DATA LOGGER AND COMPUTER-READABLE STORAGE MEDIUM APPLIED TO THE DATA LOGGER

According to one embodiment, a data logger driven by a battery, includes a sensor, a log creation module, a detection module, a communication module, and a controller. The sensor measures a predetermined physical quantity. The log creation module creates a log based on the predetermined physical quantity. The detection module detects a take-over state that another data logger takes over creation of the log. The communication module communicates with said another data logger synchronized with the data logger. The controller performs a process to cause said another data logger to take over the creation of the log by communicating with said another data logger by the communication module when the take-over state is detected by the detection module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-234133, filed Nov. 30, 2015, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a data logger driven by a battery and a computer-readable storage medium applied to the data logger.

BACKGROUND

In order to acquire data in different environments, usually, a data logger capable of recording the acquired data as a log is widely used. This data logger is driven by a battery because it is used in a situation where it cannot be charged.

In this data logger, continuous operating time such as time periods and days for which the data logger continuously operates, is one of the important indices indicating the performance of the data logger. Accordingly, the data logger employs a method of lengthening the continuous operating time by increasing the capacity of the battery.

Recently, however, it has been required to downsize a data logger. If the battery of the data logger simply increases in capacity, the downsizing becomes difficult. The increase in capacity upsizes the data logger itself and thus lowers the commercial value thereof.

Even though a single data logger increases in its battery capacity, the battery capacity will go dead to make it impossible to create a log continuously.

It has also been required to increase the storage capacity for recording a log created by a data logger. However, a large-capacity storage increases costs and, in this case, too, the commercial value of the data logger lowers.

DETAILED DESCRIPTION

In general, according to one embodiment, a data logger driven by a battery, includes a sensor, a log creation module, a detection module, a communication module, and a controller. The sensor measures a predetermined physical quantity. The log creation module creates a log based on the predetermined physical quantity. The detection module detects a take-over state that another data logger takes over creation of the log. The communication module communicates with said another data logger synchronized with the data logger. The controller performs a process to cause said another data logger to take over the creation of the log by communicating with said another data logger by the communication module when the take-over state is detected by the detection module.

First Embodiment

A first embodiment according to the present invention will be described below with reference to the accompanying drawings.

First, an overview of the first embodiment will be described with reference toFIG. 1.FIG. 1is a diagram showing a logger control system1in the first embodiment.

In the first embodiment, a sensing logger10ais placed as a data logger for freight in, e.g. a box containing freight such as a baggage. The sensing logger10ais a data logger that acquires sensing information as a log. The sensing information includes climate information about climate such as atmospheric pressure, temperature and humidity, environment information such as oscillation and acceleration, and event information about an event such as impact and light quantity. This event will be described later. The log is referred to as data on which sensing information is recorded. The sensing logger10ahas, e.g. waterproof property and pressure resistance and can be used in environment other than normal environment, such as water and a high-pressure place.

The sensing logger10ais driven by a battery (not shown) which is built in the sensing logger10a. If the sensing logger10adecreases in its battery remaining amount7while it is creating a log, it carries out wireless communications8with another sensing logger10bto perform a process for transferring the log creation to the sensing logger10b. Thus, the sensing logger10bis placed in the same environment as the sensing logger10ais. The sensing logger10bhas the same configuration as the sensing logger10ahas. The sensing logger10balso has, e.g. waterproof property and pressure resistance and can be used in environment other than normal environment, such as water and a high-pressure place. To describe the sensing loggers10aand10b, hereinafter, they will be collectively called a sensing logger10when necessary.

For example, it is feared that the battery remaining amount7will become zero while only one sensing logger10ais creating a log continuously for a long time in environment that makes it impossible to charge the sensing logger10, such as the inside of freight in a ship or the like. It is thus necessary to transfer the log creation to the sensing logger10bwith appropriate timing before the battery remaining amount7becomes zero.

Assume the case where the sensing loggers10aand10bare placed together with freight. In this case, even though after a fixed period of time after the sensing logger10astarts to create a log, the sensing logger10btakes over the log creation using a timer or the like, if the battery of the sensing logger10ais exhausted more quickly than expected, the sensing logger10astops its log operation before the sensing logger10bstarts to create a log; thus, no log can be created. It is thus necessary to take measures to transfer the creation of a log from the sensing logger10ato the sensing logger10bwithout interruption.

