JP5035612B2 - 2-wire transmitter - Google Patents

Description

  The present invention relates to a two-wire transmitter, and more particularly to a two-wire transmitter that improves the measurement accuracy of a physical quantity.

Japanese Patent Laid-Open No. 5-166093

  Patent Document 1 discloses the same configuration and operation as described below.

The two-wire transmitter constitutes a part of plant equipment that performs process control, detects and calculates a flow rate, pressure, temperature, or the like, which is a physical quantity (process quantity), and transmits the calculated value as a current signal to the controller. . This two-wire transmitter will be described with reference to FIG.

  In FIG. 4, the two-wire transmitter 21 includes a variable regulator 23, a constant voltage circuit 24, and a signal processing circuit 25.

  The 2-wire transmitter 21 transmits a transmission current Io corresponding to the physical quantity detected by the signal processing circuit 25 to the controller, and surplus current obtained by subtracting the current consumed in the 2-wire transmitter 21 from the transmission current Io. I22 is passed through the load 22.

The positive electrode (+) of the DC power supply 20 is connected to the terminal T1 of the two-wire transmitter 21 via the transmission line L1, and the negative electrode (−) is connected to the terminal T2 via the load resistor 11 and the transmission line L2. The

  The transmission current Io flows from the positive electrode (+) of the DC power source 20 to the inside of the two-wire transmitter 21 via the terminal T1, and flows to the negative electrode (−) of the DC power source 20 via the terminal T2 and the load resistor 11.

  At this time, the transmission current Io is controlled by the operational amplifier Q5 and the transistors Q3 and Q4 to which the signal voltage Vs1 corresponding to the physical quantity detected by the signal processing circuit 25 and the feedback voltage Vf1 proportional to the transmission current Io are input. The current corresponds to the voltage Vs1 (for example, a range of 4 mA to 20 mA).

  The transmission current Io is divided into a consumption current I2 of the internal circuit and a current I22 flowing through the load 22, and this current I22 is a current obtained by subtracting the consumption current I2 of the internal circuit from the transmission current Io (hereinafter referred to as “excess current I22”). is there. The surplus current I22 is controlled by changing the impedance of the load 22 based on the output VC1 of the operational amplifier Q5.

Further, the collector voltage V2 of the transistor Q3 and the feedback voltage Vf1 are added to the variable regulator 23, and the voltage V3 and the current I3 corresponding to the feedback voltage Vf1 are output.

The output voltage V3 is input to the constant voltage circuit 24, and the constant voltage circuit 24 outputs the constant voltage Vd1 and the current Id1. The constant voltage Vd1 and the current Id1 supply power to the signal processing circuit 25 including a sensor (not shown).

In the variable regulator 23, the feedback voltage Vf1 (proportional to the transmission current Io) and the output voltage V3 have an inverse function relationship. Furthermore, the output voltage V3 and the output current I3 have an inverse function relationship. For this reason, when the transmission current Io increases, the output voltage V3 decreases and the output current I3 increases.

For example, when the transmission current Io is 4 mA, the output voltage V3 of the variable regulator 23 is 11 V and the output current I3 is 3.2 mA. At this time, the surplus current I22 flowing through the load 22 is about 0.8 mA.

When the transmission current Io is 20 mA, the output voltage V3 of the variable regulator 23 is 7 V and the output current I3 is 5.1 mA. At this time, the surplus current I22 flowing through the load 22 is about 14.9 mA.

  If the power supplied to the sensor included in the signal processing circuit 25 is increased, the voltage of the physical quantity detection signal increases, and the S / N ratio (detection signal voltage to noise voltage ratio) of the physical quantity detection signal increases. Measurement accuracy is improved.

  For this reason, the two-wire transmitter 21 reduces the surplus current I22 as much as possible, and sends this decrease to the sensor included in the signal processing circuit 25 as the output current Id1 of the constant voltage circuit 24, thereby supplying the current supplied to the sensor. It is desirable to increase.

  However, the two-wire transmitter 21 does not detect and monitor the surplus current I22. Therefore, when the variable regulator 23 and the constant voltage circuit 24 increase the supply current to the sensor included in the signal processing circuit 25, the surplus current I22 becomes 0 mA, the collector voltage V2 of the transistor Q3 decreases, and the variable current becomes variable. Internal circuits such as the regulator 23, the constant voltage circuit 24, and the signal processing circuit 25 may not operate.

