JPH05106602A - Current/voltage conversion device - Google Patents

Abstract

PURPOSE:To simplify the circuitry by causing the input electric signal to be converted by a power source circuit into a single low-impedance constant voltage level power source voltage, causing this power source voltage to be converted by an input resistor into a voltage signal, and causing an electromagnetic drive circuit to produce a displacement signal in response to the voltage signal on the basis of the difference between this signal and a feedback signal. CONSTITUTION:When a current signal Ii is inputted from, for example, an automatic controller into input terminals 1 and 2, a constant voltage circuit 11 produces a single low-impedance power source voltage Vb. On the other hand, an input voltage is generated at each end of an input resistor Ri by the input signal Ii and this input voltage is outputted, via a resistor R17, into an inversion input terminal (-) of a deviation amplifier Q3. The deviation amplifier Q3 calculates the deviation between a feedback voltage Vf and the input voltage to drive the base of a transistor Q4. As a result, an electromagnetic drive coil EC is energized to cause a flapper FL to be displaced. Correspondingly to this displacement, the back pressure of a nozzle Nz is changed to produce a pneumatics signal Po, which is converted via a pressure sensor 12 into an electric signal Ef1. This signal becomes the feedback voltage Vf via a buffer amplifier Q5, a buffer amplifier Q6 and deviation amplifiers Q7 and Q8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current / pressure conversion device for converting a current transmitted through two transmission lines into a corresponding pneumatic signal or the like, and more particularly to this current / pressure conversion device. The present invention relates to a current / pressure conversion device modified so as to be driven by a single power source.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a configuration of an electropneumatic converter as an example of an electric / pressure converter disclosed in Japanese Patent Publication No. 2-43234.

Reference numerals 1 and 2 are, for example, 4 to 20 from a controller or the like.
An input terminal 3 for receiving a current output Ii such as mA as an input current Ii is a power supply circuit.

A Zener diode Z1 and an input resistor Rs are connected in series between the input terminals 1 and 2. Also,
Connection point A between Zener diode Z1 and input resistance Rs
A resistor R1 and a Zener diode Z2 are connected in series between the input terminal 1 and the input terminal 1.

The power supply voltage of -V is taken out from the connection point A,
The voltage of + V is taken out from the input terminal 1, and the circuit is driven by these two voltages of ± V. Further, a series circuit of resistors R2 and R3 is connected between a connection point B between the resistor R1 and the Zener diode Z2 and the input terminal 2.

At the connection point C between the resistors R2 and R3, the voltage generated across the Zener diode Z2 and the input resistor Rs is
A divided voltage divided by the resistors R2 and R3 and the input resistor Rs is generated, and this divided voltage is output to the non-inverting input terminal (-) of the operational amplifier A1 which constitutes the integrating circuit 4 through the resistor R4. It A capacitor C1 for integration is provided between the output terminal and the inverting input terminal (-) of the operational amplifier A1 energized by the voltage of ± V.
Are connected.

A feedback voltage fed back from the deviation amplifier 10 is applied to the non-inverting input terminal (+) of the operation amplifier A1, and the operation amplifier A1 performs an operation so as to eliminate these deviations and changes it via a resistor R6. Non-inverting input terminal (+) of amplifier A2
Output to. At the same time, the feedback voltage is applied from the deviation amplifier 10 to the non-inverting input terminal (+) of the variable amplifier A2 through the resistor R7.

The sum of the voltage divided by the variable resistor RG connected between the output terminal of the variable amplifier A2 and the connection point A and the divided voltage obtained at the connection point C is the resistances R5 and R8. The voltage is divided by and is applied to the non-inverting input terminal (-) of the variable amplifier A2. The voltage obtained at the output end of the variable amplifier A2 is applied to the piezoelectric element 6, and the nozzle 11 is arranged facing it.

Air pressure is applied to the nozzle 11 from a pilot relay 7 to which air is supplied, and the back pressure of the nozzle is output as an air output. A constant voltage circuit 9 that is energized to generate a constant voltage supplies a constant voltage to the power source terminal of the bridge that constitutes the pressure sensor 8, and the air output is converted into an electric signal and output from the output terminals E and D.