In the first embodiment, the log creation is transferred from the sensing logger10ato the sensing logger10busing a decrease in the battery remaining amount7as a trigger.

More specifically, assume the case where the battery remaining amount7of the sensing logger10adecreases to a battery remaining amount7b(e.g. 40%) which is smaller than a battery remaining amount7aand then to a battery remaining amount7c(e.g. 20%) which is smaller than the battery remaining amount7b, as shown inFIG. 1. In this case, for example, wireless communication8with the sensing logger10bis carried out using a decrease in the battery remaining amount7from the battery remaining amount7bto the battery remaining amount7cas a trigger. The sensing logger10bstarts to create a log using an establishment of the wireless communication8with the sensing logger10aas a trigger and, in other words, the sensing logger10bstarts to take over the log creation from the sensing logger10a.

The sensing logger10or the sensing loggers10aand10beach includes a display screen6for displaying different items of information such as sensing information, as will be described with reference toFIG. 10.

An example of the configuration of the sensing logger10according to the first embodiment will be described with reference toFIG. 2. Though the sensing loggers10aand10bhave a similar configuration as described above, they may have different configurations as will be described in the last part of the first embodiment.

The sensing logger10includes a battery module11, a sensor12, a log data storage13, a communication module (RF)14, a real time clock (RTC)15, an external interface module16, a display module17and a controller20.

The sensing logger10creates a log on the basis of a predetermined physical quantity measured by the sensor which will be described later, and records the created log. The predetermined physical quantity is, for example, atmospheric pressure, temperature, humidity, oscillation, acceleration, impact and light quantity.

The battery module11includes a battery (not shown) for driving the sensing logger10. The battery is connected to the controller20and can be charged through the external interface module16connected to an external power source. In the first embodiment, however, it is assumed that the battery is not charged while the sensing logger10is creating a log.

The battery module11sends information indicative of a state of the battery, such as information about the battery remaining amount7, to the controller20.

The sensor12measures a predetermined physical quantity about a log to be created by the sensing logger10. The sensor12includes an atmospheric pressure sensor, a temperature sensor, a humidity sensor, an oscillation sensor, an acceleration sensor, an impact sensor for sensing an impact on the sensing logger10, and a light quantity sensor for sensing light quantity. The predetermined physical quantity measured by the sensor12is output to the controller20as an electrical signal.

The log data storage13is connected to the controller20and stores data (referred to as “log data” hereinafter) about a log created by a log creation module21provided in the controller20which will be described later. The log data storage13is a storage for recording log data as, e.g. a nonvolatile recording element.

The log data storage13sends, for example, information indicative of free space of the log data to the controller20.

The communication module (RF)14carries out wireless communication with another sensing logger10(which corresponds to the sensing logger10bwhen the sensing logger10is the sensing logger10a). The wireless communication is, for example, Bluetooth®, WiFi® or Transfer Jet®. The communication module14is started, for example, in response to an instruction from the controller20and performs wireless communication. Hereinafter, a wireless communication available state will be referred to as “RF mode.” Unlike the power-on state (referred to as “power-on mode” hereinafter) of the sensing logger10, the RF mode is, for example, a state in which only a function necessary for performing wireless communication is effective.

The communication module14also performs communication using, for example, Bluetooth® low energy. The Bluetooth® low energy is, for example, Bluetooth® of the version of four or more. Accordingly, for example, the sensing logger10bthat takes over the creation of a log need not always be driven in the power-on mode but can be driven in the RF mode which reduces power consumption to take over the log creation from the sensing logger10a.

The RTC15has a function of continuing to show the current time, which is provided in a generally-used computer. For example, the RTC15continues to show the current time even though the sensing logger10is in a power-off state (referred to as “power-off mode” hereinafter).

Furthermore, the RTC15is used to cause the communication module14to carry out a synchronization process necessary for wireless communication between the sensing loggers10aand10b. More specifically, the controller20, which will be described later, synchronizes time of the RTC15of the sensing logger10awith that of the RTC15of the sensing logger10b.

The external interface module16is an interface for connecting the sensing logger10to an external device. For example, it is an interface for connecting an external device such as a USB device to the sensing logger10to charge the sensing logger10. The foregoing synchronization process can be performed using a USB device such as a USB hub.

The controller20includes a log creation module21, a battery register22, a take-over state detection module24and a mode selection module25.

