Abstract:
There is provided a field device activated by a battery and housed in a pressure-resistant and explosion-proof container. The device includes: an external interface unit comprising: an infrared communication unit configured to communicate with an external infrared communication device through a window attached to the container; and a display unit configured to display status information about the field device; and a power controller configured to determine whether power from the battery should be switched on or off, in response to a request from the external interface unit.

Description:
FIELD DEVICE 
       [0001]    This application claims priority from Japanese Patent Application No. 2010-168219, filed on Jul. 27, 2010, the entire contents of which are herein incorporated by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Embodiments described herein relate to a field device which incorporates a battery as a power source and is housed in a pressure-resistant, explosion-proof container so as to be usable in a dangerous atmosphere. 
         [0004]    2. Related Art 
         [0005]    General field devices such as pressure/differential pressure gauges, various flowmeters, thermometers, and valve positioners which are distributed in a plant, a factory, or the like are connected to a higher-level control computer system by a two-wire signal line, for example. Each field device exchanges current signals of 4 mA to 20 mA with the control computer system, whereby each field device generates power and sends collected data to a higher-level device. 
         [0006]    In recent years, wireless field devices have been developed which incorporate a wireless communication unit and send detected or collected data to a control computer system by radio (see e.g., JP-A-2003-134030 and JP-A-2003-134261). 
         [0007]      FIG. 4  is a functional block diagram of a communication system in which wireless communication is performed between a higher-level device and field devices. A differential pressure gauge  3  which measures a process flow rate on the basis of a pressure difference between flows upstream and downstream of an orifice plate  2  and a valve positioner  4  which controls the opening/closure of a control valve are connected to a process fluid pipe  1 . Each of the differential pressure gauge  3  and the valve positioner  4  communicates with a relay apparatus such as a gateway  7  using a radio signal  6 . 
         [0008]    The gateway  7  has functions of a system manager which relays a communication between each of the field devices  3  and  4  and a host  9  via a communication network  8 , for example, converts a communication signal, and manages a wireless communication device network and system. 
         [0009]    The host  9  can receive process values, send control signals, set the field devices  3  and  4 , and monitor alarm information by exchanging signals with the field devices  3  and  4  via the gateway  7 . 
         [0010]    A site-instruction-type field device  5  which measures a pressure, temperature, flow rate, or the like of a process fluid and does not perform wireless communication is also connected to the process fluid pipe  1 . Among site-instruction-type field devices are ones that perform measurement and display all the time and ones that are used for a very long pipeline and powered on only when a worker comes to the site in making a round. 
         [0011]    Such field devices that are distributed in a plant, a factory, or the like are usually disposed at places that are not suitable for wiring and are of a battery-driven type (i.e., they are not supplied with power by a two-wire line for transmission of signals of 4 to 20 mA). To enable long-term operation, a lithium primary battery is used. 
         [0012]      FIG. 5  is a functional block diagram showing an example configuration of a conventional field device  10  having a wireless communication unit. The field device  10  includes a sensor  11 , a CPU  12 , a wireless communication module  13 , an antenna  14 , a battery  15 , and a power controller  16 . The battery  15  can be attached or removed by opening the lid (not shown) of an explosion-proof container. 
         [0013]    A process quantity P is detected and converted by the sensor  11 . The CPU  12 , which is a central processing unit, has a computing unit such as a microprocessor and a storage unit such as a RAM and an EEPROM. The CPU  12  converts, corrects, or converts, into a user-specified scaling value such as a percentage value, a process quantity P detected by the sensor  11 . 
         [0014]    The CPU  12  provides a calculation result to the wireless communication module  13 , and then sends it to a higher-level device such as a host via the antenna  14 . The CPU  12  receives a setting change request etc. from the user by radio via the antenna  14  and performs a setting change. 
         [0015]    The CPU  12  controls and diagnoses the peripheral components such as the sensor  11 , the wireless communication module  13 , and the power controller  16  and, if a problematic diagnosis result is obtained, informs the user of failure information etc. via the wireless communication module  13 . 
         [0016]    The power controller  16  receives a voltage from the battery  15  and regulates it. The power controller  16  provides a necessary voltage to the CPU  12 . Furthermore, the power controller  16  provides power to the sensor  11  and the wireless communication module  13  intermittently at a prescribed cycle by performing an on/off power control (switching) according to a user-specified intermittent operation cycle under the control of the CPU  12 . 
         [0017]    Wireless field devices are in a battery-removed state from shipment from a factory to immediately before installation at a site or a start of communication after installation. This is for the following reasons: 
         [0018]    a) To prevent unnecessary use of a battery during transport or storage. 
         [0019]    b) To prevent emission of possibly harmful radio waves during transport by a transport means such as an airplane. 
         [0020]    c) To prevent emission of radio waves that violate regulations during transport (radio waves are restricted under the radio law of each country). 
