JP2008107224A - Analog output device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog output device capable of detecting wiring abnormalities and hardware abnormalities in a separated state, accurately acquiring current that flow in external equipment, and executing proper fail-safe processing according to the abnormal state. <P>SOLUTION: This analog output device for supplying output current in a set reference range from a voltage source to the external equipment via an output end is equipped with a return current detection means for detecting the return current that flows in the external equipment, and an abnormality diagnosis means for determining to be abnormal, when the return current value acquired from the return current detection means and led back is out of a prescribed tolerance, relative to the set output voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an analog output device that supplies an output current in a set reference range from a voltage source to an external device via an output terminal.

  FIG. 4 is a functional block diagram showing an example of a system configuration in which a conventional analog output device having a disconnection diagnosis function is duplicated. Regarding an analog output device having a disconnection detection circuit, Patent Document 1 discloses a technical disclosure.

  Reference numeral 1 denotes a host processor, which instructs the analog output device 2 on the operating side to supply an output current I0 in a reference range of 4 to 20 mA from the voltage source VDA to an external device 3 such as a valve of a plant.

  With the external device 3 in common, the right area is the active side (A) and the left area is the standby side (B). On the standby side (B), an analog output device 4 that can supply an output current I0 in a reference range of 4 to 20 mA to the external device 3 from the voltage source VDB is disposed.

  The analog output device on the operating side (A) has a multi-channel configuration, uses a common voltage source VDA, and supplies an output current to another external device (not shown) in response to a command from the processor 1. An analog output device is arranged. For simplicity, one other channel analog output device 5 is shown as a representative.

  On the operating side (A), the output setting value of 4 to 20 mA commanded by the output setting means 11 of the processor 1 is converted into an analog setting value Vi by the D / A converter 21, and the multiplexer 22 for switching other channels is provided. Through the capacitor C and input to the operational amplifier 23. The output of the operational amplifier 23 is connected to the control terminal of the transistor element 24.

  The transistor element 24 operates an output current I0 supplied from the voltage source VDA to the external device 3 connected between the output terminals P1 and P2. A current detection resistor 25 is inserted between the voltage source VDA and the transistor element 24.

  Since the voltage generated at the connection point between the transistor element 24 and the current detection resistor 25 has a value proportional to the output current I0, this is set as the source current value Vs. The operational amplifier 23 receives the source current value Vs and the output set value Vi given from the processor 1, operates the potential of the control terminal of the transistor element 24 based on the deviation, and executes feedback control of Vs = Vi. .

  The source current value Vs is read back to the processor 1 via the multiplexer 26 and the A / D converter 27. The disconnection diagnosis means 12 provided in the processor 1 compares the output set value currently set by the output setting means 11 with the read back source current value Vs, and executes disconnection diagnosis between the output terminals P1 and P2. .

  The shunt switch 28 connected between the output terminals P1 and P2 is operated to be opened by the duplex control signal from the processor 1 if the own apparatus is on the operating side. If the own device is on the standby side, the shunt switch is closed as shown in the analog output device 4 to bypass the output current I0 to the external device 3.

The analog output device 5 of the other channel switches and shares the D / A converter 21 and the A / D converter 27 by the multiplexers 22 and 26, but other components include the same element for each channel. It has a configuration.

JP 2001-034348 A

  In the conventional analog output device that reads back the source current value, the current flowing through the external device is not directly measured. Therefore, the following problems cannot be addressed on the active side and the standby side.

(1) On the operating side, in the case of a multi-channel configuration, if the user performs an erroneous operation to connect the output end of another channel to the output end (hereinafter referred to as inter-channel short-circuit), the output setting value is set to the external device. However, since the output current I0 supplied from the voltage source does not change according to the output set value, this abnormality cannot be determined.

  In addition, when an internal hardware abnormality occurs, the source current value read back is the same as the output setting value even though the current corresponding to the output setting value is not output, and this abnormality cannot be detected.

(2) In the case of a duplex configuration, since the shunt switch of the analog output device on the standby side is closed, no current is output from the standby side to the external device. However, when an abnormality occurs in which the shunt switch is opened on the standby side, current flows from the standby side to the external device.

  As a result, current flows from the active side and the standby side to the external device, and a current different from the output set value flows. In the case of this abnormality, in the conventional configuration, the source current value read back on both the operating side and the standby side is the current value as the output set value, and this abnormality cannot be detected.

  The present invention has been made in order to solve the above-described problems, and separately detects a wiring abnormality and a hardware abnormality, and accurately grasps a current flowing through an external device and appropriately fails depending on the abnormal state. It aims at realization of the analog output device which can perform safe processing.

