JP2000298515A - On-line diagnostic method and device for fail-safe switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the on-line diagnosis of a fail-safe switch for normally interrupting current supply by a 'emergency stop' or 'fail-safe' command through a conductive field effect transistor(FET) or the like. SOLUTION: An on-line diagnostic device for a fail-safe switch (FET) 10 for supplying current normally from an AC power supply 2 to an equipment 7 and interrupting current supply to the equipment 7 when an 'emergency stop' or 'fail-safe' control command is outputted from a controller or the like is provided with a detection circuit 20 for detecting the load current of the equipment 7, a diagnostic timing generation circuit 30 for generating a diagnostic pulse for controlling the FET 10 to an off state at timing for outputting '1' when a detection value V (converted into a voltage value) from the circuit 20 exceeds a prescribed reference (Ref) and a judgment circuit 44 for comparing a held detection value Vhold held at the timing and a detection value V detected immediately after the value Vhold, and when Vhold >= V, judging the off of the FET 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch for performing "emergency stop" and "fail safe" of an operating device such as an operating end of a plant (hereinafter, collectively referred to as a fail safe switch). FET (Field Efec
The present invention relates to online failure diagnosis of a fail-safe switch using a semiconductor device such as a transistor (t Transistor).

[0002]

2. Description of the Related Art In a system or a system in which a plurality of devices such as a plant are operated in a coordinated manner, in order to prevent the spread of accidents caused by abnormalities, "emergency stop" and "fail-safe" are performed on related devices according to predetermined logic. A fail-safe switch for performing the operation is provided. For example, the FET element connected between the power supply and the device is normally used in a conductive state (on state), and when abnormal, the device is turned off by a control command to disconnect the device from the power supply.

[0003]

It is necessary to check on a daily basis whether a fail-safe switch that is always on and emergency-off can be correctly turned off in an abnormal situation. Conventionally, inspections were performed manually during off-line such as regular inspections.

[0004] However, in the offline inspection, when the inspection cycle of the plant becomes long, a problem occurs in the soundness of the switch. In addition, when the operation end and the switch are separated,
Inspection work may be performed by a plurality of people.

SUMMARY OF THE INVENTION An object of the present invention is to provide a failure diagnosis method and apparatus capable of overcoming the above-mentioned problems of the prior art and automatically performing online inspection of a fail-safe switch.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a switch which constantly supplies power to an apparatus from an AC power supply and cuts off the power to the apparatus by an "emergency stop" or "fail safe" command. In an on-line diagnostic method (hereinafter referred to as a fail-safe switch), the switch that is energizing the device is controlled to transition from an on state to an off state for a predetermined time, and a normal change (sine) of the AC power supply is performed. (Wave) before the control (on state) in response to the change in the detected value of the load current or the load voltage during the control (off state) whether or not the detection value is changed to determine the soundness of the switch. Features.

[0007] The predetermined short time is a required time determined from the on / off response characteristics of the switch, starting from when the detected value increases from zero to a reference value (Reff) smaller than the maximum value. For example, a response time of several microseconds is sufficient for FET response characteristics. The predetermined time is set to a range that does not affect the load operation.

An on-line diagnostic device for a fail-safe switch realizing the method of the present invention comprises a detecting means for detecting a load current or a load voltage of the device, and a detecting value from the detecting means when a diagnostic command is on. A predetermined reference value (Re
ff) The diagnostic signal generating means for generating a diagnostic signal for controlling the switch to be in the OFF state at a timing exceeding, and comparing the hold detection value held at the timing with the immediately following detection value. And determining means for determining that the state has shifted to the off state.

Further, there is provided a diagnostic command issuing means for issuing the diagnostic command by ANDing the diagnostic command information issued manually or by software with the detection information of the zero cross point where the detected value changes from negative to positive. It is characterized by.

[0010] The invention is characterized in that the online diagnostic device is attached to a process input / output device or the device.

The operation of the present invention will be described. The present invention is based on the fact that a detected value of a load current or a load voltage of a device that is energized from an AC power supply via a fail-safe switch causes a change different from an on-state sine wave when the switch is turned off. Use.

When an FET is used for a fail-safe switch, its response characteristic is as fast as several nanoseconds. On the other hand, the relationship between the electromagnetic force F, the voltage V, and the current I required to move a device (for example, a solenoid valve) connected as a load is expressed by the following equation (1).
It is represented by

[0013]

F = K × I = 1 / L∫ΔVdt I = 1 / L ・ Vdt Therefore, a change in the load current (voltage) in a very short time depends on the electromagnetic force for opening or closing the solenoid valve. Does not affect F. That is, the on / off operation of the FET is performed in a few nanoseconds to a few microseconds, while the electromagnetic force F of the device does not malfunction even when the power is cut off for several tens of milliseconds to several seconds. If this characteristic difference is used, the FET can be turned off instantaneously, and its soundness can be confirmed from the behavior of the change in the load current (voltage).