This electric signal is applied to the resistors R9 and R10 ±
It is output to the inverting input terminal (-) and the non-inverting input terminal (+) of the deviation amplifier A3 energized by the power source voltage of V. A resistor R11 is connected between the non-inverting input terminal (+) and the output terminal,
The feedback voltage is output from this output terminal to the non-inverting input terminal (+) of the operational amplifier A1.

The voltage across the Zener diode Z2 is divided by the variable resistor Rz and applied as a zero voltage to the non-inverting input terminal (+) of the deviation amplifier 10 via the resistor R12. As described above, each component is energized with a voltage of ± V and converted into an air output proportional to the voltage generated in the input resistance Rs.

[0012]

However, the current / pressure conversion device as described above uses two Zener diodes Z1 and Z2 to operate the circuit to generate a low-impedance power supply voltage. Therefore, it has a drawback that the circuit becomes complicated and the cost becomes high.

[0013]

The present invention has a main structure for solving the above problems, in which a current signal is transmitted to an input end through two transmission lines and the conversion circuit is performed using this current signal. Power supply circuit for generating a single constant voltage power supply voltage with low impedance, an input resistance connected in series to the power supply circuit for converting the current signal into a voltage signal, and energized with this constant voltage. An electromagnetic drive circuit that is driven by a deviation between the voltage signal and the feedback signal to convert into a displacement signal corresponding to the voltage signal, and a displacement / air pressure conversion means that receives air pressure and converts into a pneumatic signal corresponding to the displacement signal. And a feedback circuit which receives the air pressure signal and outputs a feedback signal corresponding to the air pressure signal.

[0014]

[Operation] In the power supply circuit, a current signal is transmitted to the input end through two transmission lines, and this current signal is used to generate a low-impedance single constant voltage power supply voltage used in the conversion circuit. The input resistor is connected in series with this power supply circuit and converts the current signal into a voltage signal.

On the other hand, the electromagnetic drive circuit is energized with this constant voltage and driven by the deviation between the voltage signal and the feedback signal to convert into a displacement signal corresponding to the voltage signal. Further, the displacement / pneumatic pressure converting means is supplied with an air pressure, which is converted into an air pressure signal corresponding to the displacement signal and output. Then, the air pressure signal is input to the feedback circuit, and a feedback signal corresponding to the air pressure signal is output to realize highly accurate current / pressure conversion.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. The parts having the same functions as those of the conventional current / pressure conversion device shown in FIG.

A current signal Ii is input between the input terminals 1 and 2 from a controller or the like. A constant voltage circuit 11 and an input resistor Ri are connected in series to the input terminals 1 and 2. The constant voltage circuit 11 includes resistors R13, R14, R
It is composed of 15, an operational amplifier Q1, a diode group D1, a transistor Q2, a zener diode Z3, a resistor R16, etc., and makes the only low-impedance power supply voltage Vb used in the circuit.

The resistor R13, the zener diode Z3, and the input resistor Ri are connected in series, and the connection point between the zener diode Z3 and the input resistor Ri is a common potential point COM.
A resistor R13 and a Zener diode Z3 are connected in series between the input terminal 1 and the common potential point COM.
A part of the input current Ii is applied to both ends of the switch Z3 to generate a reference voltage V
make s This reference voltage Vs functions as a reference voltage for producing the power supply voltage Vb in the constant voltage circuit 11.

Further, resistors R14 and R15 are connected in series between the input terminal 1 and the common potential point COM, and these connection points and the reference voltage Vs are applied to the input terminal of the operational amplifier Q1. Due to the voltage at the output terminal, a diode group D1 and a transistor Q2 are connected between the input terminal 1 and the common potential point COM.
And a resistor R16 are applied to the base of a transistor Q2 connected in series.