The controller20is connected to the battery module11, sensor12, log data storage13, communication module14, RTC15, external interface module16and display module17.

When the take-over state detection module24detects a state in which the creation of a log is taken over to the sensing logger10b(referred to as “take-over state” hereinafter), the controller20communicates with the sensing logger10bthrough the communication module14to cause the sensing logger10bto take over the log creation. The controller20is achieved as, for example, a microcomputer.

The log creation module21creates a log on the basis of a predetermined physical quantity measured by the sensor12. More specifically, a predetermined physical quantity is processed as data and stored in, e.g. a register (not shown) provided in the log creation module21. On the basis of the stored data, the log creation module21creates a log. The created log is sent to the log data storage13and stored therein. More specifically, log data is created in association with a predetermined physical quantity and time and the created log data is stored in the log data storage13.

The battery register22acquires information about a battery remaining amount7and stores the battery remaining amount7on the basis of the information. This information is, for example, a voltage value of the battery or a variation in the voltage value. The information may contain information indicating a time-series variation of the battery remaining amount7. The battery register22holds the acquired information about the battery remaining amount7, the detected information indicating the battery remaining amount7, or the like.

Furthermore, the battery register22need not detect the battery remaining amount7in real time. The battery register22has a fixed storage capacity, and sets a flag indicating that the voltage value decreases to change the flag from, e.g. “0” to “1” and record the battery remaining amount7or the flag.

The take-over state detection module24detects a take-over state as described above. For example, the take-over state detection module24detects a decrease in the battery remaining amount7as a take-over state. More specifically, the take-over state detection module24detects a take-over state in accordance with the battery remaining amount7detected by the battery register22. For example, the take-over state detection module24detects a take-over state when the battery remaining amount7is smaller than a predetermined threshold value.

Assume here that the predetermined threshold value is a preset voltage value of the battery, e.g. 3.6 V. When the total capacity of the battery is, e.g. 4.1 V and the detected battery remaining amount7is smaller than 3.6 V, the take-over state detection module24determines that the battery is in a take-over state.

The predetermined threshold value can be determined by, for example, a preset percentage of the total capacity of the battery. In this case, the take-over state detection module24determines that a battery that is usable for about twenty-five days is in a take-over state when the preset percentage of a battery that can continuously be used for about fifty days is 50%.

The predetermined threshold value can be set in accordance with, for example, the rate of decrease in the battery remaining amount7. The rate of decrease in the battery remaining amount7means, for example, the percentage of the total capacity of the battery which decreases in a given period of time to total capacity of the battery. In this case, the take-over state detection module24determines that the battery is in a take-over state when the rate of decrease in the battery remaining amount7is higher than a preset rate of decrease or the rate of decrease which is higher than the preset rate of decrease is continued for a given period of time.

The take-over state detection module24recognizes the battery to be in a take-over state when the sensor12senses an abnormal event. If an impact that is greater than expected is sensed by the impact sensor of the sensor12or light quantity that is not expected is sensed by the light quantity sensor of the sensor12, the take-over state detection module24determines these detections as an abnormal event and determines that the battery is in a take-over state.

The take-over state detection module24may determines that the battery is in a take-over state even though the foregoing abnormal event is sensed by a sensor other than the impact sensor or light quantity sensor.

When the take-over state detection module24detects a take-over state, the controller20causes the communication module14to perform a process to try wireless communication at regular intervals during the creation of a log.

When the communication module14was not able to carry out wireless communication with the sensing logger10b, the controller20may perform a process to stop trying the wireless communication by the communication module14.

The mode selection module25performs a process to select one of the power-off mode, RF mode and power-on mode.

The sensor configured to measure a predetermined physical quantity in the claims corresponds to, for example, the sensor12. The log creation module configured to create a log based on the predetermined physical quantity in the claims corresponds to, for example, the log creation module21. The detection module configured to detect a take-over state that another data logger takes over creation of the log in the claims corresponds to, for example, the take-over state detection module24. The communication module configured to communicate with said another data logger synchronized with the data logger in the claims corresponds to, for example, the RTC15. The controller configured to perform a process to cause said another data logger to take over the creation of the log by communicating with said another data logger by the communication module when the take-over state is detected in the claims corresponds to, for example, the controller20.

An example of a logger control procedure according to the first embodiment will be described with reference toFIGS. 3 and 4. This example will be described on the basis of the case where the sensing logger10btakes over the creation of a log from the sensing logger10aas illustrated inFIG. 1.

