JP3210127B2 - Voltage pulse width conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used as a circuit for converting an analog quantity into a digital quantity (pulse width). Although the present invention has been invented for use in an automatic control device, it can be used as an element of another analog-to-digital conversion circuit. INDUSTRIAL APPLICABILITY The present invention is used for a device that adjusts and controls a valve opening of a process control system by a DC control signal transmitted to a two-wire transmission line. In particular, the present invention relates to a voltage pulse width conversion circuit of a valve position meter that converts an actual opening of a controlled valve into a pulse width signal in a two-wire transmission path, and superimposes this pulse signal on a DC control signal for transmission. .

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a first conventional remote control measuring apparatus. FIG. 7 is a block diagram showing a second conventional remote control measuring apparatus. FIG. 8 is a block diagram of a third conventional remote control measuring device.

Conventionally, a remote control measuring device has a configuration as shown in FIGS. That is, FIG. 6 shows an example in which a control device sends a DC control signal to an automatic control valve, which is an operation unit, to perform control. In this case, the control device cannot detect the control result of the operation unit or the failure. FIG. 7 shows an example in which a control device side can detect a control result or a failure of the operation unit, and is an example in which wiring different from a control signal is provided from the control device to the operation unit. FIG. 8 shows a configuration in which the control device can detect a control result of the operation unit or a failure without providing a separate wiring from the control signal.
A control signal of ~ 20 mA is sent to control the operation unit, the operation amount of the operation unit is detected, the operation amount is converted into a feedback signal voltage, and a pulse signal corresponding to the feedback signal voltage is superimposed on the control signal to control the operation amount. (Japanese Patent Laid-Open No. 4-6993)
0).

[0004]

However, the voltage pulse width conversion circuit used in such a conventional remote control device has the following points to be improved. That is, the feedback signal voltage and the pulse signal width have a linear proportional relationship, and the control device can easily detect the mechanical displacement by the feedback signal. Further, since the operation unit is installed in the field, it is necessary to endure a wide range of environmental conditions. The operation unit and the feedback circuit side do not have a separate power supply, and the power supply of the pulse width conversion unit is a direct current of a control signal of 4 to 20 mA. It is necessary that the feedback circuit can be driven with a minimum current of 4 mA or less.
The allowable resistance value of the control signal of 4 to 20 mA from the control system of the control device is usually about 600Ω, and therefore, it is necessary to maximize the line resistance of the operation unit and the transmission line. The voltage is 4 V or less and it is necessary to drive at this voltage. Generally, since the output impedance of the sensor is high, the impedance of the analog-to-digital converter on the receiving side in the feedback circuit on the receiving side needs to be high. That is, the operation of the feedback circuit does not affect the control output of the operation unit.

[0005] The present invention has been made in such a background, and it is possible to feed back a feedback signal which can be easily detected on the control device side without requiring a separate transmission line and a separate power source, and An object of the present invention is to provide a voltage pulse width conversion circuit for a remote control measurement device which can be driven at 4 V or less, has high impedance, and does not affect a controlled device.

[0006]

According to a first aspect of the present invention, an RS flip-flop circuit (16) includes a resistor (14) and a capacitor (14) connected in series between an inverted output of the RS flip-flop circuit and a common potential. 13), and compares the voltage (Vi) of the input signal with the charging voltage of the first temporary constant circuit.
A first comparator (12) connected to a set input of the flip-flop circuit; and a resistor (17) and a capacitor (26) connected in series between the output of the RS flip-flop circuit and a common potential. The second time constant circuit compares the first reference voltage (V5) with the charging voltage of the second time constant circuit , and the comparison output is fed back to the second time constant circuit .
A system that changes one reference voltage to a second reference voltage
Tsu Preparative second comparator (20) compares the comparison result output and the first reference voltage of the second comparator, by resetting the previous SL RS flip-flop circuit at its output And a third comparator ( 25) for outputting the inverted output of the RS flip-flop circuit as a pulse width pulse signal.

A second invention is a first invention comprising an RS flip-flop circuit (16) and a resistor (14) and a capacitor (13) connected in series between the output of the RS flip-flop circuit and a common potential. A time constant circuit, a first comparator connected to a reset input of the RS flip-flop circuit, comparing a voltage (Vi) of an input signal with a charging voltage of the first temporary constant circuit, 12),
A second time constant circuit including a resistor (17) and a capacitor (26) connected in series between the inverted output of the RS flip-flop circuit and a common potential; a first reference voltage (V5); Comparison with the charging voltage of the time constant circuit
And the comparison output is fed back, so that the first reference
Schmitt-type second voltage
Second comparator (20) compares the comparison result output and the first reference voltage of the second comparator, the output of its R
Characterized in that a S third comparator which outputs the output of the flip-flop circuit set pre Symbol RS flip-flop circuit as a pulse width pulse signal (2 5).

