JP2013211694A - Radio network system and time management device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio network system, etc. capable of implementing both normal operation in the radio network system and appropriate control in a field control system.SOLUTION: A radio network system having a first clock for giving time to a radio network and a second clock for specifying time in a field control system receives data to which time based on the first clock is added as a time stamp, from the radio network, and converts the time of the time stamp added to the received data to time of the second clock on the basis of difference between the time of the first clock and the time of the second clock.

Description

  The present invention relates to a wireless network system or the like in which a wireless network is connected to a field control system, and more particularly to a wireless network system or the like that can appropriately manage time.

  In a synchronous wireless network such as ISA100, all wireless nodes belonging to the wireless network operate in synchronization with one clock source, but generally all wireless nodes need to be accurately synchronized with an accuracy of 1 ms or less. There is.

  Usually, a wireless node installed in a plant uses a battery as a power source, and sleeps most of the time when communication is not performed. At the time of data transfer, the upper wireless node and the lower wireless node wake up at the same time and perform wireless communication with each other to transfer data, and the lower wireless node receives the time of the upper wireless node and keeps its own clock Synchronize with the clock of the wireless node. At this time, if the clocks of both nodes are shifted by, for example, 1 ms or more at the time of getting up, the communication fails. This means losing the means to synchronize the clock, so that the lower-level wireless node falls into an unrecoverable situation.

  Each wireless node holds its own hardware clock, but if the clock deviation (speed of time advance: ppm) of the two wireless nodes that communicate with each other is significantly different, There is a possibility that the timing difference of the hardware clock is accumulated and communication at the timing of waking up becomes impossible. For this reason, it is generally necessary to suppress the clock deviation of the wireless node to ± several ppm. Similarly, an accuracy of about ± several ppm is required for a clock source of a wireless network to which these wireless nodes are synchronized.

  On the other hand, a clock (time source) used in a normal field control system does not require high accuracy. Since a high-accuracy clock source as required for a wireless network is expensive, there are rare cases where it is installed in a field control system.

JP 2010-028503 A

  As described above, there is a large difference in performance required for the clock source between the wireless network and the field control system. For this reason, if a clock source of an inaccurate (large deviation) control system is connected to the wireless network, the clock of the inaccurate control system flows into the wireless network, so that time synchronization between wireless nodes cannot be performed and communication is not possible. There is a risk of falling into a possible state. This risk can be avoided by introducing a high-accuracy clock source for the field control system. However, in this case, the cost is increased, and it is particularly difficult to introduce it to a small-scale system.

  As another method, it is conceivable to disconnect the clock source of the control system with low accuracy (large deviation) from the wireless network. In this case, a built-in clock of a wireless device (for example, ISA100 system manager (System Manager)) in the wireless network is used as a clock source of the wireless network. Since such a built-in clock has a high precision, the wireless network operates normally.

  However, in the latter case, the time stamp of the data transmitted by the wireless node in the wireless network is inconsistent with the time in the field control system.

  An object of the present invention is to provide a wireless network system or the like that can achieve both normal operation in a wireless network and appropriate control in a field control system.

The wireless network system of the present invention is a wireless network system in which a wireless network is connected to a field control system, and a first clock that gives time to the wireless network and a second clock that defines time in the field control system Receiving means for receiving data with the time based on the first clock as a time stamp from the wireless network, and the time of the time stamp attached to the data received by the receiving means, Conversion means for converting to the time of the second clock based on the difference between the time of the first clock and the time of the second clock.
According to this wireless network system, the time of the time stamp attached to the data is converted into the time of the second clock based on the difference between the time of the first clock and the time of the second clock. It is possible to achieve both the normal operation of and the appropriate control in the field control system.

  You may provide the transfer means which transfers the said data in which the time stamp was converted by the said conversion means in the said field control system.

  The wireless network may be a synchronous network that synchronizes internal clocks between wireless nodes.

  A wireless node participating in the wireless network may use a battery as a power source.

  The first clock, the second clock, the reception unit, and the conversion unit may be provided in a relay device that relays the field control system and the wireless network.

