GB2635484A

GB2635484A - Heated liquid dispenser

Info

Publication number: GB2635484A
Application number: GB2502217.9A
Authority: GB
Inventors: Wong Francis; Hunt Andrew
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 2022-10-07
Filing date: 2022-10-07
Publication date: 2025-05-14
Also published as: GB2623302B; GB2623302A; GB202214738D0; CN221403497U; GB202502217D0

Abstract

A heated liquid dispenser 10 comprises a controller 3 and dispenses a first fraction of a required volume of liquid heated to a high temperature by a flow-through heater 4 in a first stage, and a second fraction at a lower temperature in a second subsequent stage so that the dispensed liquid is at the required temperature. The heating of the liquid is controlled using a PID algorithm responsive to the measured temperature. The second fraction of liquid may bypass the flow-through heater so as to avoid residual heating of dispensed liquid by the heater. During the second stage the second fraction of liquid may be heated to the lower temperature in response to the measured temperature of the heated liquid, the heating being controlled by the PID algorithm. Different PID constants may be used between the first and second stages. Between the first and second stages liquid may be passed through the heater and return to a liquid supply 1 so as to remove residual heat from the heater.

Description

Heated Liquid Dispenser Field of the Invention

mon This present invention relates to an apparatus and method for heating and dispensing liquid.

Background of the Invention

[0002] One type of apparatus for dispensing heated liquid comprises a flow through heater in which liquid is heated as it flows. These may be used for example for continuous or near-instantaneous dispensing of hot or boiling water, for use for example in hot water dispensers or coffee makers.

[0003] One application of such an apparatus is in dispensing water for mixing with baby milk powder to make baby milk. The water is dispensed in two stages: a first quantity of water is heated and dispensed at a high temperature, preferably above 70°C, to sterilize the milk powder, then a second quantity of water is dispensed at a lower temperature, so that the final temperature of the baby milk formula is suitable for feeding, such as around 37°C.

[0004] An example of a heated liquid dispenser for baby milk is disclosed in WO-A-2014/114935, in which a controller detects the temperature of water upstream of a flow-through heater, calculates how much energy is required to heat a predetermined volume of water from the detected temperature to a required final temperature, and energises the flow-through heater for a calculated period to deliver that amount of energy to the liquid. After the heater is de-energised, the liquid flowing through the heater removes the residual heat from the heater so that the calculated amount of energy is transferred to the liquid.

[0005] The above example has a number of disadvantages. The first is that any variation in the flow rate of the liquid caused by, for example, a change to the supply voltage or ambient temperature will result in a variation in the temperature of the dispensed liquid. A further disadvantage is that if the temperature of the liquid in the reservoir is relatively high and there is significant residual heat in the heater it may not be possible to produce a mixture with an acceptably low final temperature.

[0006] GB-A-2600398 discloses another example of a heated liquid dispenser for baby milk, in which a temperature sensor senses the outlet temperature of a flow-through heater during a first stage, and the energisation of the flow-through heater is controlled in response to the sensed 30 outlet temperature.

Statements of the Invention

[0007] Aspects of the invention are defined by the accompanying claims.

[0008] Embodiments of the invention relate to an apparatus and method for heating and dispensing a predetermined volume of liquid (e.g. water) using an electrically powered flow-through heater such that the temperature of the dispensed predetermined volume of liquid is at a required temperature. The apparatus comprises a source of liquid, such as a reservoir or mains supply, a pump, a flow-through heater and a controller arranged to control the pump and the flow-through heater.

[0009] In a first stage, a first fraction of the liquid may be dispensed at a high temperature, such as greater than 70°C, for sterilising material such as baby milk powder in a receptacle such as a bottle, to which the liquid is added. In a second, subsequent stage, a second, remaining fraction of the liquid is dispensed at a lower temperature, so as to bring the temperature of the dispensed liquid in the receptacle down to the required temperature.