According to the present invention, the on-line diagnosis of the fail-safe switch is made possible, so that a highly reliable health check can be performed with a short inspection cycle, and the occurrence and expansion of an accident due to a switch closing failure can be prevented. In addition, the inspection is easy, and the working time can be greatly reduced.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows a schematic configuration of a plant control device as an application example of the diagnostic device of the present invention. The computer 2 for monitoring and controlling the entire system and a plurality of control controllers 3 are connected via a network, and are arranged in a computer room or the like. Each controller 3 has a process input / output device (PI /
O) The operation terminal (equipment) 7 at the site is controlled via 4 or the device net 5. FET10 is used as a fail-safe switch for "emergency stop" and "fail-safe".
And is always connected between the AC power supply 6 and the device 7 in a conductive state. An object of the present invention is an FET diagnostic circuit 1 for checking the health of the state transition of the FET 10 online.

FIG. 1 is a configuration diagram of an FET diagnostic apparatus according to one embodiment. In the present embodiment, the FET 10 serving as a “fail-safe switch” of the solenoid valve 7 at the operation end is connected to the diagnostic circuit 1.
Together with PI / O4. The drain D of the FET 10 is connected to the power supply 2, the source S is connected to the solenoid valve 7,
The gate G is connected to the drive circuit 11 through the switch control circuit 12.
It is connected to the.

The drive circuit 11 generates a control signal for turning on / off the FET 10. For example, a junction type FET 10
Is used as an analog switch, the gate G is set to 0
V (or floating) to turn on (conduction state). Further, a voltage Vgs higher than the pinch-off voltage Vp is applied to the gate G to turn off the gate G. Therefore,
The drive circuit 11 generates Vgs, and normally opens IN-OUT of the switch control circuit 12 to turn on the FET 10. On the other hand, when an emergency stop or fail-safe control command is applied to the control terminal 121 from the controller 3,
By closing the area between N and OUT, the FET 10 is turned off and the power supply to the solenoid valve 7 is cut off. Further, in the present embodiment, a test terminal 122 is provided in the switch control circuit 12 to close a section between IN and OUT by application of a diagnostic pulse described later,
To the off state.

The diagnosis circuit 1 includes a detection circuit 20 for detecting a load current supplied from the AC power supply 2 to the solenoid valve 7, a diagnosis timing generation circuit 30 for generating a diagnosis pulse at a timing based on the detected value, and a diagnosis result. A determination circuit 40 for determining and outputting is provided. The current detection circuit 20 includes a CT 21 for detecting a load current and a voltage detection circuit 22 for converting the detected current into a voltage.

The diagnostic timing generation circuit 30 compares the detected voltage V with a reference value Vreff (for example, 10 V), and
a comparison circuit 34 that outputs “1” at reff and outputs “0” at V <Vreff, and an AND circuit that performs an AND operation on the 1/0 output of the comparison circuit 34 and the 1/0 output of the diagnostic command output circuit 33 35, and a diagnostic pulse generation circuit 36 that generates a diagnostic pulse based on the "1" output of the AND circuit 35.

The diagnostic command output circuit 33 is operated manually or by software for at least one cycle of the power supply.
The diagnostic instruction information 31 that outputs “1” and the information from the zero-cross detection circuit 32 that detects the zero-cross point (t0) at which the detection voltage V (load current I) becomes negative to positive and outputs “1” are input. The logic "1" is output during the period from t0 to T1 when the AND of both information is established.

The judgment circuit 40 receives the detection voltage V, and holds a detection value (= Vreff) at the timing of the diagnosis pulse. The judgment circuit 40 compares the output value of the hold circuit 41 with the detection voltage V, and Vreff ≧ V , A flip-flop 43 that latches the output “1” of the comparison circuit 42 at the falling edge of the diagnostic pulse, and a display (eg, LED) 4 that displays the latched output “1”.
Consists of four.

Next, the operation of the diagnostic apparatus will be described. FIG.
5 is a time chart showing signal changes at various parts of the FET diagnostic device. a is a waveform of the detection voltage V obtained by converting the load current I, which is usually the same as the sine wave (50/60 Hz, cycle 20 ms) of the AC power supply 2.

