Abstract:
An object of the present invention is to realize a measured data synchronization system wherein data processing is performed using measured data for which synchronization among measuring instruments is ensured.  
     The present invention is characterized by improvements applied to a measured data synchronization system comprising a plurality of measuring instruments for measuring objects under measurement and outputting measured data, and a data processing apparatus connected to the plurality of measuring instruments via a signal line and which acquires and processes the measured data output by the measuring instruments. More specifically, the present invention relates to a measured data synchronization system which performs data processing using measured data for which synchronization among measuring instruments is ensured. The measuring instruments of the measured data synchronization system are given an input of reference times from the data processing apparatus and append these reference times to the measured data before outputting the data. The data processing apparatus outputs the reference times at prescribed intervals to each of the measuring instruments; receives an input of the measured data appended with the reference times from each of the measuring instruments; and performs data processing using measured data appended with desired reference times.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a measured data synchronization system comprising a plurality of measuring instruments (for example, measuring devices and sensors) for measuring objects under measurement and outputting measured data, and a data processing apparatus connected to the plurality of measuring instruments via a signal line and which acquires and processes the measured data output by the measuring instruments. More specifically, the present invention relates to a measured data synchronization system which performs data processing using measured data for which synchronization among measuring instruments is ensured.  
           [0003]    2. Description of the Prior Art  
           [0004]    If a plurality of measuring instruments are used for measurement and measured data is acquired from these measuring instruments for data processing, it is necessary to ensure the synchronization of measurement results among the measuring instruments. A measured data synchronization system is intended to ensure the synchronization of measured data before data processing. Traditionally, there have been various kinds of systems for ensuring synchronization (for example, refer to the Japanese Laid-open Patent Application 1999-355256).  
           [0005]    [0005]FIG. 1 illustrates an example of prior art measured data synchronization systems. In FIG. 1, data processing apparatus  10  is a computer or the like and is connected to general-purpose signal line  100 . Measuring devices  2 A to  2 C are measuring instruments, have clocks  21  and synchronization circuits  22 , and are connected to general-purpose signal line  100 . Clock  21  outputs times. Synchronization circuit  22  is connected to clock  21 , as well as to the synchronization circuits  22  of mutually adjacent measuring devices  2 A to  2 C via dedicated signal lines  200 . General-purpose signal line  100  is, for example, an Ethernet (registered trademark). Dedicated signal line  200  is less susceptible to signal deterioration and reliably transmits signals.  
           [0006]    Behaviors of such a system as mentioned above are explained here.  
           [0007]    First, the behavior of achieving synchronization among the clocks  21  of measuring devices  2 A to  2 C is explained. Of the clocks  21  of measuring devices  2 A to  2 C, the clock  21  of the measuring device  2 A, for example, is defined as the reference clock. The synchronization circuit  22  of measuring device  2 A acquires times from clock  21  and outputs the acquired time as a synchronization signal to the synchronization circuit  22  of measuring device  2 B via the dedicated signal line  200 . When given an input of the synchronization signal from measuring device  2 A, the synchronization circuit  22  of measuring device  2 B immediately outputs this synchronization signal to the synchronization circuit  22  of measuring device  2 C via dedicated signal line  200 . Then, according to the time contained in the synchronization signal, the synchronization circuits  22  of measuring devices  2 B and  2 C synchronize their respective clocks  21  with the clock  21  of measuring device  2 A. Synchronization circuits  22  perform these behaviors as frequently as possible to achieve synchronization. Next, behaviors wherein measuring devices  2 A to  2 C perform measurements and data processing apparatus  10  processes data are explained. Data processing apparatus  10  outputs a start measurement command towards measuring devices  2 A to  2 C via general-purpose signal line  100 , thereby enabling measuring devices  2 A to  2 C to perform measurements. When measurement is completed, measuring devices  2 A to  2 C append the time of synchronized clocks  21  to the measured data and output the measured data containing the time towards data processing apparatus  10  via general-purpose signal line  100 . Moreover, the data processing apparatus uses the measured data and the time contained therein to achieve synchronization among measuring device  2 A to  2 C before performing data processing.  
           [0008]    Another example of prior art systems is explained by referring to FIG. 2.  