  An object of the present invention relates to a two-wire transmitter, and by increasing the power supplied to a physical quantity detector including a sensor within a range that does not hinder the operation of the two-wire transmitter, It is to provide a two-wire transmitter that increases the N ratio to improve the physical quantity measurement accuracy.

In order to achieve such an object, the invention of claim 1
In a two-wire transmitter in which a physical quantity is detected by a physical quantity detector and a transmission current corresponding to the physical quantity is supplied,
A variable voltage output unit that outputs a variable voltage, detects a surplus current that is part of the transmission current, and outputs a detection signal;
A variable voltage setting unit that outputs a variable voltage setting signal for changing the variable voltage based on the detection signal to the variable voltage output unit;
A constant voltage output unit that receives the variable voltage and supplies power to the physical quantity detection unit based on the input voltage;
It is provided with.

The invention of claim 2 is the invention of claim 1,
The variable voltage setting signal is:
Changing the variable voltage stepwise based on the detection signal;
It is characterized by that.

The invention of claim 3 is the invention of claim 1,
The variable voltage setting signal is:
Changing the variable voltage in proportion to the detection signal;
It is characterized by that.

The invention of claim 4 is the invention of claim 1,
The variable voltage setting signal is:
Changing the variable voltage into a curve based on the detection signal;
It is characterized by that.

The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The variable voltage setting signal is:
Changing the variable voltage by a signal obtained by smoothing a pulse width modulation signal having a duty ratio corresponding to the detection signal;
It is characterized by that.

The invention of claim 6 is the invention according to any one of claims 1 to 4,
The variable voltage setting signal is:
The variable voltage is changed by a signal obtained by DA-converting a digital signal corresponding to the detection signal.
It is characterized by that.

The invention according to claim 7 is the invention according to any one of claims 1 to 6,
The detection signal is
AD conversion of the voltage corresponding to the surplus current,
It is characterized by that.

The invention of claim 8 is the invention according to any one of claims 1 to 6,
The detection signal is
VF conversion of the voltage corresponding to the surplus current,
It is characterized by that.

The invention of claim 9 is the invention according to any one of claims 1 to 8,
The variable voltage output unit includes:
The variable voltage is output using an operational amplifier that controls the surplus current through a transistor so that the voltage obtained by dividing the variable voltage and the voltage of the variable voltage setting signal are equal to each other.
It is characterized by that.

According to the present invention, the power supplied to the physical quantity detection unit including the sensor is increased based on the detection signal of the surplus current within a range that does not interfere with the operation of the two-wire transmitter. Thus, it is possible to realize a two-wire transmitter that increases the S / N ratio of the physical quantity detection signal and improves the physical quantity measurement accuracy.

[First embodiment]
FIG. 1 is a block diagram of a two-wire transmitter to which the present invention is applied, and a first embodiment will be described using this.

The two-wire transmitter 100 of the present invention detects and calculates a flow rate, pressure, temperature, etc., which are physical quantities (process quantities), and transmits the calculated value as a current signal to a controller (not shown).

In this embodiment, the surplus current Ir is detected, and the power supplied to the physical quantity detection unit including the sensor is changed based on the detection signal.

  The two-wire transmitter 100 includes a physical quantity detection unit 30, a calculation unit 40, a variable voltage output unit 50, a variable voltage setting unit 60, a constant voltage output unit 70, a current transmission unit 80, and a transmission current control unit 90.

  The positive terminal (+) of the DC power supply 110 provided outside the two-wire transmitter 100 is connected to the terminal T100 of the two-wire transmitter 100 via the transmission line L100, and the negative terminal (−) is a load. The resistor Rs110 and the transmission line L101 are connected to the terminal T101. Terminals T100 and T101 are connected to the current transmission unit 80.

  Next, the configuration of the current transmission unit 80 will be described.

  Terminal T100 is connected to the emitter terminal of transistor Q80, and the base terminal of transistor Q80 is connected to the collector terminal of transistor Q82.

The emitter terminal of the transistor Q82 is connected to one end of the transmission current detection resistor Rs80 via the resistor R83 and the diode D80, and the other end of the transmission current detection resistor Rs80 is connected to the terminal T101.