[0010] The temperature of the dispensed liquid, in particular the temperature of the first fraction of liquid, may be controlled using a proportional, integral and differential (PID) algorithm. A temperature sensor downstream of the heater may provide a feedback signal to the temperature controller, which uses a PID algorithm to control the heating and/or flow of liquid through the heater so as to achieve a target temperature (such as 70°C) or temperature range (such as 68-72°C) as monitored by the temperature sensor. This may allow improved control of the dispensed liquid temperature.

[0011] The second fraction of liquid may be dispensed at a lower temperature to bring the temperature of the dispensed liquid to the required temperature, which in the case of making baby formula milk is preferably in the range 35°C to 40°C. To achieve the required temperature when the liquid in the reservoir is at a relatively high temperature, it may be desirable that the second fraction of liquid is not heated, and therefore the heater is not energised, whilst dispensing the second fraction of liquid. Conversely, if the liquid in the reservoir is at a relatively low temperature, it may be desirable to heat the second fraction of the liquid. This heating may also be controlled by the PID algorithm. The parameters of the PID algorithm may be set differently during the first and second stages.

[0012] If the temperature of the liquid in the reservoir is too high, it may not be possible for the second fraction of liquid to cool the dispensed liquid to the required temperature. One possible solution is to reduce the volume of the first fraction of liquid and consequently increase the volume of the second fraction of liquid so as to make up the required total volume of liquid. However, when making baby formula milk a minimum volume of water is desirable as the first fraction, in order to dissolve and sterilize the milk powder before the second fraction of liquid is dispensed.

[0013] One problem in achieving the required temperature is the residual heat remaining in the heater (i.e. from the heat capacity of the heater itself) after the first stage, which tends to heat the second fraction of liquid even though the heater is de-energised. In one solution according to an embodiment of the invention, the effect of residual heat after the first stage is mitigated by bypassing the heater during the second stage, so that liquid is dispensed from the reservoir without passing through the heater. In this way, the second fraction of liquid may be dispensed at approximately the temperature of liquid in the reservoir, without the liquid being heated by residual heat from the heater. Bypassing the heater may be achieved for example by a three-way valve upstream of the heater. When the second fraction of liquid is dispensed, the valve is positioned so that the liquid bypasses the heater and flows directly to the dispensing point, for example into the receptacle holding the first fraction of liquid in which the milk powder is dissolved.

100141 One alternative or additional solution is to transfer the residual heat back to the reservoir, where it is dispersed in a larger volume of liquid than the second fraction, thereby reducing the temperature increase in the second fraction caused by the residual heat. After the first fraction of liquid is dispensed, the heater is de-energised and liquid is pumped through the heater to cool it down, this liquid then being returned to the reservoir. This may be achieved by a three-way valve positioned down-stream of the heater, which can be switched between outputting liquid to the dispensing point and outputting liquid to the reservoir.

[0015] Another alternative or additional solution is to de-energise the heater during a final part of the first stage, so that any residual heat is transferred to the first fraction of liquid. A 30 target temperature during heating of the first fraction of liquid may be increased to compensate for the reduced heating (i.e. by the residual heat without energising the heater) during the final part of the first stage.

[0016] The target temperature of the first fraction of liquid dispensed during the first stage may be adjusted depending on a number of factors. For example, the target temperature when dispensing a small volume may be increased to offset the cooling effect of the receptacle. The target temperature may be adjusted depending on the temperature of liquid in the reservoir, which will influence the temperature of the second fraction of liquid dispensed during the second stage.

[0017] The heater may be pre-heated before the pump is started in the first phase such 10 that liquid already contained within the flow-through heater is heated. Any residual heat remaining in the heater from a previous operation may assist with this pre-heating.

[0018] The heater may be a thick film flow-through heater, for example as disclosed in GB-A-2580948, comprising a thick film heating element and a channel plate fixed to the heating element so as to form a channel for heating fluid. This type of flow-through heater has a low thermal mass such that the liquid is heated quickly up to temperature when the heater is energised, and has low residual heat.

Brief Description of the Drawings

[0019] There now follows, by way of example only, a detailed description of preferred embodiments of the present invention, with reference to the figures identified below.

[0020] Fig. 1 is a schematic diagram of the main components of a liquid heating and dispensing apparatus in a first embodiment of the invention.

