GB2298723A - Thermopot - Google Patents

Description

THERMOPOTS The invention relates to thermopots.

The invention relates more particularly to electric thermopots for use predominantly in the home for storing a supply of hot water for making tea and the like. Traditionally, especially in Eastern countries a supply of hot water is required to be constantly available in a domestic kitchen.

It is known generally to provide thermopots with a temperature sensitive electric element set to determine that water in the pot has reached at temperature of 10000 so that an electric heating element can be turned off as soon as the water reaches its boiling point. It is also possible to provide a thermo couple adjacent an outlet to detect the emission of steam from the thermopot and turn off the electric heating element as soon as steam is generated. Two particular problems arise with such methods of controlling the heating element. Firstly, the actual temperature at which water boils depends on atmospheric pressure which varies somewhat from time to time in all places but is significantly different at elevated attitudes.

Secondly, it is often a requirement or at least desirable for the water to be allowed to boil for a period of time to sterilise the water fully or remove, where necessary, odours by such boiling.

It is an object of the invention to overcome or at least reduce these problems.

According to the invention, there is provided a thermopot having a container for water, an electric heating element for heating the water, a temperature sensor arranged to provide signals dependent on the temperature of the water in the container, and a microcomputer programmed to control a power supply to the heating element and to turn off the power in response to signals from the sensor when the rate of rise of temperature of the water becomes substantially zero.

The thermopot may have a second temperature sensor arranged to provide signals dependent on the temperature of an outer case of the container and in which the microcomputer is programmed to turn off the power whenever the outer case temperature rises above a predetermined temperature.

A water level sensor may be provided comprising a tube in communication with the container and mounted on a side thereof, and an infrared emitter and detector at either side of the tube arranged so that a direction of a beam of infrared radiation is altered due to changes in diffraction when the tube is filled with water opposite the emitter and detector, whereby such beam alteration is indicative that the water level in the tube, and the container, is adjacent at a certain level.

A second electric heating element for the water may be included, and the microcomputer programmed to control a supply of power to the second heating element during a keep warm cycle for the thermopot.

A thermopot according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sectional side view of the thermopot; Figure 2 is an enlarged layout out of a liquid level sensor for the thermopot; Figure 3 is a diagram of a circuit and electrical components for use in the thermopot; Figure 4 is a flow chart of a protection cycle for the thermopot; Figure 5 is a flow chart of a timer cycle; Figure 6 is a first part of a boil, re-boil and keep warm cycle; and Figure 7 is the second part of the cycle of Figure 6.

Referring to the drawings, in Figure 1 the thermopot comprises a water container 10 surrounded by an outer casing 11. A lid 12 hinged at 13 fits over the top of the container 10 and seals 14 are provided between the lid and the top of the container 10. The lid is normally provided with securing clips (not shown) and a steam vent (not shown).

A main electrical heating element 15 surrounded by an auxiliary heating element 16 is mounted to the base of the container 10. Two temperature sensors 17 and 18 are provided for mounting the temperature of water in the container 10 and the temperature of the exposed surface of the outer casing 11, respectively. An insert 19 supported by bellows 20 is provided to pump a quantity of hot water out of the container 10 via a tube 21 and a spout 22 in generally known fashion. A printed circuit brand 23 and a microprocessor 24 are mounted inside the base of the thermopot.

In Figure 2, the tube 21, normally made of glass, and relative positions of an infrared transmitter 25 and a receiver 26 are shown.

A solid line extending between the transmitter and receiver represents the direction of a beam of infrared radiation when water occupies the inside of the tube 21. The dotted line represents the path of the beam if the tube is empty, that is, occupied by air. In practice, the transmitter and receiver are mounted at a chosen level, say A in Figure 1, and when the water falls below level A, the receiver 26 will no longer receive infrared radiation and as such this condition represents or provides a low water level indication. Alternatively, the receiver 26 can be positioned where shown dotted in Figure 2, so that a low water level indication is provided by the first receipt of infrared signals at the receiver when the water level falls.