           [0009]    Note that elements identical to those of FIG. 1 are referenced alike and excluded from the description. In FIG. 2, data processing apparatus  11  is provided in place of data processing apparatus  10 . Data processing apparatus  11  has clock  12  and is connected to general-purpose signal line  100 . In addition, measuring devices  3 A to  3 C are provided in place of measuring devices  2 A to  2 C. Measuring devices  3 A to  3 C are connected to general-purpose signal line  100 .  
           [0010]    Behaviors of such a system as mentioned above are explained below.  
           [0011]    Data processing apparatus  11  outputs a start measurement command to measuring devices  3 A to  3 C via general-purpose signal line  100 , and also retains the time of clock  12  when the command is output. Then, measuring devices  3 A to  3 C perform measurements according to the start measurement command from data processing apparatus  11 . When measurement is completed, the measuring devices output measured data to data processing apparatus  11  via general-purpose signal line  100 . Data processing apparatus  11  processes the measured data sent from measuring devices  3 A to  3 C, assuming that the measured data was acquired at the point of time that the apparatus retains. This type of system configuration is generally referred to as SCADA (Supervisory Control and Data Acquisition).  
           [0012]    As described above, the system shown in FIG. 1 ensures synchronization in such a way that synchronization circuits  22  adjust the times of clocks  21  to each other via dedicated signal lines  200 . However, each of measuring devices  2 A to  2 C requires a clock  21  and synchronization circuit  22 . Moreover, dedicated signal lines are required to connect synchronization circuits  22 . Synchronization circuits  22  require complicated processing (for example, compensation for the time delays of synchronization signals resulting from the lengths of dedicated signal lines  200  or reconstruction of deteriorated waveforms) to achieve synchronization. In addition, dedicated signal line  200  tends to be more expensive than general-purpose signal line  100  because the dedicated signal line is specifically designed to reliably send synchronization signals. In addition, if a dedicated signal line is extended due to an increase in the number of measuring devices including  2 A to  2 C or for reasons of the locations where measuring devices  2 A to  2 C are installed, the waveforms of synchronization signals may deteriorate or the delay time may be prolonged, thereby significantly increasing synchronization errors among measuring devices  2 A to  2 C. These factors restrict the number of measuring devices, including  2 A to  2 C, that can be connected or the locations where these measuring devices can be installed.  
           [0013]    On the other hand, systems such as the SCADA system shown in FIG. 2 do not achieve synchronization among measuring devices  3 A to  3 C but use, as a reference, the time when data processing apparatus  11  outputs a command. However, the time required for measuring devices  3 A to  3 C to acquire measured data or the communication delay involved in data transmission generally differs among measuring devices  3 A to  3 C: these effects would result in synchronization errors. Needless to say, the synchronization errors become larger as the number of measuring devices including  3 A to  3 C increases, or depending on the locations where measuring devices  3 A to  3 C are installed. It becomes especially difficult to synchronize measured data if the sampling frequency is made higher, causing the measurement interval to become shorter.  
         SUMMARY OF THE INVENTION  
         [0014]    An object of the present invention is to realize a measured data synchronization system wherein data processing is performed using measured data for which synchronization among measuring instruments is ensured. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a first schematic view of a prior art multi-point data acquisition system.  
         [0016]    [0016]FIG. 2 is a second schematic view of a prior art multi-point data acquisition system.  
         [0017]    [0017]FIG. 3 is a schematic view showing an embodiment of the present invention.  
         [0018]    [0018]FIG. 4 is a detailed configuration diagram of the data processing apparatus  40  in the system shown in FIG. 3.  
         [0019]    [0019]FIG. 5 is a timing chart explaining examples of the behaviors of the systems shown in FIGS. 3 and 4.  
         [0020]    [0020]FIG. 6 is a first schematic view illustrating an example of the behaviors of the means of selection  46  shown in the systems of FIGS. 3 and 4.  
         [0021]    [0021]FIG. 7 is a second schematic view illustrating an example of the behaviors of the means of selection  46  shown in the systems of FIGS. 3 and 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Preferred embodiments are described in detail below by referring to the accompanying drawings.  
