Systems and methods for correcting lag between sensor temperature and ambient gas temperature

Various embodiments of the invention provide systems and methods for accurately determining temperatures in harsh environments such as, for example, in a steam autoclave chamber during a sterilization cycle. In certain embodiments, temperature data accuracy is increased by utilizing an IC-based temperature logging device that monitors and compensates for inherent thermal delays that would otherwise cause a discrepancy between temperature as measured by a temperature sensor and the actual ambient gas temperature. By properly correcting for the thermal delay, the data accuracy of the measured gas temperature is thus greatly enhanced.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This is a U.S. 371 National Stage of PCT Patent Application No. PCT/US2016/61884, entitled, “SYSTEMS AND METHODS FOR CORRECTING LAG BETWEEN SENSOR TEMPERATURE AND AMBIENT GAS TEMPERATURE,” naming as inventors Victor Levi, Michael James D'Onofrio, and Raghunath Puttaiah, and filed Nov. 14, 2016, which application claims priority benefit, under 35 U.S.C. § 119(e), to co-pending and commonly assigned U.S. Provisional Patent Application No. 62/261,783, entitled “ALGORITHM TO CORRECT LAG BETWEEN INTERNAL TEMPERATURE SENSOR AND AMBIENT GAS,” naming as inventors Victor Levi, Michael James D'Onofrio, and Raghunath Puttaiah, U.S. Provisional Patent Application No. 62/261,749, entitled, “APPARATUS FOR LOGGING DATA IN HARSH ENVIRONMENTS,” naming as inventors Jeffery Alan Gordon, Scott Edward Jones, and Hal Kurkowski, and U.S. Provisional Patent Application No. 62/261,782, entitled, “INDICATOR OF STERILIZATION EFFICACY USING A DATA LOGGER WITH CLOUD/SOFTWARE APPLICATION,” naming as inventors Michael James D'Onofrio, Carlos Manuel Contreras, and Raghunath Puttaiah, which applications were filed Dec. 1, 2015, and which applications are hereby incorporated herein by reference in their entireties.

BACKGROUND

A. Technical Field

The present invention relates to data processing, and more particularly, to systems and methods for correcting lag between internal temperature sensor and ambient gas.

B. Background of the Invention

Over the years, various devices for acquiring and storing temperature data have been developed to trace the history of ambient temperature surrounding the devices. Manufacturers and/or distributors send the device along with their products, such as drugs, that are sensitive to temperature changes, where the products need to remain within a preset temperature range to keep their original efficacy. The receivers of the products retrieve the temperature data stored in the device and check if the temperature of the products was outside the preset range during transportation.

Some conventional devices for logging temperature data have been designed to operate at relatively large time constants. For instance, a typical device for monitoring the ocean temperature may have a water-proof capsule and take a sample at every hour. Typically, the capsule is made of thick metal plate, and there is a time lag between the ocean water and the temperature inside the capsule. In such a case, the time constant for the device is in the order of minute, and thus, the time lag due to the large thermal mass of the capsule may not affect the accuracy of the data.

In other applications, such as autoclave for steam sterilization, the time constant is relatively short since the ambient gas temperature inside the autoclave rises from room temperature to 100° C. quite quickly. When a conventional device for logging temperature data is placed inside the autoclave, the device may not be able to keep up with the temperature change due to the thermal resistance of the capsule material. The thermal resistance may result in false reading of the ambient gas temperature. For instance, the conventional device may take longer to heat up relative to the ambient gas in the autoclave than to cool down relative to the ambient gas. As a result, the device may indicate that the autoclave is maintained at the intended sterilization temperature shorter than it actually does. As such, there is a need for a device for electronically logging temperature data, where the time constant of the capsule is short enough to accurately keep track of the ambient gas temperature.

The delay between the ambient gas temperature and the temperature measured by the device may be affected by several factors including the thermal mass of the capsule. If the delay is corrected properly, the accuracy in reading the ambient gas temperature would be enhanced. As such, there is also a need for systems and methods for correcting the delay to thereby accurately track the ambient gas temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for the purposes of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, described below, may be performed in a variety of ways and using a variety of means. Those skilled in the art will also recognize additional modifications, applications, and embodiments are within the scope thereof, as are additional fields in which the invention may provide utility. Accordingly, the embodiments described below are illustrative of specific embodiments of the invention and are meant to avoid obscuring the invention.

A reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearance of the phrase “in one embodiment,” “in an embodiment,” or the like in various places in the specification are not necessarily all referring to the same embodiment.

Connections illustrated in the figures between components may be modified or otherwise changed through the addition thereto of intermediary components, without departing from the teachings of the present invention.

Furthermore, one skilled in the art shall recognize: (1) that certain steps may optionally be performed; (2) that steps may not be limited to the specific order set forth herein; and (3) that certain steps may be performed in different orders, including being done contemporaneously.

FIG. 1Ashows an exploded view of a package10for logging temperature data according to one embodiment of the present invention. As depicted inFIG. 1A, the package10includes: a capsule having a plug12, a base40and O-rings22,24, and30; and a temperature data logger (or, shortly, data logger)28for logging temperature data under harsh environments. In embodiments, the data logger28may be an integrated circuit (IC)-based temperature data logger.FIG. 1Bshows a cross sectional view of the package10, taken along the direction1B-1B, where the male thread16of the plug12is slightly engaged into the female thread42of the base40.FIG. 1Cshows the package10, where the plug12is fully engaged into the base40.

For the purpose of illustration, the package10is described as a temperature data logging device for a steam autoclave chamber, i.e., the package10is mounted inside a steam autoclave chamber and logs temperature data during sterilization cycles of the autoclave. For instance, an exemplary operational condition of the steam autoclave has the temperature of 140° C. and the pressure of 2 atmosphere, and each cycle may last 35-40 minutes, and the package10is designed to survive more than hundred cycles without being damaged by the ambient gas. However, it should be apparent to those of ordinary skill in the art that the package10may be applied to other test environments. Also, it should be apparent to those of ordinary skill in the art that the package10may be calibrated to accommodate different operational temperature ranges.

The plug12includes: a slot20for receiving a tool, such as torque wrench, for turning the plug12relative to the base40; and a through hole18that allows the ambient gas to directly contact the top surface of the data logger28during operation. Since the ambient gas including hot steam is in direct contact with the data logger28, the thermal lag between the chamber environment and the data logger28is reduced so that the data logger28can accurately track the temperature variation inside the chamber.

The O-rings22,24, and30are used to prevent ingress of moisture into the data logger28. The O-ring22rests on a groove14that is formed on the plug12. The O-ring22is compressed by the lip41of the base40when the plug12is fully engaged into the base40, as shown inFIG. 1C, to thereby preventing ingress of the ambient gas through the gap between the male thread16and the female thread42.

The O-rings24and30rest on grooves25and33, respectively. When the package10is assembled, the O-rings24and30are compressed by the top and bottom surfaces of the data logger28, respectively, to thereby prevent ingress of the ambient gas through the gaps between the capsule and the data logger28.

The base40includes a through hole32that allows the ambient gas to directly contact the bottom surface of the data logger28during operation. Since the ambient gas is in direct contact with the data logger28, the thermal lag between the chamber environment and the data logger28is reduced so that the data logger28can accurately track the temperature variation inside the chamber. The base40also includes a notch/recess41so that a proper device securely holds the base in place during assembly of the package10.

If the package10is assembled while the O-rings22,24, and30are dry, the O-rings may not properly seal the space surrounding the data logger28due to pinching, crimping, or twisting of the O-rings. To avoid such deformation of the O-rings, small amount of grease is applied to the O-rings. The grease also holds the O-rings in their corresponding grooves temporarily during assembly. For instance, the O-rings22and24remain seated on the grooves14and25, respectively, by the grease when the plug12is flipped over during assembly, as shown inFIG. 1B.

It is noted that the package10may be mounted in the autoclave chamber with other items, such as medical instruments, being sterilized. If the package10releases any toxic material into the autoclave chamber, the items may be contaminated by the toxic material. As such, all of the components, including the grease, of the package10are tested to ensure that none of the components release toxins during sterilization cycles.

The capsule is reusable, i.e., the user can disengage the male thread16from the female thread42, replace the data logger28, and reassemble the package10. During this process, the user may not place one or more of the O-rings22,24and30properly i.e., the user may misalign the O-rings on resealing. In embodiments, to obviate the improper reassembly by the user, small amount of glue may be applied to the threads so that the plug and base are glued together.

FIG. 2shows a cross sectional view of a base42of a capsule according to one embodiment of the present invention. As depicted, the base42is similar to the base40inFIGS. 1A-1C, with the difference that the base42includes an O-ring groove44that the O-ring22rests on. It should be apparent to those of ordinary skill in the art that the package10may include other suitable types of sealing mechanisms to prevent the ingress of the ambient gas into the data logger28.

