JP2008107170A - Analog output device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog output device with external interference diagnostic functions in addition to impedance diagnostic functions. <P>SOLUTION: The analog output device with the impedance diagnostic means for diagnosing the short circuit or the open circuit by reading back the terminal voltage of the output terminal and the current value of the output current, while supplying the prescribed current to the external equipment via the output terminal from the voltage source. The analog output device includes a return current detecting resistor inserted into the return current circuit in series from the external equipment to the voltage source, and an external interference diagnostic means for detecting the interference current flowing the voltage source via the external circuit from the output terminal to the voltage source. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  According to the present invention, a predetermined output current is supplied from a voltage source to an external device via an output terminal, and a terminal voltage value of the output terminal and a current value of the output current are read back to diagnose short circuit or open of the output terminal. The present invention relates to an analog output device provided with impedance diagnosis means.

  Patent Document 1 discloses an impedance diagnosis unit that reads back a terminal voltage value of an output terminal and a current value of an output current and diagnoses a short circuit or an open of the output terminal in an analog output device.

  FIG. 7 is a functional block diagram showing a configuration example of a conventional analog output device having an impedance diagnosis function. The host processor 1 includes an impedance diagnosis unit 11 and outputs a signal for setting an output current I0 to be supplied to the external device 3 to the current output module 2.

  The current output module 2 supplies an output current I0 from the voltage source 21 to the external device 3 connected between the output terminals 24 and 25 through the constant current circuit 22 and the sneak prevention diode 23 in the duplex system. The constant current circuit 22 controls the output current I0 based on the setting signal passed from the processor 1.

  The arithmetic unit 26 digitally outputs the output value of the output current I0 given as a digital value from the constant current circuit 22 and the terminal voltage value V0 periodically acquired via the terminal voltage value read-back switch 27 by the A / D converter 28. The converted terminal voltage value is acquired and passed to the impedance diagnosis means 11 of the processor 1 as a read back signal.

  The impedance diagnosis unit 11 diagnoses a short circuit failure and an open failure between the output terminals 24 and 25. When the read-back signal of the output current I0 matches the setting signal and is in a normal state, a short-circuit fault is diagnosed if the read-back signal of the terminal voltage value V0 is 0 V, and an open fault if the read-back signal of the output current I0 is zero Diagnose.

JP 2001-034348 A

  In the conventional impedance diagnosing means 11 for diagnosing a short-circuit failure and an open-circuit failure between the output terminals, a part of the output current flows to the output terminal side of another channel that supplies the output current to other external devices using the voltage source 21 in common. The so-called channel short circuit failure cannot be diagnosed.

  FIG. 8 is a functional block diagram showing a configuration example of a two-channel current output module sharing a voltage source. The voltage source 21 of the current module 2 that constitutes the first channel CH1 is shared, and the current module 4 that constitutes the second channel CH2 is connected to the external device 5 based on the setting signal from the processor 1. An output current is supplied through 44 and 45.

  In a normal state, it is assumed that 20 mA is supplied from the current output module 2 of the first channel CH1 to the external device 3, and 4 mA is supplied from the current output module 4 of the second channel CH2 to the external device 5.

  FIG. 9 is a functional block diagram for explaining an interference current path at the time of a short circuit failure between channels. In the figure, the output terminal 24 of the current output module 2 of the first channel and the output terminal 44 of the current output module 4 of the second channel are shown in a channel-to-channel short circuit state that is erroneously connected by the user.

  Due to this short circuit between channels, an interference current of 8 mA flows from the output terminal 24 to the output terminal 44, so the output current of 20 mA supplied to the external device 3 is reduced to 12 mA and 4 mA supplied to the external device 5. Output current increases to 12 mA.

  However, since the constant current circuits of the current output module 2 and the current output module 4 output 20 mA and 4 mA according to the setting signal of the processor 1, even if the current values of these output currents are read back, the external current due to the short circuit between the channels Interference cannot be diagnosed.

  The present invention has been made to solve the above-described problems, and aims to realize an analog output device having an external interference diagnosis function in addition to an impedance diagnosis function.

In order to achieve such a subject, the present invention has the following configuration.
(1) A predetermined output current is supplied from a voltage source to an external device via an output terminal, and a terminal voltage value of the output terminal and a current value of the output current are read back to diagnose short-circuiting or opening of the output terminal. In an analog output device having an impedance diagnosis means,
A return current detection resistor inserted in series in a return current circuit from the external device to the voltage source;
Read back the return voltage value generated in the return current detection resistor, external interference diagnostic means for detecting the interference current flowing from the output terminal to the voltage source via the external circuit, and
An analog output device comprising:

(2) The external interference diagnostic means detects an interference current flowing from the output terminal to the output terminal side of another channel that supplies the output current to another external device using the voltage source in common ( The analog output device according to 1).

(3) The analog output device according to (1) or (2), further comprising switch means for periodically switching and reading back the terminal voltage value and the return voltage value.