The voltage at the connection point between the cathode terminal of the diode D80 and one end of the transmission current detection resistor Rs80 is the common voltage Vcom.

The collector terminal of the transistor Q80 is connected to the anode terminal of the diode D81, and the cathode terminal of the diode D81 is connected to the drain terminal of the transistor (for example, field effect transistor) Q50 of the variable voltage output unit 50. A constant voltage diode and a capacitor are connected in parallel between the cathode terminal of D81 and the common voltage Vcom.

Next, the configuration of the transmission current control unit 90 will be described.

The output of the arithmetic unit 40 is connected to the non-inverting input terminal (+) of the operational amplifier A90 via the resistor R90, and the capacitor C90 is connected between the non-inverting input terminal (+) of the operational amplifier A90 and the common voltage Vcom. Connected. The calculation unit 40 will be described later.

The output terminal of the operational amplifier A90 is connected to the inverting input terminal (−) of the operational amplifier A91 via the resistor R91, and the inverting input terminal (−) of the operational amplifier A91 is connected to the transmission current detection resistor via the resistor R92. It is connected to the connection point between Rs80 and terminal T101.

The output terminal of the operational amplifier A91 is connected to the base terminal of the transistor Q82 via a resistor R80 and a resistor R81.

Next, the configuration of the calculation unit 40 and the physical quantity detection unit 30 will be described.

  The physical quantity detection unit 30 includes a sensor (not shown), and detects and outputs a physical quantity such as a flow rate, pressure, or temperature by the sensor.

The calculation unit 40 receives the physical quantity detection signal output from the physical quantity detection unit 30 and calculates the physical quantity.

Next, the configuration of the variable voltage output unit 50 will be described. The variable voltage output unit 50 includes a surplus current detection unit 51.

The drain terminal of the transistor Q50 is connected to one end of the resistor R50 and the input of the constant voltage output unit 70. The voltage of the drain terminal of the transistor Q50 is the variable voltage V50 of the variable voltage output unit 50.

The other end of the resistor R50 is connected to one end of the resistor R51, and the other end of the resistor R51 is connected to the common voltage Vcom.

The connection point between the resistor R50 and the resistor R51 is connected to the inverting input terminal (−) of the operational amplifier A50, and the output terminal of the operational amplifier A50 is connected to the gate terminal of the transistor Q50. The source terminal of the transistor Q50 is connected to the common voltage Vcom via the surplus current detector 51.

The surplus current detection unit 51 includes a surplus current detection resistor Rs50 and an AD conversion unit 52. One end of the surplus current detection resistor Rs50 is connected to the source terminal of the transistor Q50, and the other end is connected to the common voltage Vcom.

A connection point between the surplus current detection resistor Rs50 and the source terminal of the transistor Q50 is connected to an input of the AD conversion unit 52. The output of the AD conversion unit 52 is connected to the input of the variable voltage setting control unit 61 of the variable voltage setting unit 60.

Next, the configuration of the variable voltage setting unit 60 will be described. The variable voltage setting unit 60 includes a variable voltage setting control unit 61.

The output of the variable voltage setting control unit 61 is connected to one end of the resistor R62. The other end of the resistor R62 is connected to the non-inverting input terminal (+) of the operational amplifier A50, and a capacitor C62 is connected between the other end of the resistor R62 and the common voltage Vcom.

The power supply terminal of the variable voltage setting control unit 61 is connected to the output voltage V70 of the constant voltage output unit 70, and the reference voltage terminal is connected to the common voltage Vcom.

Next, the constant voltage output unit 70 will be described. The output voltage V70 of the constant voltage output unit 70 is connected to the power supply terminals of the physical quantity detection unit 30, the calculation unit 40, and the variable voltage setting control unit 61, and these reference voltage terminals are connected to the common voltage Vcom.

Next, the operation of the two-wire transmitter 100 will be described.

First, operations of the physical quantity detection unit 30 and the calculation unit 40 will be described.

The physical quantity detection unit 30 and the calculation unit 40 detect and calculate a physical quantity such as a flow rate, pressure, or temperature.

