U.S. patent application number 16/752507 was filed with the patent office on 2022-05-26 for method of heat sanitization of a haemodialysis water circuit using a calculated dose.
This patent application is currently assigned to QUANTA DIALYSIS TECHNOLOGIES LIMITED. The applicant listed for this patent is QUANTA DIALYSIS TECHNOLOGIES LIMITED. Invention is credited to Clive BUCKBERRY, Eduardo ESSER, Keith HEYES.
Application Number | 20220160943 16/752507 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-26 |
United States Patent
Application |
20220160943 |
Kind Code |
A9 |
BUCKBERRY; Clive ; et
al. |
May 26, 2022 |
METHOD OF HEAT SANITIZATION OF A HAEMODIALYSIS WATER CIRCUIT USING
A CALCULATED DOSE
Abstract
A method of sanitizing liquid for use in a. medical device, the
method comprising the steps of providing a medical device defining
a water circuit with a volume of liquid, sensing the temperature of
the volume of liquid with a sensor, heating the volume of liquid
from an initial temperature to exceed a threshold temperature,
maintaining the volume of liquid above the threshold temperature,
determining a time-temperature value for the volume of liquid
periodically once the threshold temperature has been exceeded,
calculating a. cumulative time-temperature value and providing an
output signal once the cumulative time-temperature value has
reached a level indicative of a sanitizing dose. A medical device
and a liquid sanitizer are also disclosed.
Inventors: |
BUCKBERRY; Clive;
(Warwickshire, GB) ; HEYES; Keith; (Warwickshire,
GB) ; ESSER; Eduardo; (Warwickshire, GB) |
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Applicant: |
Name |
City |
State |
Country |
Type |
QUANTA DIALYSIS TECHNOLOGIES LIMITED |
Warwickshire |
|
GB |
|
|
Assignee: |
QUANTA DIALYSIS TECHNOLOGIES
LIMITED
Warwickshire
GB
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20200330671 A1 |
October 22, 2020 |
|
|
Appl. No.: |
16/752507 |
Filed: |
January 24, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15315114 |
Nov 30, 2016 |
10543305 |
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PCT/GB2015/051610 |
Jun 2, 2015 |
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16752507 |
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International
Class: |
A61M 1/16 20060101
A61M001/16; C02F 1/02 20060101 C02F001/02; A61L 2/04 20060101
A61L002/04; A61L 2/24 20060101 A61L002/24; C02F 1/00 20060101
C02F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2014 |
GB |
1409796.8 |
Claims
1. A method of sanitizing liquid for use in a medical device, the
method comprising the steps of: providing a medical device defining
a water circuit with a volume of liquid; sensing the temperature of
the volume of liquid with a sensor; heating the volume of liquid
from an initial temperature to exceed a threshold temperature;
maintaining the volume of liquid above the threshold temperature;
determining a time-temperature value for the volume of liquid
periodically once the threshold temperature has been exceeded;
calculating a cumulative time-temperature value; and providing an
output signal once the cumulative time-temperature value has
reached a level indicative of a sanitizing dose.
2. The method according to claim 1 wherein the cumulative
time-temperature value is calculated by a processor.
3. The method according to claim 1 wherein the cumulative
time-temperature value is calculated from a lookup table.
4. The method according to claim 1 any preceding claim further
comprising the step of setting a target cumulative time-temperature
value and providing the output signal once the target cumulative
time-temperature value is reached.
5. The method according to claim 4 wherein the output signal is in
the form of an audible or visual alarm.
6. The method according to claim 4, wherein the output signal
automatically causes termination of the liquid heating.
7. The method according to claim 1, further comprising the step of
maintaining the volume of liquid below an upper temperature.
8. The method according to claim 7 comprising the further step of
setting the upper temperature.
9. The method according to claim 1, further comprising the further
step of setting the threshold temperature.
10. The method according to claim 1, further comprising the further
step of setting an overall heating time.
11. The method according to claim 1, wherein the threshold
temperature is between 55.degree. C. and 65.degree. C.
