JPH06119589A - Valve aperture meter - Google Patents

Abstract

PURPOSE:To reversely send the practical aperture of a regulating valve controlled by a DC control current from the control valve side to the control device side. CONSTITUTION:A pulse signal is generated by an electric signal outputted from a displacement/electric conversion means 35 mechanically connected to the regulating valve 31 and superimposed on a DC control current and a signal expressing aperture is transmitted to a control signal transmission line 21. The control device separates and identifies the pulse signal. A power supply current for generating the pulse signal can be obtained also from the DC control current. Consequently an aperture signal can be reversely transmitted without providing a specific transmission line. The control device can execute highly accurate and sure control by using the aperture signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used in an automatic control device. INDUSTRIAL APPLICABILITY The present invention is used in a device for adjusting and controlling the valve opening of a process control system by a DC control signal transmitted to a two-wire transmission line. The present invention relates to a valve opening meter for transmitting an actual opening of a controlled valve on a two-wire transmission line by superimposing it on a DC control signal.

[0002]

2. Description of the Related Art In a plant including a thermal power plant, a petroleum refining device, a chemical factory that manufactures substances by chemical reactions, and other devices that control the flow path of fluids with an on-off valve, each control site installed in a control room A standard method is widely used in which a measurement signal such as the temperature and pressure is captured and the control device remotely controls the opening degree of the on-off valve installed at each site. The typical standard method is that the control signal sent from the control device for valve adjustment is a DC control signal generated from a constant current power source in the range of 4 to 20 mA, and the value of the current generated by the constant current power source. According to the method, the mechanical opening of the valve is regulated and controlled according to the above, and the control device and the controlled valve are electrically connected in series by a two-wire transmission line that transmits this DC control signal. .

[0003]

Conventionally, this standard system has been widely used, but a control device transmits a control signal for valve adjustment, and this control signal is received by the valve device side to be controlled. Although the opening / closing control of the valve is performed, the actual mechanical opening of the controlled valve which responds to it is not transmitted to the control device side in reverse.

When it is necessary for the control device to take in the actual mechanical opening of the controlled valve into the control device and use it as a control parameter in order to execute the control reliably or precisely. There is. Conventionally, when it is absolutely necessary to measure the mechanical opening of the controlled valve in this way, a valve opening measuring device is separately attached to the controlled valve, and the electric signal generated by the measuring device is measured by another system. It was necessary to transmit to the vicinity of the control device via the transmission line. In such a conventional device, it is necessary to install another power supply circuit in the vicinity of the controlled valve in order to operate the valve opening measuring device and its signal transmitter.

The present invention has been made against such a background. The mechanical opening of the controlled valve does not require a separate transmission path, and a power circuit is provided near the controlled valve. It is an object of the present invention to provide a device that can reversely transmit this to the control device side without the need to provide it.

[0006]

The first aspect of the present invention is to:
The valve opening meter detects an actual opening of a controlled valve as an electric signal, converts the detection result into a pulse signal, superimposes it on a DC control signal, and transmits the signal.

That is, the present invention relates to a displacement electric conversion means which is connected to a valve device whose opening is adjusted according to the value of a DC control signal and which generates an electric signal according to its mechanical valve opening.
A pulse signal generating circuit for superimposing a pulse signal according to the electric signal on the DC control signal and sending the pulse signal, and a separation circuit for separating the pulse signal from the path of the DC control signal are provided.

The pulse signal generating circuit uses the DC current of the DC control signal as an energy source, and further, if necessary, a power supply circuit for supplying a power supply current for operation to the displacement electrical conversion means. Is good.

A second aspect of the present invention is a process control device using the above valve opening meter, wherein the displacement electrical converting means, the pulse signal generating circuit, and the power supply circuit are provided in the vicinity of the valve device. The separating circuit is arranged in the vicinity of the control device, and the valve device and the control device are connected by a two-wire transmission line that transmits the DC control signal.

[0010]

The actual opening of the controlled valve is detected as an electric signal, the electric signal is converted into a pulse signal, and the pulse signal is superimposed on the transmission path through which the control signal of the valve is transmitted. Then, the pulse signal can be separated from the transmission line at a position where the measurement result of the valve opening is desired to be used. Further, since the valve control signal is a DC signal, the DC current can be used to obtain the power supply current for generating the pulse signal.

Therefore, a separate transmission line for transmitting the valve opening signal is unnecessary, and a separate power supply for supplying a power supply current to the circuit for obtaining the valve opening signal is also unnecessary.