For example, in the case of an electromagnetic flow meter, the physical quantity detection unit 30 applies a magnetic field to the measurement fluid and detects an electromotive force generated in the measurement fluid by electromagnetic induction. Since this electromotive force corresponds to the flow velocity of the measurement fluid, the calculation unit 40 receives the physical quantity detection signal output from the physical quantity detection unit 30 and calculates the flow rate and the flow rate.

The flow rate measurement may be a vortex flow rate measurement. The physical quantity detection unit 30 detects pressure in the case of a pressure transmitter, and detects temperature in the case of a temperature transmitter.

Next, operations of the current transmission unit 80 and the transmission current control unit 90 will be described.

The computing unit 40 outputs a signal corresponding to the computed value. For example, the output of the computing unit 40 is a pulse width modulation signal having a duty ratio corresponding to the computed flow rate value.

The output of the arithmetic unit 40 is attenuated and smoothed by a high-frequency signal component by a low-pass filter including a resistor R90 and a capacitor C90. The smoothed signal is output via an operational amplifier A90 that constitutes a voltage follower.

The output of the operational amplifier A90 is input to the inverting input terminal (−) of the operational amplifier A91 via the resistor R91, and the voltage Vs80 at the connection point between the transmission current detection resistor Rs80 and the terminal T101 is input via the resistor R92. The

The output of the operational amplifier A91 is passed through the resistor R80 and the resistor R81 so that the voltage at the inverting input terminal (−) of the operational amplifier A91 is substantially equal to the voltage at the non-inverting input terminal (+) (common voltage Vcom). A base current is passed through transistor Q82.

Due to the base current of transistor Q82, a collector current of transistor Q82 (base current of transistor Q80), an emitter current and a collector current of transistor Q80 flow.

As a result, the transmission current Is flows from the positive terminal (+) of the DC power supply 110 into the two-wire transmitter 100 via the terminal T100, and passes through the transmission current detection resistor Rs80, the terminal T101, and the load resistor Rs110. It flows out to the negative terminal (−) of the DC power supply 110.

The inside of the two-wire transmitter 100 operates by receiving a voltage between the terminals T100 and T101 and a transmission current Is from a DC power supply 110.

For example, when the calculated flow rate value is 0 cubic meters per hour, the duty ratio of the output signal of the calculation unit 40 is 20% and the transmission current Is is 4 mA. In the case of 6 cubic meters per hour, the duty ratio is 80% and the transmission current Is is 20 mA. Thus, the two-wire transmitter 100 is supplied with the transmission current Is corresponding to the calculated value from the DC power supply 110.

Next, operations of the variable voltage output unit 50 and the constant voltage output unit 70 will be described.

The transmission current Is flows to the variable voltage output unit 50 via the emitter and collector terminals of the transistor Q80 and the diode D81.

The current I50 output from the variable voltage output unit 50 flows to the input of the constant voltage output unit 70 and is consumed by the constant voltage output unit 70, the variable voltage setting unit 60, the calculation unit 40, and the physical quantity detection unit 30.

The surplus current Ir flows to the common voltage Vcom via the drain and source terminals of the transistor Q50 and the surplus current detection unit 51. The surplus current Ir is a part of the transmission current Is, and is obtained by subtracting the consumption current I50 of the internal circuit from the transmission current Is. In other words, the surplus current Ir is a margin of current consumption of the internal circuit of the two-wire transmitter 100.

The operation is performed so that the voltage Vdiv input to the inverting input terminal (−) of the operational amplifier A50 of the variable voltage output unit 50 is equal to the voltage of the variable voltage setting signal V60 input to the non-inverting input terminal (+). The output of the amplifier A50 controls the surplus current Ir through the transistor Q50.

With this control, the variable voltage V50 output from the variable voltage output unit 50 can be expressed by the following equation (1).

The voltage Vdiv is a voltage obtained by dividing the variable voltage V50 of the variable voltage output unit 50 by the resistor R50 and the resistor R51.

The relationship among the variable voltage V50, the input current I50, the output voltage V70, and the output current I70 input to the constant voltage output unit 70 can be expressed by the following formula (2) using the conversion efficiency T of input / output power. The conversion efficiency T is a value between 0 and 1. The output voltage V70 of the constant voltage output unit 70 is a constant voltage value.