         [0023]    [0023]FIG. 3 is a schematic view showing an embodiment of the present invention. Elements identical to those of FIG. 1 are referenced alike and excluded from the description. In FIG. 3, data processing apparatus  40  is, for example, a computer and is connected to general-purpose signal line  100 . Data processing apparatus  40  has communication circuit  41 . This communication circuit  41  is connected to general-purpose signal line  100  to exchange signals therewith. Measuring devices  5 A to  5 C are measuring instruments, contain communication circuits  51  and measurement sections  52 , and are connected to general-purpose signal line  100 . Communication circuit  51  is connected to general-purpose signal line  100  to exchange signals therewith. Measurement section  52  has time value memory  53 , which stores reference times output from communication circuit  51 . In addition, measurement section  52  measures objects under measurement according to setup conditions and/or commands, appends the reference time stored in time value memory  53  to measured data, and outputs the measured data to communication circuit  51 . Next, a specific system configuration is explained. FIG. 4 is a configuration diagram of data processing apparatus  40 . In FIG. 4, real-time clock  42  is a means of time output and outputs the current time. Delay time memory  43  is a first means of memory and stores communication delay times that are required for data transmission between data processing apparatus  40  and each of measuring devices  5 A to  5 C. Here, the communication delay times between data processing apparatus  40  and each of measuring devices  5 A to  5 C are defined as  τ A,  τ B and  τ C, respectively. Communication delay times  τ A to  τ C are calculated from the quantity of packets which are communicated on general-purpose signal line  100 . Alternatively, communication delay times  τ A to  τ C are determined by transmitting test packets from data processing apparatus  40  to measuring devices  5 A to  5 C, thus actually measuring the time taken until responses to the test packets are returned from measuring devices  5 A to  5 C, more than once, then averaging these times.  
         [0024]    Means of reference time generation  44  corrects the times output from clock  42  using communication delay times  τ A to  τ C that are read from delay time memory  43 , and outputs the corrected times as reference times to communication circuit  41 .  
         [0025]    Data memory  45  is a means for storing data and stores data that is sent from communication circuit  41  (i.e., measured data appended with the reference times and the names of measuring devices  5 A to  5 C that have output the measured data). Means of selection  46  reads data from data memory  45 , selects from the read data items according to the times sent from clock  42 , and outputs the selected data items. Means of calculation  47  performs desired data processing upon the data that means of selection  46  has selected and output.  
         [0026]    Behaviors of the systems shown in FIGS. 3 and 4 are described below. Data processing apparatus  40  outputs setup conditions used for measurement (such as measurement intervals and measurement ranges) and outputs signals consisting of commands, such as a start measurement command and an end measurement command, to measuring devices  5 A to  5 C in sequence. These signals, together with the reference times generated from means of reference time generation  44 , are converted by communication circuit  41  into communication signals (packets, which means blocks of data), and are output to general-purpose signal line  100 .  
         [0027]    Reference times mean the times which are obtained by adding the communication delay times  τ A to  τ C of respective measuring devices  5 A to  5 C to the times output from clock  42 . For example, if the current time is t 1 , the reference time for measuring device  5 A is (reference time t 1 +communication delay time  τ A).  
         [0028]    Even if data processing apparatus  40  does not output signals, such as setup conditions and commands, it is preferable that data processing apparatus  40  include reference times from means of reference time generation  44  in packets and output the packets at desired measurement intervals shorter than those of measuring devices  5 A to  5 C. For example, assuming that the measurement interval of measuring device  5 A id  Δ t, packets should be output to measuring device  5 A at a measurement interval of  Δ t/2 to  Δ t/10. Preferably, the resolution of reference times should be, for example, 1 [ms], which is approximately  Δ t/10 if the measurement interval  Δ t=10 [ms]; that is, “hh hours, mm minutes, ss seconds, xxx.” 
