprises means to calculate an initial water level, based on the temperature curve of first warm-up, means to calculate at each sample the product of the mass flow rate of water vapor over time corresponding to the mass of water taken in the form of vapor, and means for calculating each residual water level.

The electronic device includes a tank temperature sensor. It is preferable to use the sensor used simultaneously to regulate the temperature or, in an equivalent and simultaneous manner, the pressure. A microprocessor makes it possible to calculate the initial water mass as a function of the temperature rise and the duration of a measurement during the first heating according to the formula m ₀ = a × t / ( _final T- _initial T) + b , m ₀ being the initial mass of water, a and b being constants related to the construction of the tank, t being the duration of the measurement, T _final being the temperature at the end of the measurement and T _initial being the temperature at the beginning of measurement. The duration t at the start of heating can be quite long, the temperature difference large, which gives good accuracy to the calculation, even on a large tank. The initial water mass is memorized by the microprocessor. Preferably, this microprocessor also regulates temperature and pressure. Equivalently, one can use analog electronics or an ASIC which is an application-specific integrated circuit.

Subsequently, the samples and reheating induce small temperature differences and disturbances, which affect the accuracy of a simple determination of the level according to the previous formula. It is therefore preferable to calculate the mass of water extracted at each withdrawal and to deduct it from the initial water mass according to the formula m = m ₀ - flow time of sampling. This is made possible because, in most cases of use, the pressure-dependent flow rate is practically limited only by the pressure drops of the user device and varies very little according to the conditions of use. For example, the steam flow rate of an iron depends little on the way in which the iron is applied to the fabric; the vapor pressure of the tank, for example three bars, is much higher than the pressure necessary to pass through the tissue. This pressure mainly relaxes in the various pipes and orifices of the apparatus. On the other hand, the pressure and therefore the flow rate varies a lot with the temperature of the tank. The microprocessor delivers a signal representative of the water level.

Preferably, the means determine the flow as a function of the temperature of tank.

The pressure being a saturated vapor pressure, it is directly linked to the tank temperature. The calculation of the flow linked to the pressure by a function does not depending on whether constructive arrangements of the device are possible. Of preferably, a table of correspondence of the measured vapor flow is established at different temperatures of the tank in the working range. This table is memorized by the electronic device and the instantaneous value of the flow is determined from this table as a function of the instantaneous temperature of the tank. The advantage of this calculation is to allow the user acting on a setpoint, large temperature and pressure adjustments amplitude. In this way the user can vary the flow rate of their device, without disturbing the determination of the water level.

In one version, the generator includes a pressure sensor, and the means calculate the flow according to the pressure in the tank.

The calculation is then more direct. Preferably a table of flow and pressure correspondence in the useful operating range. This table is stored in the electronic device and the instantaneous value flow is calculated from this table.

Of course, in a use of the generator where the other conditions of use would be variable, determining with regard to the flow, and known, the flow could be corrected based on these instant conditions. Through example, it could be corrected according to the progressive opening of an orifice steam sampling.

The generator tank is equipped with a heating element which operates at substantially constant and known power. Power variations of heating that we observe following fluctuations in the sector, or an element heating to another in mass production, normally remain in acceptable limits for the desired precision. However, if we wish high precision, it is possible to add known electronic means voltage measurement, or even power consumption, to correct the flow calculated, as a result of these variations.

Preferably the display device displays the level in a relative value at full tank level.

The indication of the percentage of filling is more readable for the user than the indication of an absolute value.

The signal representative of the water level can be adapted to control all analog or digital display means, for example a display numeric indicating a value from zero to one hundred. Preferably zero is representative of an empty tank and a hundred of a full tank.

The signal can be analog and activate a needle galvanometer. The full deviation is then obtained for the full tank and zero deviation for a empty tank, or vice versa. Pictograms then indicate the meaning of deviation for the full tank.

Preferably the display range is split into several contiguous ranges corresponding to predetermined intervals where the level can be found instantaneous, each track being provided with an indicator.