12. The method according to claim 7, wherein the upper temperature
is between 70.degree. C. and 99.degree. C.
13. The method according claim 1, wherein multiple temperature
sensors provide the temperature of the volume of liquid.
14. The method according to claim 1, wherein the cumulative
time-temperature value is calculated according to A 0 = 1 .times. 0
.function. [ ( T - 80 ) z ] dt ##EQU00003## Where: A.sub.0 is the A
value when z is 10.degree. C.; t is the chosen time interval, in
seconds; and T is the temperature in the load in .degree. C.
15. The method according to claim 1, wherein the A.sub.0 value is
equal to 1800.
16. A medical device defining a water circuit, including: a tank
containing a volume of liquid; a sensor arranged to sense the
temperature of the volume of liquid; a heater arranged to heat the
volume of liquid from an initial temperature to exceed a threshold
temperature, and maintain the volume of liquid above the threshold
temperature; and a processor, wherein the processor is configured
to determine a time-temperature value for the volume of liquid
periodically once the threshold temperature has been exceeded and
calculate a cumulative time-temperature value so as to provide an
output signal once a cumulative time-temperature value indicative
of a sanitizing dose is reached.
17. (canceled)
18. (canceled)
19. A liquid sanitizer comprising a pneumatic pump; a tank
containing a volume of liquid; a sensor arranged to sense the
temperature of the volume of liquid; a heater arranged to heat the
volume of liquid from an initial temperature to exceed a threshold
temperature, and maintain the volume of liquid above the threshold
temperature; and a processor, wherein the processor is configured
to determine a time-temperature value for the volume of liquid
periodically once the threshold temperature has been exceeded and
calculate a cumulative time-temperature value so as to provide an
output signal once a cumulative time-temperature value indicative
of a sanitizing dose is reached.
20. The liquid sanitizer of claim 19 wherein the processor is
programmable to alter at least one of the threshold temperature and
the cumulative time-temperature value.
21. (canceled)
22. (canceled)
23. The medical device of claims 16, wherein the processor performs
the steps of any claims 4, 7 to 10.
24. The medical device of claim 16, wherein the medical device is a
kidney dialyser.
25. (canceled)
26. (canceled)
Description
[0001] The present invention relates to the preparation of dialysis
fluid for hemodialysis and related therapies and substitution fluid
for use in online therapies, such as hemodiafiltration and
hemofiltration. In particular, the present invention relates to a
method for heat sanitization of a liquid used in one of the above
processes.
[0002] It is flown to use heat to destroy microorganisms. During a
thermal destruction process, the rate of destruction of
microorganisms is logarithmic, as is the rate of growth of the
microorganisms. Thus bacteria subjected to heat are killed at a
rate that is proportional to the number of organisms present. The
process is dependent both on the temperature it exposure and the
time required at this temperature to accomplish to desired rate of
destruction.
[0003] Thermal calculations thus involve the need for knowledge of
the concentration of organisms to be destroyed, the acceptable
concentration of organisms that can remain behind (spoilage
organisms for example, but not pathogens), the thermal resistance
of the target organisms (the most heat tolerant ones), and the
time-temperature relationship required for destruction of the
target organisms.
[0004] Disinfection of many water based systems in medical devices
is frequently achieved by elevating the temperature for a
stipulated period of time. thereby using heat to destroy the
microorganism in the water. In dialysis it is common for a
combination of 80 degrees Celsius (.degree.C.) to be maintained for
30 minutes.
[0005] There are several well-established time-temperature
relationships for moist heat disinfection which are regarded as
equally acceptable. For moist beat disinfection a particular time
at a particular temperature can be expected to have a predictable
lethal effect against a standardised population of organisms. It is
therefore possible to define a standard exposure which will yield a
disinfected product in a correctly operated Washer Disinfector
(WD). Actual exposures can then be related to these standard
exposure conditions.
[0006] Definition of such disinfection processes may be achieved by
means of the A.sub.0 method which uses a knowledge of the lethality
of the particular process at different temperatures to assess the
overall lethality of the cycle and express this as the equivalent
exposure time at a specified temperature.