In order to achieve such a subject, the present invention has the following configuration.
(1) In an analog output device that supplies an output current in a set reference range to an external device from a voltage source via an output end,
Return current detection means for detecting a return current flowing through the external device;
An abnormality diagnosing unit that determines that the return current value acquired and read back from the return current detecting unit is abnormal when the output current that is set is out of a predetermined allowable range;
An analog output device comprising:

(2) The abnormality diagnosing means changes the output current below the lower limit of the reference range when the return current value to be read back is outside the allowable range, and the return current value read back in that state. When the value is equal to or less than the lower limit value, it is determined that the wiring is abnormal. The analog output device according to (1),

(3) The abnormality diagnosing means, when judging that the wiring is abnormal, estimates that either the output terminal is open or the channel is short-circuited to another channel device sharing the voltage source ( The analog output device according to 2).

(4) The abnormality diagnosing means changes the output current below the lower limit value of the reference range when the return current value to be read back is out of the allowable range, and the return current value read back in that state. When the value is equal to or greater than the lower limit value, it is determined that the hardware of the device is abnormal. The analog output device according to (1),

(5) The analog output device according to (4), wherein the abnormality diagnosis means cuts off the voltage supply of the voltage source when it is determined that the hardware of the device is abnormal.

(6) When the self-device is on the standby side in the duplex system configuration, the abnormality diagnosis unit bypasses output current supply to the external device when the return current value to be read back is equal to or greater than a predetermined value. The analog output device according to any one of (1) to (5), wherein it is determined that the shunt switch is abnormal and the voltage supply of the voltage source is cut off.

According to the present invention, the following effects can be expected.
(1) By reading back the return current value, it is possible to accurately detect the current flowing through the external device, and to detect a state different from the output-set current value.

(2) Generally, it is necessary to distinguish between a wiring abnormality and an internal hardware abnormality. According to the present invention, it is possible to clearly distinguish a wiring abnormality (open end of output, short circuit between open channels, etc.) caused by a user's erroneous operation and an abnormality occurring in the hardware.

(3) In the multi-channel configuration, when one channel is abnormal in wiring, the other channels are normal, so that the operation can be continued as it is in consideration of the operation rate.

(4) In a redundant system configuration, when a hardware error occurs, the redundant system is switched to the standby side, and in the case of a wiring error caused by the user, such as a short circuit between channels, switching to the redundant system may not be executed. it can.

(5) Since it is possible to detect the abnormal current in the above item (1) and to identify the abnormal state in the above item (2), it is possible to perform a fail-safe operation corresponding to the abnormal state, and there is a risk to external equipment. Can be avoided reliably.

(6) Similarly, in the duplex system, it is possible to detect a hardware failure of the standby shunt switch, and to perform a fail-safe operation according to the hardware failure, thereby reliably avoiding risks to external devices.

  The present invention will be described in detail below with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of an analog output device to which the present invention is applied. The same elements as those of the conventional apparatus described with reference to FIG.

  The characteristic part of the present invention added to the conventional apparatus is that the return current detection means 100 inserted in series in the return current circuit of the external device 3 and the return current value acquired from the return current detection means 100 is read to the processor 1. These are the multiplexer 200 and the A / D converter 300 that perform back-up, the cut-off switch 400 that interrupts voltage supply from the voltage source, and the abnormality diagnosis unit 500 that is provided in the processor 1.

  In this embodiment, the connection of the multiplexer 26 and the A / D converter 27 for reading back the source current value Vs to the processor 1 provided in the conventional apparatus of FIG. 4 is omitted. An embodiment in which the source current value Vs is read back to the processor 1 will be described with reference to FIG.

  The return current detection means 100 is realized by a resistor r, one end is connected to the return side P2 of the output end, and the other end is connected to the ground potential together with one end of the shunt switch 28. A voltage Vr generated with respect to the ground potential by the return current Ir flowing through the resistor r is a return current value read back to the processor 1.

  The multiplexer 200 switches and acquires the return current value from the analog output device 5 of the other channel, and reads back the return current value of each channel to the processor 1 via the A / D converter 300 that is used in common.

  The cut-off switch 400 is forcibly controlled to be turned off when receiving a hardware abnormality notification from the abnormality diagnosis unit 500, and cuts off the voltage supply from the voltage source VDA.

  The abnormality diagnosing unit 500 includes an abnormality diagnosing unit 501, a return current value read back unit 502, and an output changing unit 503 that changes the set value of the output current to a predetermined value, and has a function of separately reporting a wiring abnormality and a hardware abnormality. Prepare.

  Next, the operation when the analog output device 2 is on the operating side (A) will be described. The abnormality diagnosis unit 501 of the abnormality diagnosis unit 500 inputs the return current value Vr read back to the return current value read back unit 502 and constantly monitors it.

  The return current value Vr is compared with the set value of the output current set by the output setting means 11 to determine whether it is within a predetermined allowable range. It is determined that a current other than the output current flows and is abnormal.

