Field apparatus

Abstract

A field apparatus (1a) comprises a diagnosis unit (11) diagnosing abnormality of oneself or a controlled element and a bidirectional digital communication means (22) to send a digital signal which shows a diagnosis result to outside and to receive the digital signal from outside in order to execute a control of controlled element and other predetermined functions based on a command signal received by a analog communications means (17) that can receive a analog signal from outside. A electric power for operation is supplied through a switching means (18, 53) that can switch either a electric power that is supplied by the analog communications means (17) or a electric power that is supplied by the bidirectional digital communication mean (22).

Description

FIELD OF THE INVENTION

The present invention relates to a field apparatus of positioners having a communication function.

BACKGROUND ART

Generally in a control system operating a control apparatus of valves by remote control, a detection sign from the field apparatus measuring a quantity of physics such as flow quantity, pressure force and temperature are gathered to a controller as a superior apparatus, the controller operates opening and shutting of valves by remote control based on those detection signals. In such the control system, generally a communication cable of 4-20 mA is used as a transmission channel transmitting the detection signal from a detection port of feld apparatuses to the controller and transmitting a control signal from the controller to an operation port of valves. The controller receives an analog signal (following, “4-20 mA signal”) with an electric current of 4-20 mA normalized to 0-100% from the detection port by this communication cable. Further it establishes a PID parameter so that a detection data in the detection port will become a predetermined target value (set point) at every operation port. And it sends the 4-20 mA signal as the control signal normalized to 0-100% towards the operation port.

In late years, the field apparatus comprising the function transmitting the diagnosis information of valve and oneself to the controller is developed in addition to the control function of the valve. As an example of such the field apparatus, there is the positioner disclosed by Japanese Patent Laid-Open No. 1-141202. According to this, because the diagnosis result of valve and oneself are informed to the controller via the transmission channel, the controller can analyze the diagnosis result and take the correspondence step. Therefore a bidirectional digital communication of field bus communications (following “FB communication”) is used and the control system by such the bidirectional digital communication will be replaced to the control system from the conventional analog communication. In such a digital control system, in addition to operating by remote control the operation port of valves as before, the controller instructs the diagnosis of the valve and own diagnosis of the field apparatus by remote control and it manages each field apparatus by acquiring the diagnosis information. In the control system that utilized such the FB communication, it is advantageous that setting and maintenance of the valve and the field apparatus are easy.

However, it is needed to exchange the interface of all apparatuses to the interface for FB communication from the existing interface for 4-20 mA communication in order to change the existing control system using the communication cable of 4-20 mA to the control system by the FB communication. Moreover, very many costs are needed in a cage of such the system.

Moreover in the control system which used the FB communication, because the control information that operate by remote control of the operation port and the diagnosis information of the apparatus intermingle, the inside of the transmission channel is crowded by the transmission information and may give bad influence to the control.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide the field apparatus which can introduce the control system by the digital communication easily without wasting the control system by the existing 4-20 mA communication, and can transmit information between the outside device and the operation port precisely and speedily.

The present invention is the field apparatus comprising the analog communications means that can receive the analog signal from outside, and executing the control of controlled element and other predetermined functions based on a command signal received by the analog communications means. The field apparatus of the present invention is characterized by comprising a diagnosis unit diagnosing abnormal of oneself or the controlled element and a bidirectional digital communication means to send a digital signal which shows the diagnosis result to outside and to receive the digital signal from outside.

The embodiment of the present invention comprises a switching means for example, a power supply changeover unit 18 of FIG. 2) that can switch either a electric power that is supplied by the above analog communications means or a electric power that is supplied by the above bidirectional digital on means is used as the electric power for the field apparatus operation.

The other embodiment uses either a power supply from the analog communications means or a power supply from the bidirectional digital communication means as the electric power for the field apparatus operation and if the power supply in use runs out, it comprises an automatic switching means (for example, an automatic changeover switch 53 of FIG. 5) that can switch to the other power supply automatically.

According to the present invention, the existing equipment can be utilized usefully without setting up new communication equipment in order to control the controlled object of valves because communication with the existing control system is possible by the analog communications means. At the same tine an advantage of the bidirectional communication of the setting and the diagnosis of own diagnosis or the controlled object is provided by utilizing the digital communication with the outside by the bidirectional digital communication means. Moreover, because management/diagnosis information of the control information and the apparatus does not intermingle, congestion of the transmission channel is prevented and bad influence does not give to the control.

According to the embodiment of the present invention, it can switch optionally either the electric power supplied by the analog communications means or the electric power supplied by the bidirectional digital communication means is used as the electric power for the field apparatus operation. Therefore, if the power supply by the FB communication is stopped, the electric power is secured by switch to the power supply by the analog communication, and influence to the control of the controlled object can be prevented.

According to other embodiment, if the power supply in use runs out, it can be changed to the other power supply automatically. Therefore, even if either the power supply stops, the influence can be prevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an embodiment of a control system constituted by using a positioner of the present invention.

FIG. 2 shows a circuit composition of a positioner of an embodiment.

FIG. 3 shows a circuit composition of an I/V block.

FIG. 4 shows a circuit composition of a FB block.