The material for the plug12and base40(or42) may be chosen for its mechanical properties (i.e., they remain stable during both long and short-term exposure to high temperature and pressure), inherent flame resistance, and outstanding chemical resistance (i.e., inert to high temperature steam, strong bases, fuels and acids). In embodiments, the plug and base are formed of a polymer, such as polyphenylene sulfide (PPS). Likewise, the material for the O-rings22,24, and30may be chosen for their mechanical strength and chemical qualities. In embodiments, the O-rings are formed of silicon, where the silicon O-rings are also resistant to sunlight, ozone, oxygen, and UV light.

FIG. 3shows an integrated circuit (IC)-based temperature data logger28according to one embodiment of the present invention. As depicted, the temperature logger28includes: a top cover50; a bottom cover51; an electrical circuitry52for measuring and storing the temperature data; and a securing element53that secures the electrical circuitry52to the bottom cover51. When the data logger28is assembled, the top and bottom covers50and51form a housing and the electrical circuitry52is disposed in the inner space of the housing. In embodiments, the top and bottom covers50and51may provide water-proof sealing against fluid.

In embodiments, the top and bottom covers50and51may be formed of electrically conducting material and operate as two electrodes that are electrically connected to the electrical circuitry52. For instance, a suitable electrical device may communicate the data logged in the data logger28through the top and bottom covers50and51. The top and bottom covers50and51are formed of material having high thermal conductivity, such as metal, so that the lag between the temperature of the autoclave chamber and the temperature inside the covers50and51is minimized. The securing element53is formed of material having a high thermal conductivity, such as heat conducting glue, to minimize the thermal lag between the temperature inside the covers50and51and the temperature outside the covers.

Unlike the conventional temperature loggers, a portion155of the top cover50is directly exposed to the ambient gas via the through hole18without damaging the electric circuitry52during operation. Likewise, a portion of the bottom cover51is directly exposed to the ambient gas via the through hole32during operation. This feature allows the data logger28to have minimal temperature lag, i.e., the data logger28can track the ambient gas temperature more accurately.

FIG. 4shows a schematic diagram of the electronic circuitry52of the IC-based temperature data logger28inFIG. 3according to one embodiment of the present invention. In embodiments, the electrical circuitry52may be an application-specific integrated circuit (ASIC) and include: a processor54for operating various components of the circuitry52; a sensor56for measuring temperature; a battery58for providing electrical power to the circuitry52; a communication unit57for communicating data to an external device; a memory55for storing the measured temperature data; and a system clock59for generating clock signals for the circuitry52. It is noted that, depending on the application, the circuitry52may include additional components, such as additional sensors, and one or more of the components of the circuitry52may be omitted.

In embodiments, the processor54may be programmed to measure the temperature inside the data logger28at a preset time and/or repeat measurements at a preset time interval. In embodiments, the processor54may receive the clock signals from the system clock59and cause the sensor56, such as digital temperature sensor, to measure the temperature as scheduled. Then, the processor54may store the data into the memory55, where the memory55may be a static RAM, for instance. In embodiments, to minimize the power consumption, the processor54may wake up at the scheduled time to measure the temperature and goes back to sleep mode after measurement is completed.

In embodiments, the processor54may communicate the stored data to an external device through the communication device57and/or the processor54may be controlled/programmed through the communication device57. In embodiments, the communication unit57may be a wireless communication device.FIG. 5shows a data communication between the package10and a mobile device60according to one embodiment of the present invention.

In embodiments, the user may install an application on the mobile device60so that the user can set up the parameters on the circuitry52, such as time and frequency of data sampling, before the package10is mounted in the autoclave. After a sterilization cycle(s), the user may retrieve the stored data from the package10using the mobile device60and a suitable application may display the temperature data on the display61of the mobile device60. It is noted that the user may control and communicate to the package10using other suitable external devices. For instance, in embodiments, the user may use a computer/server in place of the mobile device60.

FIG. 6shows a data communication between the package10and a mobile device64according to one embodiment of the present invention. As depicted, the package10may be docked in a reader62that can retrieve data stored in the package10and send the retrieved data to the mobile device64. In embodiments, the reader62may have two spring-loaded electrodes71and72that make electrical contact to the top and bottom surfaces of the data logger28, respectively, and extract the data stored in the package10. Also, in embodiments, the reader62may be used to transmit electrical signals from the mobile device64to the package10so that the user can program the electrical circuitry52.