         [0029]    On the other hand, packets are input from data processing apparatus  40  to the communication circuits  51  of measuring devices  5 A to  5 C via general-purpose signal line  100 . Then, communication circuits  51  select desired signals (such as setup conditions, commands, and reference times) from the packets. Measurement sections  52  store reference times out of signals output from communication circuits  51  in time value memories  53 . Measurement sections  52  provide settings according to the setup conditions, start measurements according to the start measurement command, append reference times stored in time value memories  53  to measured data, and output the measured data to communication circuits  51 . Then, communication circuits  51  output measured data including reference times to the communication circuit  41  of data processing apparatus  40  via general-purpose signal line  100 . As a result, the communication circuit  41  of data processing apparatus  40  extracts data from packets and stores the data in data memory  45 .  
         [0030]    Here, by referring to FIG. 5, a specific example of behaviors in which data processing apparatus  40  outputs reference times, measuring devices  5 A to  5 C perform measurements and acquire measured data, and the measured data is stored in data memory  45  is explained. FIG. 5 is a timing chart illustrating the behaviors of data processing apparatus  40  and measuring devices  5 A to  5 C. FIG. 5 shows, from the top down, the behaviors of data processing apparatus  40 , measuring device  5 A, measuring device  5 B and measuring device  5 C. The horizontal axis represents time. To simplify the explanation, data processing apparatus  40  outputs packets including reference times to each of measuring devices  5 A to  5 C at almost the same measuring intervals as those of measuring devices  5 A to  5 C.  
         [0031]    First, behaviors of data processing apparatus  40  are explained.  
         [0032]    Data processing apparatus  40  outputs reference times to measuring devices  5 A to  5 C in sequence at a given interval. That is, data processing apparatus  40  adds a communication delay time  τ A to times t 1 , t 4  and t 7  and outputs them as reference times to measuring device  5 A; adds communication delay time  τ B to times t 2 , t 5  and t 8  and outputs them as reference times to measuring device  5 B; and adds communication delay time  τ C to times t 3 , t 6  and t 9  and outputs them as reference times to the measuring device  5 C. Although FIG. 5 provides illustrations only up to time t 9 , data processing apparatus  40  also continues to output reference times after this time t 9  until a desired time is reached.  
         [0033]    Next, behaviors of the measuring devices  5 A to  5 C are explained. When the reference time (t 1 + τ A) output from data processing apparatus  40  at time t 1  is input to measuring device  5 A, the measurement section  52  of measuring device  5 A stores the reference time (t 1 + τ A) in time value memory  53 . Similarly, when the reference time (t 4 + τ A) output at time t 4  is input to measuring device  5 A, the reference time (t 4 + τ A) is newly stored in time value memory  53 . Then, when the reference time (t 7 + τ A) output at time t 7  is input to measuring device  5 A, the reference time (t 7 + τ A) is newly stored in time value memory  53 .  
         [0034]    Similarly, when the reference times (t 2 + τ B) , (t 5 + τ B) and (t 8 + τ B) output from the data processing apparatus at t 2 , t 5 , and t 8  respectively are input to measuring device  5 B, the measurement section  52  of measuring device  5 B stores these reference times in time value memory  53 . Also similarly, when the reference times (t 3 + τ C), (t 6 + τ C) and (t 9 + τ C) output from the data processing apparatus at t 3 , t 6 , and t 9  respectively are input to measuring device  5 C, the measurement section  52  of measuring device  5 C stores these reference times in time value memory  53 .  
         [0035]    Note that, even if reference times output at given intervals from data processing apparatus  40  reach measuring devices  5 A to  5 C at uneven intervals (for example, reference times (t 3 + τ C) and (t 6 + τ C) in FIG. 5) due to the communication conditions of general-purpose signal line  100 , measurement section  52  stores the latest input reference time in time value memory  53 .  
         [0036]    Here, it is assumed that the measurement section  52  of measuring device  5 A acquires measured data A 1  during the time from the entry of the reference time (t 1 + τ A) until the entry of the next reference time (t 4 + τ A), that is, during the time while the time value memory  53  of measuring device  5 A is storing the reference time (t 1 + τ A). Then, while time value memory  53  is storing the reference times (t 4 + τ A) and (t 7 + τ A), measurement section  52  acquires measured data A 2  and A 3 , respectively.  
