JPS6052111A - voltage frequency converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage frequency converter for converting a supplied voltage into a frequency.

When physical quantities such as temperature and pressure are detected by a temperature sensor or pressure sensor and used as a temperature correction signal or pressure correction signal in a flow rate measuring device, for example, the obtained analog electrical signal, that is, analog voltage, is converted into a digital signal. A voltage frequency converter may be used to convert. By the way, an integrating circuit with a capacitor is generally used in this voltage frequency converter, but in order to obtain a sawtooth wave voltage in cooperation with this integrating circuit, in the past, an on/off element was connected in parallel to the capacitor of the integrating circuit. For example, when a transistor is connected and the transistor is turned on, the potential difference across the capacitor is zero and the integrated voltage is set to the initial value. Therefore, as the capacitance of the capacitor increases or the internal resistance of the transistor in the ON state increases, the setting time to the initial value becomes longer, and as the setting time increases in this way, the voltage-frequency The linearity of the conversion characteristics cannot be obtained, and this tendency becomes more pronounced as the frequency becomes higher.

The present invention has been made in view of the above-mentioned points, and an object thereof is to omit an on/off element that makes the potential difference between both ends of a capacitor zero when setting an integral voltage to an initial value. It is an object of the present invention to provide a voltage frequency converter that can eliminate the influence caused by the internal resistance of on/off elements and improve the linearity of voltage-frequency conversion characteristics.

According to the present invention, the object is to provide an integrating circuit having a capacitor, a comparator circuit for comparing an integrated voltage outputted from the integrating circuit with a reference voltage, and an integrating circuit for time-refining the supplied voltage. an inverting circuit that inverts the connection of the capacitor of the integrating circuit, and a command signal that inverts the connection of the capacitor of the integrating circuit according to the comparison result signal output from the comparator circuit when the integrated voltage crosses the reference voltage. This is achieved by a voltage frequency conversion circuit consisting of an inversion command circuit.

The present invention will be explained in detail below using one preferred example.

In the figure, resistors 1 and 2 are resistors of pressure sensors, etc.
For example, it is placed in the pipe of a flowmeter, and its resistance value changes depending on the pressure P of the fluid to be measured. In addition, so that the resistance values of resistors 1 and 2 change in different directions due to changes in the pressure P of the fluid to be measured,
That is, for example, the resistors 1 and 2 are arranged so that when the resistance value of the resistor 1 increases, the resistance value of the resistor 2 decreases. The resistors 3 and 4 form a bridge circuit together with the resistors 1 and 2, and a voltage v1 from a power supply is supplied to this bridge circuit via a terminal 5. The voltage ■2 generated at the connection point between the resistors 1 and 2 is supplied to the inverting input of the operational amplifier 7 via the resistor 6, and the voltage ■3 generated at the connection point between the resistors 3 and 4 is supplied to the non-inverting input of the amplifier 7. Supplied to the inverting input.

In the resistors 8, 9, 10 and 11 that divide the voltage vl, the voltage ■4 generated at the connection point between the resistors 8 and 9 is the voltage that is generated by the comparator 12.
The voltage v5 generated at the connection point between the resistors 10 and 11 is supplied to the inverting input of the comparator 13. Note that the connection point between resistors 3 and 4 is also connected to the connection point between resistors 9 and 10. Here, Vl −V4
It is assumed that each of the resistors 3.4.8 to 11 is set so that =V4-V3 =V3 Vs =Vs. The inverting input terminal W of the amplifier 7 is further connected to analog switches 14 and 1.
5, switches 14 and 15 are connected to respective ends 19 and 20 of capacitor 16 and analog switches 17 and 18, switches 17 and 18 are connected to the output terminal of amplifier 7 and the comparator. It is connected to the non-inverting input terminals of 12 and 13. When switches 14 and 18 are conducting, ie on, and switches 15 and 17 are non-conducting, ie off, one terminal 19 of capacitor 16 is connected to the inverting input of amplifier 7 and the other terminal 2
0 are respectively connected to the output terminals of the amplifier 7, and when the switches 14 and 18 are turned off and the switches 15 and 17 are turned on, the terminal 19 is connected to the output terminal of the amplifier 7, and the terminal 20 is connected to the output terminal of the amplifier 7. are connected to the inverting input terminal of the amplifier 7, respectively.