B is diagnosis command information 31, c is detection information of the negative voltage ⇒ positive zero cross point t0 of the detection voltage V, and d is the comparison circuit 3
With the output of 4, the detection voltage V becomes "1" from time t1 when it reaches the reference value Vref (10v). The zero-cross detection information b starts at time t0 and includes time t1, and is output as a signal width T1 slightly longer than that.

When the three AND conditions of the diagnosis command b, the zero-cross detection information c, and the output d of the comparison circuit 34 are satisfied,
The diagnostic pulse e is output at a timing slightly delayed from t1. The pulse width of the diagnostic pulse e is necessary for the state transition of the FET 10 and does not affect the operation of the solenoid valve 7, and is about several μs to 1 ms. This diagnostic pulse e
Is input to the test terminal 121 of the control circuit 12, the turn-off signal f from the drive circuit 11 is applied to the gate G. If the FET 10 is normal, the FET state g transitions from the ON state to the OFF state during the period T2. When the diagnostic pulse e disappears, the FET state g is restored from the off state to the on state.

Since the diagnostic pulse e is also applied to the HOLD terminal, the hold circuit 41 sets the detected voltage (approximately Vreff) at that timing as the hold output h and compares the detected voltage with the hold circuit h.
2 + input. On the other hand, when the energization of the solenoid valve 7 is cut off due to the OFF state of the FET 10, the detection voltage V of the negative input of the comparison circuit 42 drops sharply. At t2, which is slightly after t1, Vref ≧ V, and the detected V drop information i Is output. The drop information i from the comparison circuit 42 lasts for approximately T2 from t2 to t4 and is input to the F / F circuit 43. Also, F
The fall of the diagnostic pulse e is applied to the LATCH end of the / F circuit 43. At the timing t3 (before t4), the fall information i is latched and the FET off detection information j is output to the display 44. In other words, the generation of the diagnostic pulse e
It can be confirmed from the display (lighting) of the indicator 44 that the device 10 has normally transitioned to the off state.

The output d of the comparison circuit 34 is an FET
Returns to the ON state, it starts outputting "1" again.
However, since the zero-crossing point that changes from negative to positive does not appear until the next power supply cycle, the diagnostic pulse e is not issued. If the diagnostic command b is maintained for several cycles, the normal diagnostic operation described above is repeated, so that the display 44 can be blinked.

Further, there is no fear of erroneous detection even when the FET under diagnosis has a closed fault. That is, if the diagnostic pulse e is applied at the timing t1 and the FET does not transition to the off state, the detection voltage V changes according to the load current I. During this time, since the hold circuit 41 holds Vreff at the timing t1, the detection voltage V becomes Vref⇒Vmax⇒Vref
During this period, the output of the comparison circuit 42 is "0". Also, F /
F43 is latched at the falling edge (t3) of the diagnostic pulse e. As a result, erroneous output of "1" to the display 44 can be prevented twice.

As described above, according to the FET diagnostic apparatus of the present embodiment, the diagnosis of the transition to the OFF state with respect to the FET that is always in the ON state can be performed online.
It is possible to confirm the soundness of T, and it is possible to reliably prevent the occurrence and expansion of a plant accident due to the failure of the FET. In addition, the inspection work can be performed simply and in a short time because only the instruction for the inspection and the confirmation of the display are performed. Furthermore, since the erroneous detection at the time of diagnosis is double prevented, the reliability of the diagnosis result is high.

It should be noted that the diagnostic circuit 1 of the present embodiment has a PI / O4
However, as shown in a part of FIG. 2, it may be configured to be attached to the device 7 at the operation end. The input of the diagnostic command information 31 and the display of the diagnostic result may be performed by the input / output device of the computer 2.

Next, another embodiment of the present invention will be described. FIG. 4 is a configuration diagram of an FET diagnostic apparatus according to another embodiment, and the same parts as those in FIG. 1 are denoted by the same reference numerals. The difference from the above embodiment is that the diagnostic circuit 1 is attached to the device (electromagnetic valve) 7 and a voltage detecting circuit 25 is provided instead of the current detecting circuit 20.

As shown in FIG. 4, the voltage (load voltage) across the coil 71 for generating the electromagnetic force F of the solenoid valve 7 is set to PT26.
And amplified by the AMP 27 to obtain the same detection voltage V as in FIG. The subsequent diagnostic operation is the same as the method described with reference to FIGS.

The diagnostic method and the diagnostic device of the fail-safe switch according to the present invention have been described through two embodiments.
In the above embodiment, the FET is used for the fail-safe switch, but the present invention is not limited to this. Widely applicable if it is an electronic switch element that has low on-resistance, high off-resistance, and has bidirectionality regardless of the polarity of the power supply waveform (mechanical contacts such as reed relays have a problem in response speed). It is possible.