[0021] Fig. la is a flow diagram of a method of operation of the liquid heating and dispensing apparatus in the first embodiment.

[0022] Fig. 2 is a schematic diagram of the main components of a liquid heating and 25 dispensing apparatus in a second embodiment of the invention.

[0023] Fig. 2a is a flow diagram of a method of operation of the liquid heating and dispensing apparatus in the second embodiment.

[0024] Fig. 3 is a schematic diagram of the main components of a liquid heating and dispensing apparatus in a third embodiment of the invention.

[0025] Fig. 3a is a flow diagram of a method of operation of the liquid heating and dispensing apparatus in the third embodiment.

[0026] Fig. 4 is a schematic diagram of a PID algorithm which may be used in at least some embodiments.

[0027] Figure 5 is a flowchart of a method of determining parameter values which may be used in at least some embodiments.

[0028] Figure 6 is a graph showing measured outlet temperature and heater power against 10 time in a first operational example of an embodiment.

[0029] Figure 7 is a graph showing measured outlet temperature and heater power against time in a first operational example of an embodiment.

[0030] Fig. 8 is a perspective view of one example of the flow-through heater suitable for use in the embodiments.

Detailed Description of the Embodiments

[0031] Liquid heating and dispensing apparatus 10 in at least some embodiments of the invention comprises a liquid flow path comprising a liquid supply 1, such as a reservoir or mains supply, a pump 2 for pumping liquid through the flow path, a flow-through heater 4 for heating liquid and an outlet 6, such as a dispensing nozzle or spout, through which the heated liquid is dispensed into a receptacle 7 such as a baby milk bottle.

[0032] A controller 3, such as an electronic processor or microcontroller, receives an output of one or more temperature sensors 5a, 5b arranged to sense liquid temperature at one or more points on the flow path, and controls energisation of the pump 2 and the flow-through heater 4 so as to dispense a required volume of liquid at a required temperature, for example as in the specific embodiments described below.

[0033] A first, downstream temperature sensor 5a may be positioned between the flow-through heater 4 and the outlet 6, and arranged to sense the temperature of liquid downstream of the flow-through heater 4.

[0034] A second, upstream temperature sensor 5b may be arranged to sense the 5 temperature of liquid upstream of the heater 4, for example the temperature of liquid in the liquid supply 1, in the pump 2, or elsewhere between the liquid supply 1 and the heater 4.

[0035] In the following embodiments the pump 2 is shown between the liquid supply 1 and the heater 4, but the pump 2 may alternatively to positioned elsewhere in the liquid flow 10 path, or may be replaced by a shutoff or variable flow valve if the pressure of the liquid supply 1 is sufficient to cause the required liquid flow through the flow path.

[0036] User input to the controller 3, and optionally a display of the operational state of the apparatus 10, may be provided by a user interface (UI) 8, such as a touchscreen and/or push buttons. The UI may be used to select the required volume of liquid to be dispensed, for example between 120 ml and 330 ml, in incremental steps or by selecting one of a plurality of pre-set volumes. The UI may also be used to select the required temperature of the dispensed liquid, or this may be pre-set and not variable by the user. The UI 8 is operable by the user to initiate the dispensing process, for example by selecting 'Start' or immediately by selecting a pre-set volume of liquid to be dispensed.

[0037] The apparatus 10 may be operated to dispense the predetermined required volume of liquid in two stages: at a first stage, a first fraction of the required volume of liquid may be dispensed at a high temperature, such as greater than 70°C, for sterilising material such as baby milk powder, in the receptacle 7. In the second stage, a second, remaining fraction of the required volume of liquid is dispensed at a lower temperature, so as to bring the temperature of the dispensed liquid in the receptacle 7 down to the required temperature; in the case of baby milk formula, this may be a suitable feeding temperature such as around 38°C, or at least within a desired range of 35°C to 40°C.

[0038] The controller may wait for a predetermined interval between the first and second stages, or wait for a further user input to initiate the second stage, to allow the user to mix 30 the material with the first fraction of liquid. Alternatively the controller may proceed directly from the first stage to the second stage, for example if the user is required to mix the material with the first fraction of liquid during the first stage.