(4) The analog output device according to any one of (1) to (3), wherein the impedance diagnosis unit reads back a difference voltage between the output terminals.

(5) The analog output device according to any one of (1) to (4), wherein a diode for preventing wraparound is inserted into the return current detection resistor in a series forward direction.

(6) The analog output according to any one of (3) to (5), further comprising anti-turn-in means for forcibly turning off the circuit of the switch means when the voltage source is off. apparatus.

According to the present invention, the following effects can be expected.
(1) By reading the return current value flowing through the external device, it is possible to diagnose external interference due to a short circuit failure between channels, etc., which can contribute to improving the reliability of the analog output device in combination with the impedance diagnostic function provided conventionally.

(2) The return current value can be detected and read back with a simple resistor and a switch, and a high-performance analog output device can be realized without increasing the cost of the device.

  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.

  A feature of the present invention added to the configuration of the conventional apparatus is that a return current detection resistor 100 inserted in series in the return current circuit of the external device 3 and a return current generated in the return current detection resistor 100 by the return current Ir. A return current value read-back switch 200 that periodically passes the value Vr to the A / D converter 28 and an external interference diagnosis means 300 provided in the processor 1.

  The terminal voltage value read-back switch 27 that periodically acquires the terminal voltage value V0 and passes it to the A / D converter 28 and the return current value Vr generated in the return current detection resistor 100 are periodically acquired and A / D converted. Return current value read-back switches 200 to be passed to the device 28 are reversibly turned on and off.

  The A / D converter 28 alternately inputs the terminal voltage value V0 and the return current value Vr by these read back switches, converts the values into digital values, and passes them to the arithmetic unit 26. The arithmetic unit 26 passes the read signal of the return current value Vr to the processor 1 in addition to the output value of the output current I0 and the terminal voltage value V0.

  The external interference diagnosis means 300 provided in the processor 1 compares the output value of the output current I0 read back and the return current value Vr. If they match, the external interference diagnosis means 300 determines that “no external interference current” is normal and returns. If the current value is less than or equal to the output value of the output current I0, it is determined that there is an “external interference current” abnormality.

  With the added external interference diagnostic means 300, the device of the present invention has both an impedance diagnostic function for monitoring its own output terminal state and an external interference diagnostic function for monitoring external interference current. Impedance diagnosis is performed only when the output value of the current I0 matches the return current value (no external interference current), and in the case of a mismatch (with external interference current), priority is given to measures such as a short circuit between channels. So take an operation that does not perform impedance diagnosis.

  FIG. 2 is a functional block diagram showing another embodiment of the analog output device to which the present invention is applied. The difference from the embodiment of FIG. 1 is that a difference calculator 29 is inputted to input the potential of the output terminal 24 and the potential of the output terminal 25 and calculate the difference between them, and the calculated difference value is passed to the switch 27. is there.

  Due to the voltage drop due to the return current Ir flowing through the return current detection resistor 100 inserted in series in the return current circuit of the external device 3, the output terminals 24 and 25 viewed from the reference potential point (negative electrode) of the voltage source 21. The potential fluctuates.

  Therefore, in the impedance diagnosis, an accurate terminal voltage value cannot be obtained by measuring only the voltage V0 at the output terminal 24 as in the embodiment of FIG. By introducing a difference calculator 29 that inputs the potential of the output terminal 24 and the potential of the output terminal 25 and calculates the difference between them, this problem is solved, and the obstacle to impedance diagnosis is eliminated.

  FIG. 3 is a functional block diagram for explaining the wraparound to the return current detection resistor circuit when the analog output device of the present invention has a two-channel duplex system configuration. With the external devices 3 and 5 in common, the right area is the active side (A) and the left area is the standby side (B).

  On the operating side (A), a second current is supplied to the external device 5 by using the voltage source 21A in common for the current output module 2A constituting the first channel CH1A that supplies the current to the external device 3. A current output module 4A constituting the channel CH2A is connected.

  On the standby side (B), a second current is supplied to the external device 5 by using the voltage source 21B in common with respect to the current output module 2B constituting the first channel CH1B that supplies the current to the external device 3. A current output module 4B constituting the channel CH2B is connected.

  In such a connection form, when the output current I0 is supplied from the current output module 2A on the operating side to the external device 3, all of the current I0 flows through the return circuit of the current output module 2A and does not return to the voltage source 21A. Voltage source via return current circuit of current output module 2B of standby side first channel, return current circuit of current output module 4B of standby side second channel, return current circuit of current output module 4A of operation side second channel A wraparound to 21A occurs.

  Since the return current detection resistor is inserted in the return current circuit of each current output module, the current output module 2A reduces its own return current due to this sneak current, and the return current is reduced in each of the other current output modules. Since it decreases or increases, a malfunction occurs in the external interference diagnosis function that monitors the return current value.

