JP3719196B2 - Slave output unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  This inventionSlave output unitIt is about.
[0002]
[Prior art]
An example of a network system including a PLC is as shown in FIG. That is, the PLC unit 1 and the master unit 2 having a communication function are integrated, and the master unit 2 is connected to the field network 3. The field network 3 is connected to an OUT slave 4 or the like. In this example, an output device 5 such as a valve or a motor is connected to the OUT terminal of the OUT slave 4.
[0003]
The internal structure of the OUT slave 4 is as shown in FIGS. 2 and 3, for example. That is, a communication interface (communication connector) 4a for connecting to the field network 3 is provided. A frame, a message, etc. addressed to itself received through the communication interface 4a are analyzed by the communication unit 4b, and necessary information is obtained. It is given to MPU4c. When the MPU 4c receives OUT data from the master unit 2, it sends a control signal to turn on / off the corresponding OUT terminal. Specifically, the ON / OFF information (1/0) is written into the flip-flop 4d.
[0004]
The output of the flip-flop 4d (equivalent to the value of the given control signal) is given to the short circuit detection built-in output circuit 4f via the photocoupler 4e. As shown in FIG. 3, the short-circuit detection built-in output circuit 4f includes a transistor 4f ′ having a short-circuit prevention function. By turning on / off the transistor 4f ′, an OUT terminal 4f ″ to which an output device is connected is provided. Turn ON / OFF.
[0005]
Furthermore, the line for sending the control signal is provided with an I / O_LED 4g indicating the state of the OUT terminal 4f ″ (contact ON / OFF). This I / O_LED 4g is turned on when the control signal is ON, The color to be lit is changed by / OFF.
[0006]
Furthermore, the illustrated OUT slave 4 is divided into an internal circuit that performs signal processing and the like, and an output circuit that drives and operates the output device 5, and each circuit is driven by a separate power source. In other words, the output circuit is supplied with power from the external I / O power supply 4i, and the above-described transistor 4f 'is provided in this power supply line. Thus, when the transistor 4f ′ is turned on based on the control signal, the circuit is closed and the OUT terminal 4f ″ and consequently the output device 5 are energized from the I / O power source 4i. Further, the I / O power source 4i is connected to the switch 4i. 'Is provided, and by opening and closing the switch 4i', it is possible to manage ON / OFF of the power supply of the entire output circuit.
[0007]
On the other hand, power is supplied to the internal circuit from the internal circuit power supply 4h. The internal circuit power supply 4h may be, for example, an independent power supply, or appropriately converts the power supplied via the field network 3, You may make it supply to each element etc. which comprise the internal circuit in OUT slave 4.
[0008]
Furthermore, although the illustrated OUT slave 4 has a short-circuit prevention function as described above, specifically, the transistor 4f ′ determines whether or not the output device 5 connected to itself is short-circuited, and the short-circuit is prevented. If detected, the contact is turned off and a short circuit detection signal is output. That is, when the output device 5 is short-circuited, a large short-circuit current flows and heat is generated with the energization. Therefore, by detecting such overcurrent and heat generation, it is determined that a short circuit has occurred, and a predetermined operation is performed.
[0009]
Then, the short circuit detection signal is given to the bus buffer 4j through the photocoupler 4e and transmitted to the MPU 4c at a predetermined timing. Further, the MPU 4 c that has received this short-circuit detection signal sends it to the master unit 2 and then to the PLC unit 1 via the field network 3, for example. As a result, the PLC unit 1 performs a process for turning on a predetermined alarm lamp or sounding an alarm buzzer, and notifies that an abnormality has occurred. In some cases, abnormal processing such as stopping the system is performed.
[0010]
In this way, in the case of such a system, when the output device is short-circuited, it is notified to a higher-level PLC or the like, and an alarm is output from there to notify the monitoring staff or the like that there is an abnormality. Therefore, it is possible to perform maintenance such as replacement work of the output device that is short-circuited by a worker going to the site where the short-circuit has occurred quickly.
[0011]
[Problems to be solved by the invention]
However, in the case of a system including an OUT slave to which the conventional short-circuit detection function described above is added, there are the following problems. That is, when performing maintenance (repair or replacement work) on an output device (load) that is short-circuited, the switch 4i ′ is normally opened and the I / O power supply 4i is turned off in order to prevent danger due to malfunction. The maintenance work is done at.