Generally, the DC control signal is transmitted from the constant current circuit as described above. Therefore, if an extra signal is superposed on this DC control signal, the extra signal is absorbed by the constant current circuit and is transmitted from the transmission line. It may not be detected. In particular, if the repetition period of the superimposed signal is increased (the frequency is lowered), the superimposed signal is absorbed by the constant current circuit and cannot be detected. On the other hand, in the present invention, since the signal to be superposed is a pulse signal, even if a repetitive cycle is considerably large and a signal is generated intermittently and superposed on a DC control signal subjected to constant current control, at least that Since the signal in the transient portion contains a high frequency component, the rate of absorption in the constant current circuit is small and the signal is effectively transmitted. Therefore, it is possible to reduce the power consumption of the device on the site side that transmits the signal because the repetition cycle can be set to a large value, and it is possible to reduce the influence of disturbance and receive the superimposed signal on the control device side. There are advantages.

[0013]

1 is a block diagram of an apparatus according to an embodiment of the present invention. This example is a diagram showing a main part of the process control device according to the present invention. As shown by being divided by a chain line, the left side of the figure is a device arranged in a control room, and the right side is a device arranged on site. , And the space between them is connected by a transmission line.
A control device 11 for generating a DC control signal is arranged on the control room side. This DC control signal is transmitted to the site side via the two-wire transmission path 21, and the electropneumatic converter 3 that controls the control valve 31.
Connected to 2. The electro-pneumatic converter 32 changes the output air pressure according to the DC control signal, and is supplied to an actuator 34 that controls a valve via an air passage 33. The DC control signal generated by the control device 11 is generated from a constant current source and its current value range is 4 to 20 mA, 4 mA indicates the fully closed state of the control valve 31, and 20 mA indicates the control valve 31.
To indicate the fully open state.

Here, the characteristic part of the present invention is the part surrounded by the alternate long and short dash line.

That is, according to the present invention, the displacement electric conversion means is mechanically connected to the control valve 31 whose opening is adjusted according to the value of the DC control signal and generates an electric signal according to the mechanical valve opening. A potentiometer 35 is provided. The potentiometer 35 is a two-terminal circuit whose resistance value changes according to the mechanical displacement of the control valve 31. The potentiometer 35 is provided with a pulse signal generation circuit 36 that superimposes a pulse signal corresponding to a current signal flowing through the resistance value on the DC control signal and sends the superimposed signal. Further, a transformer for coupling this pulse signal to the two-wire transmission path 21 and a power supply circuit 38 for taking in the direct current flowing through the two-wire transmission path 21 and supplying a power supply current to the pulse signal generation circuit 36 as an energy source are provided. .

On the other hand, on the control room side, a transformer 12 for separating a pulse signal from the two-wire transmission line 21 and this transformer 12 are provided.
The conversion circuit 13 detects the pulse signal separated by the above and converts it into a signal indicating the opening, and a power supply circuit 14 that supplies an operating current to the conversion circuit 13. A signal indicating the opening is output to the terminal 15. This signal is used in the control device 11 and the like, and the signal form can be set to the conversion circuit 13 by selecting a DC signal, an AC signal, a frequency signal, or any other form that is easy to use.

The operation of the thus constructed device will be described. When the DC control signal generated by the control device 11 is transmitted to the two-wire transmission line 21 as described above and the opening of the control valve 31 is controlled. A resistance value corresponding to the actual opening is generated in the potentiometer 35. This potentiometer 35
The pulse signal generation circuit 36 generates a pulse signal having a cycle t as illustrated in FIG.

FIG. 2 is a graph in which the horizontal axis represents time and the vertical axis represents the current value of the two-wire transmission line 21, and the DC level S thereof is a DC control signal. The transformer 37 superimposes a pulse signal of cycle t on this DC control signal. This cycle t corresponds to the resistance value exhibited by the potentiometer 35, that is, the actual opening of the control valve 31.

On the control room side, this pulse signal transmitted to the two-wire transmission line 21 is separated by the transformer 12, and this is detected by the conversion circuit 13 to obtain a signal indicating the opening of the control valve 31 at the terminal 15.

As described above, in the device of the present invention, the signal indicating the opening degree of the control valve detected on the site side is transmitted by being superimposed on the DC control signal for controlling the control valve, so that it is separated into the site side and the control room side. It is not necessary to provide the transmission line of. Further, since the power supply current required by the pulse signal generation circuit 36 is obtained from the DC control signal by the power supply circuit 38, it is not necessary to provide a special power supply device on the site side.