         [0037]    Similarly, while time value memory  53  is storing (t 2 + τ B), (t 5 + τ B) and (t 8 + τ B), the measurement section  52  of measuring device  5 B acquires measured data B 1 , B 2  and B 3 , respectively. While time value memory  53  is storing (t 3 + τ C) , (t 6 + τ C) and (t 9 + τ C) , the measurement section  52  of measuring device  5 B acquires measured data C 1 , C 2  and C 3 , respectively.  
         [0038]    Then, upon acquiring measured data A 1 , the measurement section  52  of measuring device  5 A appends the reference time (t 1 + τ A) being stored by time value memory  53  to measured data A 1 , and immediately outputs measured data A 1  to communication circuit  51 . Similarly, the measurement section  52  of measuring device  5 A appends the reference times (t 4 + τ A) and (t 7 + τ A) to measured data A 2  and A 3 , and outputs these measured data to communication circuit  51 . In addition, upon acquiring measured data B 1 , B 2 , B 3 , C 1 , C 2  and C 3 , the measurement sections  52  of measuring devices  5 B and  5 C append the reference times (t 2 + τ B), (t 5 + τ B) , (t 8 + τ B) , (t 3 + τ C) , (t 6 + τ C) and (t 9 + τ C) , to these measured data and immediately output the data to communication circuits  51 . As a result, communication circuits  51  output the measured data, including the appended reference times, in the form of packets to data processing apparatus  40  via general-purpose signal line  100 .  
         [0039]    Then, the communication circuit  41  of data processing apparatus  40  extracts measured data A 1  to A 3 , B 1  to B 3 , and C 1  to C 3 , all of which include reference times, from the packets output from measuring devices  5 A to  5 C respectively, and stores the measured data in data memory  45 .  
         [0040]    Next, by referring to FIG. 6, a specific example of data processing behaviors in which data processing apparatus  40  processes measured data A 1  to A 3 , B 1  to B 3 , and C 1  to C 3  is explained. Note that elements identical to those of FIG. 5 are referenced alike and excluded from the description. FIG. 6 illustrates the behaviors of the means of selection  46  of data processing apparatus  40 . In FIG. 6, the measured data of measuring devices  5 A,  5 B, and  5 C are graphically indicated from the top down, with reference to the time axis. The horizontal axis represents time. Here, it should be understood that when the current time tn is input from clock  42 , means of selection  46  stores measured data A 1  to A 3 , B 1  to B 2 , and C 1  to C 2  in data memory  45 . In addition, it is assumed that the reference time (t 1 + τ A)=(t 2 + τ B) and (t 4 + τ A)=(t 5 + τ B), and (t 3 + τ C)&lt;preset time ts&lt;(t 6 + τ C).  
         [0041]    The means of selection  46  of data processing apparatus  40  specifies the time ts (for example, time (t 4 + τ A)) as the preset time, which is the time t 0  earlier than the current time tn input from clock  42 . Time t 0 , which precedes the current time tn, is set in advance according to the communication delay times  τ A,  τ B, and  τ C of delay time memory  43  and the measurement times and measurement intervals of measuring devices  5 A to  5 C. For example, time t 0  may be the sum of all these times.  
         [0042]    Then, the means of selection  46  selects measured data A 2  and B 2  appended with the reference times (t 4 + τ A) and (t 5 + τ B) which are the same as the preset time ts, and outputs the data to the means of calculation  47 . If data appended with the same reference times as the preset time ts does not exist, in other words, if the reference times (t 3 + τ C) and (t 6 + τ C) which have been appended to measured data C 1  and C 2  sent from measuring device  5 C do not agree with the preset time ts, the means of selection  46  applies interpolation (for example, primary or secondary approximation) according to measured data C 1  and C 2  at the reference times (t 3 + τ C) and (t 6 + τ C) before and after the preset time ts, and outputs the interpolated measurement data to the means of calculation  47 .  
         [0043]    Then, the means of calculation  47  uses measured data A 2  and B 2  and the interpolated measured data output from the means of selection  46  to perform data processing. Moreover, results of data processing performed by the means of calculation  47  are indicated on the display processing apparatus which is not illustrated here.  