FIG. 3is a flowchart showing an example of a logger control procedure to be performed by the sensing logger10aof the first embodiment.

The sensing logger10astarts a logger control process when the sensing logger10ashifts from the power-off mode to the power-on mode. More specifically, the logger control process is started by depressing a power button98provided in the sensing logger10aas will be described later with reference toFIG. 10.

The time of the sensing logger10aand that of the sensing logger10bare synchronized in advance by the RTC15of each of the sensing loggers. The synchronization allows the sensing loggers10aand10bto perform wireless communication at the same time as will be described later. The synchronization allows a sensing logger to take over a log created by another sensing logger and also allows a time-series variation of the log to be easily understood.

The sensing loggers10aand10bneed not be paired in advance using Bluetooth®.

When a logger control process is started, the log creation module21starts to create a log (step S20)

The battery module11detects a battery remaining amount7and sends it to the battery register22. The battery remaining amount7is recorded in the battery register22. In accordance with the battery remaining amount7, the controller20determines whether or not the battery register is in a take-over state, or whether or not the battery remaining amount7decreases (step S22). The battery register22may have a function of showing a decrease in the battery remaining amount7on, e.g. the display screen6as an indicator. In step S22, the controller20may determine whether the battery remaining amount7shown as an indicator decreases or not.

When the controller20determines that the battery remaining amount7does not decrease (No in step S22), the flow returns to step S20, in which the log creation is continued. When it determines that the battery remaining amount7decreases (Yes in step S22), the controller20causes the communication module14to perform a process to try wireless communication at regular intervals while the log creation module21continues the log creation (step S24). The regular intervals in step S24may be, for example, several minutes, several hours or one day and, in other words, the communication module14tries wireless communication only at, e.g. several-minute intervals a day. Accordingly, the sensing logger10can be inhibited from decreasing in power consumption.

For example, the mode selection module25selects one of the power-on mode and the RF mode and thus these modes are switched to each other at regular intervals. The RF mode in the sensing logger10ais set as a client of, e.g. Bluetooth® low energy to send a request for establishing wireless communication to the sensing logger10bas a host. Furthermore, the RF mode in the sensing logger10aincludes a wireless communication available state in the power-on mode.

The controller20determines whether the sensing logger10bis detected or not (step S26). When the controller20determines that the sensing logger10bis not detected (No in step S26), the flow returns to step S24. When the number of times the controller20determines that the sensing logger10bis not detected reaches a predetermined number of times, the controller20may cause the communication module14to perform a process to stop trying wireless communication. When it reaches the predetermined number of times, a timeout occurs, and the battery remaining amount7of, e.g. the sensing logger10acan be inhibited from decreasing by stopping trying wireless communication. When it is unnecessary to take over the log creation, such as when, e.g. the sensing logger10bis not placed in advance, the battery remaining amount7can be inhibited from decreasing.

Since the sensing loggers10aand10bare synchronized as described above, they can perform wireless communication and their connection can be established, for example, at the same time.

When the controller20determines that the sensing logger10bis detected (Yes in step S26), the sensing logger10astarts to carry out wireless communication with the sensing logger10b(step S28). After the sensing logger10aestablishes a connection of wireless communication with the sensing logger10b, the wireless communication with the sensing logger10bis finished (step S30).

The take-over of the log creation to the sensing logger10bis completed by establishing a connection of wireless communication with the sensing logger10bby the sensing logger10ain steps S28and S30. Therefore, the sensing logger10aneed not send to the sensing logger10binformation about a log that has already been created by the sensing logger10aafter the sensing logger10aestablishes a connection of wireless communication with the sensing logger10b. In other words, the sensing logger10bstarts to create a log using the establishment of a connection of wireless communication as a trigger

The log creation module21of the sensing logger10acontinues to create a log as long as possible. In other words, the sensing logger10acontinues to create a log until the battery remaining amount7becomes zero (step S32).

After step S30, the logger control process can be finished without performing the process of step S32. In other words, the logger control process can be finished when the sensing logger10acompletes wireless communication with the sensing logger10b.

FIG. 4is a flowchart showing an example of a logger control procedure to be performed by the sensing logger10bof the first embodiment.

