Patent Application
20180220665
The present invention relates to the monitoring of the state of produce within transport containers. It has particular application to dynamic monitoring of the respiration rate of produce in controlled atmosphere container systems used in cargo container transportation.
It is common for storing and shipping of perishable products such as fruits or vegetables over extended periods to provide refrigeration to maintain the freshness of the goods. As many agricultural products must be shipped relatively long distances to remote markets, it is necessary to maintain the freshness of these goods after harvest during the sometimes lengthy time periods required for shipping and distribution.
In addition to refrigeration, it is also well known that perishable products can be maintained in fresher condition at refrigerated temperatures by maintaining in an atmosphere which is less conducive to rapid ripening and spoilage.
In early examples of controlled atmosphere systems for refrigerated containers, the modified atmosphere within the container was established after loading, and not further modified during the period of storage or transportation. Problems with such systems included leakage both into and out of the container which had the effect of changing the atmosphere.
Subsequent advances have provided for monitoring of oxygen and carbon dioxide levels within the container and have included providing sources of gas, such as nitrogen and/or carbon dioxide sources, to allow selective modification of the atmosphere during storage and transportation. However, the need for supplies of gases required to maintain the desired atmosphere during normal durations of transportation presented a drawback to such solutions.
In more recent known systems, a container loaded with perishable products is initially flushed with a nitrogen gas to reduce the oxygen level to an initial base level, and thereafter oxygen levels are controlled by selective inflow of ambient air, under control of a controller configured to receive data regarding gas constituents of the container atmosphere from one or more sensors. The carbon dioxide levels (CO2) are maintained below a predetermined maximum by the use of a suitable CO2 scrubber device.
As an example of this, the applicant's patented method and system (see U.S. Pat. No. 8,677,893, the entire content of which is included herein by reference) involves apparatus for adjusting an atmosphere within a shipping container containing respiring produce, comprising an inlet to permit ambient atmosphere to enter the container, an outlet arranged to permit container atmosphere to exit the container, a controller having an O2 concentration sensor and a control device responsive to the O2 concentration sensor, the control device configured to admit ambient atmosphere into the container via the inlet following the O2 concentration sensor detecting that the O2 concentration has fallen below a predetermined level, and a CO2 remover adapted to remove CO2 at a predetermined rate so that the container CO2 concentration will not substantially exceed a predetermined non-zero level, the apparatus not having a device to actively monitor and control CO2 levels within the container.
As the produce continues to consume O2, and hence CO2 will continue to be produced, a prediction is made based on the desired CO2 setpoint, that is, the difference between the predicted CO2 level (based on the predicted rate of consumption of O2 by the produce) and the desired level. Independent control of the CO2 level is achieved by introducing a number of standard size bags of hydrated lime (CO2 scrubbers) as CO2 removers into the container, the bag contents enclosed within a membrane of known permeability to CO2, so as to absorb the difference between the predicted and desired levels. In practice this is done by the use of lookup tables, the result indicating exactly how many bags to load into the container.
This approach provided a major breakthrough in CA systems, in that it allowed carbon dioxide levels in the chamber to be adjusted to a required level merely by monitoring of the O2 levels around an oxygen setpoint. CO2 levels in the chamber can be accurately predicted before transport of the produce, thus avoiding the requirement for active monitoring and control of the CO2 levels during transport. This obviates the need for complex and costly CO2 monitoring and control apparatus. The prediction of the CO2 level is based on, amongst other things, the weight of the cargo, the type of produce (and thus its respiration quotient), the temperature in the chamber, and the time during which the cargo will be in transit.
In such dynamic controlled atmosphere systems, the CA controller uses a microprocessor to control the system (i.e. to operate the ambient atmosphere admission in response to the measured O2 level) according to a specific control algorithm.
The admitting of ambient atmosphere in response to the monitoring of the container atmosphere can be realised by positive infusion of air into the container (e.g. by operating a fan or other pumping means), or by opening a valve to permit air ingress, or by a combination of the two.