  If the abnormality diagnosing means 501 determines that there is an abnormality, it instructs the output changing means 503 to change the set value of the output current to a predetermined value below the lower limit value 4 mA of the reference range, for example 1.25 mA, The output current I0 flowing through the device 3 is changed.

  If the return current value Vr read back in this changed state is equal to or lower than the lower limit 4 mA of the reference range, the abnormality diagnosis unit 501 determines that there is a wiring abnormality such as an output end open or a short circuit between channels.

  If the return current value Vr read back in this changed state is equal to or higher than the lower limit value 4 mA of the reference range, the abnormality diagnosis unit 501 determines that there is a hardware abnormality. If the hardware is abnormal, it is possible that the output current cannot be output according to the set value. Therefore, turning off the cut-off switch 400 completely cuts off the output current and executes fail-safe processing. To do.

  When two channels are short-circuited, an abnormality is detected in both of them. Since there is no internal failure, it is possible to change the output current. Further, depending on the wiring conditions of the external devices, both output currents may flow into one channel. Therefore, when an abnormality is detected and 1.25 mA is set, the maximum value of the flowing output current is 2.5 mA.

  Also, the reason why 4 mA is used as a reference value for changing the set value is that the driving range of an external device such as a valve generally used at the operation end of a plant is 4 mA to 20 mA. There is a history of thinking that is in an off state, that is, a safe direction.

  In the case of a duplex system, it is necessary to switch the duplex system under certain conditions. On the other hand, in the case of a wiring abnormality caused by a user such as a short circuit between channels, there is a request not to switch the duplex system.

  According to the present invention, the wiring abnormality and the hardware abnormality are reliably separated. When it is determined that the hardware is abnormal in the abnormality determination, a request for duplex switching is generated, the operation side becomes the standby side, the shunt switch 28 is switched from OFF to ON, and the standby side becomes the operation side. The shunt switch 28B is reliably switched from on to off.

  Next, the operation when the analog output device is on the standby side (B) will be described. On the standby side of the duplex system, the shunt switch 28B is normally turned on and the output current I0 is bypassed to the inside so that no output current flows through the external device 3.

  Therefore, in a normal state, no current flows through the resistor r of the return current detecting means 100, and the read back return current value Vr is 0 mA. When an abnormality occurs in which the shunt switch 28B is turned off on the standby side, the output current I0 set on the standby side flows through the external device 3. Accordingly, at this time, a current obtained by adding the set current values of both the operating side and the standby side flows to the external device 3.

  When the value obtained by reading back the return current value Vr is not 0 mA in the abnormality diagnosis unit 500, it is determined that a current value other than the set current flows through the output terminal or the external device 3 and is abnormal. In this case, it is determined that the hardware of the shunt switch 28B is abnormal, and the fail-safe process for completely shutting off the output is performed by turning off the cut-off switch 400B.

  FIG. 2 is a functional block diagram showing another embodiment of the present invention. The feature of this embodiment is that the function of the abnormality diagnosis unit 500 realized by the software function provided in the processor 1 in the embodiment of FIG. 1 is realized by hardware.

  Considering the case where a current other than the set output current flows through the external device 3, the return current value Vr read back from the return current detecting means 100 and the set value Vi of the output current held in the capacitor C are considered. Is detected by a comparator 601 having an appropriate hysteresis characteristic.

  At this time, the output change switch 700 is operated to switch the set value to the 1.25 mA side, and the output current passed through the external device 3 is set to 1.25 mA. The return current value Vr and the set value of 4 mA at this time are compared and diagnosed by a comparator 602 having appropriate hysteresis characteristics.

  When the return current value Vr is 4 mA or less, it is determined that the wiring is abnormal (output terminal open, short between channels, etc.). Therefore, the wiring abnormality is detected by the AND circuit 801 that inputs the output of the comparator 601 and the inverted output of the comparator 602. 1 is notified.

  When the return current value Vr is 4 mA or more, it is determined that the hardware is abnormal. Therefore, the hardware abnormality is notified to the processor 1 from the AND circuit 802 that inputs the output of the comparator 601 and the output of the comparator 602. In this case, Since the current flowing through the external device 3 cannot be controlled, the cut-off switch 400 is turned off and the voltage source VDA is shut off to prevent overcurrent to the external device.

  FIG. 3 is a functional block diagram showing still another embodiment of the present invention. A feature of this embodiment is that, in addition to the embodiment of FIG. 1, a multiplexer 26 and an A / D converter 27 for reading back the source current value Vs to the processor 1 provided in the conventional apparatus of FIG. It is in the structure which connected.