Unlike the logger control process to be performed by the sensing logger10a, the logger control process to be performed by the sensing logger10bis started from the power-off mode (step S40). As described above, in the power-off mode, the function of continuing to show the current time by the RTC15is in an active state. After step S40, therefore, the controller20determines whether a given period of time has elapsed (step S42). This determination process is performed in the power-off mode.

When the controller20determines that a given period of time does not elapse (No in step S42), the flow returns to step S40to maintain the power-off mode. When it determines that a given period of time has elapsed (Yes in step S42), the mode selection module25switches the power-off mode to the RF mode (step S44). Thus, the mode selection module25selects one of the power-off mode and RF mode; thus, these modes are switched to each other at regular intervals. The RF mode in the sensing logger10bis set as a host of, e.g. Bluetooth® low energy to search for the sensing logger10aas a client.

The controller20determines whether the sensing logger10ais detected or not (step S46). When the controller20determines that the sensing logger10ais not detected (No in step S46), the flow returns to step S40, in which the mode selection module25switches the RF mode to the power-off mode. When the sensing logger10ais not detected, for example, until the battery remaining amount7becomes zero, before the battery remaining amount7of the sensing logger10bbecomes smaller than the battery capacity necessary for performing wireless communication in the RF mode, the logger control process to be performed by the sensing logger10bcan be finished.

When the controller20determines that the sensing logger10ais detected (Yes in step S46), wireless communication with the sensing logger10ais started (step S48).

In accordance with the fact that wireless communication with the sensing logger10ais started or a connection of wireless communication with the sensing logger10ais established, the mode selection module25switches the sensing logger10bfrom the RF mode to the power-on mode, and the sensing logger10bstarts to create a log (step S50). Thus, in the RF mode, the sensor12of the sensing logger10bstarts to measure a predetermined physical quantity using the establishment of wireless communication with the sensing logger10ain the RF mode as a trigger.

The wireless communication with the sensing logger10ais completed (step S52). The process of step S52can be performed before the sensing logger10bstarts to create a log after the power-on mode is selected in step S50.

The log creation module21of the sensing logger10bcontinues to create a log as long as possible. In other words, the log creation is continued until the battery remaining amount7of the sensing logger10bbecomes zero (step S54).

The sensing loggers10aand10beach have a configuration as shown inFIG. 2. For example, the sensing logger10bneed not include the battery register22or the take-over state detection module24.

For example, the controller20of the sensing logger10bis set as a central device in Bluetooth® low energy in the RF mode such that the communication module14of the sensing logger10bcommunicates with the sensing logger10ausing Bluetooth® low energy. The controller20of the sensing logger10ais set as a peripheral device in Bluetooth® low energy such that the communication module14of the sensing logger10acommunicates with the sensing logger10busing Bluetooth® low energy.

When the sensing loggers10aand10beach have a configuration as shown inFIG. 2, for example, the sensing logger10bcan take over the log creation from the sensing logger10aand then another sensing logger10(e.g. a sensing logger10cnot shown) can take over the log creation from the sensing logger10b. In other words, the foregoing logger control process can be performed for n (n is three or more) sensing loggers10to take over the log creation from each of the sensing loggers10.

In the first embodiment, it is assumed that a plurality of sensing loggers10are placed at once in the same environment, but for example, the sensing loggers10aand10bare placed in a predetermined environment and then the creation of a log is taken over and the sensing logger10ais placed in another environment by a user or the like. Furthermore, it can be assumed that instead of the sensing logger10a, the sensing logger10c(not shown) is placed in the same environment as the sensing logger10b.

The take-over state detected by the take-over state detection module24will be described in detail. The take-over state includes the following first to fifth states.

The first take-over state is a natural decrease state in which for example, the battery remaining amount7or the storage remaining amount decreases as expected and becomes smaller than a predetermined threshold value. This natural decrease state is detected by the take-over state detection module24that acquires an alarm indicating the battery remaining amount7or the storage remaining amount from the battery register22or the storage register23described later.

The second take-over state is an abnormal decrease state in which the battery remaining amount7or the storage remaining amount decreases earlier than expected. Though described in detail in the second embodiment, when the storage remaining amount of the log data storage13as a storage decreases abnormally, for example, the sensor12can measure a predetermined physical quantity. Since, however, a case where a log cannot be recorded is assumed, it is necessary to take over the creation of the log.