Parameters such as O2 concentration and temperature are measured by suitable sensors operatively coupled to a digital data logger (as part of the controller, or operatively connected to the controller) or other type of memory upon which the measurements can be stored. Other data associated with the transportation container and/or controlling apparatus (such as valve opening times and durations) can also be measured and stored on the data logger. The data thus gathered over the course of a voyage can be accessed for analysis. Typically this is done by making a wired connection to the data logger once the shipping container has reached its destination, and downloading the data therefrom. More recently, remote monitoring has been made possible by data loggers equipped with wireless communications functionality (e.g. a GSM or GPRS modem), allowing remote data acquisition from containers in transit.
In the applicant's invention described in PCT/AU2014/050215 a communication module is provided in a shipping container, operatively coupled to the data logger, controlled to periodically perform time-limited network searches and to power down between searches, resulting in very low power consumption. The entire content of PCT/AU2014/050215 is included herein by reference.
Any discussion of documents, acts, materials, devices, articles and the like in this specification is included solely for the purpose of providing a context for the present invention. It is not suggested or represented that any of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of each claim of this application.
The invention provides, in a first aspect, a method for tracking, over an extended period, the respiration rate of produce contained in a leaky transport container, including the steps of:
at intervals during said extended period, for a prescribed period, being a respiration rate data block (RRDB) cycle, ensuring that there is substantially no air passage between the interior and the exterior of the transport container other than leakage;
identifying the leakage rate of the transport container;
measuring, at intervals over said RRDB cycle, the concentration of one or more constituent gases in the transport container as the produce respires;
calculating, at a logic unit, from said measurements of concentrations of said one or more constituent gases and said leakage rate, a respiration rate of the produce for each RRDB cycle.
The term ‘leaky transport container’ relates to the fact that in practice most if not all transport containers have a degree of leakage between the interior and the exterior. So long as the leakage rate is substantially less than the respiration rate of the produce, such leakage is generally acceptable.
The step of ensuring that there is substantially no air passage between the interior and the exterior of the transport container other than leakage may involve closing or maintaining closed any valves or outlets in the transport container generally used for atmosphere control or other purposes, and/or by shutting off operation of a fan or other forced air means.
The step of identifying the leakage rate of the transport container may involve measuring container leakage for each RRDB cycle.
Alternatively, the step of identifying the leakage rate of the transport container may involve accessing or inputting a stored leakage rate for the particular transport container. This may be measured at the beginning of the extended period (e.g. after cargo loading and container closure), or it may be a standard leakage rate, i.e. a recognised leakage rate for a particular container or type of container.
The step of measuring, at intervals over said RRDB cycle, the concentration of one or more constituent gases in the transport container, preferably involves sensing and storing the concentration of oxygen. In addition or alternatively it may involve sensing and storing the concentration of carbon dioxide and/or other gases.
The step of calculating the respiration rate of the produce for each RRDB cycle may involve a differential analysis of the concentration of one or more of the constituent gases. Preferably, it involves analysing the regression slope of the concentration of one or more of the constituent gases, ideally the oxygen concentration.
The prescribed period (of the RRDB cycle, being the period over which RRDB measurements are taken, referred to below as ‘RRM mode’) need not be a set length of time, but may be determined on the basis of measurements made. In particular, it may be the shorter of (a) a set length of time and (b) the period until which the concentration of one or more of the constituent gases is determined to have reached a threshold. That threshold may be an absolute value, or may be a deviation from a prescribed value. Preferably, the threshold is a deviation from an oxygen setpoint which has been determined for that produce.
The extended period may be over a voyage of the transport container from an origin to a destination. Alternatively it may be over a period of stationary storage, or a combination of transport and storage.
The method may in whole or in part be carried out under management by a transport container controller, the controller programmed to provide control of the atmosphere within the transport container during said extended period.
The controller may include or be in operative connection with a communication unit arranged to transmit data to a remote site for storage and analysis of the measured data. The data may be transmitted wirelessly. The remote site may be a central server arranged to process the data from a plurality of transport containers.