The time management device of the present invention is a time management device that performs time management between a field control system and a wireless network, and a second clock that defines a time in the field control system and a first clock that gives time to the wireless network. And a receiving means for receiving data with a time based on the first clock attached as a time stamp from the wireless network, and a time of the time stamp attached to the data received by the receiving means, Conversion means for converting to the time of the second clock based on the difference between the time of the first clock and the time of the second clock.
According to this time management device, the time of the time stamp attached to the data is converted to the time of the second clock based on the difference between the time of the first clock and the time of the second clock. It is possible to achieve both the normal operation of and the appropriate control in the field control system.

  According to the wireless network system of the present invention, the time of the time stamp attached to the data is converted into the time of the second clock based on the difference between the time of the first clock and the time of the second clock. It is possible to achieve both normal operation in the wireless network and appropriate control in the field control system.

  According to the time management device of the present invention, the time management device that performs time management between the field control system and the wireless network uses the time of the time stamp attached to the data as the time of the first clock and the second time. Since the time of the second clock is converted to the time of the second clock, normal operation in the wireless network and appropriate control in the field control system can be compatible.

1 is a block diagram showing a configuration of a wireless network system according to an embodiment. The figure which shows operation | movement in the case of transferring the data from an I / O device to the control apparatus of a field control system.

  Hereinafter, an embodiment of a wireless network system according to the present invention will be described.

  FIG. 1 is a block diagram showing the configuration of the wireless network system of this embodiment.

  As shown in FIG. 1, the radio network system of this embodiment includes a field control system 1 that controls processes in a plant, a radio network 2 that is a synchronous radio network according to the ISA100 standard, a field control system 1 and radio A relay device 3 provided between the networks 2 and relaying between the field control system 1 and the wireless network 2 is provided. The relay apparatus 3 includes an ISA100 system manager (System Manager) or an ISA100 gateway (Gateway).

  As shown in FIG. 1, the field control system 1 includes a control device 12 that controls field devices arranged in a plant, and a time source 13 that defines the time in the field control system 1. The time source 13 is connected to each other by a wired communication line 11. A clock from the time source 13 is given to the control device 12 and other devices (not shown) included in the field control system 1 via the communication line 11. Further, data transmitted / received in the field control system 1 is given a time stamp (time stamp based on the time in the field control system 1) based on the clock from the time source 13.

  As shown in FIG. 1, the wireless network 2 includes an ISA100.11.a backbone router 21a, 21b connected to a wired communication line 25, an ISA100 device functioning as a router 22a, 22b, and a wireless field. It includes an ISA100 I / O device (I / O Device) 23 that functions as a device (or a part thereof). The backbone router in the wireless network 2 is operated by an AC power supply (commercial power supply), and other wireless devices such as a router and an I / O device are powered by a battery.

  The communication state in the wireless network 2 is managed by the ISA100 system manager. ISA100 system manager collects information on ISA100 devices and networks including backbone routers and I / O devices, manages wireless communication resources such as frequency, communication path, communication time loss, and assigns these wireless communication resources to ISA100 devices And the setting of the frequency used for each device and neighboring device information based on the calculation result.

  As shown in FIG. 1, the relay device 3 includes a control clock 31 that indicates time in the field control system 1 and a built-in clock 32 that functions as a time source in the wireless network 2, and performs field control via the communication line 11. The system 1 is connected to the wireless network 2 via the communication line 25.

  The built-in clock 32 has an accuracy (for example, an accuracy of about ± several ppm) necessary for the operation of the wireless network 2. On the other hand, the control clock 31 is periodically calibrated at the time indicated by the time source 13, for example, and is synchronized with the time source 13. The accuracy of the time source 13 is not as high as that of the built-in clock 32, and naturally the accuracy of the control clock 31 is in accordance with the accuracy of the time source 13. In the wireless network system of the present embodiment, there is no function for synchronizing the control clock 31 and the built-in clock 32, and the control clock 31 and the built-in clock 32 usually indicate different times at the same time.

  In FIG. 1, only some elements necessary for the description of the present invention are illustrated in the configuration of the field control system 1, the wireless network 2, and the relay device 3. Further, illustration of an ISA100 security manager (Security Manager) and the like that are not directly related to the functions according to the present invention is omitted.

  Next, the operation in the wireless network system of this embodiment will be described.

  In the wireless network system of this embodiment, the wireless network 2 is given a clock from the internal clock 32 of the relay device 3. As shown in FIG. 1, this clock is sequentially given to the wireless devices below the backbone router via the communication line 25. In FIG. 1, a clock from an internal clock 32 is given to the router 22a via the backbone router 21a and to the I / O device 23 via the backbone router 21a and the router 22a.