The third take-over state is a malfunction state in which, for example, the battery remaining amount7decreases due to a malfunction of the battery, the log data storage13as a storage, or the sensor12. In this malfunction state, a case where information indicative of a malfunction of the battery is included in information indicative of a state of the battery sent to the controller20from the battery module11is assumed. When, for example, the sensor12malfunctions, log creation cannot be continued; thus, the log creation needs to be taken over. The malfunction state represents an abnormal state of, e.g. the battery and includes a state in which, e.g. the battery does not function normally.

The fourth take-over state is an abnormal event detection state in which an abnormal event is detected by the impact sensor or the like, as described above. In the abnormal event detection state, for example, the sensing logger10awhich detects an abnormal event needs to take over the log creation because it is assumed that a time period for which it can operate normally as the sensing logger10becomes shorter.

The fifth take-over state is a data abnormality state in which sensing information is abnormal. When the log data includes abnormal data, such as data that is broken and cannot be recovered, the controller20detects, e.g. an error and notifies the take-over state detection module24of the abnormal data.

As described above, according to the first embodiment, the log creation time period of a battery-driven sensing logger10can be extended by transferring the log creation from the sensing logger10ato the sensing logger10bwith appropriate timing. More specifically, if the battery remaining amount7of a first sensing logger10adecreases, the log creation can be taken over to a second sensing logger10b. For example, even though the battery remaining amount7of the sensing logger10adecreases earlier than expected, it is possible to avoid a period of time for which a log cannot be created.

Second Embodiment

A second embodiment of the present invention will be described below with reference toFIGS. 5-8. The same configurations or contents as those in the first embodiment are denoted by the same reference numbers or same step numbers and their descriptions are omitted.

First, an overview of the second embodiment will be described with reference toFIG. 5.FIG. 5is a diagram showing a logger control system1in the second embodiment.

In the second embodiment, when a storage remaining amount9decreases while a log is being created, a sensing logger10acarries out wireless communication8with a sensing logger10bto transfer the log creation to the sensing logger10b.

In other words, in the second embodiment, the sensing logger10btakes over the log creation from the sensing logger10ausing a decrease in the storage remaining amount9of the sensing logger10aas a trigger.

More specifically, assume the case where the storage remaining amount9of the sensing logger10adecreases to a storage remaining amount9b(e.g. 50%) which is smaller than a storage remaining amount9aand then to a storage remaining amount9c(e.g. 20%) which is smaller than the storage remaining amount9b, as shown inFIG. 5. InFIG. 5, the storage remaining amounts9a,9band9care shown as capacities excluding used capacities5a,5band5c, respectively from the total capacity of the storage.

In this case, for example, wireless communication8with the sensing logger10bis carried out using a decrease in the storage remaining amount9from the storage remaining amount9bto the storage remaining amount9cas a trigger. The sensing logger10bstarts to create a log using an establishment of the wireless communication8with the sensing logger10aas a trigger and, in other words, the sensing logger10bstarts to take over the log creation from the sensing logger10a.

An example of the configuration of the sensing logger10according to the second embodiment will be described with reference toFIG. 6.

The sensing logger10includes a storage register23in the controller20in addition to the structural elements shown inFIG. 2. In the second embodiment, the sensing logger10need not include a battery register22.

The storage register23stores the storage remaining amount9on the basis of information indicative of free space (the storage remaining amount9) of the log data acquired from the log data storage13having a function as a storage. The storage remaining amount9corresponds to a capacity excluding the capacity of stored log data, or the capacity5of used log data from the total capacity of the log data storage13. The information indicating the storage remaining amount9may contain, for example, information indicating a time-series variation of the storage remaining amount9. The storage register23holds, for example, information indicating the storage remaining amount9.

The take-over state detection module24detects as a take-over state the fact that the storage remaining amount9detected by the storage register23is smaller than a predetermined threshold value.

The predetermined threshold value can be determined by, for example, a preset percentage of the total capacity of the log data storage13. In this case, the take-over state detection module24determines that the storage that is usable for about twenty-five days is in a take-over state when the percentage of the storage which is used for about fifty days is assumed to be about 100% of the total capacity of the log data storage13.

The predetermined threshold value can be set according to the rate of decrease in the storage remaining amount9. In this case, for example, the take-over state detection module24determines that the storage is in a take-over state when the rate of decrease in the storage remaining amount9is higher than a preset rate of decrease or the rate of decrease which is higher than the preset rate of decrease is continued for a given period of time.