  FIG. 4 is a functional block diagram showing still another embodiment of the analog output device to which the present invention is applied. A feature of this embodiment is that in order to prevent sneaking through the plurality of current output modules described in FIG. 3, a return current detection resistor (101A, 102A, 101B, 102B) is connected to a series forward prevention diode ( 401A, 402A, 401B, 402B) are inserted. Thereby, the wraparound development of the output current I0 of the current output module 2A is canceled, and the entire output current I0 returns to the voltage source 21A.

  FIG. 5 is a functional block diagram for explaining the wraparound of the terminal voltage value and the return current value to the read-back switch circuit in the duplex system. The figure shows a duplex system in which a current output module 2A on the operating side (A) and a current output module 2B on the standby side (B) are connected to the external device 3.

  If the voltage source 21B of the current output module 2B on the standby side (B) is normal, the switches 27B and 200B that read back the terminal voltage value and the return current value are regulated to be off, but there is a failure that the voltage source 21B goes down. When the switch 27B and the switch 200B are turned on with the normal close characteristic, a wraparound occurs so as to short-circuit the external device 3, and an abnormality occurs in which the current of the external device fluctuates even though the return current value is normal. However, this cannot be detected.

  FIG. 6 is a functional block diagram showing still another embodiment of the analog output device to which the present invention is applied. The feature of this embodiment is that, in order to prevent the standby side (B) current output module 2B described in FIG. 5 from sneaking into the switch, the terminal voltage value and return when the voltage source is off in each current output module. A sneak prevention means for forcibly turning off the circuit of the switch that reads back the current value is provided.

  In the current output module 2A on the operating side (A), the FET switches Q1A and Q2A inserted in series with the switch 27A and the switch 200A have their gate potential controlled by the voltage source 21A, and are regulated to be on when the voltage source 21A is normal. When the voltage source 21A is down, it is regulated to turn off, and the circuits of the switch 27A and the switch 200A are forcibly turned off.

  Similarly, in the current output module 2B on the standby side (B), the FET switches Q1B and Q2B inserted in series with the switch 27B and the switch 200B have their gate potential controlled by the voltage source 21B, and when the voltage source 21B is normal It is regulated to be on and regulated to be off when the voltage source 21B is down, forcibly turning off the circuits of the switch 27B and the switch 200B.

  In the embodiment, monitoring of interference current due to short circuit between channels has been described as a typical target of external interference diagnosis, but part or all of the current flowing through the external device due to a short circuit factor other than short circuit between channels passes through the external circuit. Faults returning to the voltage source can also be diagnosed.

It is a functional block diagram which shows one Embodiment of the analog output device to which this invention is applied. It is a functional block diagram which shows other embodiment of the analog output device to which this invention is applied. It is a functional block diagram explaining the wraparound to the return current detection resistor circuit in the two-channel duplex system. It is a functional block diagram which shows other embodiment of the analog output device to which this invention is applied. It is a functional block diagram explaining the wraparound to the switch circuit for read-back of the terminal voltage value and return current value in a duplex system. It is a functional block diagram which shows other embodiment of the analog output device to which this invention is applied. It is a functional block diagram which shows the structural example of the conventional analog output device provided with an impedance diagnostic function. It is a functional block diagram which shows the structural example of the current output module of 2 channels which makes a voltage source common. It is a functional block diagram explaining the interference current path at the time of the short circuit failure between channels.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processor 11 Impedance diagnostic means 2 Current output module 21 Voltage source 22 Constant current circuit 23 Anti-rotation diode 24, 25 Output terminal 26 Arithmetic device 27 Terminal voltage value read-back switch 28 A / D converter 3 External device 100 Return current detection resistance 200 Return current value read back switch 300 External interference diagnostic means

Claims (6)

Impedance diagnosing means for supplying a predetermined output current from a voltage source to an external device via an output terminal and diagnosing a short circuit or opening of the output terminal by reading back the terminal voltage value of the output terminal and the current value of the output current In an analog output device comprising:
A return current detection resistor inserted in series in a return current circuit from the external device to the voltage source;
Read back the return current value generated in this return current detection resistor, external interference diagnostic means for detecting the interference current flowing from the output terminal to the voltage source via the external circuit,
An analog output device comprising:   The external interference diagnosis unit detects an interference current flowing from the output terminal to an output terminal side of another channel that supplies an output current to another external device using the voltage source in common. The analog output device described.   3. The analog output device according to claim 1, further comprising switch means for periodically switching and reading back the terminal voltage value and the return voltage value.   The analog output device according to claim 1, wherein the impedance diagnosis unit reads back a difference voltage between the output terminals.   5. The analog output device according to claim 1, wherein a diode for preventing wraparound is inserted into the return current detection resistor in a series forward direction. 6.   6. The analog output device according to claim 3, further comprising anti-turn-in means for forcibly restricting the circuit of the switch means to off when the voltage source is off.

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