It will be understood that the step of calculating the respiration rate of the produce for each RRDB cycle may be carried out locally, or may be carried out at the remote site, in other words, the logic unit that carries out the step of calculating may be wired into or part of the controller or may be remote therefrom, e.g. at the central server.
The method may include measuring other parameters during said extended period, and correlating the calculated respiration rates with said other parameters measured during. Such parameters may include, for example, component gas concentration, temperature and humidity.
The invention provides, in a further aspect, a method for use in monitoring, over an extended period, the respiration rate of produce contained in a container, the container having an atmosphere control system including sensor means to measure the concentration of one or more constituent gases in the container, and a controller programmed to operate in one of two modes, namely atmosphere control mode and respiration rate monitoring mode, wherein:
atmosphere control mode (CA mode) involves measuring the concentration of one or more constituent gases at prescribed atmosphere control (CA mode) sampling intervals; and effecting adjustment of the atmosphere in the container in response to said measurement,
respiration rate monitoring mode (RRM mode) involves measuring the concentration of one or more constituent gases in the container as the produce respires at prescribed respiration rate (RRM mode) sampling intervals,
and wherein the method includes, at intervals during said extended period, suspending said CA mode and initiating said RRM mode and, in accordance with a set RRM mode end trigger, discontinuing said RRM mode and recommencing said CA mode.
The adjustment of the atmosphere in the container may involve effecting selective admission of air into the container.
In accordance with this embodiment, during RRM mode, admission of air into the container is substantially precluded (other than by way of any leakage).
Typically, the container is a leaky transport container, and the method preferably includes identifying a leakage rate of the container. This may be done by, under control of the controller, measuring the leakage rate of the container each time the controller applies said RRM mode.
In this way, at cycle intervals during the voyage, a measure of the change in gas constituents within the container is made and, based on that measured change and the identified leakage of the container, it is possible to determine the respiration rate of said produce at each cycle based on a mathematical model.
The set RRM mode end trigger may be based on the elapsing of a prescribed time in respiration rate monitoring mode. Alternatively, it may be based on the concentration of one or more of the constituent gases in the container as measured during RRM mode. The prescribed time may be in the range between 2 and 6 hours, for example around 4 hours.
Preferably, the method includes providing data to a logic unit, the data including or derived from the RRM mode measurements, the logic unit programmed to calculate from the data a respiration rate of the produce corresponding to each application of the RRM mode.
The CA mode sampling intervals may be in the range between 2 and 30 minutes, for example around 10 minutes.
The RRM sampling intervals may be in the range between 1 second and 10 minutes, for example around 1 minute. Generally, more data points (i.e. a shorter interval) will provide improved autocorrelation of the data set and are therefore preferred.
The interval between each initiation of the RRM mode may be between 1 hour and 4 days, for example around 24 hours. The interval should be such that sufficient RRM mode data blocks are gathered during the extended period to enable meaningful monitoring of respiration rate over the period or over a substantial part of the period.
Generally, the interval between each initiation of the RRM mode will be set to be a regular time interval. However, the interval may be governed by another parameter, or may depend on a combination of timing and one or more other parameters. For example, RRM mode may be initiated if a set time duration has not yet elapsed but the oxygen concentration in the container has deviated a prescribed amount from a setpoint, or if the measured temperature in the container has exceeded a set value.
The invention provides, in a further aspect, a method for tracking, over an extended period, the respiration rate of produce contained in a leaky transport container, including the steps of:
receiving data from a controller installed in said transport container, the controller equipped with sensors to measure the concentration of one or more constituent gases within said container, the data representing measurements taken during prescribed periods occurring at intervals during said extended period, each being a respiration rate data block (RRDB) cycle, each RRDB cycle being a period during which substantially no air passage between the interior and the exterior of the transport container other than leakage is permitted;
receiving a value of the leakage rate of the transport container applicable to each RRDB cycles;
calculating, from said data and from said leakage rate, a respiration rate of the produce for each RRDB cycle.
