JP2010152596A - Current input and output device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current input and output device including a switching function between a current output operation and a current input operation and an overcurrent protection function, by a common voltage/current conversion means having no movable component. <P>SOLUTION: This current input and output device outputs a prescribed value of operation current to equipment connected thereto, based on a current command value from a control means, or inputs an operation current from the equipment connected thereto, and includes the voltage/current conversion means for inputting the current command value from the control means, via a DA converter, and for answering back a voltage proportional to the operation current of the equipment, to the control means, via an AD converter, the voltage/current conversion means outputs the operation current proportional to the current command value from the control means to the equipment, at the time of the current output operation, and the voltage/current conversion means limits the current input from the equipment, to the current command value from the control means, at the time of the current input operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a current input / output device that outputs an operating current of a predetermined value to a connected device or inputs an operating current from a connected device based on a current command value from a control means.

  FIG. 5 is a functional block diagram showing a configuration example of a conventional current input / output device disclosed in Patent Document 1. In FIG. FIG. 5A shows a configuration during a current output operation, and FIG. 5B shows a configuration during a current input operation.

  In the current output operation of FIG. 5A, a load L such as a valve operated by a current output signal Iout supplied from the terminal T1 is connected between the input / output terminals T1 and T2. The current flowing through the load L flows through the current detection resistor R1 via the terminal T2, and generates the feedback voltage Vo.

  The changeover switch SW selects the contact S1 side and applies the feedback voltage Vo to the negative input terminal of the differential amplifier A1. A set voltage value Vi from a current setting means (not shown) is given to the plus input terminal of the differential amplifier A1.

  The output of the differential amplifier A1 is given to the base of the current control transistor Q1. The collector of the current control transistor Q1 is connected to the DC power supply Vcc, and the emitter is connected to the input / output terminal T1.

  In such a circuit configuration, a constant current circuit is formed in which the current output signal Iout is controlled so that the feedback voltage Vo becomes equal to the set voltage value Vi. By changing the set value Vi, a predetermined value is applied to the load L. A current in an operating range (eg, 4 to 20 mA) can be output.

  In the current input operation of FIG. 5B, the current corresponding to the measurement span of the physical quantity P (eg, 4 to 20 mA) is driven between the input / output terminals T1 and T2 by the power supply voltage Vout supplied from the terminal T1. A load L such as a differential pressure transmitter that outputs Iin is connected. The current Iin from the load L is input via the terminal T2, and flows through the answerback resistor R1 to generate the answerback voltage Va.

  The changeover switch SW selects the contact S2 side, and applies a voltage Vf obtained by dividing the voltage of the terminal T1 by the resistors R2 and R3 to the negative input terminal of the differential amplifier A1. A set voltage value Vs from a voltage setting means (not shown) is given to the plus input terminal of the differential amplifier A1.

  In such a circuit configuration, a constant voltage circuit is formed in which the voltage Vout between the terminals T1 and T2 is controlled so that the voltage Vf is equal to the set voltage value Vs. Based on the set voltage value Vs, the terminals T1 and T2 are formed. The power supply voltage Vout between them can be held at a predetermined value.

Japanese Patent Laid-Open No. 5-134701

The operation switching method of the current input / output device according to the conventional configuration has the following problems.
(1) In order to switch between the current output operation and the current input operation, a movable part such as a changeover switch SW is required, and the circuit configuration becomes complicated.

(2) When an overcurrent exceeding the operating span flows due to a failure of the load L or transmission line during the current input operation of FIG. It is necessary to add it separately, which makes the configuration complicated and increases the cost.

  The present invention has been made to solve the above-described problems, and has a function of switching between current output operation and current input operation and an overcurrent protection function by a common voltage / current conversion means having no moving parts. The purpose is to realize a current input / output device.

In order to achieve such a subject, the present invention has the following configuration.
(1) In a current input / output device that outputs an operating current of a predetermined value to a connected device based on a current command value from a control means, or inputs an operating current from a connected device,
Voltage / current conversion means for inputting a current command value from the control means via a DA converter and answering back to the control means via the AD converter a voltage value proportional to the operating current of the device With
At the time of current output operation, the voltage / current conversion means outputs an operation current proportional to the current command value from the control means to the device,
During the current input operation, the voltage / current conversion means limits the current input from the device to a current command value from the control means,
A current input / output device characterized by that.

(2) The voltage / current conversion means includes a differential amplifier that inputs an output voltage of the DA converter and a voltage of a current detection resistor of the device, and an output of the differential amplifier is input to a gate to detect the current. The current input / output device according to (1), further comprising: an FET having a resistor connected to a source and a drain connected to the device.

(3) In the current output operation, the control unit provides the voltage / current conversion unit with a current command value in a range corresponding to the operating current range of the device. Current input / output device.

(4) In the current input operation, the control means provides the voltage / current conversion means with a current command value corresponding to a limit current value exceeding a predetermined value of the operating current range of the device (1). Or the current input / output device according to (2).

(5) The control unit includes an erroneous connection monitoring unit that monitors the current command value and the answerback voltage and checks an erroneous connection of the device connected during a current output operation or a current input operation. The current input / output device according to any one of (1) to (4).

According to the configuration of the present invention, the following effects can be expected.
(1) The function of the current output operation and the current input operation can be switched with a common circuit configuration having no moving parts by simply changing the output value of the DA converter that gives the current command value from the control means.

(2) An overcurrent protection function during a current input operation can be realized without specially providing an overcurrent protection mechanism.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of a current input / output device to which the present invention is applied. The current input / output device 100 to which the present invention is applied includes input / output terminals 101 and 102, and a device 200 serving as a load of current input / output is connected between the input / output terminals.