         [0044]    Thus, data processing apparatus  40  outputs reference times output from the means of reference time generation  44  to measuring devices  5 A to  5 C. The means of selection  46  outputs to the means of calculation  47 , those measured data whose reference times are the same as the preset time ts or those measured data which have been interpolated using measured data whose reference times are close to the preset time ts, among the measured data items to which reference times output from each of measuring devices  5 A to  5 C are appended. Then, the means of calculation  47  performs data processing. Consequently, it is possible to perform data processing using synchronized measurement data without being constrained by the number of measuring devices including measuring devices  5 A to  5 C, or by the locations where the measuring devices are installed.  
         [0045]    In other words, unlike the system shown in FIG. 1, the system of the above-described embodiment can perform data processing using measured data synchronized among measuring devices  5 A to  5 C, even if clocks  21 , synchronization circuits  22  and dedicated signal lines  200  are not present. In addition, the system is immune to synchronization errors due to the lengths of dedicated signal lines  200 . Consequently, it is possible to perform data processing using synchronized measurement data without being constrained by the number of measuring devices including measuring devices  5 A to  5 C, or by the locations where the measuring devices are installed. Moreover, it is possible to suppress costs and reduce the burden of measuring devices  5 A to  5 C.  
         [0046]    Similarly, even if the sampling frequency is higher and the measurement interval is shorter than those of the system shown in FIG. 2, or even if the sampling frequency differs among measuring devices  5 A to  5 C, it is possible to perform data processing using measured data synchronized among measuring devices  5 A to  5 C. Moreover, the system of the above-described embodiment is immune to the effects of difference in the time required for data transfer that is caused by an increase in the number of measuring devices including  5 A to  5 C or by the locations where measuring devices  5 A to  5 C are installed. Consequently, it is possible to perform data processing using synchronized measured data without being constrained by the number of measuring devices including measuring devices  5 A to  5 C, or by the locations where the measuring devices are installed.  
         [0047]    Moreover, since the means of selection  46  outputs those measured data whose reference times are the same as the preset time ts or those measured data which have been interpolated using measured data whose reference times are close to the preset time ts, the number of measured data for use in selection or interpolation is low. In other words, not all of the measured data stored in data memory  45  but only the measured data appended with reference times close to the preset time ts are used. This makes it possible to reduce the burden of the means of selection  46  and to output measured data to the means of calculation at higher speeds.  
         [0048]    The present invention is not limited to the above-described embodiment but may be embodied in the following manners:  
         [0049]    (1) In the above-described embodiment, a system configuration is shown in which the means of selection  46  outputs to the means of calculation  47 , those measured data whose reference times are the same as the preset time ts or those measured data which have been interpolated using measured data whose reference times are close to the preset time ts, among the measured data appended with reference times output from each of measuring devices  5 A to  5 C. Alternatively, if the measured data sent from the same measuring device, for example, measuring device  5 A, contains a plurality of data items appended with the same reference time, measured data can be selected and output according to the difference between this reference time and the next reference time and to the number of measured data appended with the same reference time.  
         [0050]    The alternative system configuration discussed above is described with reference to FIG. 7. FIG. 7 illustrates behaviors of the means of section  46 . Note that elements identical to those of FIG. 6 are referenced alike and excluded from the description. In FIG. 7, the measured data of measuring device  5 A is graphically indicated with reference to the time axis. The horizontal axis represents time. Here, it should be understood that measured data a 1  to a 5  appended with the reference time (t 1 + τ A) and measured data a 6  to a 8  appended with the reference time (t 4 + τ A) are stored in data memory  45 . The preset time tx is set so as to satisfy (t 1 + τ A&lt;tx&lt;t 4 + τ A) . The means of selection  46  determines the difference between the reference times (t 1 + τ A) and (t 4 + τ A). It also determines the number of measured data a 1  to a 5 , selects measured data a 4  that has a reference time closest to the preset time tx and outputs the data to the means of calculation  47 .  
         [0051]    For example, assuming that the reference time (t 1 + τ A) is 10 hours:00 minutes:00 seconds, the reference time (t 4 + τ A) is 10 hours:00 minutes:05 seconds, and preset time tx is 10 hours:00 minutes:03 seconds, then the means of selection  46  selects measured data a 4 . Consequently, it is possible to perform data processing using synchronized measured data even if the measurement intervals of measuring devices  5 A to  5 C are shorter than the interval between reference times output from data processing apparatus  40 .  
