JPH05216501A - Output circuit for digital controller - Google Patents

Abstract

PURPOSE:To output a plant trip signal by setting an output inhibiting element to the conductive state at the time when an output signal off command is inputted from an operation part through an isolator. CONSTITUTION:If a short-circuit fault of an output element 3 occurs, that is, the output of an arithmetic part 8 is turned off, a light emitting element 1a of an isolator 1 extinguishes the light and light receiving elements 1b and 1c are made non-conductive, but the output element 3 is in the conductive state. A current flows to an output inhibiting element 6 through a resistance 5 because the light receiving element 1c is non-conductive, and the current flowing to the short-circuited output element 3 is shunted to the series circuit of a current limiting resistance 7 and the output inhibiting element 6 and an auxiliary relay 4 because the output inhibiting element 6 is in the conductive state. Therefore, the auxiliary relay 4 can be set to the non-exciting state by reducing the current flowing to the auxiliary relay 4 to the holding current of this relay or smaller. Thus, the plant trip signal is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output circuit of a digital controller.

[0002]

2. Description of the Related Art The application of digital control devices to plants requiring high reliability, such as thermal power plants, is increasing, and digital control devices are also applied to plant trip circuits that were conventionally composed of electromagnetic relays. Started to be played.

The plant trip circuit is provided in order to safely stop the main equipment of the power plant, such as a boiler, a turbine, and a generator, in any case (such as in the event of an accident). It was configured with negative logic (the protection circuit operates with the output signal "zero") so that the plant trip circuit operates even if the output signal of the trip command is cut off due to the failure of.

In the conventional plant trip circuit, the output signal of the digital controller is amplified by the output board,
It was output to an electromagnetic relay that operated protective equipment for the boiler, turbine, and generator. An output circuit of a digital control device according to the prior art will be described with reference to FIG.

The isolator 1 insulates the internal circuit of the digital control device from the circuit outside the control device, and 1a is a light emitting element and 1b is a light receiving element. This is because the resistor 2 limits the current flowing through the light receiving element 1b of the isolator 1. The output element 3 controls the excitation / non-excitation of the auxiliary relay 4, and the contact 4b of the auxiliary relay 4 is opened / closed accordingly. The contact 4b is a b contact that closes the auxiliary relay 4 without excitation. The calculation unit 8 of the digital control device outputs an ON / OFF command to the isolator 1. Here, O
If it is N, it will be normal, and if it is OFF, it will be a trip state command output. The auxiliary relay 4 is designed to be non-excited when the power plant is in an abnormal state so that the plant can be safely stopped even in the non-excited state when the power is cut off.

In the normal state of the plant, the light emitting element 1a of the isolator emits light, the output element 3 becomes conductive, the auxiliary relay 4 is excited and the contact 4b is opened, and the plant trip signal is not output.

[0007]

However, when the output element 3 is short-circuited for some reason, the computing unit 8 outputs a plant trip command and the isolator 1 is turned off even if an abnormality occurs in the power plant. However, the auxiliary relay 4 remains in the excited state through the short-circuited output element 3.

Therefore, the plant trip signal is not output, leading to an accident that damages important equipment of the plant, and it takes a lot of time and cost to restore the equipment. Of course, conventionally, as a check method to prevent such accidents, all output signals are re-input to the input board, the command signal is compared with the output signal in the digital controller, and if the output signal and the command signal do not match, It has been considered that an accident can be minimized by judging an abnormal condition and appropriately processing other output signals.

However, in order to check all the output signals, not only the same number of input circuits as the number of output signal points were required, but even if this method is used, the auxiliary relay 4 is in a non-excited state when the output element 3 is short-circuited. I couldn't.

Therefore, in the present invention, even when the output element 3 fails, when the plant trip command is output, the auxiliary relay 4 is deenergized and the operation signal (trip signal) of the plant protection device is output. It is an object of the present invention to provide an output circuit of a digital control device that can be used.

[0011]

[Means for Solving the Problems] An output element which is rendered conductive or non-conductive in response to a command signal from an arithmetic unit, an auxiliary relay which is excited by the conductive state of the output element, and an auxiliary relay which is interlocked with the auxiliary relay. Digital control including a normally-closed contact that opens and closes to output an output signal, and an output prohibiting element that is provided in parallel with the auxiliary relay and is in a non-conducting state or a conducting state in a state opposite to the output element according to the command It is an output circuit of the device.