The constant voltage output unit 70 supplies electric power (product of V70 and I70) related to the variable voltage V50 of the variable voltage output unit 50 to the variable voltage setting unit 60, the calculation unit 40, and the physical quantity detection unit 30.

The variable voltage V50 of the variable voltage output unit 50 is related to the variable voltage setting signal V60 of the variable voltage setting unit 60, and the variable voltage setting signal V60 is related to the output voltage V51 of the surplus current detection unit 51 and the surplus current Ir. The variable voltage setting unit 60 outputs a variable voltage setting signal V60 having an arbitrary characteristic with respect to the output voltage V51 of the surplus current detection unit 51.

The relationship between the variable voltage V50 of the variable voltage output unit 50 and the surplus current Ir will be described with reference to FIG.

In FIG. 2A, the surplus current Ir is proportional to the variable voltage V50 of the variable voltage output unit 50. In FIG. 2B, the variable voltage V50 of the variable voltage output unit 50 changes stepwise with respect to the change of the surplus current Ir. In FIG. 2C, the variable voltage V50 of the variable voltage output unit 50 changes in a curve with respect to the change of the surplus current Ir.

First, the operation of FIG. 2A will be described. When the transmission current Is is 4 mA, the surplus current Ir has a value IrA, and the variable voltage V50 of the variable voltage output unit 50 has a value V50A (point A).

When the physical quantity such as the flow rate becomes large and the transmission current Is becomes 20 mA, the surplus current Ir increases, the surplus current Ir becomes the value IrB, and the variable voltage V50 of the variable voltage output unit 50 becomes the value V50B (B point).

At this time, since the variable voltage V50 of the variable voltage output unit 50 increases, the output current I70 of the constant voltage output unit 70 also increases from Equation (2). As the output current I70 of the constant voltage output unit 70 increases and the surplus current Ir decreases, the surplus current Ir becomes the value IrC, and the variable voltage V50 of the variable voltage output unit 50 becomes the value V50C (point C).

The operation of FIG. 2C is as follows. When the transmission current Is is 4 mA, the surplus current Ir has a value IrG, and the variable voltage V50 of the variable voltage output unit 50 has a value V50G (point G).

When the physical quantity such as the flow rate increases and the transmission current Is becomes 20 mA, the surplus current Ir increases, the surplus current Ir becomes the value IrH, and the variable voltage V50 of the variable voltage output unit 50 becomes the value V50H (H point).

At this time, since the variable voltage V50 of the variable voltage output unit 50 increases, the output current I70 of the constant voltage output unit 70 also increases and the surplus current Ir decreases from the equation (2). The value IrI and the variable voltage V50 of the variable voltage output unit 50 become the value V50I (point I).

Next, the operation of FIG. 2B will be described. When the transmission current Is is 4 mA, the surplus current Ir has a value IrD, and the variable voltage V50 of the variable voltage output unit 50 has a value V50D (point D).

When the physical quantity such as the flow rate becomes large and the transmission current Is becomes 20 mA, the surplus current Ir increases, the surplus current Ir becomes the value IrE, and the variable voltage V50 of the variable voltage output unit 50 becomes the value V50E (E point).

At this time, since the variable voltage V50 of the variable voltage output unit 50 increases, the output current I70 of the constant voltage output unit 70 also increases from Equation (2). As the output current I70 of the constant voltage output unit 70 increases and the surplus current Ir decreases, the surplus current Ir becomes the value IrF, and the variable voltage V50 of the variable voltage output unit 50 becomes the value V50E (point F). ).

During the change from the point E to the point F, the variable voltage V50 of the variable voltage output unit 50 is constant to the value V50E. Therefore, the variation of the variable voltage V50 of the variable voltage output unit 50 is compared with FIG. Can be suppressed.

2 will be described in detail using the operations of the surplus current detection unit 51 and the variable voltage setting unit 60 of the variable voltage output unit 50.

The surplus current detection resistor Rs50 detects the surplus current Ir flowing through the resistor, and the voltage of the detection signal is proportional to the surplus current Ir. The AD converter 52 receives the voltage of the detection signal, converts it to a digital signal corresponding to this voltage, and outputs the digital signal to the variable voltage setting controller 61.

The variable voltage setting control unit 61 outputs a pulse width modulation signal V61 having a duty ratio corresponding to the digital signal output of the AD conversion unit 52.