As a result, the operational amplifier Q1 has the reference voltage V1.
By adjusting the current flowing through the transistor Q2 so as to be equal to s, the voltage at the connection point between the resistors R14 and R15 is controlled. As a result, a low impedance power supply voltage Vb is obtained between the input terminal 1 and the common potential point COM. An input voltage Vi is generated across the input resistance Vi by the input current Ii. This input voltage Vi is output to the inverting input terminal (-) of the deviation amplifier Q3 via the resistor R17. A resistor R is provided between the inverting input terminal (-) and the output terminal of the deviation amplifier Q3.
A series circuit of 18 and a capacitor C1 is connected. A resistor R19 is connected between the non-inverting input terminal (+) and the common potential point COM.

The output terminal of the deviation amplifier Q3 is connected to the base of the transistor Q4 via a resistor R20. A parallel circuit of a diode D2 and an electromagnetic drive coil EC, a series circuit of a collector and an emitter of a transistor Q4, and a resistor R21 are connected between the power source voltage Vb and the common potential point COM.

The electromagnetic drive coil EC has a flapper FL.
Is fixed and is displaced in proportion to the current flowing through the electromagnetic drive coil EC. A nozzle Nz is arranged so as to face the flapper FL. A supply air pressure SUP is supplied to the pilot relay PL, and this supply air pressure SUP is a throttle S.
Air pressure is applied to the nozzle Nz via the. The pilot relay PL detects the nozzle back pressure of the nozzle Nz and outputs an air pressure signal P0 to its output end.

On the other hand, the pneumatic signal P0 is the power supply voltage V0.
b is a pressure sensor 12 energized via a constant current element CC
, Where the pneumatic signal P0 is converted to an electrical signal Ef1. As the pressure sensor, for example, a pressure sensor using a shear gauge capable of highly accurate pressure / voltage conversion is used. This electric signal Ef1 is applied to the deviation amplifier Q7 through the buffer amplifiers Q5 and Q6 and the resistors R22 and R6.
Applied via 23. A resistor R24 is connected between the inverting input terminal (-) and the output terminal of the deviation amplifier Q7, and the non-inverting input terminal (+) thereof has a divided voltage obtained by dividing the power supply voltage Vb by the resistors R25 and R26. Applied via resistor R27.

The output voltage of the deviation amplifier Q7 is applied to the inverting input terminal (-) of the operational amplifier Q8 through the resistor R28,
The divided voltage divided by the resistors R25 and R26 is applied to the non-inverting input terminal (+) via the resistor R29. The power supply voltage V is applied to the inverting input terminal (-) of the operational amplifier Q8.
A zero adjustment voltage Vz0 obtained by dividing b by a resistor R30, a volume VR1 and a resistor R31 is applied via a resistor R32.

Further, between the output terminal of the operational amplifier Q8 and the common potential point COM, the voltage is divided by the resistor R33, the volumes VR2 and R35, and the divided voltage is supplied via the resistor R35 to the inverting input terminal (- ) Is applied as a span adjustment voltage Vs0. Then, from the output terminal of this operational amplifier Q8 to the resistor R
The feedback voltage Vf is output to the inverting input terminal (-) of the deviation amplifier Q3 via 36. The circuit for obtaining the feedback voltage Vf from the above pneumatic signal P0 constitutes a feedback circuit,
As the deviation amplifier Q3 or the like or the operational amplifier Q8 or the like, an element whose operating voltage can be operated from almost zero volt is used.

In the above structure, the input current Ii flows through the input terminals 1 and 2 to generate the low-impedance power supply voltage Vb in the constant voltage circuit 11, which are used to energize each amplifier. Is applied. Also, the input current Ii
Flows into the input resistance Ri and generates an input voltage Vi across the resistance Ri. The deviation of the feedback voltage Vf output from the output terminal of the deviation amplifier Q3 is calculated from this input voltage Vi, and the output voltage drives the base of the transistor Q4. As a result, the electromagnetic drive coil EC is driven and the flapper F
Displace L.

The nozzle back pressure of the nozzle Nz changes in response to this displacement, and an air pressure signal P0 is output. The air pressure signal P0 is converted into an electric signal Ef1 via the pressure sensor 12 and is supplied to the deviation amplifier Q3 as a feedback voltage Vf via buffer amplifiers Q5, Q6, deviation amplifier Q7 and deviation amplifier Q3.
Then, the deviation amplifier Q3 is controlled so that Vi = Vf. Therefore, the air pressure signal P0 proportional to the input current Ii is obtained.