[0039] A first specific embodiment of the apparatus 10 is shown in Figure 1. In this embodiment, a valve 9 is located in the flow path upstream of the heater 4, and receives liquid output by the pump 2. The output of the valve 9 is switchable by the controller 3 between a first state in which the liquid is output to the heater 4, and a second state in which liquid bypasses the heater 4 and passes directly to the outlet 6, for example through a bypass channel 9a (e.g. a pipe). The valve 9 may be a three-way valve, with one inlet and two outlet ports.

[0040] The valve 9 may additionally be operable as a shut-off valve, so as to close both outlets; the shutoff valve may be used to prevent flow into the heater 4 when the pump 2 is not energised.

[0041] One example of a method of operation of the apparatus of the first embodiment is shown in Fig. la. At step Si, the user selects via UI 8 a volume of liquid to be dispensed, and 15 optionally the required temperature of the dispensed liquid and starts the dispensing operation, as described above.

[0042] The first dispensing stage now begins. During this stage, the valve 9 is set by the controller 3 to its first state, in which liquid is output to the heater 4.

[0043] At step S2 the controller 3 measures the temperature of liquid from the liquid supply 1, using for example the second temperature sensor 5b, and calculates a target temperature and volume fraction for the first dispensing stage, for example by using a look up table of data obtained empirically or by using ratios of the water temperature in the supply and the target temperature and the ratio of the volumes of liquid to be dispensed during the first and second stages, examples of which are disclosed in more detail below.

[0044] At step S3, the controller 3 energises the flow-through heater 4, so that the temperature of the flow-through heater 4 and any liquid already held within the flow-through heater 4 begins to rise. Optionally at step S4, the controller 3 waits for a predetermined time to, such as 3 seconds. The controller 3 then energises the pump 2 at step S5 so that the liquid begins to flow through the flow path.

[0045] At step S6, the controller 3 measures the outlet temperature as sensed by the first temperature sensor 5a and controls energisation of the heater 4 (step 57) throughout the first dispensing stage using a PID algorithm so as to maintain the outlet temperature close to the target temperature. Using the PID algorithm, the controller 3 calculates an error value between the temperature measured by first temperature sensor Sa and the target temperature, then uses a weighted sum of the error value, its integral and its derivative over time to calculate the power delivered to the heater. The weightings given to each of the terms may be derived and optimised empirically, as discussed in more detail below.

[0046] The pump 2 may be operated at a constant rate at this stage, or may be controlled 10 by the controller 3 to vary the flow rate so as to control the outlet temperature.

[0047] At step S8, the controller 3 de-energises the pump 2 and/or the heater 4, and the first stage is complete. There may be an interval between the first and second stages, as described above.

[0048] The second stage then begins. At step S9, the controller 3 operates the valve 9 so that the flow path bypasses the heater 4. At step 510, the controller energises the pump 2 so that the second fraction of liquid is dispensed, substantially at the temperature of the liquid supply 1. The heater 4 remains de-energised, but in any case the second fraction of liquid bypasses the heater 4 and is not heated by residual heat in the heater 4. At the end of the second stage (step 511), the pump 2 is de-energised and the second stage is complete.

[0049] Figure 2 shows apparatus 10 in a second embodiment which differs from the first embodiment in that the valve 9 is positioned downstream of the heater 4. The output of the valve 9 is switchable by the controller 3 between a first state in which liquid from the heater 4 is output to the outlet 6, and a second state in which liquid from the heater is returned via a return channel 9b (e.g. a pipe) to the liquid supply 1, which may be a reservoir in this case. The valve 9 may be a three-way valve, with one inlet and two outlet ports, and may additionally operate as a shut-off valve.

[0050] One example of a method of operation of the apparatus of the second embodiment is shown in Fig. 2a. Steps 51 to S8 proceed as in the first embodiment, except that the valve 30 9 is in its first state so that liquid passes from the heater 4 to the outlet 6.