An example of a logger control procedure according to the second embodiment will be described with reference toFIG. 7. This example will be described on the basis of the case where the sensing logger10btakes over the creation of a log from the sensing logger10aas illustrated inFIG. 5. The same steps as those of the first embodiment are denoted by the same step numbers and their descriptions are omitted.

FIG. 7is a flowchart showing an example of a logger control procedure to be performed by the sensing logger10aof the second embodiment.

The logger control process of the second embodiment differs from that of the first embodiment in steps S60and S70described below.

The controller20determines whether the storage is in a take-over state or whether the storage remaining amount9decreases in accordance with the storage remaining amount9detected by the storage register23(step S60).

When the controller20determines that the storage remaining amount9does not decrease (No in step S60), the flow returns to step S20and the log creation is continued. When the controller20determines that the storage remaining amount9decreases (Yes in step S60), the flow goes to step S24.

After step S30, the log creation is continued as long as possible by the log creation module21of the sensing logger10a. In other words, the log creation is continued until the storage remaining amount becomes zero (step S70).

Another example of the logger control procedure according to the second embodiment will be described with reference toFIG. 8. This example will be described on the basis of the case where the sensing logger10btakes over the creation of a log from the sensing logger10aas illustrated inFIG. 5. The same steps as those of the first embodiment are denoted by the same step numbers and their descriptions are omitted.

FIG. 8is a flowchart showing another example of the logger control procedure to be performed by the sensing logger10aof the second embodiment.

The logger control process shown inFIG. 8is based upon the case where the sensing logger10btakes over the log creation in accordance with the battery remaining amount7and the storage remaining amount9.

The process of step S22is performed prior to that of step S60in the logger control procedure shown inFIG. 7.

More specifically, after step S20, the controller20determines whether the battery is in a take-over state or whether the battery remaining amount7decreases in accordance with the battery remaining amount7detected by the battery register22(step S22).

When the controller20determines that the battery remaining amount7decreases (Yes in step S22), the flow goes to step S24. When the controller20determines that the battery remaining amount7does not decrease (No in step S22), the flow goes to step S60. The controller20determines whether the storage is in a take-over state or whether the storage remaining amount9decreases in accordance with the storage remaining amount9detected by the storage register23(step S60).

When the controller20determines that the storage remaining amount9does not decrease (No in step S60), the flow returns to step S20. In other words, when neither the battery remaining amount7nor the storage remaining amount9decreases, the sensing logger10acontinues to create a log without transferring the log creation to the sensing logger10b.

When the controller20determines that the storage remaining amount9decreases (Yes in step S60), the flow goes to step S24.

InFIG. 8, the process of step S22can be performed in place of that of step S60, and the process of step S60can be performed in place of that of step S22.

After step S30, the log creation module21of the sensing logger10acontinues to create a log as long as possible and, in other words, the log creation is continued until the battery remaining amount7or the storage remaining amount9becomes zero (step S80).

When the controller20determines that the battery remaining amount7or the storage remaining amount9decreases inFIG. 8, the processes of steps S24to S80can be performed.

As described above, according to the second embodiment, the log creation time period of a battery-driven sensing logger10can be extended by transferring the log creation from the sensing logger10ato the sensing logger10bwith appropriate timing. More specifically, if the controller20detects that the storage remaining amount9of a first sensing logger10adecreases, the log creation can be taken over to a second sensing logger10b. For example, even though the storage remaining amount9of the sensing logger10adecreases earlier than expected, it is possible to avoid a period of time for which a log cannot be created.

Furthermore, for example, if the controller20detects that the battery remaining amount7and the storage remaining amount9of a first sensing logger10adecrease, the log creation can be taken over to a second sensing logger10b.

The log data stored in the log data storage13, which is applied to the first and second embodiments, will be described below.FIG. 9shows an example of log data tables80aand80bindicating log data.

The log data table80aincludes a log number item81, a date and time item82, an environment data item83, an impact event data item84and a light quantity event data item85.

The log number item81indicates information about a number for identifying a created log.

The date and time item82indicates information about a date and time including a year/month/day when a log is created or information about a date and time including a year/month/day when log data is stored in the log data storage13.