The respiration rate may be calculated from a measure of oxygen depletion over the RRDB cycle.
The invention provides, in a further aspect, a system for tracking, over an extended period, the respiration rate of produce contained in a leaky transport container, including the steps of:
means for measuring, at intervals during said extended period, over a prescribed period, being a respiration rate data block (RRDB) cycle, the concentration of one or more constituent gases in the transport container as the produce respires, substantially no air passage between the interior and the exterior of the transport container other than leakage having been allowed during said RRDB cycle;
means for storing said measurements of concentrations of said one or more constituent gases;
means for measuring and/or storing a leakage rate of the transport container;
means for calculating from said measurements of concentrations of said one or more constituent gases and said leakage rate, a respiration rate of the produce for each RRDB cycle.
The invention provides, in a further aspect, a system for use in monitoring, over an extended period, the respiration rate of produce contained in a container, the container having an atmosphere control system including sensor means to measure the concentration of one or more constituent gases in the container, the system including a controller operably connectable to the sensor means and operably connected to a means to effect adjustment of the atmosphere in the container, the controller programmed to operate in one of two modes, namely atmosphere control mode and respiration rate monitoring mode, wherein:
atmosphere control mode (CA mode) involves measuring, under control of the controller and using the sensor means, the concentration of one or more constituent gases at prescribed atmosphere control (CA mode) sampling intervals; and, under control of the controller and using the atmosphere adjustment means, adjusting the atmosphere in the container in response to said measurement, and
respiration rate monitoring mode (RRM mode) involves measuring under control of the controller and using the sensor means, the concentration of one or more constituent gases in the container as the produce respires at prescribed respiration rate (RRM mode) sampling intervals,
and wherein the controller is programmed to, at intervals during said extended period, suspend said CA mode and initiate said RRM mode and, in accordance with a set RRM mode end trigger, discontinue said RRM mode and recommence said CA mode.
The means to effect adjustment of the atmosphere in the container may be means to effect selective admission of air into the container.
Hence, in RRM mode, there is substantially no admission of air into the container (other than by way of any leakage).
Typically, the container is a leaky transport container, and the controller may be programmed to record a leakage rate of the container. In a preferred embodiment, the system includes means for, under control of the controller, measuring a leakage rate of the container in accordance with employing said RRM mode.
Preferably, the system includes means for providing data to a logic unit, the data representing or derived from the RRM mode measurements (and, if appropriate, container leakage rate), the logic unit programmed to calculate from the data a respiration rate of the produce corresponding to each application of the RRM mode. Said means for providing data to a logic unit may comprise remote wireless means programmed to communicate said data during said extended period.
The invention, then, provides a system and method which affords tracking of the respiration rate of perishables in a transport container during a voyage of that container, including, at cycle intervals during the voyage, obtaining a measure of the change in gas constituents within the container (such as a measure of oxygen depletion over a defined period) and, based on that measured change (and, if appropriate, a measure of leakage of the container), determining the respiration rate of said produce at each cycle based on a mathematical model.
When applied in an atmosphere control container, which includes ongoing monitoring of the atmosphere in the container and adjusting it by selectively admitting ambient air, the invention involves regularly interrupting that atmosphere control for a defined period to take the respiration rate measurements.
It should be noted that, while experiments have been conducted in the past to measure respiration rates of produce (e.g. to determine the effect of different conditions on respiration, to test stress levels of different fruits and vegetables and to provide useful information in determining the best conditions for subsequent transport or storage of the produce), this has conventionally been done in laboratory conditions, generally in sealed containers (respirometers). As will be appreciated by the skilled reader, this is very different to gathering data during a voyage itself to allow the calculation of dynamic respiration rate at multiple points in time across that voyage.
Container 10 is fitted with valve means diagrammatically shown as reference 18, which includes in air inlet means, and may also include an air outlet means and/or one or more fan means to drive air into or out of container 10. Valve means 18 is connected to and controlled by controller 20, which is also connected to sensors to measure gas concentrations within container atmosphere 11, including an oxygen sensor 22 and (optionally) a CO2 sensor 24.