[0012]
As is clear from the circuit configuration shown in FIG. 3, when the I / O power supply 4i is turned off in this way, the transistor 4f 'is not energized. As a result, there is no overcurrent and no heat is generated, so it is determined that there is no short circuit, and the short circuit detection signal is turned off. As a result, the MPU 4c operating upon receiving power supply from the internal circuit power supply 4h determines that the short circuit has been eliminated, and performs a predetermined operation associated with the elimination.
[0013]
That is, for example, the short circuit cancellation is notified to the PLC unit 1, and the PLC unit 1 starts normal cyclic control accordingly. However, since the short circuit condition is not actually solved, there is a risk of malfunction. Further, for example, when a lamp (status LED) for specifying a short-circuited terminal is turned on according to a control command from the PLC unit 1 or a command from the MPU 4c, the lamp is turned on when the I / O power supply 4i is turned off. Therefore, the operator cannot determine which output device the short circuit has occurred based on whether or not the lamp is lit, and the maintenance target identification process becomes complicated.
[0014]
  Therefore, in the present invention, even when the power supply for the output device is turned off, the alarm means for specifying the output device (OUT terminal) in which an abnormality such as a short circuit has occurred can be continuously operated, and the maintenance target can be easily specified. Can beSlave output unitThe purpose is to provide.
[0015]
[Means for Solving the Problems]
  According to this inventionSlave output unitIs used, for example, in a PLC system, and has an output terminal for connecting an output device.Slave output unitIt is.Specifically, it is a slave output unit that communicates with a master unit having a communication function via a field network, and receives and analyzes a self-addressed frame and message from the master unit, and an output A plurality of output terminals for connecting devices, a plurality of output circuits for turning each of the output terminals ON / OFF, and receiving OUT data from the master unit, and controlling the ON / OFF to the corresponding output circuit A control means for sending a signal; and a plurality of alarm means for displaying a short circuit abnormality in the output circuit corresponding to each of the output circuits, and an internal circuit including the communication unit, the control means, the alarm means, and the output circuit Is configured to receive power supply for internal circuits and power supply for output circuits respectively by separate power supply lines. Each of the output circuits has a function of outputting a short circuit detection signal toward the control means when a short circuit abnormality is detected, and the control means outputs a corresponding output when receiving the short circuit detection signal from the output circuit. A control signal for turning off the circuit is sent, an operation signal is output so as to operate an alarm means corresponding to the output circuit, and the fact that a short circuit has occurred is notified to the master unit via the field network. Furthermore, the ON / OFF state of the power supply line for the output circuit is monitored, and even if the power supply line is turned from ON to OFF, the short-circuit detection signal is output immediately before the operation signal to the alarm means. If it is outputting, the output is continued by supplying power for the internal circuit, and alarm means when the power supply line returns from OFF to ON It was to release the output continuation of the operation signal.
[0020]
According to the present invention, when an abnormality such as a short circuit occurs in the output device or the like, the output circuit detects it and outputs an abnormality detection signal. When the control means receives the abnormality detection signal, it outputs an output signal to operate the alarm means. Thereby, a worker, a supervisor, etc. can know that there was abnormality.
[0021]
Next, when performing maintenance processing to eliminate the abnormality, the power supply of the output circuit is turned off. Then, the output circuit is also stopped and the abnormality detection signal is turned OFF. Even in this case, the power supply for the internal circuit is continued, so the control means operates normally and continues to output the output signal. Means continue to operate (alarm output).
[0022]
  According to this inventionSlave output unitEach means configuring the above can be realized by a dedicated hardware circuit, or can be realized by a programmed computer.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
4 and 5 show a preferred embodiment of a slave according to the present invention. This slave is connected to the field network as shown in FIG. 1, and performs master-field communication with the master to send and receive I / O data and output a short-circuit detection signal to the master unit. It has come to do.
[0024]
The basic structure of the internal structure is the same as the conventional one. That is, a communication interface (communication connector) 11 for connecting to a field network is provided, and a frame, a message, etc. addressed to itself received via the communication interface 11 are analyzed by the communication unit 12 and necessary information is stored in the MPU 13. Given to.
[0025]
The MPU 13 is connected to an 8-bit bus, and transmits and receives data via the bus. In other words, two flip-flops 14a and 14c and one bus buffer 14b are connected to this bus, and the MPU 13 selects one selected from the flip-flops 14a and 14c and the bus buffer 14b. (Data is written to the flip-flops 14a and 14c and data is read from the bus buffer 14b).