The indicator may be a light emitting diode, or an element of a screen with liquid crystals for example.

The indicators are arranged side by side so as to represent a scale of filling. Each indicator is excited when the level is in the interval predetermined that corresponds to it. The indicators and the intervals are arranged to the ladder gradually comes to life or goes out from one end to the other when the level goes from 100% to 0%.

The number of LEDs can be very large, the level indication will then be almost continuous, or very reduced, for example reduced to four, indicating only if the filling is a quarter of the capacity or half, or at three quarters, or if the filling is complete.

Preferably, the generator includes a warning light or an audible warning empty tank, controlled by the empty tank detection means and / or by the system level detection, when the level drops below a threshold predetermined.

This system allows the user to anticipate the complete cessation of operation. The indicator light then indicates operation on the water reserve, until the steam production. The indicator light threshold can be set so that allow the user a few minutes before spraying stops completely. She can then make arrangements to stop her work in the best conditions.

The invention also covers a method for determining the level of water in a steam generator comprising a tank intended to be filled with water and then heated to produce steam at a pressure higher than the atmospheric pressure, which consists in calculating an initial water level in function of the temperature curve of first heating, to be calculated at each sample produces the mass flow rate of water vapor over time of said withdrawal corresponding to the mass of water withdrawn in the form of steam, to calculate each residual water level.

The invention will be better understood on the basis of the description below and of the drawings attached.

Figure 1 is a schematic view of an ironing apparatus comprising a generator according to the invention.

In a preferred embodiment of the invention, the generator comprises a cylindrical tank 1 provided with an electric heating element 11, a switch safety thermal, a filling orifice closed by a plug 12 of safety with regard to overpressures, a steam withdrawal orifice provided a solenoid valve 13. The solenoid valve 13 is controlled by the device 20 steam user, in this case an iron, fitted with a vaporization 21 capable of causing the solenoid valve 13 to open.

An electronic circuit 30, placed in the immediate vicinity of a visible facade of the generator, groups together the maximum active control components, as well as the operating control and display components. The circuit 30 also supports power components acting inter alia on the heating element 11. A microprocessor 31 receives the information from temperature of the tank 1 provided by a sensor 14 placed on the bottom of said tank 1, and information on the opening or closing status of the solenoid valve 13. The operator can observe a group of four LEDs 32 aligned and lighting up successively for a tank filled to the quarter respectively, at the half, three quarters and up to the capacity. A so-called tank light vacuum 33 lights up flashing for a tank filled to within 5% of the maximum. When the tank is completely empty, the usual means of empty tank detection keep the LED 33 permanently on. The circuit 30 also supports a command 34 by which the user regulates the flow of its iron, that is to say in reality, the set temperature of the tank 1.

The other usual commands and displays on this kind of device, such as on-off controls, heating indicator, etc. are not represented.

When the user wants to start an ironing session, she removes the safety cap 12, fills the tank 1 with water, which it closes, displays a flow rate steam desired by acting on the control 34, and puts the appliance under voltage. The microprocessor 31 records the initial temperature given by the sensor 14 and totals the time which elapses. Simultaneously the microprocessor 31 regulates the temperature of the tank 1.

The power to the heating element is cut off when the sensor 14 indicates a temperature equal to the set temperature, for example 115 ° C, supplied by command 34. At this time, the microprocessor registers the difference temperature of sensor 14 with the initial temperature and stops counting time. The ratio of the temperature difference to the measured time gives a heating rate which, the power of the heating element being constant and known, makes it possible to determine the mass of water contained by the tank 1.

The value of this mass is recorded and compared to four thresholds corresponding respectively to a filling substantially equal to 5%, to quarter, half, three quarters of the maximum permissible mass of water in tank 1. If the amount of water is less than 5% of the possible capacity on empty tank light flashes or stays on continuously if there are no more left of water, otherwise if the amount of water is less than a quarter the first indicator is on, otherwise if the amount of water is less than half the second indicator is on, otherwise if the amount of water is less than three quarters the third LED is on, otherwise the fourth LED is on. The user thus has a satisfactory display of the order of magnitude of the filling of its tank.