As explained in more detail in U.S. Pat. No. 8,677,893, in accordance with measurement of oxygen concentration by sensor 22, controller 20 operates valve means 18 to cause or permit ambient atmosphere to enter container 10, the hydrated lime bags 14 removing CO2 from the container atmosphere 11 at a predetermined rate in such a way that the CO2 concentration within the chamber atmosphere is maintained at a prescribed non-zero level.
It will be understood that the present invention is independent of the atmosphere control methodology applied. For example, the present invention is equally applicable to a membrane CA system, in which container atmosphere is drawn through a membrane of selected permeability to a particular gas. Indeed, the present invention in at least some forms can be used with a transport container not equipped with a CA system.
After harvesting, fruit and other perishable items continue respiring, using up oxygen and giving off CO2. The rate of respiration can fluctuate widely, and is affected greatly by factors including temperature and oxygen levels in the atmosphere around the products.
The respiration rate of the produce can be seen as its heart rate; it increases or decreases in accordance with the activity of the produce. Higher respiration rates are associated with increased ripening and therefore are a good pointer to the maturity of the fruit. Respiration data can therefore have important value:
In accordance with one form of the present invention, the respiration rate is measured as follows:
The calculation of respiration rate is somewhat complex, as live data tends to fluctuate significantly. The inventors have therefore devised a novel mathematical technique for the analysis. It is necessary to factor in the container leakage rate and cargo weight in order to calculate the respiration rate.
Most if not all shipping containers have inherent leakage. Causes of leakage in such containers is twofold:
The applicant's MAXtend system classifies containers into three bands on the basis of leakage, CI.1 being the least leaky, CI. 3 the most leaky.
Since a static leakage measurement before the voyage is often not a true measure of dynamic leakage occurring while the container is on a vessel, the preferred form of the method of the invention includes in-transit measurement of leakage rates at the time (generally, shortly before) respiration rate measurements are made. This affords a true dynamic picture.
The dynamic leakage rate is measured as follows:
For each data block sampling, a leakage measurement means 26 is used in carrying out the following process to obtain a measure of container leakage:
MAXtend container leak classifications are based on measured flow (SLPM) at a maintained pressure of 250 Pa.
Other measures can be used to determine leakage for each RRDB cycle. For example, this can involve a measure of rate of change of AP. In accordance with this approach, the system is configured to operate the fan to drive AP to a prescribed value, and then to measure the time taken for it to drop by a predetermined amount. A further alternative involves releasing a dose of trace gas and measuring the change of concentration of that trace gas over time.
The MAXtend controller range includes units able to measure and log either O2, or both O2 and CO2. More recently, and particularly for high value cargo, the controllers are also equipped with a GPRS communications module 28 connected to controller 20, which allows them to auto-transmit logged data (when in range of a suitable communications network) to the MAXtend central server for storing and analysis.
In addition to controlling the valve operation in accordance with the applicant's CA method, this allows quality control monitoring of CA data at critical points of the transit, including:
In addition the operation of controller 20 can include auto data scanning and alerts, and monitoring and logging of other parameters, such as temperature and humidity.
In the process flow illustrated, in a pre-voyage phase 30 the cargo 16 to be shipped is weighed and loaded into transport container 10, and a nitrogen purge is conducted (step 32). An initial leakage measurement is then made (step 34, methodology as discussed above) and recorded, and the controller initiated (step 36) prior to the container being loaded.