[0026]
Then, the MPU 13 writes the OUT data received from the master unit to a predetermined address of the flip-flop 14a. Each output of the flip-flop 14a is given to the base of each transistor 16 'constituting the short circuit detection built-in output circuit 16 via the photocoupler 15a, and the transistor 16' is turned ON / OFF. Since each transistor 16 'is connected to an I / O power source 19, by turning ON / OFF the transistor 16', an OUT terminal 16 "that is an I / O terminal connected to the transistor 16 'and thus its terminal The output device 25 connected to is turned on / off.Also in this embodiment, the switch 19 'is installed in the I / O power source 19 so that the I / O power supply can be cut off as a whole.
[0027]
Further, an I / O_LED 17 indicating the state of the OUT terminal 16 ″ (contact ON / OFF) is connected to the line for sending the control signal. This I / O_LED 17 lights up when the control signal is ON, The color to be lit is changed by ON / OFF.
[0028]
Furthermore, the slave 10 is divided into an internal circuit that performs signal processing and the like, and an output circuit that drives and operates the output device 25, and each circuit is driven by a separate power source. That is, as described above, the output circuit (transistor 16 ′) is configured to receive power from the external I / O power source 19. Then, power is supplied to the internal circuit from the internal circuit power supply 18. For example, the internal circuit power supply 18 may be an independent power supply, or may be appropriately converted from the power supplied via the field network and supplied to each element or the like constituting the internal circuit in the slave 10. .
[0029]
Further, the transistor 16 ′ has a short-circuit prevention function, and detects a short circuit of the output device 25 connected to the transistor 16 ′. When the transistor 16 ′ is detected, the transistor 16 ′ turns off the contact and outputs a short circuit detection signal. That is, when the output device 25 is short-circuited, a large short-circuit current flows, and heat is generated with the energization. Accordingly, by detecting such overcurrent and heat generation, it is determined that a short circuit has occurred, and the contact OFF process and the short circuit detection signal output process described above are performed.
[0030]
The short circuit detection signal is given to the bus buffer 14b via the photocoupler 15b and transmitted to the MPU 13 at a predetermined timing. Receiving this short circuit detection signal, the MPU 13 turns on the input terminal of the corresponding flip-flop 14c and lights the status LED 20 connected to the flip-flop 14c. Thereby, it can be easily recognized which output device 25 is short-circuited by checking which status LED 20 is lit. Further, the MPU 13 notifies the master unit and thus the PLC unit via the field network that a short circuit has occurred.
[0031]
Here, in the present invention, the power supply line from the I / O power supply 19 is branched and supplied to the MPU 13 via the photocoupler 15c. That is, when the I / O power supply 19 is turned on and power is supplied, the output of the photocoupler 15c is turned on.
[0032]
When the switch 19 'is opened for maintenance and the I / O power supply 19 is turned off, the output of the photocoupler 15c is also turned off. Therefore, the MPU 13 can recognize the operation state of the I / O power supply 19 by monitoring the output (I / O power supply detection signal) of the photocoupler 15c.
[0033]
Therefore, in the present embodiment, when the power is turned off, the MPU 13 continues to turn on the status LED 20 when a short circuit detection signal is output when the power is turned off (immediately before). That is, since the short circuit detection signal from the transistor 16 ′ is also turned off as the I / O power source 19 is turned off, the MPU 13 normally determines that the short circuit state has been resolved and turns off the status LED 20. When the / O power source 19 is OFF, the detection signal is also OFF due to the absence of such power supply, and it is determined that the short-circuit state is actually continued and the status LED 20 is kept on. To make it work. Thus, even if the I / O power supply 19 is turned off for maintenance, the predetermined status LED 20 is lit, so that the OUT terminal (output device) that has caused a short circuit can be easily identified.
[0034]
In order to realize the processing functions described above, the MPU 13 has a function for implementing the flowchart shown in FIG. First, the MPU 13 takes in each value of the bus buffer 14b, has a function of determining whether or not a short circuit detection signal is output from the transistor 16 ', and further determines whether or not to perform such determination (short circuit detection). Settings can also be made. That is, when the short circuit detection is valid, the value of the bus buffer 14b is actually taken in, and it is determined whether or not the short circuit is detected. In other words, when the short circuit detection is invalid, the presence / absence of the short circuit is not determined regardless of the ON / OFF state of the short circuit detection signal. Of course, the validity / invalidity of this short-circuit detection is switched for each bit.