[0007] The A value is a measure of the heat resistance of a
microorganism.
[0008] A is defined as the equivalent time in seconds at 80.degree.
C. to give a disinfection effect.
[0009] The z value indicates the temperature sensitivity of the
reaction. It is defined as the change in temperature required to
change the A value by a factor of 10.
[0010] When the z value is 10.degree. C., the term A.sub.0 is
used.
[0011] The A.sub.0 value of moist heat disinfection process is the
equivalent time in seconds at a temperature of 80.degree. C.
delivered by that process to the product with reference to
microorganisms possessing a z value of 10.degree. C.
A 0 = 1 .times. 0 .function. [ ( T - 80 ) z ] dt ##EQU00001##
[0012] Where:
[0013] A.sub.0 is the A value when z is 10.degree. C.;
[0014] t is the chosen time interval, in seconds;
[0015] and T is the temperature in the load in .degree. C.
[0016] In calculating A.sub.0 values a temperature threshold for
the integration is set at 65.degree. C. since for temperatures
below 65.degree. C. the z and D value of thermophillic organisms
may change dramatically and below 55.degree. C. there are a number
or organisms which will actively replicate.
[0017] In dialysis current practice, raising the temperature to
80.degree. C. for 30 minutes gives a benchmark value A.sub.0equal
to 1800.
[0018] The present invention aims to provide an efficient method of
heat sanitization of a haemodialysis water circuit.
[0019] According to the first aspect of the present invention,
there is provided a method of sanitizing liquid for use in a
medical device, comprising the steps of sensing the temperature of
a volume of liquid with a sensor; heating the volume of liquid from
an. initial temperature to exceed a threshold temperature;
maintaining the volume of liquid above the threshold temperature;
determining a time-temperature value for the volume of liquid
periodically once the threshold temperature has been exceeded;
calculating a cumulative time-temperature value; and providing an
output signal once the cumulative time-temperature value has
reached a level indicative of a sanitizing dose.
[0020] Calculation of the time-temperature value for the volume of
liquid based on the cumulative effect of heating the water provides
a more accurate model of the sanitization process by ensuring a
fixed dose of heat sanitization is applied to the volume of liquid.
Furthermore, it maximizes the benefits of high temperatures (in
particular those above 80.degree. C.) thereby reducing the time for
which components are exposed to elevated temperatures. Natural
variation in the control loop and water recirculation will cause
natural temperature oscillations. Those time periods below
80.degree. C. but above the minimum temperature range are
integrated into the dose and those above are not leveraged
according to the power law relationship.
[0021] The cumulative time-temperature value may be calculated by a
processor. Alternatively, the cumulative time-temperature value may
be calculated from a lookup table.
[0022] The method may comprise the further step of setting a target
cumulative time-temperature value and providing the output signal
once the target cumulative time-temperature value is reached.
[0023] The output signal may be in the form of an audible or visual
alarm. This informs the user or operator that the sanitization
process is complete.
[0024] The output signal may automatically cause termination of the
liquid heating. This prevents the heat sanitization cycle from
running for longer than is necessary.
[0025] The method may comprises the further step of maintaining the
volume of liquid below an upper temperature. This may be to prevent
boiling of the sanitizing liquid, or prevent unnecessary thermal
stress on the components of the heat sanitization device.
[0026] The method may comprise the further step of setting the
threshold temperature. The method may comprise the further step of
setting an overall heating time. This allows the process to be
tailored according to the environmental conditions (for example
room temperature, liquid input temperature) the situational
conditions, (for example emergency procedure, routine procedure,
clinic timetables) and the patient's needs. Thus the time and/or
temperature may be selected without compromising the dose of heat
sanitization applied to the volume of liquid.
[0027] The threshold temperature may be between 55.degree. C. and
65.degree. C.
[0028] The upper temperature may be between 70.degree. C. and
99.degree. C.
[0029] Multiple temperature sensors may be used to provide the
temperature of the volume of liquid.