From that point onwards the container is considered to be in transit and, generally, subject to atmosphere control as regulated by programmed controller 20. Normal mode is thus controlled atmosphere mode (CA mode—step 38), with regular measurement of one of more of the constituent gases in the container and adjustment of the atmosphere accordingly (by causing or permitting inflow of air from the outside of the container, e.g. by opening a valve or valves and/or operating a fan or fans for forced flow). During CA mode the data regarding gas measurements and valve control is recorded and saved in accordance with a set sampling frequency (step 40). After a prescribed time interval (decision box 42) CA mode is suspended and a leakage measurement is made at step 44 (as discussed above) and the data recorded, and the process switches into respiration rate monitoring mode (RRM mode—step 46), as discussed above and in further detail below. The RRM mode data is recorded by the controller, and terminated in accordance with the programmed trigger (decision box 48), as discussed further below (a prescribed length of time, or earlier if the O2 concentration departs from its setpoint by a set amount). If the container is still in transit the process switches back into CA mode and the process repeats. As the figure shows, the data recorded and stored by the controller, including the data gathered during RRM mode (the respiration rate data block RRDB) is regularly transmitted wirelessly by way of a GSM or GPRS modem to a remote server for near-real-time update and analysis.
Once the voyage is over (decision box 50) and the process is in a post-voyage phase 58, the controller operation can be terminated, the cargo unloaded (step 54), and any post-voyage activity completed (step 56). The controller can then be re-initiated for the next voyage.
As
Test Units and Result Graphs from Test Units
In
The labelling at the head of the graphs in
The use of data loggers allow monitoring of conditions within a shipping container, allowing analysis across each voyage. Use of wireless communications allows this data to be relayed to a central server remotely and with minimum delay, and as the data set grows analysis at the server across multiple containers, multiple vessels, multiple routes, multiple voyages and multiple cargo types and sizes, etc, provides a very valuable source of information for all stakeholders in the chain, including shippers, producers, importers, insurers, and dock handling companies.
In addition to analysis of conditions within the container (in particular, temperature, pressure, gas components), the present invention thus provides a way of monitoring the health of the produce through calculation of respiration rate over a voyage. The inventors implemented this for the trials by modifying an existing CA controller. In particular, as described above, in addition to normal operation, the controller was programmed to initiate respiration rate monitoring mode (RRM mode) by, once a day, shutting all valves, and allowing O2 to deplete and CO2 to increase by natural cargo respiration. The only air transfer across the container wall is therefore due to leakage. During this time (the respiration rate data block RRDB cycle period), data is measured and logged, that being O2 concentration, and/or CO2 concentration. Other variables, may also be measured and logged, such as temperature.
The measured data is transmitted to a central server for analysis. This is preferably done in transit (if the controller is equipped with a communications modem), or alternatively can be done after transit when the data log is downloaded.
A logic unit at the server is programmed to identify each RRDB, by virtue of the prescribed RRM mode tag attached to the block of data associated with RRM application. The data within this block is then processed to calculate the respiration rate (calculated as ml O2/Kg-hr consumed or ml CO2/Kg-hr produced).
The data block for each RRDB cycle passed from the controller to the central server may a number of different items of information, including parameters measured and values determined from those parameters. In addition to headers, footers, appropriate identifiers, timestamps, data block time length values, etc., such information may include data minimum, maximum and mean values, data correlation coefficients, data variance values, data sample counts, data regression slope values (i.e. the regression slope of the measured concentration of one or more of the constituent gases in the container) and leakage values. As will be understood, the respiration rate for each RRDB cycle may be calculated from the oxygen value regression slope and mean oxygen measurements. In the case of noisy data, consideration of the sample count, variance, minimum, maximum may be used to determine the reliability of the calculation.
The data block may also include a termination code specifying whether the RRDB cycle was terminated by virtue of the time limit, the oxygen low deviation limit, or the oxygen high deviation limit, and this information may also be employed to determine the reliability of the respiration rate calculation.
As will be understood, RRM mode suspends atmosphere control and can therefore interfere with the CA process, but with proper selection of programmed parameters this interference can be kept to a minimum. In fact ripening is reduced during this period, as there is less O2 than would be the case under normal operation. The data block cycle time (i.e. the time in RRM mode) is set for a prescribed duration (e.g. 4 hours), but is terminated earlier if the O2 concentration departs from its setpoint by a prescribed value, to minimise this interference. In the embodiments tested the allowed deviation, which could be adjusted to any value in the range 0-1%, was set at 0.5%. That means, with an O2 concentration setpoint of 5%, RRM mode was only maintained if 4.5%<O2 concentration <5.5%.