After a sterilization cycle(s), the user may retrieve the stored data from the package10using the mobile device64and a suitable application installed in the mobile device64displays the temperature data on the display65of the mobile device64. It is noted that the user may control and communicate to the package10using other suitable external device. For instance, in embodiments, the user may use a computer/server in place of the mobile device64. In some embodiments, the reader62may exchange electrical signals with the mobile device64through wireless communication69, as shown inFIG. 6, or through wire68, such as universal serial bus (USB) connection.

FIG. 7shows an exemplary plot of ambient gas temperature84and the temperature82measured by the package10during a sterilization cycle according to one embodiment of the present invention. As depicted, there is a lag between the ambient gas temperature84and the measured temperature82, i.e., the measured temperature82shows that the ambient gas reaches the target sterilization temperature, Ts, several minutes after the ambient gas actually reached Ts. InFIG. 7, T1represents the time interval during which the ambient gas is actually maintained at Ts while the measured temperature82indicates that the ambient gas is maintained at Ts during the time interval T2. For the purpose of illustration, it is assumed that T1is longer than the required time interval for proper sterilization while T2is shorter than the required time interval for proper sterilization. If the pass/fail test of the sterilization cycle is determined based on whether the ambient gas is maintained at Ts longer than the required time interval, the measured temperature82may indicate that the sterilization cycle failed the test, while the sterilization cycle actually passed the test.

To correct the lag, the mobile device60, computer/server, or any other computing device may have a software program (or, shortly, algorithm) that analyzes the measured temperature82. In embodiments, the algorithm may be based on phenomenological model of heat transfer between ambient gas (A) and probe/sensor (P)56via the probe enclosure (E), where the enclosure may collectively refer to the plug12, base40, and top and bottom covers50and51.

Assuming that the enclosure temperature TEdiffers from both actual ambient gas temperature TAand probe temperature TP, the rate of heat transfer between the probe enclosure and the probe is expressed as:

Cp⁢dTpdt=k1⁡(TE-Tp)(1)
where, the parameters CPand k1are the heat capacity and heat transfer coefficient of the probe, respectively.

Likewise, the rate of heat transfer between the ambient gas and probe enclosure is expressed as:

CE⁢dTEdt=k2⁡(TA-TE)(2)
where, the parameters CEand k2are the heat capacity and heat transfer coefficient of the probe enclosure, respectively.

Combining Eq. (1) and Eq. (2), the relation between the ambient gas temperature TAand the probe temperature TPis expressed as:

TA=Tp+(τ1+τ2)⁢dTpdt+(τ1⁢τ2)⁢d2⁢Tpdt2(3)
where, τ1(=Cp/k1) and τ2(=CE/k2) are time constants for the probe and probe enclosure, respectively.

In embodiments, several factors may affect the actual values of the time constants, τ1and τ2.FIG. 8shows multiple devices under test (DUT)102a-102elocated inside an autoclave100according to one embodiment of the present invention. In embodiments, each of the DUT102may be similar to the package10. As depicted, depending on the locations where the DUT102are installed, the time constants (τ1and τ2) of each device may have different values.

In embodiments, the values of the time constants may vary depending on other parameters: (1) whether the package is bagged or unbagged in a pouch during the sterilization cycle; (2) whether the autoclave is unloaded or loaded with other items, such as medical instruments, during the sterilization cycle; (3) whether the autoclave is already warm before the cycle; (4) the type of cycles, such as vacuum or gravity; (5) the time interval during which the target sterilization temperature Ts is maintained; and (6) the value of Ts. It is noted that other factors may affect the values of the time constants.

In embodiments, the time constants τ1and τ2in Eq. (3) may be determined, considering the factors described above. For instance, test cycles may be repeated to measure temperature while one or more of the factors are varied. Then, using the obtained temperature data, the time constants may be determined/calibrated.

Eq. (3) includes the first and second derivatives of the probe temperature TPwith respect to time. In embodiments, temperature data may be obtained as an array of samples taken at preset time intervals. Then, the derivatives may be calculated by applying the finite-difference-approximation to the obtained data. In embodiments, a filter, such as low pass filter, may be used to filter the noise in the obtained data before the data is analyzed.