FIG. 3 is an explanatory view of another embodiment of the pulse signal. Also in this figure, the horizontal axis represents time, and the vertical axis represents the two-wire transmission line 21.
Is a graph in which the current value of is taken, and its DC level S is a DC control signal. In this example, the pulse signal generation circuit 36
Generates a positive pulse P1 with a constant interval t1 continuously, and a negative pulse P2 with a delay of time t2 from the pulse P1. The ratio between the time t1 and the time t2 is configured to change according to the opening degree of the control valve 31. That is, in this example, the potentiometer 35 may have a three-terminal structure, and the ratio of the two resistance values appearing at the three terminals may correspond to the ratio of the time intervals of the pulse signals. The conversion circuit 13 on the control room side can detect the opening degree of the control valve 31 from the time t2 or the ratio of the times t1 and t2. By taking the ratio, there is an effect that the disturbance is less likely to occur as compared with the case where the pulse interval is directly detected as shown in FIG. Further, by taking the ratio, it is possible to easily realize a circuit for making it difficult to receive disturbance.

FIG. 4 is a block diagram of the essential parts of another embodiment of the device of the present invention. This figure shows a part of the equipment installed on the site side. This embodiment is characterized by the structure of the power supply circuit 38. That is, the power supply of the power supply circuit 38 is not obtained from the current of the transmission line, but is obtained from the power supplied to the separately provided power supply terminal 40. Others are the same as those in the above-mentioned embodiment, and therefore the description will not be repeated.

The configuration of FIG. 4 is advantageous when a power source can be easily obtained on the site side. That is, when the DC control current transmitted to the transmission line 21 is used as the power source, the power source of the control device 11 on the control room side is burdened, but the configuration on the site side makes it easy in relation to nearby devices. When an external power source is available, the load on the control device 11 can be reduced by using the external power source.

FIG. 5 is a block diagram of the essential parts of another apparatus according to the present invention. This drawing shows a part of the apparatus installed on the control room side. In this embodiment, the power supply current used in the conversion circuit 13 on the control room side is obtained from the DC control signal flowing through the transmission path 21. However, there is a feature.
That is, in this example, the power supply circuit 14 is not provided with a terminal for supplying an external power supply, but is obtained from the DC control current flowing through the two-wire transmission path 21. This is advantageous when the load on the control device 11 increases but it is difficult to obtain power from the control room.

[0025]

As described above, according to the present invention, a signal indicating the mechanical opening of the controlled valve is provided in the vicinity of the controlled valve without requiring a separate transmission path. This can be transmitted back to the controller side without the need for provision. By utilizing the signal indicating the opening degree, which is transmitted in reverse, in the control device, it is possible to realize highly accurate and accurate control.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram illustrating the operation of the device according to the embodiment of the present invention.

FIG. 3 is a signal waveform diagram for explaining the operation of the apparatus according to another embodiment of the present invention.

FIG. 4 is a block diagram showing another example of the configuration of the field device for the device of the embodiment of the present invention.

FIG. 5 is a block diagram showing another example of the configuration of the control-room-side device for the device according to the embodiment of the present invention.

[Code]

 11 Control Device 12 Transformer 13 Conversion Circuit 14 Power Supply Circuit 15 Terminal to Output Opening Signal 16 Power Supply Terminal 21 Two-Wire Transmission Line 31 Control Valve 32 Electro-Pneumatic Converter 33 Air Passage 34 Actuator 35 Potentiometer 36 Pulse Signal Generator circuit 37 Transformer 38 Power circuit 40 Power supply terminal

Claims (3)

[Claims] 1. Displacement electric conversion means which is connected to a control valve whose opening is adjusted according to the value of a DC control signal and which generates an electric signal according to its mechanical valve opening, and a displacement electric conversion means according to this electric signal. A valve opening degree meter, comprising: a pulse signal generating circuit that superimposes the pulse signal on the DC control signal and sends the pulse signal; and a separation circuit that separates the pulse signal from the path of the DC control signal. 2. The valve opening meter according to claim 1, further comprising a power supply circuit that supplies a power supply current to the pulse signal generation circuit by using a DC current of the DC control signal as an energy source. 3. The valve opening meter according to claim 2, wherein the displacement electrical conversion means, the pulse signal generation circuit, and the power supply circuit are arranged in the vicinity of the valve device, and the separation circuit is a control device. A process control device which is arranged in the vicinity and in which the valve device and the control device are connected by a two-wire transmission path for transmitting the DC control signal.