[0030] In one embodiment, the cumulative time-temperature value may
be calculated according to
A 0 = 10 .function. [ ( T - 80 ) z ] dt 5 ##EQU00002##
[0031] Where:
[0032] A.sub.0 is the A value when z is 10.degree. C.;
[0033] t is the chosen time interval, in seconds;
[0034] and T is the temperature in the load in .degree. C.
[0035] This allows the destruction of organisms at 65.degree. C. to
80.degree. C. to be included in the calculation of the cumulative
time-temperature value.
[0036] The A.sub.0 value may be equal to 1800.
[0037] According to a second aspect of the present invention, there
is provided a liquid sanitizer comprising a tank containing a
volume of liquid; a sensor arranged to sense the temperature of the
volume of liquid; a heater arranged to heat the volume of liquid
from an initial temperature to exceed a threshold temperature, and
maintain the volume of liquid above the threshold temperature; and
a processor, wherein the processor is configured to determine a
time-temperature value for the volume of liquid periodically once
the threshold temperature has been exceeded and calculate a
cumulative time-temperature value so as to provide an output signal
once a cumulative time-temperature value indicative of a sanitizing
dose is readied.
[0038] The processor may be programmable to alter at least one of
the threshold temperature and the cumulative time-temperature
value.
[0039] According to a third aspect of the present invention, there
is provided a dialyser incorporating the liquid sanitizer according
to the second aspect of the present invention.
[0040] An embodiment of the present invention will now be
described, by way of example only, with reference to the
accompanying figures, in which:
[0041] FIG. 1 is a schematic of a dialysis machine incorporating
the liquid sanitizer;
[0042] FIG. 2 is a magnified detail view of the liquid sanitizer of
FIG. 1;
[0043] FIG. 3 is a temperature profile of the liquid in a liquid
sanitizer undergoing a typical sanitization cycle; and
[0044] FIG. 4 is a temperature profile of the liquid in the liquid
sanitizer of FIG. 1 undergoing a typical sanitization cycle.
[0045] FIG. 5 shows the non-linear contribution to the cumulative
time-temperature value, during a single sanitization cycle referred
to in the typical temperature profile of FIG. 4.
[0046] Referring to FIG. 1, a dialysis machine 10 is shown having a
main body 12 and a hinged door 14. The door 14 is hinged so as to
allow a dummy dialysis cartridge 16 to be received between the main
body 12 and the door.
[0047] The machine 10 has a blood pumping portion indicated
generally at 9 for pumping patient blood to and from a dialyser
(not shown for clarity) in a known manner. The main body 12 has a
platen 21 behind which is an engine portion (not shown for
clarity). The platen 21 is configured to receive the dummy
cartridge 16 within a recessed portion 25.
[0048] The engine portion includes a pneumatic pump for providing
pressure and vacuum to operate the machine and a controller to
control retention of the dummy cartridge 16 within the machine 10
and fluid flow on the dummy cartridge 16 as will be discussed in
further detail below.
[0049] The door 14 has an outer side including a user interface 2.
The door 14 includes an actuator in the form of an airbag (not
shown), operable by the engine portion to provide a closure load to
close the dummy cartridge 16 onto the platen 21 and to ensure that
a continuous seal fully engages the dummy cartridge 16.
[0050] The dummy cartridge 16 will now be described in further
detail. The dummy cartridge 16 has a chassis defining a door side
and a platen side. In use the platen side of the cartridge 16
engages the platen 21 on the main body 12 of the machine 10, and
the door side engages an interface plate (not shown) on the door 14
of the machine 10.
[0051] The dummy cartridge 16 is formed from an acrylic such as
SG-10 which is moulded in two parts (a platen side and a patient
side) before being bonded together to form the chassis. Both the
platen side and door side are covered in a clear flexible membrane
formed from, for example, DEHP-free PVC which is operable by
pneumatic pressure applied to the membrane by the pneumatic
compressor in the main body via the platen 21. In this way a series
of flow paths 17 are formed in the cartridge for carrying
sanitizing water.