  The source current value Vs passed from the A / D converter 27 is acquired by the source current value readback means 900 provided in the processor 1 and passed to the abnormality diagnosis means 501. Hereinafter, an example of diagnosis by Vs readback of the source current value will be described.

Normally, the voltage (V1) of the output terminal P1 is calculated from the output current Iz, the load resistance value Z, and the resistance r.
V1 = (Z + r) × Iz
For example, if the output current Iz = 20 [mA] and Z + r = 500 [Ω], 10 [V] is calculated.

  However, when a load having a large impedance is connected between the terminals P1 and P2, the voltage value V1 is determined by the voltage of the voltage source VDA (referred to as Vda), the operating voltage of the resistor R, and the operating voltage of the transistor element. Let me limit. At this time, the output current Iz does not flow as an output-set current, but a current Iz according to the voltage value V1 flows.

When a large load is connected to the output terminal, V1 is calculated from the following equation.
V1 = Vda-{(operating voltage of resistor R) + (operating voltage of transistor element)}
The current value Iz is calculated from the following equation.
Iz = V1 / (Z + r)
For example, if Z + r = 1000 [Ω] and V1 = 18 [V], the current value Iz is calculated as 18 [mA], and a current value lower than the set current flows.
At this time, the source current value Vs and the return current value Vr corresponding to 18 [mA] are read.
That is, when a large load is connected to the output terminal, the output current becomes low, and both the source current value Vs and the return current value Vr become abnormal.

  In this state, if the setting of the output current is changed to 1.25 mA, the output current is also changed to 1.25 mA, and since it becomes 4 mA or less, it can be determined that the wiring is abnormal.

  Further, when an abnormality occurs in the current conversion circuit unit, a hardware-like fixing failure is conceivable. In this case, both the source current value Vs and the return current value Vr become abnormal. In this state, even if the output setting is changed to 1.25 mA, the output is not changed due to the fixing failure, and becomes 4 mA or more. At this time, it is determined that the hardware is abnormal, and the cut-off switch 400 is restricted to off. The diagnostic functions in this embodiment are summarized as shown in Table 1.

  When an abnormality occurs, it is possible to isolate each abnormal state according to the source current value state, return current value state, and return current value state after output change, and it has a highly reliable diagnostic function. An analog output device can be configured.

  In the embodiment described above, the valve used at the operation end of the plant is exemplified as the external device 3, but the present invention is not limited to this, and the present invention can be applied to a device driven by a current signal in general. .

It is a functional block diagram which shows embodiment of the system which duplexed the analog output device to which this invention is applied. It is a functional block diagram which shows other embodiment of this invention. It is a functional block diagram which shows other embodiment of this invention. It is a functional block diagram which shows the system configuration example which duplicated the conventional analog output device with a disconnection diagnostic function.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processor 11 Output setting means 2 Operation side analog output device 21 D / A converter 22 Multiplexer 23 Operational amplifier 24 Transistor element 25 Current detection resistor 26 Multiplexer 27 A / D converter 28 Shunt switch 3 External device 4 Standby side analog output device 5 Other channel analog output device 100 Return current detection means 200 Multiplexer 300 A / D converter 400 Cut-off switch 500 Abnormality diagnosis unit 501 Abnormality diagnosis means 502 Return current readback means 503 Output change means

Claims (6)

In the analog output device that supplies the output current of the set reference range to the external device from the voltage source via the output end,
Return current detection means for detecting a return current flowing through the external device;
An abnormality diagnosing unit that determines that the return current value acquired and read back from the return current detecting unit is abnormal when the output current that is set is out of a predetermined allowable range;
An analog output device comprising:   The abnormality diagnosing means changes the output current below the lower limit value of the reference range when the return current value to be read back is outside the allowable range, and the return current value read back in that state is the lower limit value. The analog output device according to claim 1, wherein if it is less than the value, it is determined that the wiring is abnormal.   3. The abnormality diagnosis unit according to claim 2, wherein when it is determined that the wiring is abnormal, the abnormality diagnosis unit estimates that either the output terminal is open or the channel is short-circuited to another channel device sharing the voltage source. The analog output device described.   The abnormality diagnosing means changes the output current below the lower limit value of the reference range when the return current value to be read back is outside the allowable range, and the return current value read back in that state is the lower limit value. The analog output device according to claim 1, wherein if the value is equal to or greater than the value, it is determined that the hardware of the device is abnormal.   5. The analog output device according to claim 4, wherein the abnormality diagnosis unit cuts off the voltage supply of the voltage source when it is determined that the hardware of the device is abnormal.   In a duplex system configuration, when the self-device is on the standby side, the abnormality diagnosis unit bypasses output current supply to the external device when the return current value to be read back is equal to or greater than a predetermined value. 6. The analog output device according to claim 1, wherein the voltage output of the voltage source is cut off and the analog output device is cut off.

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