As discussed above, monitoring and analysis of cargo conditions in accordance with the present invention allows the calculation of the respiration rate of the goods at points throughout the shipment, which thus provides a dynamic indication of the ripening state. This can be done in real time by the controller, or transmitted to the MAXtend server for near real time analysis, or (in the absence of GPRS capability) after the shipment has been received and the controller accessed.
Analysing the resulting RR data provides very valuable information. For example, the RR data in the early part of a voyage provides an indication of the quality of the cargo. High RR at a particular point in the voyage provides an indication of an interruption of normal operation. For example, at a transhipment location, a sudden rise in RR might suggest the refrigeration unit, having been disconnected from shore power or shipboard power, was then not promptly reconnected to another source of power (shipboard power or shore power, or to a genset).
This can then provide objective data useful in, for example, cargo insurance claim negotiations. The data can assist the various stakeholders in the value chain in understanding, for example, concentration of claims from particular customers or regions or under particular climate effects (e.g. seasonal).
Further, particularly for high value or very sensitive produce, the RR may be used as direct feedback into the dynamic CA operation. In this form, the controller calculating the RR in real time and adjusting the atmosphere to maintain a desired RR throughout the voyage, and therefore minimise stress on the produce.
Whilst it has been convenient to describe the invention herein in relation to particularly preferred embodiments, it is to be appreciated that other constructions and arrangements are considered as falling within the scope of the invention. Various modifications, alterations, variations and/or additions to the constructions and arrangements described herein are also considered as falling within the scope and ambit of the present invention.
The following passages set out the parameters used in the trials discussed above with reference to
In operation the AVCA controller intermittently commands the shutting of the atmosphere control valves and the measurement of the container oxygen fraction until the shorter of:
Assuming a linear model starting at (0,0) the flow-pressure curve slopes for these values is as follows.
This calculation assumes that the container leakage is primarily driven by the pressure drop generated by the operation of the container fan, and occurs in the resulting low and high pressure areas close to the fan.
The pressure drop generated by the fan is denoted Pf [Pa]
Atmospheric pressure is denoted Patm[Pa]
The pressure immediately upstream of the fan will be Patm−Pf/2 while the pressure immediately downstream will be Patm+Pf/2.
Now, the leakage driving pressure in these areas will be:
o2 change due to valve leakage (do2v)
External air leaking in: o2in[SLPM)=Pl[Pa] *Lv[SLPM Pa−1] *o2atm[fraction]
Internal air leaking out: o2out[SLPM)=Pl[Pa] *Lv[SLPM Pa−1] *o2[fraction]
Total: do2v=o2in −o2out
Similarly, o2 change due to container leakage [do2l]
do2l=Pl*Lv*(o2atm−o2)
Now, the total flow balance of o2 is:
do2=do2v+do2l−do2r (where do2r is the change in o2 due to respiration)
do2r=do2v+do2l−do2
Now do2 is measured and do2v and do2l calculated, so that do2r can be
calculated, as can, given the cargo properties, rro2.
do2 is the measurement returned by the rr measurement.
Change in oxygen due to valve leakage
do2v=Lv*Pl*(o2atm−o2avg)
Change in oxygen due to container leakage
do2l=Lc*Pl*(o2atm−o2avg)
Change in oxygen due to respiration rate:
do2r=do2v+do2l−do2
rro2=do2r*60*1000/Mp
([SLPM]*[min h−l]*[ml l−l]*[kg−1] [ml kg−1 h−1])
The Maxtend AVCA7 controller process returns a block of statistics as an XML block (corresponding to the RRDB) embedded in the GPRS modem data stream.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015902983 | Jul 2015 | AU | national |
| 2015903843 | Sep 2015 | AU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2016/050664 | 7/26/2016 | WO | 00 |