[0051] Between the first and second stages, at step S9 the controller 3 switches the valve 9 to its second state and operates the pump 2 so that water flows from the liquid supply 1 through the heater 4 and back to the liquid supply 1, while the heater 4 is de-energised. Any residual heat in the heater 4 is thereby returned to the liquid supply 1. The controller 3 then switches the valve 9 back to its first state (step 510) and begins the second stage by energising the pump 2 to dispense the second fraction of liquid via the heater 4, which is de-energised and from which residual heat has been removed. Hence the second fraction of liquid is substantially at the temperature of the liquid supply 1, which is not significantly increased by the residual heat as this is dispersed throughout the volume of liquid in the liquid supply 1.

[0052] In a variant of the second embodiment, instead of the return channel 9b returning liquid to the liquid supply, the valve 9 in its second state outputs the liquid to a waste channel which may lead to a waste liquid reservoir or drain. In this way, the apparatus disposes of liquid heated by the residual heat, which therefore does not affect the temperature of the second volume of liquid.

[0053] Figure 3 shows apparatus 10 in a third embodiment which differs from the first and second embodiment in that there is no valve 9. Instead, residual heat is removed from the heater 4 by de-energising the heater 4 before the end of the first stage, as explained in the method below.

[0054] One example of a method of operation of the apparatus of the third embodiment is shown in Fig. 3a. Steps S1 to S8 proceed as in the first embodiment, except that the valve 9 is not present. At the end of the first stage, the controller 3 continues to energise the pump 2 after the heater is de-energised (step S9), so that liquid heated by the residual heat of the heater 4 is dispensed at the end of the first stage.

100551 The second stage starts at step S10, optionally after an interval for mixing material with the first fraction of liquid as described above. The pump 2 is energised to dispense the second fraction (step S11) while the heater 4 is de-energised, and there is substantially no residual heat remaining in the heater 4. At the end of the second stage (step S12), the pump 2 is de-energised and the second stage is complete.

[0056] The PID algorithm as executed by the controller 3 in the above embodiments will now be described in more detail with reference to Figure 4. The PID algorithm is executed iteratively, for example at predetermined time intervals. A temperature error calculation stage 40 calculates a temperature error TE by subtracting the measured liquid temperature Inn, for example as measured by the first temperature sensor Sa, and the target temperature IT as determined from a lookup table as described below. The temperature error TE is then input to each of a proportional stage 43, an integral stage 44 and a differential stage 45. The proportional stage 43 multiplies the temperature error TE by a proportional constant P. The integral stage 44 multiplies an integral over time of the temperature error TE by an integral constant I. The differential stage 45 multiplies a differential with respect to time of the temperature error TE by a differential constant D. The outputs of the proportional stage 43, integral stage 44 and differential stage 45 are combined by a correction summing stage 41 to output a power correction value which is then added at a power correction stage 42 to the previous power level PLE_i to calculate the power level PL of the heater 4. At the first iteration, the power level PL may be set at a predetermined value, or at the last value from the previous operation.

[0057] The values of the proportional constant P, integral constant I and differential constant D may be predetermined and may vary between the first and second stages. In one example, in the first (hot) dispensing stage, P=2.55, 1=0.255 and D=0.6, while in the 20 second (cold) dispensing stage, P=1.7, 1=0.005 and D=2.55.

[0058] Examples of how the controller 3 determines the target temperature, volume fractions and PID constants will now be discussed in more detail with reference to Figure 5. First (step P1), the controller 3 determines a parameter set number based on the liquid supply temperature as measured by the second temperature sensor 5b, for example as shown in Table 1 below:

Table 1

Parameter Set no. Liquid supply temperature range °C 1 5 -8.5 2 8.5 -10.5 3 10.5 -15.5 4 15.5 -27.5 27.5 -30 [0059] Next (step P2), the controller 3 determines parameter values based on the parameter set number, based on the total required liquid volume. The parameter values may include target temperature and first volume fraction. For example, Table 2 shows the parameter values for parameter set number 1, and Table 3 below shows the parameter values for parameter set number 5.