  In the current input / output device 100, one of the input / output terminals 101 is connected to the DC power supply 103, and the other 102 is connected to the drain of the current output FET Q2 of the voltage / current conversion means 104. The source of the FET Q2 is connected to the reference potential via the feedback resistor Rf.

  The output of the differential amplifier Q2 in the voltage / current conversion means 104 is connected to the drain of the FET Q1, and the voltage Vf generated in the feedback resistor Rf is applied to the negative input terminal of the differential amplifier Q2.

  A voltage Vi obtained by converting the digital current command value Di from the control means 105 into an analog value by the DA converter 106 is input to the positive input terminal of the differential amplifier Q2. The answerback voltage Vf generated in the feedback resistor Rf is converted into a digital value Df by the AD converter 107 and passed to the control means 105.

  FIG. 2 is a functional block diagram for explaining the current output operation. Connected between the input / output terminals 101 and 102 is a valve 300 operated at a predetermined current span (4 to 20 mA) of the output current Io.

  The control means 105 inputs the voltage Vi at which the output current Io span is 4 to 20 mA to the differential amplifier Q2 via the DA converter 106. If the value of the feedback resistance Rf is 250Ω, Vi has a span of 1 to 5V. The configuration during this current output operation is basically the same as the configuration of the constant current circuit shown in FIG.

  FIG. 3 is a functional block diagram for explaining the current input operation. A two-wire differential pressure transmitter 400 is connected between the input / output terminals 101 and 102, and an output current Io having a span of 4 to 20 mA corresponding to the measurement span of the pressure P flows into the current input / output device 100.

  The control means 105 supplies, via the DA converter 106, a voltage higher than the voltage of the span 1 to 5V at which the span of the output current Io is 4 to 20 mA, for example, a fixed voltage Vi of 6V, to the positive input terminal of the differential amplifier Q2. To give.

  When the differential pressure transmitter 400 operates normally and its output current span is 4 to 20 mA, the answer back voltage Vf generated in the feedback resistor Rf (250Ω) has a span of 1 to 5V. Accordingly, the output of the differential amplifier Q2 to which 6V is applied to the plus input terminal is saturated to the plus side, the conduction between the drain and source of the FET Q1 becomes conductive, and the output current Io passes between the drain and source of the FET Q1 as it is.

  If the upper limit of the output current Io exceeds 20 mA due to a short circuit fault such as the differential pressure transmitter 400 or the lead wire, the answerback voltage Vf generated at the feedback resistor Rf (250Ω) increases beyond 5 V. However, when the output current Io is about 24 mA (Vf = 6V) or more, the differential amplification function of the differential amplifier Q2 is restored, the constant current circuit functions and the output current Io is maintained at 24 mA. Overcurrent protection is realized.

  FIG. 4 is a functional block diagram showing another embodiment of the present invention. The difference from FIG. 1 lies in the configuration in which the erroneous connection monitoring means 108 is provided in the control means 105. The control means 105 checks the abnormal connection of the devices connected between the input / output terminals 101 and 102 by monitoring the answer back voltage Df from the AD converter 107 during the current output operation and the current input operation. It is possible to alert the operator.

  For example, when the differential pressure transmitter 400 is mistakenly connected between the input / output terminals 101 and 102 during the current output operation of FIG. 2, the constant current circuit does not function, and the control means 105 is set to the set voltage value Vi. Since the answer-back voltage Vf equal to can not be acquired, an abnormality can be detected.

  Further, when the valve 300 is erroneously connected between the input / output terminals 101 and 102 during the current input operation of FIG. 3, a current 24 mA corresponding to a fixed set voltage value Vi (6 V) flows, and Vf is Vi. An abnormality can be detected when the voltage is equal to 6V.

It is a functional block diagram which shows one Embodiment of the current input / output device to which this invention is applied. It is a functional block diagram explaining a current output operation. It is a functional block diagram explaining a current input operation. It is a functional block diagram which shows other embodiment of this invention. It is a functional block diagram which shows the structural example of the conventional current input / output device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Current input / output device 101,102 Input / output terminal 103 Power supply 104 Voltage / current conversion means 105 Control means 106 DA converter 107 AD converter 200 Equipment

Claims (5)

Based on the current command value from the control means, in the current input / output device that outputs the operating current of a predetermined value to the connected device or inputs the operating current from the connected device,
Voltage / current conversion means for inputting a current command value from the control means via a DA converter and answering back to the control means via the AD converter a voltage value proportional to the operating current of the device With
At the time of current output operation, the voltage / current conversion means outputs an operation current proportional to the current command value from the control means to the device,
During the current input operation, the voltage / current conversion means limits the current input from the device to a current command value from the control means,
A current input / output device characterized by that.   The voltage / current conversion means includes a differential amplifier for inputting an output voltage of the DA converter and a voltage of a current detection resistor of the device, an output of the differential amplifier being input to a gate, and the current detection resistor as a source The current input / output device according to claim 1, further comprising: an FET connected to the FET and having a drain connected to the device.   3. The current input / output device according to claim 1, wherein, during a current output operation, the control unit provides the voltage / current conversion unit with a current command value in a range corresponding to an operating current range of the device. .   3. The current control value given to the voltage / current conversion unit according to claim 1, wherein the control unit provides a current command value corresponding to a limit current value exceeding a predetermined value in an operating current range of the device during a current input operation. The current input / output device described.   The said control means is provided with the misconnection monitoring means which monitors the said electric current command value and an answerback voltage, and checks the misconnection of the said apparatus connected at the time of current output operation or current input operation. The current input / output device according to any one of 1 to 4.

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