[0012]

When the output signal OFF command is input from the arithmetic unit via the isolator, a new output prohibiting element that becomes conductive is added. Therefore, even if the output element for output signal output causes a short circuit failure, the current flowing in the auxiliary relay is shunted to the output prohibiting element added above, and the current flowing in the auxiliary relay is kept below the holding current of the auxiliary relay. , It is possible to put the auxiliary relay in a non-excitation state and output an output signal such as a plant trip.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an output circuit of a digital control device according to an embodiment of the present invention. The isolator 1 has a light emitting element 1a and light receiving elements 1b and 1c, and insulates an internal circuit and an external circuit of the digital control device. Light emitting element 1
When a emits light, both of the light receiving elements 1b and 1c become conductive. The resistors 2 and 5 are limiting resistors for the current flowing through the light receiving elements 1a and 1c.

When the light receiving element 1b becomes conductive, the output element 3 becomes conductive, and when the light receiving element 1c becomes conductive, the output inhibiting element 6 becomes non-conductive. In this case, an exciting current flows through the auxiliary relay 4 via the output element 3, and the auxiliary relay 4 is in an excited state. Therefore, the normally closed contact 4b is open,
No trip signal is output.

Here, the light emitting element 1a is turned off by a trip command from the arithmetic unit 8 of the digital controller, and when the light is extinguished, both the light receiving elements 1b and 1c become non-conductive. Then, the output element 3 becomes non-conductive and the output inhibition element 6 becomes conductive. However, in this case, since the output element 3 is in a non-conducting state, no current flows through the auxiliary relay 4 and the output prohibiting element 6, and the contact point 4b of the auxiliary relay 4 for the plant trip signal is closed, so that the trip signal is reliably output. Next, a case where the output element 3 has a short circuit fault will be described.

When the output of the calculation unit 8 is OFF, the light emitting element 1 of the isolator 1 is extinguished and the light receiving elements 1b and 1c are non-conducting, but the output element 3 is not non-conducting because of a short circuit failure. It is in a conducting state. Also, the light receiving element 1
Since c is non-conducting, a current flows into the output prohibiting element 6 through the resistor 5, and the output prohibiting element 6 is in a conducting state. Therefore, the current flowing through the short-circuited output element 3 is the current limiting resistor 7 and the output prohibiting element. The current is divided into the series circuit of the element 6 and the auxiliary relay 4.

Here, by selecting an appropriate value for the current limiting resistor 7, the current shunted to the auxiliary relay 4 is supplied.
If it is set to be equal to or less than the holding current, the auxiliary relay 4 can be in a non-excited state and the contact 4b of the auxiliary relay 4 can be closed to output a plant trip signal.

In this embodiment, the alarm output at the time of abnormality is not touched, but the alarm can be easily made by adding a current operation element such as a light emitting diode, a photocoupler and an auxiliary relay in series with the current limiting resistor 7 of FIG. Can be output. Further, as shown in FIG. 2, the isolator may be divided.

[0019]

According to the present invention, the protection signal of the power plant or the like can be output even if the output element of the digital control device is short-circuited by adding several parts, and the application range of the digital control device is important. It can be expanded to equipment power plant protection circuits.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an output circuit of a digital control device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an isolator according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of an output circuit of a conventional digital control device.

[Explanation of symbols]

1 ... Isolator, 1a ... Light emitting element, 1b ... Light receiving element,
1c ... Light receiving element, 2 ... Resistor, 3 ... Output element, 4 ... Auxiliary relay, 4b ... Contact, 5 ... Resistor, 6 ... Output inhibiting element, 7 ...
Current limiting resistance, 8 ... Calculation unit.

Claims (1)

[Claims] 1. A conductive state in response to a command signal from the arithmetic unit,
An output element that is in a non-conductive state, an auxiliary relay that is excited by the conductive state of the output element, a normally-closed contact that opens and closes in cooperation with the auxiliary relay to output an output signal, and the auxiliary relay are provided in parallel. An output circuit of a digital control device, comprising: an output prohibiting element that is in a non-conducting state or a conducting state opposite to the output element in response to the command.