         [0021]    In general, field devices are not equipped with a power on/off switch. The use of a power on/off switch is difficult because they are used in a dangerous atmosphere and hence are required to have a pressure-resistant, explosion-proof structure etc. 
         [0022]    Although it is conceivable to provide a switch inside the explosion-proof container of a field device, opening its lid to turn on or off the switch is a burden to the user. It is not permitted to open the lid at a place where pressure resistance and explosion proof are required. Therefore, in most cases, a field device is powered on by inserting a battery. 
         [0023]    As a result, it is necessary for the user to insert a battery by opening the lid of the pressure-resistant, explosion-proof container of a field device and the close the lid after arrival of the field device, which is inconvenient. In a large plant, it may be necessary to install hundreds or thousands of field devices. In such a case, doing such work for all field devices not only increases personnel expenses but also increases, for example, the probability of occurrence of trouble due to scuffing of the lid of an explosion-proof container and danger in a pressure-resistant area due to incomplete closure of a lid. 
         [0024]    Even if a battery is inserted into place and the lid of its explosion-proof container is closed in a safe area such as a user work bench area, the battery energy is consumed uselessly until installation or a start of regular communications after installation. 
       SUMMARY OF THE INVENTION 
       [0025]    Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any disadvantages. 
         [0026]    Accordingly, it is an illustrative aspect of the present invention to make it possible to transport, to a dangerous atmosphere place, a field device in a state that a battery is set in place in its pressure-resistant, explosion-proof container (from shipment of the filed device) but is not supplying power and to manipulate the field device so as to start supply of power from the battery without the need for opening the container. 
         [0027]    According to one or more illustrative aspects of the present invention, there is provided a field device activated by a battery and housed in a pressure-resistant and explosion-proof container. The device includes: an external interface unit comprising: an infrared communication unit configured to communicate with an external infrared communication device through a window attached to the container; and a display unit configured to display status information about the field device; and a power controller configured to determine whether power from the battery should be switched on or off, in response to a request from the external interface unit. 
         [0028]    Other aspects and advantages of the present invention will be apparent from the following description, the drawings and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a functional block diagram of a field device according to an embodiment of the invention; 
           [0030]      FIG. 2  is a schematic diagram illustrating state transitions of the field device according to the embodiment; 
           [0031]      FIG. 3  is a table showing the details of the state transitions; 
           [0032]      FIG. 4  is a functional block diagram of a communication system in which wireless communication is performed between a higher-level device and field devices; and 
           [0033]      FIG. 5  is a functional block diagram showing an example configuration of a conventional field device having a wireless communication unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    According to an embodiment of the invention, the following advantages are expected: 
         [0035]    (1) The field device can be transported to the user in a state that the battery is set in place but is not capable of supplying power. The user can enable the battery to supply power with timing that is desired by the user without the need for opening and closing the pressure-resistant, explosion-proof container. 
         [0036]    (2) The field device can be transported with the battery set in place. Since there is no probability of radio wave emission, violation of the radio law of each country during transport can be avoided. 
         [0037]    (3) Battery energy consumption before a start of use of the field device can be avoided by enabling supply of power from the battery when use of the field device is started at an installation site. 
         [0038]    Exemplary embodiments of the present invention will be hereinafter described in detail with reference to the drawings.  FIG. 1  is a functional block diagram of a field device  10 A according to an embodiment of the invention. Components having the same or corresponding ones in the conventional field device  10  shown in  FIG. 5  are given the same reference symbols and will not be described in detail. 
         [0039]    Components that are added to the conventional field device  10  of  FIG. 5  are an external interface unit  100  which is provided inside the field device  10 A, an infrared communication device  200  which communicates with the external interface unit  100  from outside by infrared light, and a power controller  300  which is provided inside the field device  10 A and controls connection/disconnection of the battery  15  by communicating with the external interface unit  100 . 
         [0040]    The external interface unit  100  includes an infrared communication unit  101  which communicates with the external infrared communication device  200  through a glass cover (not shown) that is provided in a window of a container and a display unit  102  which displays status information etc. of the field device  10 A. The infrared communication device  200  may also be equipped with a display  201  which acquires and displays similar information. 
         [0041]    With the above configuration, the power controller  300  controls the supply of power from the battery  15  to the individual components of the field device  10 A by communicating with the external interface unit  100  which receives a battery-on or off instruction from the infrared communication device  200  by means of the infrared communication unit  101 . 
         [0042]    The user sends, for example, a setting signal for powering off the field device  10 A using the infrared communication device  200 . When receiving the setting signal, the infrared communication unit  101  of the external interface unit  100  provides it to the power controller  300 . 