The pulse width modulation signal V61 is attenuated and smoothed by a high-frequency signal component by a low-pass filter including a resistor R62 and a capacitor C62. The smoothed signal is substantially DC and is output to the non-inverting input terminal (+) of the operational amplifier A50 as the variable voltage setting signal V60 of the variable voltage setting unit 60.

For example, in FIG. 2A, when the surplus current Ir increases from the value IrA (point A) to the value IrB (point B), the digital value of the output V51 of the AD converter 52 increases. The variable voltage setting control unit 61 increases the duty ratio of the pulse width modulation signal V61 in proportion to the increase in the digital value.

Similarly, in FIG. 2B or FIG. 2C, the variable voltage setting control unit 61 increases the duty of the pulse width modulation signal V61 in a stepped or curved manner with respect to an increase in the digital value of the output V51 of the AD converting unit 52. Increase the ratio. Note that the variable voltage setting control unit 61 can arbitrarily perform any one of the operations shown in FIGS. 2A, 2B, and 2C.

As the duty ratio of the pulse width modulation signal V61 increases, the DC voltage of the variable voltage setting signal V60 of the variable voltage setting unit 60 increases. Then, as expressed in Expression (1), the variable voltage V50 of the variable voltage output unit 50 increases to become a value V50B.

2A, 2B, or 2C, when the transmission current Is changes from 4 mA to 20 mA, the variable voltage V50 of the variable voltage output unit 50 is changed from the value V50A to the value V50C, the value V50D to the value V50E, or Since the value V50G increases to the value V50I, the output power of the constant voltage output unit 70 also increases from Expression (2). Thereby, since the electric power supplied from the constant voltage output unit 70 to the physical quantity detection unit 30 increases, the voltage of the physical quantity detection signal increases, the S / N ratio increases, and the measurement accuracy of the physical quantity improves.

In addition, for example, the sensor may have a failure such as insulation deterioration, the power consumption of the physical quantity detection unit 30 may increase, and the 2-wire transmitter 100 may malfunction due to insufficient supply current.

However, at this time, in FIG. 2 (a), (b) or (c), the surplus current Ir decreases and the variable voltage V50 of the variable voltage output unit 50 also decreases. The output power of the unit 70 is also reduced. For this reason, it is possible to prevent the 2-wire transmitter 100 from malfunctioning due to insufficient supply current.

According to this embodiment, by increasing the power supplied to the physical quantity detection unit including the sensor based on the detection output of the surplus current within a range that does not hinder the operation of the two-wire transmitter in the two-wire transmitter. A two-wire transmitter that increases the S / N ratio of the physical quantity detection signal and improves the physical quantity measurement accuracy can be realized.

[Second Embodiment]
A second embodiment will be described with reference to FIG. FIG. 3 is another example of a block diagram of a two-wire transmitter to which the present invention is applied. The same components as those in FIG.

The difference between the present embodiment and FIG. 1 which is the first embodiment is the surplus current detection unit 56 and the variable voltage setting unit 65 of the variable voltage output unit 55. This difference will be described below.

First, the configuration of the surplus current detection unit 56 will be described. The surplus current detection unit 56 includes a surplus current detection resistor Rs 50 and a VF conversion unit (voltage signal-frequency signal conversion) 57.

The connection point between the surplus current detection resistor Rs50 and the source terminal of the transistor Q50 is connected to the input of the VF conversion unit 57, and the output of the VF conversion unit 57 is connected to the input of the variable voltage setting control unit 66 of the variable voltage setting unit 65. Connected.

Next, the configuration of the variable voltage setting unit 65 will be described. The variable voltage setting unit 65 includes a variable voltage setting control unit 66 and a DA conversion unit (digital signal-analog signal conversion) 67.

The output of the variable voltage setting controller 66 is connected to the input of the DA converter 67, and the variable voltage setting signal V67 of the DA converter 67 is connected to the non-inverting input terminal (+) of the operational amplifier A50.

The power supply terminals of the variable voltage setting control unit 66 and the DA conversion unit 67 are connected to the output voltage V70 of the constant voltage output unit 70, and these reference voltage terminals are connected to the common voltage Vcom.