Further, in the first invention or the second invention, it is preferable that the RS flip-flop circuit is a complementary mos. That is, by using the complementary mos, the output voltage of the RS flip-flop can be made constant with a large load resistance, so that the power consumption can be reduced.

[0009] Further, the first invention or the second invention,
The voltage pulse width conversion circuit compares the first reference voltage with the charging voltage of the second time constant circuit, and discharges the charging voltage of the second time constant circuit together with the operation of the second comparator. A third comparator (21).

[0010]

The remote control measuring device is connected to a control device and a controlled device controlled according to the value of a DC control signal from the control device, and is a measured value according to the displacement of the controlled device (operation unit). Detection circuit (sensor) that generates a pulse width signal proportional to the electric signal, a voltage pulse width conversion circuit that generates a pulse width signal proportional to the electric signal, and a pulse width signal from the voltage pulse width conversion circuit superimposed on the DC control signal. And a feedback circuit for feedback.

Here, the voltage pulse width conversion circuit is a 1-bit tracking type analog circuit in which a power supply circuit is connected in series to a current path of a DC control current, and is configured by four comparators and one flip-flop circuit. Consisting of digital converters,
Since a pulse width signal is generated according to the mechanical displacement of the controlled device, a feedback signal that is highly accurate and easily detected by the control device can be fed back without requiring a separate transmission line and a separate power supply. . Further, the drive voltage of the voltage pulse width conversion circuit is determined by the drive voltages of the comparator and the flip-flop circuit and operates at 2V, so that the voltage can be reduced to 4V or less. The input impedance is determined by the input impedance of the comparator and can be 10 MΩ or more. Further, since the current used is about 2 mA, a DC control signal of 4 to 20 mA is sufficient.

[0012]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a voltage pulse width conversion circuit according to an embodiment of the present invention. FIG. 5 is a block diagram of a remote control measuring device to which the voltage pulse width conversion circuit of the present invention is applied. In FIG. 5, the remote control measurement device includes a control device 30 and a DC control signal (4 to 2) from the control device 30.
Controlled device (operation unit) controlled according to the value of 0 mA)
A position detection circuit (sensor) 4 which is connected to the control unit 41 and generates a measured value corresponding to the displacement of the controlled device 41 as an electric signal;
2, a voltage pulse width conversion circuit 43 for generating a pulse width signal proportional to the electric signal, and a voltage pulse width conversion circuit 4
And a feedback circuit 44 for superimposing the pulse width signal from 3 on the DC control signal and feeding it back.

In FIG. 1, the voltage pulse width conversion circuit is characterized by an RS flip-flop circuit 16;
RS flip-inverted output Q of flop circuit 16 ^- resistor connected in series between the common potential 14 and the capacitor 1
3, a feedback signal voltage Vi as an input signal voltage and a charging voltage of the first temporary constant circuit, and the comparison result output is an RS flip-flop circuit 1.
6 and a second time constant comprising a resistor 17 and a capacitor 26 connected in series between the output of the RS flip-flop circuit 16 and the common potential, as a first comparator connected to the set input S of No. 6 Circuit and a first reference voltage (V
5 = VZ1) and the charging voltage of the second time constant circuit, and the comparison output is fed back to change the first reference voltage.
A comparator 20 serving as a Schmitt-type second comparator is set to a second reference voltage, and a comparison result output of the second comparator is compared with the first reference voltage (V5 = VZ1). further comprising a ratio <br/>較器25 as a third comparator to output a pulse width pulse signal ^- inverted output Q structured R S flip-flop circuit 16 resets RS flip-flop circuit 16 at its output It is in.

A third comparator which compares the first reference voltage with the charge voltage of the second time constant circuit and discharges the charge voltage of the second time constant circuit together with the operation of the comparator 20 As a comparator 21.

The operation of the remote control device having such a configuration will be described. FIG. 2 is a diagram showing a signal waveform of each part of the voltage pulse width conversion circuit of the present invention. 1 and 2, the circuit can be driven at a power supply voltage Vp of 2.5 to 5V. Feedback signal voltage Vi from controlled device 41
Is connected to the inverting input of the comparator 12. A bias resistor 15 of the comparator 12, which is an open collector output, is connected to the set input of the RS flip-flop circuit 16 at a connection point with the comparator 12, and when the output of the comparator 12 becomes high level (FIG. 2). The voltage of the RS flip-flop circuit 16 is inverted like the voltage V2 of FIG.
V4).