In the above description, the electro-pneumatic converter for converting the current signal Ii into the corresponding air pressure signal P0 has been described as a base, but a valve (not shown) is driven by this air pressure signal P0. The same operation is performed also as an electropneumatic positioner which returns the opening to the deviation amplifier Q3 as the feedback signal Vf via the displacement / electric conversion circuit.

FIG. 2 shows a partially modified embodiment in which a part of the circuit from the pressure sensor 12 to the feedback signal Vf is modified. In this case, when the electric signal Ef1 from the pressure sensor 12 is received by the differential amplifier, the first stage thereof is received by the transistor. Others are almost the same as the embodiment shown in FIG.

The differential amplifier 13 includes a resistor R37, a field effect transistor Q9, a resistor R38, a resistor R39, a field effect transistor Q10, a resistor R40, an operational amplifier Q11, resistors R41 and R42, and transistors Q12 and Q13. Resistance R43,
It is composed of R44 and R45. The resistor R37, the drain / source of the field effect transistor Q9 and the resistor R38 are connected in series, and the resistor R39 and the drain / source of the field effect transistor Q10 and the resistor R40 are also connected in series. These are the power supply voltage Vb and the transistor Q12 connected in parallel.
Connected between the collector and.

Further, signals are input to the input terminal of the operational amplifier Q11 from the drains of the transistors Q9 and Q10. A resistor R41 is connected between the output terminal of the operational amplifier Q11 and the connection point between the resistor R38 and the transistor Q9, and a resistor R42 is connected between the connection point between the resistor R40 and the transistor Q10.

The emitter of the transistor Q12 is connected to the common potential point COM via the resistor R43, and the transistor Q13 and the resistor R44 are connected in series between the base and the common potential point COM. And this transistor Q
The base and collector of 13 are connected together and the power supply voltage Vb is applied via a resistor R45.

These transistors Q12, Q13 and resistor R
43, R44, R45, etc. form a constant current circuit for differential amplification. With this structure, the electric signal Ef1 from the sensor 12 is stably transmitted to the operational amplifier Q8.

[0034]

As described above in detail with reference to the embodiments, according to the present invention, since the entire circuit can be driven by using one low-impedance power supply voltage, the cost is low and the cost is low. It is possible to realize a current / pressure conversion device that is easy to operate.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a partially modified embodiment in which a part of the embodiment shown in FIG. 1 is modified.

FIG. 3 is a block diagram showing a configuration of a conventional current / pressure conversion device.

[Explanation of symbols]

 1, 2 Input terminal 3 Power supply circuit 6 Piezoelectric element 8, 12 Pressure sensor 9, 11 Constant voltage circuit 11 Displacement / electrical signal converter 13 Differential amplifier Ii current signal Ri input resistance Vi input voltage EC Electromagnetic drive coil PL pilot relay FL flapper

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Hayashi 2-9-32 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd. (72) Takeshi Nishijima 2-9-32 Nakamachi, Musashino-shi, Tokyo Yoko Kawa Electric Co., Ltd. (72) Inventor Yasuo Kasahara 2-932 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. (72) Akira Inoue 2-932 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. (72) Inventor Minoru Midagawa 2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd.

Claims (2)

[Claims] 1. A power supply circuit in which a current signal is transmitted to an input end through two transmission lines, and the current signal is used to generate a low-impedance single constant voltage power supply voltage for use in a conversion circuit. An input resistance connected in series to the power supply circuit for converting the current signal into a voltage signal, and a displacement signal corresponding to the voltage signal driven by a deviation between the voltage signal and the feedback signal energized by the constant voltage An electromagnetic drive circuit for converting the air pressure, a displacement / pneumatic pressure converting means for supplying air pressure to convert to an air pressure signal corresponding to the displacement signal, and a feedback circuit for receiving the air pressure signal and outputting a feedback signal corresponding to the air pressure signal An electric current / pressure conversion device comprising: 2. A current / pressure conversion device according to claim 1, wherein a valve is driven by the air pressure signal and the opening thereof is used as the feedback signal via a displacement / electric conversion means.