[0035]
The MPU 13 operates as follows using the above-described function for determining short circuit detection and the function for switching validity / invalidity of short circuit detection. First, it is determined whether or not the short circuit port detects a short circuit (ST1). This determination is Yes when the short circuit detection is effective and the corresponding bit of the bus buffer 14b is ON (the transistor 16 'outputs a short circuit detection signal). In other cases, that is, when the short-circuit detection is valid but the corresponding bit of the bus buffer 14b is OFF (no short-circuit has occurred), and when the short-circuit detection is set to invalid, The branch determination is No. If the branch determination in Step 1 is Yes, the corresponding short circuit detection buffer in the MPU 13 is turned ON (ST2). Thereby, the ON state is latched.
[0036]
Next, the output of the photocoupler 15c, that is, the ON / OFF signal of the I / O power supply detection signal is acquired, and the state of the I / O power supply is confirmed (ST3). When the previous state is OFF and this time is ON, it can be determined that the power has been turned on, so the process proceeds to Step 4 where the short-circuit detection buffers are turned OFF all at once, and all output devices (OUT terminals) are connected. Make the status no short circuit. As a result, all the bits of the flip-flop 14c are turned OFF, and the status LED 20 is turned off. Thereafter, the short-circuit detection is effectively set for all the short-circuit ports (ST5) to prepare for the next monitoring.
[0037]
On the other hand, if the ON / OFF signal of the I / O power supply detection signal is not in the above state, that is, if it is OFF or both the previous time and this time are ON, the process proceeds to step 6 and the short circuit detection buffer is turned ON. / OFF is reflected in the status. Actually, a short-circuit detection buffer that is ON is reflected in the status as being short-circuited. As a result, the corresponding bit of the flip-flop 14c connected to the status LED 20 assigned to the output device (OUT terminal) causing the short circuit is turned ON, and the corresponding status LED 20 is lit.
[0038]
By executing the above-described flowchart, the short-circuit detection is effective in the initial state. Once the short-circuit detection is performed, the short-circuit detection buffer is turned on (ST2), and the status LED 20 corresponding to the presence of the short-circuit is reflected in the status. Is turned on (ST6), and short circuit detection is disabled (ST7). Therefore, until the short-circuit detection becomes valid in step 5, the status determination of the short-circuit boat itself is not performed, and the status LED 20 continues to be lit.
[0039]
On the other hand, step 5 is executed when the I / O power supply 19 is turned on after being turned off. Therefore, short-circuit detection remains invalid only by turning off the I / O power supply 19 for maintenance or the like, and the status LED 20 continues to be lit.
[0040]
When the I / O power supply 19 is turned on after the maintenance is completed, the short-circuit detection buffers are turned off all at once, so that the status LED 20 is also turned off. Thereafter, since the short circuit detection becomes effective (ST5), if the replaced output device or other output device is short-circuited, the corresponding status LED 20 is turned on again.
[0041]
The operation of the above-described embodiment will be described as a time chart shown in FIG. That is, since the I / O power supply is ON in the normal state, the I / O power supply detection signal is also turned ON. Then, since the short circuit detection signal is also turned off, the short circuit detection signal buffer is also turned off, and the status LED 20 is turned off.
[0042]
In this state, when a short circuit occurs at timing (1), the short circuit detection signal is turned ON, so that the branch determination in Step 1 is Yes (the short circuit detection is effective in the initial state). Along with this, the short-circuit detection holding buffer is turned ON, and the status LED 20 is also lit following that.
[0043]
Next, when the I / O power supply is turned off for maintenance at timing (2), the I / O power supply detection signal is also turned off. Further, since the transistor 16 'is not energized, the short circuit detection signal is also turned off. However, since the output of the short-circuit detection signal holding buffer remains latched ON, the status LED 20 continues to be lit. Thus, since the status LED 20 is lit while the I / O power supply 19 is turned off, it is possible to easily identify the location where the short circuit has occurred by checking which one is lit.
[0044]
When the maintenance work is completed at timing (3) (replaced with a normal output device) and the I / O power supply 19 is turned on, steps 4 and 5 are executed, and the short-circuit detection signal holding buffer is turned off. . Accordingly, the status LED 20 is also turned off and returns to a normal state.