[0033]

According to the present invention, a fail-safe switch, which is attached to a device such as a control terminal of a plant and performs an emergency stop or a fail-safe operation, is controlled so as to transition from an always-on state to an instantly-off state. The detected value of the load current or the load voltage supplied from the AC power supply via the switch in the (ON state) changes from a peculiar change (change different from a normal power supply change) occurring during the control (OFF state). Since the normal off operation of the switch is confirmed, the health of the switch can be diagnosed online. As a result, the diagnostic cycle can be significantly shortened, so that the reliability of the switch is significantly improved, and the occurrence of an accident due to a switch failure can be avoided. In addition, the inspection work is simple and requires no human labor.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an FET online diagnostic device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a plant control device to which the present invention is applied.

FIG. 3 is a time chart showing an operation of the online diagnostic device of FIG. 1;

FIG. 4 is a configuration diagram of an FET online diagnostic device according to another embodiment of the present invention.

[Description of Signs] 1 ... FET diagnostic circuit, 3 ... controller, 4 ... process input / output device (PI / O), 7 ... solenoid valve (equipment), 71 ...
Coil, 10 ... FET, 11 ... Drive circuit, 12 ... Switch control circuit, 20 ... Current detection circuit, 21 ... CT, 22 ...
Voltage detection circuit, 25: voltage detection circuit, 26: PT, 30
... diagnosis timing generation circuit, 31 ... diagnosis instruction information, 32
... Zero cross detection circuit, 33 ... Diagnostic command output circuit, 34
... Comparison circuit, 35 AND circuit, 36 diagnostic pulse generation circuit, 40 judgment circuit, 41 hold circuit, 42 comparison circuit, 43 flip-flop (F / F), 44 display device (LED).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisao Nagayama 5-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Process Computer Engineering Co., Ltd. (72) Inventor Sota Kumomoto 5-chome, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Hitachi Process Computer Engineering Co., Ltd. (72) Inventor Kuniyuki Inari 5-2-1 Omikacho, Hitachi City, Ibaraki Prefecture Inside the Omika Plant of Hitachi, Ltd. (72) Inventor Shuichi Nakamichi Hitachi City, Ibaraki Prefecture 5-2-1, Omikacho F-term (reference) in Hitachi Process Computer Engineering, Ltd. 5H209 AA01 BB01 CC07 DD05 EE06 GG14 HH22 5H223 AA01 BB01 CC09 EE24 FF08 5J055 AX38 AX52 AX68 BX05 CX08 CX21 DX12 DX61 EZ10 EZ25 GX02 GX04 GX05

Claims (6)

[Claims] An on-line diagnostic method for a switch (hereinafter, referred to as a fail-safe switch) that constantly supplies power to an apparatus from an AC power supply and cuts off the supply of power to the apparatus according to an “emergency stop” or “fail-safe” command. In the above, the switch that is energizing the device is controlled so as to transition from an on state to an off state for a predetermined time, and the load current or load voltage before control (on state) according to a normal change of the AC power supply is controlled. An on-line diagnostic method for a fail-safe switch, comprising: detecting whether a detected value undergoes a singular change during control (off state) to determine the soundness of the switch. 2. The fail-safe switch according to claim 1, wherein the predetermined time is a required time determined from a response characteristic of the switch based on a time when the detected value increases from zero to a reference value less than a maximum value. Online diagnostic method. 3. The online diagnosis method for a fail-safe switch according to claim 2, wherein the specific change in the detected value is a decrease from the reference value. 4. An on-line diagnostic device for a switch (hereinafter, referred to as a fail-safe switch) that normally supplies power to the device from an AC power supply and cuts off the power to the device according to a command of “emergency stop” or “fail safe”. A detecting means for detecting a load current or a load voltage of the device, and when the diagnostic command is on, the switch is turned off at a timing when a detection value from the detecting means exceeds a predetermined reference value (Reff). Diagnostic signal generating means for generating a diagnostic signal to be controlled, and determining means for comparing the hold detection value held at the timing with the immediately following detection value, and determining that the switch has transitioned to the off state if the former is greater than the other. An on-line diagnostic device for a fail-safe switch. 5. The diagnostic instruction according to claim 4, wherein the diagnostic instruction is issued by ANDing the diagnostic instruction information issued manually or by software and the zero-cross point detection information at which the detected value changes from negative to positive. An on-line diagnostic device for a fail-safe switch, comprising issuing means. 6. The online diagnostic device for a fail-safe switch according to claim 4, wherein the online diagnostic device is attached to a process input / output device or the device.