  For example, when the sleeping router 22a wakes up and communicates with the backbone router 21a, the router 22a receives the time of the built-in clock 32 via the backbone router 21a, or the time held by the backbone router 21a. Receive and synchronize its own hardware clock. Similarly, when the I / O device 23 that was sleeping wakes up and communicates with the router 22a, the I / O device 23 receives the time from the router 22a and synchronizes its own hardware clock. . As described above, each wireless device configuring the wireless network 2 receives the time from the host device and synchronizes its own hardware clock with the built-in clock 32.

  FIG. 2 is a diagram illustrating an operation when data from the I / O device 23 is transferred to the control device 12 of the field control system 1.

  As shown in FIG. 2, the I / O device 23 transmits the data with a time stamp. This time stamp is, for example, the detection time in the sensor value or the data transmission time, and the time is the time of the internal clock 32 or the time of the hardware clock of the I / O device 23 synchronized with the internal clock 32.

  Data from the I / O device 23 reaches the relay device 3 via the router 22a, the backbone router 21a, and the communication line 25.

  When the data is received, the relay device 3 converts the time of the time stamp into a time based on the control clock 31 based on the difference between the time indicated by the control clock 31 and the time indicated by the built-in clock 32. For example, when the time indicated by the control clock 31 is advanced by the difference Δ from the time indicated by the built-in clock 32, the difference Δ is added to the time of the received time stamp. The time stamp whose time has been converted is transferred to the control device 12 together with the above data, and the control device 12 provides data with a time stamp substantially based on the time of the field control system (time of the time source 13). Will receive. In this manner, two types of time stamps having different time references are not mixed in the field control system 1, and control inconvenience is not caused.

  As described above, in the wireless network system of the present embodiment, the time of the time stamp given in the wireless network 2 is converted into the time of the field control system 1 in the relay device 3, and this is given to the field control system 1. As a result, mixing of time stamps of types in the field control system 1 is avoided, and control in the field control system 1 can be made appropriate. Further, since the time in the wireless network 2 is based on the highly accurate internal clock 32, it is possible to avoid a situation in which time synchronization becomes impossible in the wireless network 2.

  In the above embodiment, the control clock 31 and the built-in clock 32 are provided in the relay device 3 and the time conversion is performed in the relay device 3, but some or all of these functions are performed in the field control system or You may provide in a wireless network.

  In the above-described embodiment, an example in which the time of the time stamp attached in the wireless network is converted into the time in the field control system has been described. However, the time stamp attached in the field control system is used in the wireless network. In such a case, the time of the time stamp added in the control system may be converted into the time in the wireless network.

  The scope of application of the present invention is not limited to the above embodiment. The present invention can be widely applied to a wireless network system in which a wireless network is connected to a field control system.

1 field control system 2 wireless network 3 relay device (reception means, conversion means, transfer means)
13 Time source (first clock)
31 Control clock (first clock)
32 Internal clock (second clock)

Claims (6)

In a wireless network system in which a wireless network is connected to a field control system,
A first clock for providing time to the wireless network;
A second clock defining a time in the field control system;
Receiving means for receiving, from the wireless network, data with a time stamp as a time stamp based on the first clock;
Conversion that converts the time of the time stamp attached to the data received by the receiving means into the time of the second clock based on the difference between the time of the first clock and the time of the second clock Means,
A wireless network system comprising: 2. The wireless network system according to claim 1, further comprising transfer means for transferring the data whose time stamp has been converted by the conversion means into the field control system. The wireless network system according to claim 1, wherein the wireless network is a synchronous network that synchronizes internal clocks between wireless nodes. The wireless network system according to claim 1, wherein a wireless node participating in the wireless network uses a battery as a power source. The first clock, the second clock, the reception unit, and the conversion unit are provided in a relay device that relays the field control system and the wireless network. The wireless network system according to claim 1. In a time management device that performs time management between a field control system and a wireless network,
A first clock for providing time to the wireless network;
A second clock defining a time in the field control system;
Receiving means for receiving, from the wireless network, data with a time stamp as a time stamp based on the first clock;
Conversion that converts the time of the time stamp attached to the data received by the receiving means into the time of the second clock based on the difference between the time of the first clock and the time of the second clock Means,
A time management device comprising:

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