         [0043]    If being in a standby state, the power controller  300  is activated by a setting signal supplied from the external interface unit  100 , an external interrupt signal, or the like. If being in operation, the power controller  300  receives a setting signal. According to the power-off setting signal received from the external interface unit  100 , the power controller  300  stops the supply of power to the sensor  11 , the CPU  12 , and the wireless communication module  13 . 
         [0044]    The power controller  300  turns on and off the supply of power to the external interface unit  100  at regular intervals (e.g., every 1 second) to allow it to detect infrared light. When the supply of power to the wireless communication module  13  from the power controller  300  is stopped, the wireless communication module  13  stops sending and reception of radio waves completely. 
         [0045]    Furthermore, when the battery  15  is removed, the supply of power to the power controller  300  is shut off and the supply of power to the sensor  11 , the CPU  12 , and the wireless communication module  13  is stopped. The field device  10 A may be configured so that when the battery  26  is inserted, the power controller  300  restarts supply of power to the sensor  11 , the CPU  12 , and the wireless communication module  13  irrespective of reception of an on/off signal from the CPU  12 . 
         [0046]    The display unit  102  can receive, from the power controller  300 , information indicating whether or not the sensor  11 , the CPU  12 , and the wireless communication module  13  receive power and display operation statuses of the individual components of the field device  10 A. 
         [0047]    For example, if the wireless communication module  13  is not supplied with power, the field device  10 A does not send or receive a radio signal. Therefore, such a phrase as “RF off” may be displayed on the display unit  102 . This allows the user to easily recognize that the field device  10 A is not emitting radio waves. 
         [0048]    If neither the sensor  11  nor the wireless communication module  13  is supplied with power, such a phrase as “all off” may be displayed on the display unit  102 . This allows the user to easily recognize that the field device  10 A is in a power saving mode. 
         [0049]    The infrared communication unit  101  of the external interface unit  100  can inform operation statuses of the individual components of the field device  10 A to the external infrared communication device  200 . Therefore, the display  201  allows the user to recognize the same information as the display unit  102  does. 
         [0050]    In this manner, the user can easily recognize that the field device  10 A is not emitting radio waves or the field device  10 A is in a power saving mode. 
         [0051]    The power controller  300  can establish a standby state such as a power saving mode. The power controller  300  can cause a transition to a standby state by itself after it has operated for a prescribed time. The standby state can be canceled when an external interrupt signal, for example, is received from the external interface unit  100 . 
         [0052]    In addition to receiving a signal from the external infrared communication device  200  through the glass cover of the container and supplying it to the power controller  300 , the infrared communication unit  101  can operate in place of the wireless communication module  13  to send a process value calculation result and a failure diagnosis result as produced by the CPU  12  to the infrared communication device  200  because the infrared communication unit  101  also has the function of sending a signal to the external power controller  300 . 
         [0053]      FIG. 2  is a schematic diagram illustrating state transitions of the field device  10 A according to the embodiment. Symbol S 1  denotes a transition from state A (no power supply from the battery  15 ) to state B (the peripheral components are operational) which is caused by insertion of the battery  15 . Symbol S 2  denotes a transition from state B to state C (the peripheral components are inactive) which is caused by reception of a power-off request by the infrared communication unit  101 . 
         [0054]    Symbol S 3  denotes a transition from state C to state B which is caused by reception of a power-on request by the infrared communication unit  101 . Symbol S 4  denotes a transition from state C to state A which is caused by removal of the battery  15 . Symbol S 5  denotes state B to state A which is caused by removal of the battery  15 . 
         [0055]      FIG. 3  is a table showing the details of the state transitions shown in  FIG. 2 . When transition S 1  has occurred, the power controller  300  starts supplying power to the peripheral components. 
         [0056]    When transition S 2  has occurred, the infrared communication unit  101  supplies the received power-off request to the power controller  300  and the power controller  300  stops the supply of power to the peripheral components excluding the infrared communication unit  101 . 
         [0057]    When transition S 3  has occurred, the infrared communication unit  101  supplies the received power-on request to the power controller  300  and the power controller  300  restarts supplying power to the peripheral components excluding the infrared communication unit  101 . 
         [0058]    When transition S 4  has occurred, the power controller  300  stops the supply of power to the peripheral components. When transition S 5  has occurred, the power controller  300  stops the supply of power to the peripheral components as in the case of transition S 4 . 
         [0059]    Although in  FIG. 1  the power controller  300  is regarded as an independent function, the management function of the power controller  300  may be provided in the CPU  12 . 
         [0060]    The display unit  102  of the external interface unit  100  is an LCD, for example. The infrared communication unit  101  may be provided on the LCD. 
         [0061]    A process value calculation result and a diagnosis result of each component of the field device  10 A that are produced by the CPU  12  may be supplied to the display unit  102  of the external interface unit  100  via the power controller  300 , in which case information relating to each component of the field device  10 A can be displayed on the display unit  102 .