         [0052]    (2) In the above-described embodiment, another system configuration is shown in which measured data is selected according to the difference between this reference time and the next reference time and to the number of measured data items appended with the same reference time if the measured data sent from same measuring devices  5 A to  5 C, contains a plurality of data items appended with the same reference time, as illustrated in FIG. 7. Alternatively, the means of selection  46  may be provided with a means of error detection to measure errors in the measurement intervals of measurement sections  52  of measuring devices  5 A to  5 C. In other words, there is a case that even if the measurement intervals of measuring devices  5 A to  5 C are set to specific values, the measurement intervals may slightly differ from each other among measuring device  5 A to  5 C. In that case, it is possible that the means of error detection determines measurement interval errors among the measurement sections  52  of measuring devices  5 A to  5 C from the number of measured data items a 1  to a 5  included in the interval between reference times (t 1 +τA) and (t 4 +τA).  
         [0053]    (3) In the above-described embodiment, yet another system configuration is shown in which the means of selection  46  applies interpolation according to measured data C 1  and C 2  and outputs the interpolated measured data. Since there is virtually no problem even if errors between the preset time ts and a reference time are ignored, provided that only marginal changes arise in measured data items C 1  and C 2  like in the case of, for example, temperature measurement, that the interval at which reference times are input is shorter than, for example, Δt/10 with reference to the measurement interval Δt, or that the interval at which the means of calculation  47  performs data processing is as long as 10 times the measurement interval Δt. Thus, alternatively, it is possible to select measured data C 2  appended with the reference time (t 6 +τC) which is closest to the preset time ts and output the measured data to the means of calculation  47 , without applying interpolation. Consequently, it is possible to reduce the burden of the means of selection  46  and select measured data at higher speeds.  
         [0054]    (4) In the above-described embodiment, yet another system configuration is shown in which the means of selection  46  applies interpolation according to measured data C 1  and C 2  (for example, primary or secondary approximation) and outputs the interpolated measured data. Alternatively, it is possible to store computational expressions used for interpolation in a storage section which is not illustrated in the figure. Consequently, by reading the computational expressions from the storage section, it is possible to restore original measured data C 1  and C 2  or perform data processing again using other interpolation or synchronization methods.  
         [0055]    (5) In the above-described embodiment, yet another system configuration is shown in which the means of selection  46  outputs to the means of calculation  47 , those measured data whose reference times are the same as the preset time ts or those measured data which have been interpolated using measured data whose reference times are close to the preset time ts, among the measured data appended with reference times output from each of measuring devices  5 A to  5 C. Alternatively, it is possible to configure the system so that the means of selection  46  outputs only those measured data whose reference times are the same as the preset time ts.  
         [0056]    (6) In the above-described embodiment, yet another system configuration is shown in which three measuring devices  5 A to  5 C are installed. Alternatively, it is possible to install as many measuring devices as desired.  
         [0057]    According to the present invention, the following advantages are provided.  
         [0058]    In one aspect of the present invention, the data processing apparatus outputs reference times to each of the measuring devices at prescribed intervals. The apparatus then performs data processing using only those measured data which are appended with the desired reference times, among the measured data appended with reference times and output from each of the measuring devices. Consequently, it is possible to perform data processing using synchronized measured data without being constrained by the number of measuring devices or by the locations where the measuring devices are installed.  
         [0059]    In another aspect of the present invention, if measured data sent from the same measuring device contains a plurality of measured data appended with the same reference time, the means of selection selects and outputs those measured data whose reference times are closest to the preset time, according to the difference between that reference time and the next reference time and to the number of measured data appended with the same time reference. Consequently, it is possible to perform data processing using synchronized measured data even if the measurement interval of a measuring device is shorter than the interval at which reference times are output from the data processing apparatus.  
         [0060]    In yet another aspect of the present invention, the means of selection specifies a time preceding the current time as the preset time and selects measured data from those which are appended with reference times close to the preset time. Consequently, the burden of the means of selection is reduced and measured data can be output to the means of calculation at higher speeds.