Table 2 -Parameter Set 1 (5 -8°C) Stage 1 (hot) Stage 2 (cold) Total vol (ml) Vol (ml) Target temp °C Vol (ml) Target temp °C 34 85 86 26 40 85 110 26 50 85 130 26 210 55 85 155 26 240 65 85 175 26 270 70 85 200 28 300 80 85 220 28 330 93 85 237 28 Table 3 -Parameter Set 5 (28 -30°C) Stage 1 (hot) Stage 2 (cold) Total vol (ml) Vol (ml) Target temp °C Vol (ml) Target temp °C 28 76 92 5 33 76 117 5 45 76 135 5 210 55 76 155 5 240 60 78 180 5 270 65 78 205 5 300 75 78 225 5 330 85 78 245 5 [0060] Finally (step P3), the controller 3 operates the pump 2 and heater 4 according to the determined parameter values for stages 1 and 2, for example as discussed below. The pump flow rate may be set to a constant rate.

[0061] The controller may switch the heater 4 on for a predetermined preheat time and/or 15 level before switching on the pump 2. The preheat time and/or power level may be determined from the selected parameter set. For example, for parameter set 1 the preheat time may be set at 5 seconds, while for parameter set 5 the preheat level may be set at 4.5 seconds. The preheat time and/or power level may be reduced depending on the time elapsed since the previous dispensing operation, to take account of the residual heat in the heater 4.

[0062] Figure 6 is a graph showing an example of heater power level PL and measured outlet temperature TM as a function of time (in units of 100 ms) in the first and second stages, for a total dispensing volume of 240 ml with parameter set 1 (liquid supply temperature 5°C), together with the target temperature IT at each stage. In stage 2, the liquid inlet temperature is lower than the target temperature of 26-28°C, so the heater 4 is operated during the second stage. The power level of the heater 4 is controlled by switching the heater 4 on and off with a duty cycle determined by the power level PL. As can be seen from the graph, the measured liquid temperature therefore fluctuates around the target temperature.

[0063] Figure 7 is a graph showing an example of heater power level PL and measured outlet temperature TM as a function of time in the first and second stages, for a total dispensing volume of 240 ml with parameter set 5 (liquid supply temperature 30°C) together with the target temperature IT at each stage. In stage 2, the target temperature (Ti = 5°C) is set below the liquid inlet temperature, so that the heater 4 is switched off during the second stage.

[0064] Fig. 8 shows an example of a flow-through heater 4 suitable for use in the above embodiment, having an inlet 21, an outlet 22 and first temperature sensor 5a arranged to sense the outlet temperature TM. A liquid channel between the inlet 21 and the outlet 22 is defined between a planar thick-film heating element 23 and a channel plate 24, such that liquid flowing through the channel is heated by the heating element 23. The heating element 23 and channel plate 24 have a low thermal mass, giving a fast heating response and low residual heat.

[0065] Another advantage of the thick-film heater 4 is that it is able to dispense water at or above 100°C e.g. as steam, which can also be used to sterilise the receptacle 7, for example before dispensing liquid into the receptacle 7.

[0066] The heater 4 preferably includes a thermal cut-out to prevent over-heating; this may comprise an overheat sensor such as the E-FAST sensing technology as described in WO-A-2008/150172 Al.

Alternative embodiments [0067] The above specific embodiment is described for use in preparing baby milk, but may be used for the preparation of other drinks (e.g. tea, instant coffee or hot chocolate) or foods (e.g. instant noodles), where a predetermined volume of liquid and/or final temperature is required.

[0068] In some embodiments, individual features as described above may be combined or 10 omitted. On reading the above description, the skilled person may contemplate alternative embodiments which nevertheless fall within the scope of the accompanying claims.

[0069] Alternative statements of invention are recited below as numbered clauses.

1. Liquid heating and dispensing apparatus comprising a flow-through heater and a controller arranged to control flow of liquid from a liquid supply through the flow-through heater and heating of liquid by the flow-through heater so as to dispense a predetermined 5 volume of liquid at a required temperature, the apparatus being arranged to: a) during a first stage, dispense a first fraction of the predetermined volume of liquid heated to a high temperature; and b) during a second, subsequent stage, dispense a second fraction of the predetermined volume of liquid at a lower temperature; wherein the second fraction of liquid is dispensed from the liquid supply without passing through the flow-through heater.