For slightly more sophisticated devices, the number of thresholds and indicators or indicators can be increased without difficulty to obtain all the precision desired display.

When the user uses the iron 20 she requests the command 21 to get steam. The microprocessor 31 then counts the opening time of the solenoid valve 13, calculates the mass flow as a function of the temperature read by the sensor 14, and calculates the quantity of water withdrawn in the form of vapor. This withdrawn quantity is subtracted from the quantity in memory, which is the initial quantity at the first sample. At the end of each withdrawal the display is updated by comparing the quantity of water memorized, with the thresholds and as previously indicated.

When the quantity of water remaining is less than the first predetermined threshold, for example at 5% of the total capacity, all the lights 32 go off and the empty tank light 33 flashes. The user then knows that she does not have a lot of autonomy in water but it can interrupt its work in the better conditions, after having finished ironing the current piece of laundry ironing. The user is not surprised by an untimely cessation of the vaporization which would light the light 33 permanently.

In the case where the tank 1 is empty the indicator 33 is kept on and the element heater 11 is turned off until the user stops completely the device to refill and restart a session of ironing.

In another version, the mass of water recorded in digital form is converted to an analog signal for display. A needle galvanometer then indicates the water level to the user. Nevertheless, we compare the value recorded at a minimum threshold so as to control the empty tank indicator like before.

In a neighboring embodiment, the initial water mass m ₀ is determined by the duration of the heating t between two predetermined temperatures, higher than the ambient temperature and lower than the lowest setpoint that the user can display, for example between 40 ° C and 80 ° C.

In another version, the command 34 acts on the average power of the heating element 11. On startup, the tank 1 heats up to a predetermined set temperature, then during sampling, the element heater 11 is supplied at a reduced power to correspond to a flow steam below the maximum possible. Pressure and temperature can then fall, but the level determination device taking into account the instant temperature is suitable for providing a correct indication with this type of regulation.

We see that the great flexibility of this device allows it to adapt to many types of regulation.

Many other known level display methods are possible while remaining within the scope of the invention, which makes it possible to determine this level economically and with good precision. Steam generators with of this device bring appreciable user comfort to the user.

Claims (7)

Steam generator comprising a tank (1) intended to be filled with water and then to be heated to produce steam at a pressure higher than atmospheric pressure, an electronic device (30) for determining and displaying the water level , characterized in that the device for determining the water level comprises means for calculating an initial water level as a function of the temperature curve for the first heating, means for calculating the product of the mass vapor flow rate at each sampling of water by the time of said withdrawal corresponding to the mass of water withdrawn in the form of vapor, and means for calculating each level of residual water. Steam generator according to claim 1, characterized in that the means calculate the flow rate as a function of the temperature of the tank (1). Steam generator according to claim 1 characterized in that the generator comprises a pressure sensor, and the means calculate the flow rate as a function of the pressure in the tank (1). Steam generator according to one of the preceding claims, characterized in that the display device (32,33) displays the level in a value relative to the level of the full tank. Steam generator according to one of the preceding claims, characterized in that the level display range is divided into several contiguous ranges corresponding to predetermined intervals where the instantaneous level can be, each range being provided with an indicator. Steam generator according to one of the preceding claims, characterized in that the generator comprises an indicator light (33) and / or an empty tank audible warning device, controlled by known means for detecting an empty tank and / or by the detection system level which activates said indicator light (33) or warning device when the level drops below a predetermined threshold. Process for determining the water level in a steam generator comprising a tank (1) intended to be filled with water and then heated to produce steam at a pressure higher than atmospheric pressure, characterized in that it consists of calculating an initial water level as a function of the temperature curve for the first heating, calculating each product the mass flow rate of water vapor by the time of said sampling corresponding to the mass of water taken in the form of steam , to calculate each residual water level.

Images