[0052] In use, the engine portion of the machine 10 applies either
a positive or negative pressure to the membrane via the platen 21
in order to selectively open and close valves and pumps to pump
sanitizing fluid through the dummy cartridge 16, which is described
in detail below.
[0053] The machine 10 has liquid sanitizer generally designated as
200. The arrows on FIG. 1 show the sanitizing water flow path when
the liquid sanitizer is in use.
[0054] With reference to FIG. 2, the liquid sanitizer will be
described in further detail.
[0055] The liquid sanitizer 200 has a tank 202, a heater 210 and a
processor 230. The tank 202 contains, in use, a volume of water
203.
[0056] The tank 202 has an inlet 204 and a drain 206. The inlet 204
is connectable to a water source (not shown) and the drain 206 is
connectable to a waste pipe (also not shown). The tank 202 also has
a feed pipe 220 connectable to the dummy cartridge 16 via the
platen 21 and a return pipe 22.4, also connectable to the dummy
cartridge 16 via the platen 21. Referring back to FIG. 1, the dummy
cartridge 16 has a sanitizing water circulation path 17 so as to
complete a sanitizing water circuit comprising the tank 202 feed
pipe 220, dummy cartridge 16 and return pipe 224.
[0057] The heater 210 has a heating element 212 arranged to heat
the volume of water 203 contained within the tank 202, in this case
by immersion in the volume of water 203 in the tank 202. The heater
210 is electronically connected to processor 230 by heater
connector 211.
[0058] Temperature sensors are arranged on the sanitizing water
circuit. A driver temperature sensor 222 is arranged on the feed
pipe 220 adjacent the water tank 202. A return temperature sensor
226 is arranged on the return pipe 224 adjacent the water tank 202.
A check temperature sensor 228 is arranged on the return pipe
adjacent, but offset from, the return temperature sensor 226. All
three temperature sensors are electronically connected to the
processor 230 via sensor connectors. Driver temperature sensor 222
is electronically connected to processor 230 by sensor connector
223. Return temperature sensor 226 is electronically connected to
processor 230 by sensor connector 227. Check temperature sensor 228
is electronically connected to processor 230 by sensor connector
229.
[0059] The electronic connectors 211, 223, 228, 229 may be wired or
wireless. The processor 203 may be remote to both the tank 202 and
heater 210.
[0060] The processor 230 thereby controls both the heating of the
water and receives the temperature values for the sanitizing water
circuit.
[0061] In use, the tank 202 of liquid sanitizer 200 is filled with
the desired quantity of water via inlet 204. This would typically
be 500 ml, which is the amount sufficient to flush out the water
circuit of a kidney dialyser.
[0062] The liquid sanitizer is then turned on. The processor 230
activates the heater 210 to heat the volume of water via the
heating element 221 and the pump draws the water around the
sanitizing water circuit. The temperature of the water exiting the
tank 202 via feed pipe 220 is periodically sensed by drive
temperature sensor 222, and the temperature data is periodically
sent to processor 230 via sensor connector 223. The temperature of
the water returning to the tank 202 via return pipe 224 is
periodically sensed by return temperature sensor 226, and the
temperature data is periodically sent to processor 230 via sensor
connector 227. The processor 230 therefore periodically receives
sensed temperature data to provide a feedback loop to moderate the
heating of the volume of water 203 to maintain the temperature of
the volume of water 203 above a threshold temperature.
[0063] When the processor 230 receives data from the sensor 220
that the volume of water 203 has exceeded the threshold
temperature, the processor 230 periodically samples the temperature
of the volume of water via the return temperature sensor 226, which
theoretically represents the lowest possible temperature of the
water on the sanitizing water circuit.
[0064] The value is checked by periodically sampling the
temperature of the volume of water via the check temperature sensor
228.
[0065] The sampling is performed periodically at, for example, 1
second intervals. The sampling intervals may be varied as
appropriate.
[0066] Each sampled temperature represents a time-temperature
value, which can be calculated by the processor 230, or
alternatively generated by a look-up table.