In this way, the resistor 6, capacitor 16 and amplifier 7 constitute an integrating circuit, and the switches 14, 15, 17 and 1
8 constitutes an inverting circuit. Comparators 12 and 1
The output of No. 3 is supplied to an exclusive NOR gate 21, and the output of the gate 21 is supplied to a terminal of a one-shot multivibrator 22 which can be retriggered. When triggered by the rising edge of the signal from the gate 21, the multipipe rake 22 outputs a pulse 25 having a time width T determined by the values of the resistor 23 and capacitor 24 from the Q terminal. Note that since the multivibrator 22 can be retriggered, the gate 2 is activated while the pulse 25 is being generated.
When a rising edge occurs again in the signal from 1, a pulse 25 is generated from the time of the rising edge to time TI. (J
The D-type flip-flop 26, which receives the signal 25 from the multivibrator 22, outputs the logic state supplied to the D terminal to the Q terminal at the rising edge of the Q signal 25. Since the D and Q terminals of the flip-flop 26 are connected, the 7 flip-flop 26 functions as a binary counter for the pulse 25. flip flop 26
The Q terminal of the 7 lip-flop 26 is connected to the on/off control terminals of the switches 15 and 17, and the Q terminal of the 7 lip-flop 26 is connected to the on/off control terminals of the switches 14 and 1B. Switches 14, 15, 17 and 18 receive a logic 1 as a command signal from the flip-flop 26 (on when the D/Q pulse is supplied to the on/off control terminal, while on the other hand, a logic 0 as a command signal). The pulse of flips 7
When it is supplied from the 0 knob 26 to the on/off control terminal, it is turned off. In this way, the gate 21, multi-by-break 22, and flip-flop 26 constitute an inversion command circuit. A voltage 2 is applied to the terminal 27, more specifically, a pulse signal 35 having a frequency proportional to the voltage ΔV (= l Va Vs I) is connected to the 7 lip-flop 26.
is supplied from the Q terminal of Terminal 28 is supplied with the same voltage as the power supply voltage for logic circuits such as data 21.

In the voltage frequency converter 30 configured in this way, when the resistances 1 and 2 have a value corresponding to the pressure P of the fluid to be measured, a voltage V2 is generated at the connection point between the resistances 1 and 2, and the voltage 1 is generated at the connection point between the resistances 1 and 2.
A voltage ΔV (=Va Va, hereinafter referred to as ΔV<0 unless otherwise specified) is supplied between the inverting and non-inverting input terminals of the amplifier 7 via the resistor 6. flip flop 2
The Q terminal of 6 outputs a logic 0.6 terminal outputs a logic 1 signal,
When the switches 14 and 18 are on and the switches 15 and 17 are off, the terminal 19 is connected to the inverting input terminal of the amplifier 7, and the terminal 20 is connected to the output terminal of the amplifier 7. Therefore, the capacitor 16, Resistor 6 and J width device 7
The integrating circuit consisting of the following integrates the voltage ΔV over time and outputs a ramp voltage signal 31 to the output terminal of the amplifier 7. When the voltage of the signal 31 increases over time and exceeds the voltage v4, that is, when the voltage of the signal 31 crosses the voltage v4, the comparator 12 outputs a signal 32 of logic 1. Since the voltage of signal 31 is always higher than voltage 5, the output of comparator 13 is logic 1. As a result, when signal 32 of logic 1 is output from the output terminal of comparator 12, data) 210 Logic O at the edge of the blade
The multivibrator 22 supplies the /ξ pulse 25 to the flip-flop 26. Upon receiving the pulse 25, the flip 70 turns the Q output to a logic 1. As a result of setting the output terminal 6 to logic 0, the switches 15 and 17 are turned on and the switches 14 and 18 are turned off, so that, contrary to the above, the terminal 19 is the output terminal of the amplifier 7, and the terminal 2o is the output terminal of the amplifier 7. are connected to the inverting input terminals of the capacitors 16 and 16, respectively.
When connected in reverse, the voltage at the output terminal of the amplifier 7 drops by the voltage applied to the capacitor 16, and the integrated voltage at the output terminal of the amplifier 7 becomes the initial value, that is, the voltage v
It is set to a value close to l.