FIG. 5 shows another embodiment of a control system constituted by using a positioner of the present invention

TNE BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows the control system constituted by using the positioner of embodiment of the present invention. The positioner 1a, 1b as the field apparatus have a positioning function to control a valve position of the valve 3a, 3b in response to the control signal from a controller 2. Each positioner 1a, 1b and the controller 2 are connected in the 4-20 mA communication cable 5a, 5b of two-line type respectively. Each positioner 1a, 1b controls the valve position of each valve 3a, 3b based on the control signal transmitted through the communication cable 5a, 5b from the controller 2 (following “4-20 mA signal”). The control signal transmitted from the controller 2 determines the PID parameter as opposed to each positioner 1a, 1b and is generated so that the detection data of the flow quantity transmitter 6 provided downstream of the valve 3a and 3b become a predetermined target value in the controller 2. Each positioner 1a, 1b move by electric power supplied through the 4-20 mA communication cable 5a, 5b from a stabilization power supply unit 7a connected to the controller 2.

Each positioner 1a, 1b have also the function to diagnose operation circumstances of own operation circumstances and the valve 3a, 3b. Information of the diagnosis result (following “diagnosis information”) is transmitted through the FB communication cable 8a, 8b of two line type to the FB setting device 4 which does the setting and the management of each field apparatus. Moreover, each positioner 1a, 1b comprise the communication function that can receive the setting ation fom the FB setting device 4 via the FB communication cable 8a, 8b.

The electric power to be necessary for movement of the above positioner 1a, 1b is supplied through the 4-20 mA communication cable 5a, 5b from the stabilization power supply with 7a of the controller 2 side. However even if this power supply was cut, the positioner 1a, 1b are composed to receive the power supply through the FB communication cable 8a, 8b. Concretely, the switch that can switch between the power supply via the 4-20 mA communication cable 5a, 5b and the power supply via the FB communication cable 8a, 8b are comprised inside the positioner 1a, 1b. The electric power via the FB communication cable 8a, 8b is supplied by the stabilization power supply unit 7b which is different from the stabilization power-supply unit 7a of the controller 2 side.

FIG. 2 shows a circuit constitution of the positioner 1a. This circuit comprises the arithmetic a processing unit 10, a voltage conversion unit 20, a valve lift detection unit 21, a I/V block 17, YB block 22, the power supply changeover unit 18 as a main constitution element.

The arithmetic processing unit 10 includes a CPU 11, a ROM 12, a RAM 13, a communication interface 14, a A/D converter 15 and a power supply unit 19 connected through a bus 16.

The CPU 11 functions as the diagnosis unit generating the diagnosis information based on the input signal from various sensors (not shows) arranged for diagnoses. The diagnosis information is sent to the FB block 22 through the communication interface 14 and it is transmitted toward the FB setting device 4 via the FB communication cable 8a, 8b from the FB block 22. Various sensors arranged for diagnoses are such as an air pressure sensor, a supersonic wave sensor, a temperature sensor.

The 4-20 mA signal sent via the communication cable 5a, 5b from the controller 2 is distributed to a 1-3V voltage signal or a power supply electric current in the I/V block 17 that is an example of the analog communications means. While the power supply electric current is supplied to the power supply unit 19 of the arithmetic processing unit 10 through the switch S₁ of the power supply changeover unit 18, a voltage signal is converted into the digital signal at the A/D converter 15. In response to the CPU 11 getting a deviation between this digital signal and a later valve lift signal, the valve lift control signal which establishes a control quantity of the valve position of the valve 3a is generated and is output from the voltage conversion unit 20. The voltage conversion unit 20 consists of a well-known converter circuit that converts the valve lift control signal to an air pressure signal and the valve position of valve 3a is controlled by the air pressure signal after the conversion. The valve lift detection unit 21 consists of a well known detection circuit that converts stem displacement of the valve 3a to the voltage signal of 1-3V The detection signal is converted to the digital signal by the above A/D converter 15 and the above valve lift control signal is used for generation

On the other hand, the digital signal sent via the FB communication cable 8a, 8b from the FB setting device 4 is distributed to the signal showing the setting information from the FB setting device 4 or the power supply electric current in FB block 22 that is an example of the bidirectional digital communication means. While the power supply electric current is supplied to the power supply unit 19 of an arithmetic processing unit 10 through the switch S₁ of the power supply changeover unit 18, the setting information signal is inputted into the communication interface 14 after the noise removal in an isolator 24 through a channel 23. The CPU 11 executes various setting processing in response to the setting signal received through the communication interface 14.

As shown in FIG. 2, the power supply changeover unit 18 of this positioner 1a includes usually a condition that the switch piece S1 connects to the I/V block 17 and the power supply electric current from the I/V block 17 is supplied to the power supply unit 19. But connection of this switch piece S₁ consists of the manual switch that can be changed to the FB block 22 side by manual. Accordingly, even if the electric power from the contoller 2 is not supplied, it is changed to supply of the power supply from the FB setting device 4 by switching a condition of this switch.