In embodiments, the software application (or algorithm) installed in the mobile device60(or, in other suitable external devices) may use Eq. (3) to compensate the lag between the actual ambient gas temperature84and measured temperature82. InFIG. 7, the compensated temperature86is obtained by compensating the lag in the measured temperature82, where the compensated temperature86indicates that the ambient gas is maintained at Ts during the time interval T3. If T3is longer than the required time interval for proper sterilization, the compensated temperature86correctly indicates that the sterilization cycle passed the test. Thus, the compensation of the lag reduces the rate of false fails.

FIG. 9is a flowchart900illustrating exemplary steps that may be carried out to compensate the thermal lag according to one embodiment of the present invention. At step902, the time constants, τ1and τ2in Eq. (3), are determined. In embodiments, the time constants are determined considering various factors that include (1) the location of the package10inside the autoclave; (2) whether the package is bagged or unbagged in a pouch during the sterilization cycle; (3) whether the autoclave is unloaded or loaded with other items, such as dental instruments, during the sterilization cycle; (4) whether the autoclave is already warm before the cycle; (5) the type of cycles, such as vacuum or gravity; (6) the time interval during which the target sterilization temperature Ts is maintained; and (7) the value of Ts. In embodiments, test cycles may be repeated to measure temperature using the package10while one or more of the factors are varied. Then, using obtained temperature data, the time constants may be determined.

Next, at step904, using a package10, temperature of the ambient gas in the autoclave is measured at a preset time and/or repeat measurements at a preset time interval. Optionally, the noise in the measured temperature data is filtered out by a filter at step906.

At step908, the lag between the actual ambient gas temperature and the measured temperature is compensated. In embodiments, Eq. (3) may be applied to the measured temperature data in order to generate compensated temperature data, where the compensated temperature data includes reduce thermal lag and thus more accurately shows the actual ambient gas temperature profile.

In embodiments, one or more computing system may be configured to perform one or more of the methods, functions, and/or operations presented herein. Systems that implement at least one or more of the methods, functions, and/or operations described herein may comprise an application or applications operating on at least one computing system. The computing system may comprise one or more computers and one or more databases. The computer system may be a single system, a distributed system, a cloud-based computer system, or a combination thereof.

It shall be noted that the present disclosure may be implemented in any instruction-execution/computing device or system capable of processing data, including, without limitation phones, laptop computers, desktop computers, and servers. The present disclosure may also be implemented into other computing devices and systems. Furthermore, aspects of the present disclosure may be implemented in a wide variety of ways including software (including firmware), hardware, or combinations thereof. For example, the functions to practice various aspects of the present disclosure may be performed by components that are implemented in a wide variety of ways including discrete logic components, one or more application specific integrated circuits (ASICs), and/or program-controlled processors. It shall be noted that the manner in which these items are implemented is not critical to the present disclosure.

Having described the details of the disclosure, an exemplary system1000, which may be used to implement one or more aspects of the present disclosure, will now be described with reference toFIG. 10. Each client/server inFIG. 1includes one or more components in the system1000. As illustrated inFIG. 10, system1000includes a central processing unit (CPU)1001that provides computing resources and controls the computer. CPU1001may be implemented with a microprocessor or the like, and may also include a graphics processor and/or a floating point coprocessor for mathematical computations. System1000may also include a system memory1002, which may be in the form of random-access memory (RAM) and read-only memory (ROM).

A number of controllers and peripheral devices may also be provided, as shown inFIG. 10. An input controller1003represents an interface to various input device(s)1004, such as a keyboard, mouse, or stylus. There may also be a scanner controller1005, which communicates with a scanner1006. System1000may also include a storage controller1007for interfacing with one or more storage devices1008each of which includes a storage medium such as magnetic tape or disk, or an optical medium that might be used to record programs of instructions for operating systems, utilities and applications which may include embodiments of programs that implement various aspects of the present disclosure. Storage device(s)1008may also be used to store processed data or data to be processed in accordance with the disclosure. System1000may also include a display controller1009for providing an interface to a display device1011, which may be a cathode ray tube (CRT), a thin film transistor (TFT) display, or other type of display. System1000may also include a printer controller1012for communicating with a printer1013. A communications controller1014may interface with one or more communication devices1015, which enables system1000to connect to remote devices through any of a variety of networks including the Internet, an Ethernet cloud, an FCoE/DCB cloud, a local area network (LAN), a wide area network (WAN), a storage area network (SAN) or through any suitable electromagnetic carrier signals including infrared signals.