[0067] The processor 230 calculates a cumulative time-temperature
value for the volume of liquid 20 by summing the sampled
time-temperature values. This is compared to a target total
time-temperature value indicative of a sanitizing dose.
[0068] Once the calculated cumulative time-temperature value and
the target cumulative time-temperature value are equal, the
processor 230 sends an output signal to indicate that a sanitizing
dose has been reached. The output signal is received by the heater
and automatically switches off the heater 210.
[0069] In an alternate embodiment, the processor 230 may switch off
the water heater 210 in advance of a sanitizing dose being reached,
by calculating that there is sufficient thermal energy contained
within the water circuit that the water temperature will remain
above the threshold temperature for long enough to ensure a
sanitizing dose is reached. In that case, periodic sampling would
be continued, such that the processor 230 is able to send the
output signal to indicate that a sanitizing dose had indeed been
reached.
[0070] The output signal is received by the LCD display unit, which
displays the text "COMPLETE" in reference to the completed
sanitizing dose. In alternate embodiments, the LCD display unit
includes an audible alarm. The audible alarm can be configured to
bleep repeatedly until the sanitizer is turned off
[0071] With reference to FIG. 3, a typical temperature profile 300
of the water in a known liquid sanitizer is shown during a single
disinfection cycle.
[0072] The water already contained within the tank is at room
temperature 301 (18.degree. C.) initially. As cool fresh water is
added from a tap to ensure the correct quantity of water is
provided in the tank (wherein the cool fresh water is typically
8.degree. C.), the overall temperature of the liquid will drop
slightly 302.
[0073] The water temperature then rises substantially linearly
towards the target temperature of 80.degree. C. 305, which is
reached at about 60 seconds. There is a slight oscillation 304 of
about one and a half wavelengths where the water temperature
exceeds and passes below 80.degree. C. (to approximately 85.degree.
C. and 75.degree. C. respectively) as the water heater finds the
correct balance to maintain a constant water temperature of
80.degree. C. After approximately 30 minutes at 80.degree. C. the
water heater is switched off 307 and the water temperature steadily
decreases to room temperature (18.degree. C.) 301.
[0074] With reference to FIG. 4 a typical temperature profile 400
of the water in the liquid sanitizer 200 is shown during a single
disinfection cycle.
[0075] Similar notable points on the temperature profile are given
similar reference numerals as that for FIG. 3, prefixed by a "4"
instead of a "3" to indicate that they represent the temperature
profile 400 of the water in the liquid sanitizer 200.
[0076] The initial drop in temperature 402 from room temperature
401 (18.degree. C.) and subsequent heating of the water occurs
following a similar time-temperature profile to that shown in FIG.
3.
[0077] However, when the temperature of the water exceeds the
threshold temperature. 65.degree. C. 403, the liquid sanitizer
begins to record a time-temperature value.
[0078] Furthermore, when the target temperature 80.degree. C. 405
is reached, the water temperature is continually raised 406 such
that a greater time-temperature value contribution can be achieved
with each sample.
[0079] The heater is switched off 407 after less than 8 minutes as
there is sufficient thermal energy within the water to ensure that
a complete sanitizing dose is achieved before the temperature of
the water falls below the threshold temperature of 65.degree. C.
403.
[0080] The overall cycle time for the sanitizing dose is slightly
more than 8 minutes. This compares to the overall cycle time for a
sanitizing dose according to the temperature profile of FIG. 3 of
over 30 minutes.
[0081] An exemplary Lookup Table may include the following values
for 1 second sampled increments:
TABLE-US-00001 TABLE 1 Lookup Table Temperature Time-temperature
(.degree. C.) value 95 35.481 94 28.184 93 22.387 92 17.783 91
14.125 90 11.22 89 8.913 88 7.079 87 5.623 86 4.467 85 3.548 84
2.818 83 2.239 82 1.778 81 1.413 80 1.122 79 0.891 78 0.708 77
0.562 76 0.447 75 0.355 74 0.282 73 0.224 72 0.178 71 0.141 70
0.112 69 0.089 68 0.071 67 0.056 66 0.045 65 0.035 64 0
[0082] Thus it can be seen that for each 1.degree. C. increase in
water temperatures above 80.degree. C., the time-temperature
contribution significantly increased. Three seconds at 85.degree.