2. Liquid heating and dispensing apparatus, comprising a flow-through heater, and a controller arranged to control flow of liquid from a liquid supply through the flow-through 15 heater and heating of liquid by the flow-through heater so as to dispense a predetermined volume of liquid at a required temperature, the apparatus being arranged to: a) during a first stage, dispense a first fraction of predetermined volume of liquid heated to a high temperature; and b) during a second, subsequent stage, dispense a second fraction of the predetermined volume of liquid at a lower temperature; wherein the controller is arranged to measure the temperature of liquid heated by the flow-through heater and control heating and/or flow of the liquid through the flow-through heater using a PID algorithm, in response to the measured temperature.

3. Apparatus of clause 2, wherein during the second stage the second fraction of the predetermined volume of liquid is heated to said lower temperature, the heating being controlled using a PID algorithm in response to the measured temperature of the heated liquid.

4. Apparatus of clause 3, wherein different PID constants are used by the PID algorithm between the first and second stages.

5. Apparatus of any one of clauses 2 to 4, wherein the second fraction of liquid is dispensed from the liquid supply without passing through the flow-through heater.

6. Apparatus of clause 1 or clause 5, including a valve arranged selectively to pass liquid through the heater during the first stage and to bypass the flow-through heater during the second stage.

7. Apparatus of any one of clauses 2 to 4, arranged to, between the first and second stage, pass liquid through the heater and return the liquid to the liquid supply so as to 10 remove residual heat from the flow-through heater.

8. Apparatus of any one of clauses 2 to 4, arranged to, between the first and second stage, pass liquid through the heater and dispose of the liquid so as to remove residual heat from the flow-through heater.

9. Apparatus of any one of clauses 1 to 4, arranged to de-energise the heater while the liquid is flowing through the heater during the first stage, so as to remove residual heat from the heater.

10. Apparatus of any preceding clause, wherein the heater comprises a thick film flow-through heater.

Claims

Claims 1. Liquid heating and dispensing apparatus, comprising a flow-through heater, and a controller arranged to control flow of liquid from a liquid supply through the flow-through 5 heater and heating of liquid by the flow-through heater so as to dispense a predetermined volume of liquid at a required temperature, the apparatus being arranged to: a) during a first stage, dispense a first fraction of predetermined volume of liquid heated to a high temperature; and b) during a second, subsequent stage, dispense a second fraction of the predetermined volume of liquid at a lower temperature; wherein the controller is arranged to measure the temperature of liquid heated by the flow-through heater and control heating and/or flow of the liquid through the flow-through heater using a PID algorithm, in response to the measured temperature.
2. Apparatus of claim 1, wherein during the second stage the second fraction of the predetermined volume of liquid is heated to said lower temperature, the heating being controlled using a PID algorithm in response to the measured temperature of the heated liquid.
3. Apparatus of claim 2, wherein different PID constants are used by the PID algorithm 20 between the first and second stages.
4. Apparatus of claim 1, wherein the second fraction of liquid is dispensed from the liquid supply without passing through the flow-through heater.
5. Apparatus of claim 4, including a valve arranged selectively to pass liquid through the heater during the first stage and to bypass the flow-through heater during the second 25 stage.
6. Apparatus of any one of claims 1 to 3, arranged to, between the first and second stage, pass liquid through the heater and return the liquid to the liquid supply so as to remove residual heat from the flow-through heater.
7. Apparatus of any one of claims 1 to 3, arranged to, between the first and second stage, pass liquid through the heater and dispose of the liquid so as to remove residual heat from the flow-through heater.
8. Apparatus of any one of claims 2 to 3, arranged to de-energise the heater while the liquid is flowing through the heater during the first stage, so as to remove residual heat from the heater.
9. Apparatus of any preceding claim, wherein the heater comprises a thick film flow-through heater.