The time constant circuit constituted by resistor 14 and capacitor 13 are inverted output Q of the RS flip-flop circuit 16 ^- is connected to the set input S is discharged with a time constant that becomes a high level (voltage in FIG 2 V1 ). On the other hand, R
The output Q of the S flip-flop circuit 16 is connected to a time constant circuit composed of a resistor 17 and a capacitor 26,
This voltage (charging voltage) V6 is connected to the comparator 20 and compared with the reference voltage V5 (VZ1), and the reference pulse width time t2
Create

The output of the comparator 20 is connected to the reset input R of the RS flip-flop circuit 16 via the comparator 25, and inverts the output of the RS flip-flop circuit 16. Resistance 18,19,22 constitutes a Schmitt circuit at a comparator 2 0, the "on" and "off" of the comparator 25 defines a voltage of two positions of the reference voltage V5. The comparator 21 constantly compares the reference voltage (V5) with the voltage V6. When the Schmitt circuit operates, the comparator 21 operates when the reference voltage drops, and has a function of rapidly discharging the electric charge charged in the capacitor 26. I do.

FIG. 3 is an enlarged view of the charging voltage of the first time constant circuit of the voltage pulse width conversion circuit of the present invention. The principle of converting the input voltage Vi into a pulse width proportional to the input voltage Vi will be described with reference to FIG. E is the maximum value of the charging voltage (power supply voltage), V
i is the input voltage, Vf is the discharge voltage value after the reference time t2 from the input voltage value, t1 is the time from the discharge voltage value Vf until the input voltage Vi is charged, and t2 is the reference time determined by the resistor 17 and the capacitor 26. is there. Assuming that T is a time constant determined by the resistor 14 and the capacitor 13, Vi = E (1−e− ^{(t1 / T)} ) + Vf (1) Vf = Vi · e− ^{(t2 / T)} ) (2) From the equations (1) and (2), Vi = E (1−e− ^{(t1 / T)} ) + Vi · e− ^{(t2 / T)} (3) Equation (3) is satisfied. Here, by selecting the resistor 14 and the capacitor 13 satisfying t1 << Tt2 << T, the equation (3) can be arranged as follows: Vi = E (1-e- ^{(t1 / T)} ) / (1-e ^{- (t2 / T)) ≒} E {1- (1-t1 / T + 0.5 (t1 / T) 2} / {1- (1-t2 /T+0.5(t2/T) 2} ≒ E (t1 / T) / (t2 / T) = E · t1 / t2 (4) That is, t1 = t2 · Vi / E (t2 = constant), which is proportional to the input voltage.

FIG. 4 is a block diagram of a voltage pulse width conversion circuit according to another embodiment. FIG. 4 shows that the first time constant circuit is RS
The output of the comparator 12 is connected to the reset input R of the RS flip-flop circuit 16 and the second time constant circuit is connected to the output of the RS flip-flop circuit 16.
Inverted output Q ^- is connected to, and that the output of the Schmitt circuit is connected to the set input S of the RS flip-flop circuit 16 is different from the circuit shown in FIG. 1, the principle is the same.

As described above, the present invention satisfies the above problems as follows. A. The measured values in the present invention show that the non-linear error of the output is ±± with respect to an input voltage of 0.3 V to 1.5 V at a power supply voltage of 3.7 V.
0.1% or less. Further, the use environment (temperature change) is 0.05% / 10 ° C. or less, which is a value sufficient for practical use, and satisfies the problem to be solved by the present invention. B. The minimum allowable power supply voltage is determined by the drive voltage of the comparator and the RS flip-flop circuit used in this circuit. Since the driving voltage of the above circuit element operates from 2 V due to recent advances in semiconductor technology, the problem to be solved by the present invention is satisfied. C. The part receiving the input signal is determined by the impedance of the input of the comparator 12 because of the non-inverting method. Usually, it is easy to set the input impedance of the comparator to 10 MΩ or more, and there is no problem at all. Further, it is convenient to operate the input voltage from the circuit common side, but in this case, if the comparator is of the NPN type, it may not operate. Therefore, as the input stage of the comparator,
By using a PNP type or FET type comparator, it is also possible to drive from a circuit common potential. D. The power supply voltage uses a control current of 4 mA to 20 mA in the transmission line. The current used in this circuit is about 2 mA and can be operated sufficiently. Therefore, the surplus current can be easily solved by using a bypass circuit, for example, a constant voltage diode. E. FIG. Another feature of the circuit according to the invention is that R
A plurality of S flip-flop circuits and comparators can be used. Further, as shown in Expression (4), since the time constant of the first time constant circuit is deleted, the capacitor 13
Inexpensive resistors and resistors 14 are used.