C. is equivalent to over 10 seconds at 80.degree. C.
[0083] In FIG. 5, the non-linear contribution to the cumulative
time-temperature value, during the single disinfection cycle
referred to in the typical temperature profile of FIG. 4, is shown
in the main graph. The main graph has the cumulative time
temperature value on the Y-axis, and the cycle time (in seconds) on
the X-axis. Three distinct periods of 10, one second samples are
represented in charts 510, 520, 530, during the disinfection cycle,
representing different regions of the main graph. The charts 510,
520, 530 show the time-temperature value contribution for each
second according to the temperature sensed during the 1 second
intervals.
[0084] In chart 510, the 10, one second samples are taken after
approximately 50 seconds. During the 10 seconds, the water
temperature increases from 64 to 67.degree. C. This is shown by the
line graph corresponding to the water temperature Y-axis on the
left hand side of the chart. The time temperature contribution at
these temperatures is represented by the bars, corresponding to the
time temperature Y-axis on the right hand side of the chart.
[0085] No contribution is made when the water temperature is
64.degree. C. A relatively small contribution to the time
temperature value is made when the water temperature is 65 to
67.degree. C. This corresponds to the flat region of the main
graph. Summing the values for the bars indicates that the total
contribution of the 10, one second intervals is 0.296. Although
these contributions are small. they are counted and do contribute
to shorten the time required for sanitization. In the prior art, no
credit is given for this heating phase.
[0086] In chart 520, the 10, one second samples are taken after
approximately 140 seconds. During the 10 seconds, the water
temperature increases from 79 to 82.degree. C. This is shown by the
line graph corresponding to the water temperature Y-axis on the
left hand side of the chart. The time temperature contribution at
these temperatures is represented by the bars, corresponding to the
time temperature Y-axis on the right hand side of the chart. Note
the difference in scale of the time temperature Y-axis of chart 520
to chart 510.
[0087] Increasing contributions to the time temperature value are
made as the water temperature increases from 79 to 82.degree. C.,
This corresponds to the steadily increasing region of the main
graph. Summing the values for the bars indicates that the total
contribution of the 10, one second intervals is 12.056.
[0088] In chart 530, the 10, one second samples are taken after
approximately 420 seconds. During the 10 seconds, the water
temperature increases from 83 to 86.degree. C. This is shown by the
line graph corresponding to the water temperature Y-axis on the
left hand side of the chart. The time temperature contribution at
these temperatures is represented by the bars, corresponding to the
time temperature Y-axis on the right hand side of the chart. Note
the difference in scale of the time temperature Y-axis of chart 530
to charts 510 and 520.
[0089] Greatly increasing contributions to the time temperature
value are made as the water temperature increases from 83 to
86.degree. C. This corresponds to the steep region of the main
graph. Summing the values for the bars indicates that the total
contribution of the 10, one second intervals is 30.282. Counting
the actual contribution to sanitization for the periods above
80.degree. C. rather than treating these as the same as 80.degree.
C. considerably shortens the required time.
[0090] The charts are exemplary in nature only, and different time,
temperature and associated time-temperature values are possible,
and indeed envisaged.
[0091] One second intervals have been chosen as a reasonable
sampling rate. The sampling interval could be longer or shorter. A
longer sampling interval would preferably be associated with a.
steady temperature profile, whilst a shorter temperature cycle
would preferably be associated with greater processing power.
[0092] In alternate embodiments of the liquid sanitizer, the
processor may be programmable. Therefore the threshold temperature
may be set manually. For example the threshold temperature may be
set to a temperature between 55.degree. C. and 65.degree. C. The
overall heating time may be set manually. For example, the heating
time may be set to 8, 9 or 10 minutes. In this case the processor
230 calculates the necessary temperature profile over the heating
time to ensure the volume of water receives a sanitizing dose.
* * * * *