Next, operations of the surplus current detection unit 56 and the variable voltage setting unit 65 will be described.

The VF conversion unit 57 receives the detection signal generated in the surplus current detection resistor Rs50, converts it to a frequency signal corresponding to the voltage of this detection signal, and outputs it to the variable voltage setting control unit 66.

The variable voltage setting control unit 66 outputs a digital value signal V66 corresponding to the frequency signal output of the VF conversion unit 57.

The DA converter 67 receives the digital signal output V66 of the variable voltage setting control unit 66, DA-converts this digital signal output V66 into a variable voltage setting signal V67 (digital signal-analog signal conversion), and non-inverts the operational amplifier A50. Output to the input terminal (+).

For example, in FIG. 2A, when the surplus current Ir increases from the value IrA (point A) to the value IrB (point B), the frequency value of the output V57 of the VF converter 57 increases. In response to the increase in the frequency value, the variable voltage setting control unit 66 increases the digital value of the output signal V66.

Along with this, the voltage of the variable voltage setting signal V67 of the DA converter 67 increases. Then, as expressed in Expression (1), the variable voltage V50 of the variable voltage output unit 55 is increased to a value V50B. Note that the variable voltage setting signal V67 of the DA converter 67 can be substituted into the variable voltage setting signal V60 of Expression (1).

According to the present embodiment, a two-wire transmitter similar to the first embodiment can be realized with respect to the two-wire transmitter.

In addition, this invention is not limited to the above-mentioned Example, In the range which does not deviate from the essence, many changes and deformation | transformation are included.

It is a block diagram of a two-wire transmitter to which the present invention is applied. It is a figure showing the relationship between the output voltage V50 of a variable voltage output part, and the surplus current Ir. It is another example of a block diagram of a two-wire transmitter to which the present invention is applied. It is a block diagram of a two-wire transmitter in the background art.

Explanation of symbols

30 physical quantity detection unit 40 calculation unit 50 variable voltage output unit 51 surplus current detection unit 52 AD conversion unit 60 variable voltage setting unit 61 variable voltage setting control unit 62 smoothing unit 70 constant voltage output unit 80 current transmission unit 90 transmission current control unit 100 2-wire transmitter

Claims (9)

In a two-wire transmitter in which a physical quantity is detected by a physical quantity detector and a transmission current corresponding to the physical quantity is supplied,
A variable voltage output unit that outputs a variable voltage, detects a surplus current that is part of the transmission current, and outputs a detection signal;
A variable voltage setting unit that outputs a variable voltage setting signal for changing the variable voltage based on the detection signal to the variable voltage output unit;
A constant voltage output unit that receives the variable voltage and supplies power to the physical quantity detection unit based on the input voltage;
A two-wire transmitter comprising: The variable voltage setting signal is:
Changing the variable voltage stepwise based on the detection signal;
The two-wire transmitter according to claim 1. The variable voltage setting signal is:
Changing the variable voltage in proportion to the detection signal;
The two-wire transmitter according to claim 1. The variable voltage setting signal is:
Changing the variable voltage into a curve based on the detection signal;
The two-wire transmitter according to claim 1. The variable voltage setting signal is:
Changing the variable voltage by a signal obtained by smoothing a pulse width modulation signal having a duty ratio corresponding to the detection signal;
The two-wire transmitter according to any one of claims 1 to 4, wherein the two-wire transmitter is provided. The variable voltage setting signal is:
The variable voltage is changed by a signal obtained by DA-converting a digital signal corresponding to the detection signal.
The two-wire transmitter according to any one of claims 1 to 4, wherein the two-wire transmitter is provided. The detection signal is
AD conversion of the voltage corresponding to the surplus current,
The two-wire transmitter according to any one of claims 1 to 6, wherein the two-wire transmitter is provided. The detection signal is
VF conversion of the voltage corresponding to the surplus current,
The two-wire transmitter according to any one of claims 1 to 6, wherein the two-wire transmitter is provided. The variable voltage output unit includes:
The variable voltage is output using an operational amplifier that controls the surplus current through a transistor so that the voltage obtained by dividing the variable voltage and the voltage of the variable voltage setting signal are equal to each other.
The two-wire transmitter according to any one of claims 1 to 8, wherein the two-wire transmitter is provided.

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