The environment data item83indicates climate information or environment information of the sensing information acquired by the sensing logger10. As shown inFIG. 9, the environment data item83includes a temperature item83a, a humidity item83b, an illuminance item83cand an atmospheric pressure item83d. The temperature item83aindicates temperature sensed by the temperature sensor of the sensor12. The humidity item83bindicates humidity sensed by the humidity sensor of the sensor12. The illuminance item83cindicates illuminance sensed by the illuminance sensor of the sensor12, such as a light quantity sensor. The atmospheric pressure item83dindicates atmospheric pressure sensed by the atmospheric pressure sensor of the sensor12.

The impact event data item84indicates information about an impact acquired as an abnormal event by the impact sensor of the sensor12. InFIG. 9, the impact event data item84includes an x-axis impact item84a, a y-axis impact item84band a z-axis impact item84cindicating information about impacts in x-axis, y-axis and z-axis directions which are predetermined for the sensing logger10.

The light quantity event data item85indicates information about light quantity acquired as an abnormal event by the light quantity sensor of the sensor12.

More specifically, as indicated in the log data table80ainFIG. 9, there is a one-to-one correspondence among the log number item81, date and time item82, environment data item83, impact event data item84and light quantity event data item85.

For example, the log data about log number # “1” indicates “yy-mm-dd hh:mm:ss1” as a date and time when a created log is acquired and also indicates temperature of “28.5(° C.),” humidity of “47.41(%),” illuminance of “727 (Lux)” and atmospheric pressure of “1020.78 (hPa)” as the environment data.

The log data about log number # “2” indicates “yy-mm-dd hh:mm:ss2” as a date and time when a created log is acquired and also indicates light quantity of “727 (Lux)” as the light quantity event data.

The log data about log number # “4” indicates “yy-mm-dd hh:mm:ss4” as a date and time when a created log is acquired and also indicates an x-axis direction impact of “0.01 (G),” a y-axis direction impact of “0.05 (G)” and a z-axis direction impact of “1.01 (G)” as the impact event data.

Data about the environment data item83is acquired, for example, at regular intervals and created as a log. Data about the impact event data item84or data about the light quantity event data item85is created as a log when, for example, an abnormal event occurs.

Next, the log data table80bwill be described.

The log data table80bshows collected information of information items shown in the log data table80a, or more specifically, the number of environment data log counts, the number of impact event counts, the number of light quantity event counts and the number of total log counts.

The number of environment data log counts “xx1” represents the number of log counts recorded in the environment data item83. InFIG. 9, for example, “xx1” corresponds to “3.”

The number of impact data log counts “xx2” represents the number of log counts recorded in the impact event data item84. InFIG. 9, for example, “xx2” corresponds to “1.”

The number of light quantity data log counts “xx3” represents the number of log counts recorded in the light quantity data item85. InFIG. 9, for example, “xx3” corresponds to “1.”

The number of total log counts “xx4” represents the total number of log counts of “xx1,” “xx2” and “xx3.” InFIG. 9, for example, “xx4” corresponds to “5.”

The log data tables80aand80bshown inFIG. 9are prepared using, e.g. a communication tool for converting a log recorded in terms of binary data into data such as CSV.

The outward appearance of the sensing logger10will be described with reference toFIG. 10.FIG. 10is a perspective view showing an example of the outward appearance of the sensing logger10.

The sensing logger10includes, for example, two regions90and91. The region90includes a display screen6and a light quantity sensor92. The region91includes a power button98for starting the sensing logger10and air holes97formed for the sensor12for sensing a predetermined physical quantity from air, such as the temperature sensor (not shown). For example, the light quantity sensor92can be included in the region91.

The light quantity sensor92is so provided that it can be viewed from outside to sense a variation in light quantity in the environment where the sensing logger10is placed.

The display screen6includes a wireless communication connection display region93indicating whether a connection of wireless communication such as Bluetooth® is established, a log creating display region94indicating whether a log is created, a battery remaining amount display region95indicating the battery remaining amount7, and a sensing information display region96displaying sensing information acquired by the sensing logger10.

The power button98may have, for example, a function of setting the sensing logger10in the power-off mode and a function of selecting one of a valid state in which wireless communication is valid and an invalid state in which wireless communication is invalid, as well as a function of starting the sensing logger10and setting it in the power-on mode.

Furthermore, the logger control system1according to the first and second embodiments as described above is achieved by a computer such as a server whose operation is controlled by, for example, programs recorded on a recording medium such as a magnetic disk and programs downloaded via a communication network such as the Internet.