[0022]

As described above, according to the present invention, the feedback signal voltage and the pulse signal width have a linear proportional relationship, and a signal corresponding to the mechanical displacement of the controlled device is accurately fed back.
Also, since the operation unit is installed in the field, it can withstand a wide range of environmental conditions. The operation unit and the feedback circuit side do not have separate power supplies, and the power supply of the pulse width conversion unit is a direct current of control signal of 4 to 20 mA. The allowable resistance of the control signal of 4 to 20 mA from the control system of the control device is usually about 600Ω, and the line resistance of the operation unit and the transmission line is minimized. The power supply voltage that can be tolerated in the feedback circuit is 4 V or less because it needs to be large, and it can be driven with this voltage. In general, the output impedance of the sensor is high. The impedance of the converter is high impedance,
There is an excellent effect that the operation of the feedback circuit does not affect the control output of the operation unit.

[Brief description of the drawings]

FIG. 1 is a block diagram of a voltage pulse width conversion circuit according to an embodiment of the present invention.

FIG. 2 is a view showing signal waveforms of respective portions of the voltage pulse width conversion circuit of the present invention.

FIG. 3 is an enlarged view of a charging voltage of a first time constant circuit of the voltage pulse width conversion circuit of the present invention.

FIG. 4 is a block diagram of a voltage pulse width conversion circuit according to another embodiment of the present invention.

FIG. 5 is a block diagram of a remote control measurement device to which the voltage pulse width conversion circuit of the present invention is applied.

FIG. 6 is a block diagram of a first conventional remote control device.

FIG. 7 is a block diagram of a second conventional remote control device.

FIG. 8 is a block diagram of a third conventional remote control device.

[Explanation of symbols]

2, 14, 15, 17, 18, 19, 22, 23, 24
Resistance 12, 20, 21, 25 Comparator 13, 26 Capacitor 16 RS flip-flop circuit 30 Control device 41 Controlled device (operating unit) 42 Position detection circuit (sensor) 43 Voltage pulse width conversion circuit 44 Feedback circuit V1-V7, Vf, Vi voltage

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-297021 (JP, A) JP-A-2-250432 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03M 1/00-1/88

Claims (4)

(57) [Claims] 1. An RS flip-flop circuit (16),
A first time constant circuit including a resistor (14) and a capacitor (13) connected in series between the inverted output of the RS flip-flop circuit and a common potential; a voltage (Vi) of an input signal; A first comparator (12) connected to a set input of the RS flip-flop circuit, for comparing the charge voltage of the constant circuit with a charge input of the RS flip-flop circuit;
A second time constant circuit comprising a resistor (17) and a capacitor (26) connected in series between the output of the flip-flop circuit and the common potential; a first reference voltage (V5); and a second time constant Compares the charging voltage of the circuit and outputs the comparison
Is fed back to change the first reference voltage,
Schmitt-type second comparator (2
0), it is compared with the comparison result output and the first reference voltage of the second comparator, by resetting the previous SL RS flip-flop circuit at its output, an inverted output of the RS flip-flop circuit A voltage pulse width conversion circuit comprising: a third comparator ( 25) for outputting a pulse width pulse signal. 2. An RS flip-flop circuit (16),
A resistor (14) and a capacitor (1) connected in series between the output of the RS flip-flop circuit and the common potential.
3) and the voltage of the input signal (V
i) is compared with the charging voltage of the first temporary constant circuit, and a comparison result output is connected to a reset input of the RS flip-flop circuit, a first comparator connected to (12), and an inversion of the RS flip-flop circuit. A second time constant circuit comprising a resistor (17) and a capacitor (26) connected in series between the output and the common potential; a first reference voltage (V5); and a charging voltage of the second time constant circuit compares the door, and out comparison
By changing the first reference voltage by the feedback of the force
Schmitt-type second comparator (2
0), the second comparison comparator comparison result output of the said first reference voltage, outputs a pulse width pulse of the RS flip-flop circuit set pre Symbol RS flip-flop circuit at the output of its Third comparator to output as signal
( 25) A voltage pulse width conversion circuit, comprising: 3. The voltage pulse width conversion circuit according to claim 1, wherein the RS flip-flop circuit is a complementary mos. 4. The voltage pulse width conversion circuit compares the first reference voltage with a charging voltage of the second time constant circuit, and operates the second time constant circuit together with the operation of the second comparator. 3. The voltage pulse width conversion circuit according to claim 1, further comprising a third comparator for discharging the charging voltage.