In Figure 3, the microcomputer 24 is supplied via a transformer, rectifiers, a filter and voltage regulator shown in drawing envelope 1A. Operating switches and indicators are provided and shown in drawing envelope 2A. A relay and power supply for the main heater 15 are shown in drawing envelope 3A and a triac power supply for the auxiliary heater 16 is shown in drawing envelope 4A. This diode 25 and receiver 26, shown in drawing envelope 5A, is arranged as discussed with reference to Figure 2.

A reset circuit is shown in drawing envelope 6A. The microcomputer 24 is reset at any starting moment by a zero to one pulse which is generated by the reset circuit. When a 5 volt supply is connected to the reset circuit, this is greater than the voltage threshold of a zener diode ZD3, a point X goes low and a transistor 4 is turned ON to charge up a capacitor C3. A point B goes high and disenables a reset pin 13 of the microcomputer 24. Whenever the voltage supply falls below the zener diode ZD3 threshold, the voltage at the base of the transistor Q4 goes high and the transistor Q4 turns OFF. The capacitor C3 then discharges via resistors R6 and R8. The point B therefore goes low to reset the microprocessor 24.The advantage of this reset circuit is that when the power to the machine is switched or turns OFF and then ON again quickly, the microprocessor 24 is properly reset because the circuit uses a high state reference for the reset point.

A sinusoidal to square wave generator is shown in drawing envelope 7A.

Square waves are used as a timing source for the microcomputer 24 and also used to synchronise operation of the triac in drawing envelope 4A.

A temperature detection circuit is shown in drawing envelope 8A. The circuit consists of resistors, a comparator IC2A and a temperature sensitive electrical component RT1, shown as 17 in Figure 1. The resistors R29, R30 and R31 are connected to different ports of the microcomputer 24 and to the component RT1. Several resistance values are provided by combination of the resistors and produce different possible dividing voltages and for the component RT1 at the same temperature. A chosen divided voltage is compared with a reference voltage in the comparator IC2A. The reference voltage is provided by using a combination of the resistors R17 and R18. Therefore the microcomputer 24 can utilise different combinations of voltages at its ports and to take corresponding action such as turning on and off the heaters at different temperatures.

The sensor 18 of Figure 8 is shown as component RT2 in drawing envelope 9A. The basic operation of this circuit is similar to the detection circuit in drawing envelope 8A. However there is only detection of one temperature, so only one resistor is required. When the outer casing temperature is higher than a preset value, the dividing voltage from the temperature sensitive component RT2 and a resistor R42 is higher than the reference voltage supplied to a comparator IC2B so the output voltage of IC2B goes positive. When the microcomputer 24 receives a positive voltage signal, it sends out signals to control the turn off both heating elements 15 and 16 and to turn off all indicators.

Broadly stated, the microcomputer 24 is provided with power and is programmed to control automatically the operation of the heaters 15 and 16, provide visual and audible signals and to respond to manual operations of the switches in drawing envelope 2A.

A special part of a programme for the microcomputer 24 enables detection of when water in the container has reached its boiling point. The programme instructs the microcomputer 24 to compare the temperature of the water by monitoring signals, provided from the component RT1, and time. Such comparison is carried out during heating of the water by the main heater 15. When the rate of temperature rise becomes zero or near zero, the microcomputer 24 is programmed to switch off the power supply to the main heater. The switch off may however be deliberated delayed for a few seconds, or for longer, say 3 minutes, if the water is to be de-odourised by boiling for a few minutes.

The important point is that the nil rate of rise of temperature serves to identify that the water has begun to boil and is independent of the actual temperature of the water. This means that this water-boiling detection programme operates independently of atmospheric pressure.

There is therefore no requirement or need to adjust a boiling temperature level sensor in the thermopot according to at what location the thermopot is being used or is likely to be used, for example.

Operation of the micropot will now be described with reference to flow charts which are themselves generally easy to follow in conventional manner and representation of the programming of the microcomputer 24.