[0045]
The above embodiment has been described for the OUT slave to which the output device is connected, but it can of course be applied to a mixed MIX slave to which the input device is also connected.
[0046]
8 and 9 show another embodiment of the present invention. This embodiment is different from the above-described embodiment, and shows an example applied to an output unit constituting a PLC. That is, as is well known, there is a type in which a unit for each function is prepared, and units having necessary functions are connected to form one PLC. In FIG. 8, an output unit 31 for connecting an output device, an input unit 32 for connecting an input device, a CPU unit 33 for executing a user program, and a power supply unit 34 for supplying power for driving each unit to the base 30. Are connected. Each unit is connected by a bus so as to transmit and receive data between units and to receive power supply. Of course, it is not necessary to mount all the illustrated units, and other types of units may be connected.
[0047]
An example of the internal structure of the output unit 31 is shown in FIG. An interface 41 is provided for connecting each unit constituting the PLC to a PLC bus that electrically connects the units. An MPU 43 is connected to the interface 41, and the MPU 43 transmits and receives data to and from other units via the interface 41.
[0048]
Further, the MPU 43 is connected to an 8-bit bus, and transmits and receives data between the two flip-flops 44a and 44c and the one bus buffer 44b via the bus.
[0049]
The MPU 43 has a function of writing OUT data sent from the CPU unit 33 to a predetermined address of the flip-flop 44a. Each output of the flip-flop 44a is given to the base of each transistor 46 'constituting the short circuit detection built-in output circuit 46 through the photocoupler 45a, and the transistor 46' is turned ON / OFF.
[0050]
Further, since an I / O power source 49 is connected to each transistor 46 ', the ON terminal OFF of the transistor 46' connects to the OUT terminal 46 "connected to the transistor 46 'and thus to the OUT terminal 46". The output device 51 turned ON / OFF. Also in this embodiment, a switch 49 ′ is installed in the I / O power supply 49 so that the I / O power supply can be cut off as a whole.
[0051]
Further, an I / O_LED 47 indicating the state of the OUT terminal 46 ″ (contact ON / OFF) is connected to the line for sending the control signal. This I / O_LED 47 lights up when the control signal is ON, The color to be lit is changed by ON / OFF.
[0052]
Furthermore, the output unit 31 is divided into an internal circuit that performs signal processing and the like, and an output circuit that drives and operates the output device 51, and each circuit is driven by a separate power source. That is, the output circuit (transistor 46 ′) is configured to receive power supply from the external I / O power supply 49, and power supply to the internal circuit is given via the PLC bus. Therefore, when the I / O power supply 49 is turned off, the internal circuit is operated although the power supply to the output device 51 is cut off.
[0053]
Further, the transistor 46 'has a short-circuit prevention function, and detects a short circuit of the output device 51 connected to the transistor 46'. When the transistor 46 'is detected, the transistor 46' turns off the contact and outputs a short circuit detection signal.
[0054]
This short-circuit detection signal is given to the bus buffer 44b through the photocoupler 45b and transmitted to the MPU 43 at a predetermined timing. Receiving this short circuit detection signal, the MPU 43 turns on the input terminal of the corresponding flip-flop 44c and lights the status LED 50 connected to the flip-flop 44c. Thereby, it can be easily recognized which output device 51 is short-circuited by checking which status LED 50 is lit.
[0055]
Here, in the present invention, the power supply line from the I / O power supply 49 is branched and supplied to the MPU 43 via the photocoupler 45c so that the state of the I / O power supply 49 can be detected. Then, when the I / O power supply is turned off, the MPU 43 is configured to continue the lighting of the status LED 50 when the short circuit detection signal is output at the time of turning off (immediately before). Specifically, it is realized by incorporating a function for executing the flowchart shown in FIG.
[0056]
Note that the short-circuit detection built-in output circuits 16 and 46 (transistors 16 'and 46') in each of the above-described embodiments output a short-circuit detection signal while detecting a short-circuit as shown in the timing chart of FIG. Although output (ON) continues, it is not always necessary to adopt such a configuration, and a single pulse may be output when a short circuit occurs. That is, in the above-described embodiment, as shown in the flowchart shown in FIG. 6, once the short circuit is detected, the state is latched, and since the short circuit detection is invalidated thereafter, the MPU is notified of the short circuit. In this case, the status LEDs 20 and 50 can continue to be lit even if the short circuit detection signal is not continuously output.