FIG. 3 shows circuit constitution of I/V block 17. Between the 4-20 mA communication cable 5a and 5b, this I/V block 17 connects a series circuit between the transistor as first variable impedance device Z1, and the resistor as impedance device RS for reception. And the transistor as second variable impedance device Z₂ is connected to the series circuit of the resistor R_c in parallel with these. At the same time an arithmetic circuit 31 is connected in parallel with the device Z₂ and was constituted to get the output from the both terminals of this arithmetic circuit 31. While the arithmetic circuit 31 controls the impedance of the device Z₁ in the course for example, 10V) keeping the line voltage V_L of the 4-20 mA communication cable 5a, 6b, the impedance of the device Z₂ is controlled in the course (for example, 4 mA) keeping the electric current I_c flowing in the resistor R_c. If the electric current which is passed in the device Z₂ is I₁, the output electric current of the I/V block 17 becomes I₂=I_c−I₁.

In the circuit of FIG. 3, if a track line electric current of the 4-20 mA communication cable 5a, 5b is I_L, the electric current passing the series circuit between the first variable impedance device Z1 and the resistor R_s is I_s=I_L−I_c. Therefore, for example, I_S becomes only a signal electric current of 0-16 mA by establishing kept I_c (for example, 4 mA) as a bias ingredient. Without giving influence on the reception of the signal shown by this I_S, the power supply electric current I₂ of maximum 4 mA can be supplied to the power supply unit 19 stably through the switch S₁ of FIG. 2. On the other hand, for example, the terminal voltage V_IN of the resistor R_s (=R_sI_s) is inputted into the A/D converter 15 as the voltage signal of 1-3V.

FIG. 4 shows circuit constitution of the FB block 22. This FB block 22 comprises a MAU (Media Attachment Unit) 41, a CPU 42, a flash memory 43, a RAM 44 and a communication interface 45.

MAU 41 distributes the transmission signal from the FB communication cable 8a, 8b to the power supply electric current or the digital signal as the setting information, and comprises a function to transmit the diagnosis information of the field apparatus (in this case, the positioner toward the FB setting device 4. The power supply electric current is supplied as the power supply for movement of this FB block 22, and when a condition of the switch S₁ of FIG. 2 was switched from an as described before usual condition, the power supply electric current is supplied to the power supply unit 19. On the other hand, the digital signal as the setting information is processed in the CPU 42, it is transmitted through the transmission channel 23 from the communication interface 45 to the arithmetic processing unit 10. The CPU 11 inside the arithmetic processing unit 10 processes the monitoring and the adjustment of the output value of the field apparatus based on this setting information, various diagnosis information to be got on the basis of these is transmitted toward the FB setting device 4 through the FB block 22.

The flash memory 43 stores a program about the FB communication, and the RAM 44 stores a variable about the FB communication.

FIG. 5 shows the circuit constitution to switch the power supply from the I/V block 17 side and the power supply from the FB setting device 4 side in response to circumstances automatically in the positioner 1a. In this circuit constitution, the respective power supply monitor circuit 51a, 51b are connected to each output port of the I/V block 17 and the FB block 22 and it always watches the output electric current from the I/V block 17 and the FB block 22. The output showing monitor circumstances of the power supply monitor circuit 51a and 51b of these two becomes the input to the OR circuit 52, and the output of this OR circuit 52 becomes the setting signal of the automatic changeover switch 53. That is, the OR circuit 52 sends the in response to the monitor output from either power supply monitor circuit 6la or 51b to the automatic changeover switch 53. The automatic changeover switch 53 is set at the power supply condition from the I/V block 17 side or the power supply condition from the FB block 22 side by the input signal.

Concretely, this automatic changeover switch 53 is usually set on the condition to supply the power supply electric current from the I/V block 17 for the power supply unit 19. If the output electric current runs out in the power supply monitor circuit 5la of the I/V block 17 side, the output from the OR circuit 52 changes. Therefore the automatic changeover switch 53 is switched to the condition that supplies the power supply electric current from the FB block 22 for the power supply unit 19. If the output runs out in the power supply monitor circuit 51b of the FB block 22 side in this condition, the output fox the OR circuit 52 changes. Therefore, the automatic changeover switch 53 returns to the usual condition that supplies the power supply electric current from the I/V block 17 for the power supply unit 19.

In thee circumstances, though the positioner of embodiment was explored, the present invention is not limited to the positioner and can apply to other field apparatuses (for example, the measurement apparatus such as the differential pressure transmitter).

Claims

1. A field apparatus comprising: a analog communications means that can receive a analog signal from outside is comprised, and executing a control of controlled element and other predetermined functions based on a command signal received by the analog communications means; a diagnosis unit diagnosing abnormality of oneself or the controlled element; and a bidirectional digital communication means to send a digital signal which shows a diagnosis result to outside and to receive the digital signal fron outside.

2. The field apparatus according to claim 1, wherein a switching means can switch either a electric power that is supplied by the analog communications means or a electric power that is supplied by the bidirectional digital communication means as a electric power for operation.

3. The field apparatus according to claim 1, wherein an automatic switching means uses either a power supply from the analog communications means or a power supply from the bidirectional digital communication means as a elecic power for operation, and if a power supply in use runs out it can switch to the other power supply automatically.