In Figure 4, the flow chart represents outer casing overheat protection and low water level detection cycle. The microcomputer 24 performs this cycle by scanning its input ports 6 and 8 at regular intervals. The supply power to heating elements 15 and 16 and to LED indicators is turned off by the microcomputer if the outer casing temperature exceeds a predetermined value. Also if the water level falls below a predetermined level, the microcomputer 24 will isolate the power from the heating elements and provide a beeping sound signal for 15 seconds or alternatively blink a keep warm temperature LED indicator until the water level recovers to above the predetermined level. Once the water level is above the predetermined level, the microcomputer performs boiling cycle or enters the timer mode depending on a timer setting.The flow chart also shows that one beep will be sounded if the mains power supply is disconnected from the thermopot.

In practice, the microcomputer is programmed to ignore any intermittent low water level signals. Such may occur during water pumping action when the level is close or fairly close to the set low level. In this respect, the microcomputer is arranged to respond to any five consecutive low level signals that occur over a period of, say, five seconds.

In Figure 5, the flow chart represents a timing operation. When the programme time have been set, the microcomputer 24 turns off the power to the heating elements and turns on the corresponding timer LED indicator. However, the de-odourise selection is not affected and its indicator remains on. When the timer has counted up to the present time, the boiling function starts.

In Figures 6 and 7, the flow chart represents the boiling/reboiling and keep warm cycle. The main heating element 15 is turned on as soon as power is supplied to the thermopot provided the outer casing temperature is lower than a predetermined value and the water level is higher than a predetermined height. When the water boiling temperature is reached (as discussed above), the microcomputer 24 normally turns off main heating element and switches immediately to a keep warm cycle if de-odourise function has not been selected by the user. Otherwise boiling continues for, say, 3 minutes to de-odourise the water and then the keep warm cycle will start. The keep warm function lasts for a maximum of 48 hours, then the thermopot sends out two beeps and the power to the keep warm heating or auxiliary element 16 is cut off and all LED indicators goes out.The thermopot will also send out one beep to remind the user 30 minutes before the keep warm cycle finishes. After keep warm cycle is over, all functions are inhibited except a reboil function. As seen in the flow chart, the microcomputer 24 provides two levels of keep warm temperatures T1 (higher level) and T2 (lower level) that can be selected at any time by the user. During normal keep warm cycles, the keep warm heating element 16 is turn on or off at the predetermined temperatures to maintain water within a certain range of temperature. The microcomputer however activates on auto boil function whenever the water temperature drops below T2+aT at higher level keep warm and below T3 at lower level keep warm setting. Moreover, if the keep warm level changes from T2 to T1, the main heating element is turned on to speed up the rate of the temperature rise until the water temperature is higher than Tl+nT.

The microcomputer is also programmed to provide a delay start or timer function so that the thermopot may be switched ON automatically reasonably close to a time of day when the hot water is required. For example, the thermopot may be set by the user to switch on automatically say 15 or 20 minutes before breakfast time. In this way power is not wasted during the night keeping water hot in the thermopot.

Claims (5)

1. A thermopot having a container for water, an electric heating element for heating the water, a temperature sensor arranged to provide signals dependent on the temperature of the water in the container, and a microcomputer programmed to control a power supply to the heating element and to turn off the power in response to signals from the sensor when the rate of rise of temperature of the water becomes substantially zero.

2. A thermopot according to claim 1, including a second temperature sensor arranged to provide signals dependent on the temperature of an outer case of the container in which the microcomputer is programmed to turn off the power whenever the outer case temperature rises above a predetermined temperature.

3. A thermopot according to claim 1 or 2, including a water level sensor comprising a tube in communication with the container and mounted on a side thereof, and an infrared emitter and detector at either side of the tube arranged so that a direction of a beam of infrared radiation is altered due to changes in diffraction when the tube is filled with water opposite the emitter and detector, whereby such beam alteration is indicative that the water level in the tube, and the container, is adjacent at a certain level.

4. A thermopot according to any one of claims 1 to 3, including a second electric heating element for the water, in which the microcomputer is programmed to control a supply of power to the second heating element during a keep warm cycle for the thermopot.

5. A thermopot substantially as herein described with reference to the accompanying drawings.