[0057]
Further, in the flowchart shown in FIG. 6, once a short circuit is detected, it is not monitored whether or not a short circuit detection signal is output even when the I / O power supply is ON, and it is estimated that a short circuit is present and short circuit detection is performed. Although the status LEDs 20 and 50 are kept on with the buffer turned on, the present invention is not limited to this, and when the I / O power is on, a short-circuit detection signal is output from the transistors 16 'and 46'. If the I / O power supply is turned off, the previous state (presence / absence of a short circuit detection signal) may be held.
[0058]
In other words, the previous short-circuit detection result is stored, and when the I / O power is turned off, the short-circuit detection signal is received immediately before and the status LEDs 20 and 50 are lit. Even after the power is turned off, it is assumed that the short circuit detection signal is received, and the status LEDs 20 and 50 are operated so as to continue to be lit. In this case as well, the status LEDs 20 and 50 can be turned off by using, for example, a trigger when the I / O power source is switched from OFF to ON.
[0059]
When such a function is incorporated, for example, when maintenance processing is performed without turning off the I / O power supply during maintenance, the short circuit state is resolved without turning off the power supply. In such a case, the status LED can be turned off along with the short circuit elimination.
[0060]
【The invention's effect】
As described above, according to the present invention, even when the power supply for the output device is turned off, the alarm means for specifying the output device (OUT terminal) in which an abnormality such as a short circuit has occurred can be continuously operated. Identification can be facilitated.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conventional example.
FIG. 2 is a diagram showing a schematic configuration of an internal structure of a conventional slave.
FIG. 3 is a diagram showing a specific configuration of the internal structure.
FIG. 4 is a diagram showing a schematic configuration of an internal structure of a slave which is a preferred embodiment of the present invention.
FIG. 5 is a diagram showing a specific configuration of the internal structure.
FIG. 6 is a flowchart showing functions of the MPU.
FIG. 7 is a timing chart for explaining the operation of the MPU.
FIG. 8 is a diagram illustrating an example of a PLC.
FIG. 9 is a diagram showing a specific configuration of an internal structure of an output unit according to a preferred embodiment of the present invention.
[Explanation of symbols]
10 Slave
11 Communication interface
12 Communication Department
13 MPU
14a, 14c flip-flop
14b Bus buffer
15a-15c Photocoupler
16 Short-circuit detection built-in output circuit
16 'transistor
16 "OUT terminal
17 I / O_LED
18 Internal circuit power supply
19 I / O power supply
19 'switch
20 Status LED
25 Output equipment
30 base
31 Output unit
32 input units
33 CPU unit
34 Power supply unit
41 interface
43 MPU
44a, 44c flip-flop
44b Bus buffer
45a-45c Photocoupler
46 Output circuit with short circuit detection
46 'transistor
46 ″ OUT terminal
47 I / O_LED
49 I / O power supply
49 'switch
50 Status LED
51 Output equipment

Claims (1)

A slave output unit that communicates with a master unit having a communication function via a field network,
A communication unit that receives and analyzes a self-addressed frame and message from the master unit, a plurality of output terminals for connecting output devices, and a plurality of output circuits that turn each of the output terminals ON / OFF; Control means for receiving OUT data from the master unit and sending an ON / OFF control signal to a corresponding output circuit; a plurality of alarm means for displaying a short circuit abnormality in the output circuit corresponding to each of the output circuits; With
The internal circuit including the communication unit, the control unit, and the alarm unit and the output circuit are configured to receive power supply for the internal circuit and power supply for the output circuit, respectively, through power supply lines of different systems,
Each of the output circuits has a function of outputting a short circuit detection signal toward the control means when a short circuit abnormality is detected,
When the control means receives a short circuit detection signal from the output circuit, it sends a control signal for turning off the corresponding output circuit, and outputs an operation signal to operate the alarm means corresponding to the output circuit. In addition, the master unit is notified of the occurrence of a short circuit via the field network, and the ON / OFF state of the power supply line for the output circuit is monitored, and the power supply line is switched from ON to OFF. Even if the short circuit detection signal is output immediately before the operation signal to the alarm means is output, the output is continued by supplying power for the internal circuit, and the power supply line is turned from OFF to ON. The slave output unit is characterized in that the output of the operation signal to the alarm means is canceled when the alarm is restored.

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