Thereafter, the integrating circuit again integrates the voltage △V over time and outputs the ramp signal 34 to the output terminal of the amplifier 7, and the above operation is completed! The operation is repeated, and the output of the amplifier 7 receives a sawtooth wave signal 36.
is generated, and a pulse signal 35 having a frequency proportional to the voltage ΔV is obtained at the terminal 27. Namely.

If the absolute value of the voltage Δ■ is set to increase as the pressure P increases, the slopes of the ramp signals 31 and 34 will increase in proportion to the magnitude of the pressure P of the fluid to be measured. 36 frequencies 1/T.

is in proportion to the magnitude of the pressure P by 1 &+1, so that the frequency of the signal 35 is proportional to the pressure P. In addition, in the above, '1
Although we have explained the case where 11 pressure △V is negative, 11-5 pressure △
When V is positive, the comparator 12 always outputs a logic O signal, the amplifier 7 outputs a ramp signal with a negative slope, and the voltage of the negative slope ramp signal from the amplifier 7 is When the voltage becomes lower than 5, the output of the comparator 13 outputs a signal that changes from logic 1 to logic 0, and at this time, the multivibrator 22 outputs logic 25. As a result, the above Similarly, when the connection of the capacitor 16 is reversed and the integrated voltage increases to its initial value, the pressure P increases, the absolute value of the voltage ΔV increases in proportion to this, so that the pressure ΔV
Even when P is negative, a signal 35 having a frequency indicating the magnitude of the pressure P of the fluid to be measured is obtained at the terminal 27.

By the way, the voltage frequency converter 30 configured as described above
Now, in order to initialize the integral voltage by alternately reversing the connection state of the capacitor 16 to the amplifier 7, in other words, an on/off element is connected in parallel to the capacitor 16 to discharge the capacitor, thereby changing the integral voltage. Since the initial setting is not performed, the time Tsf required for the initial setting can be made extremely short, and therefore, even if the voltage ΔV becomes large, the proportionality of the voltage-frequency conversion characteristic does not deteriorate.

When the integral voltage is initially set, for example, if the voltage ΔV is positive, the reverse connection of the capacitor 16 causes the voltage of the signal 36 to change to voltage V, and the output of the siggate 21, which is relatively low, to change from logic 0 to logic 1. However, this can be ignored by increasing the time ril 'i'l of /('rus 25) compared to time T8, and malfunctions caused by this can be eliminated.

In the above specific example, the voltage frequency conversion @? operates whether the voltage Δ■ is positive or negative. Although r30 has been described, the present invention is not limited thereto, and may operate in either the positive case or the negative case. Moreover, instead of the pressure P of the fluid to be measured flowing on the flow rate side, the temperature of the fluid to be measured may be electrically detected and converted into a frequency. The present invention is not limited to detecting and obtaining the frequency ia-'8, but can also be applied to detecting a general physical m and converting it into a frequency.

As described above, according to the present invention, there is no need to rapidly discharge or charge the capacitor to initialize the integral voltage, so it is possible to eliminate the adverse effects caused by the internal resistance of the on/off element, and save time for initialization. As a result, it is possible to obtain voltage-frequency conversion characteristics with excellent linearity, and in addition, since the capacitance of the capacitor can be increased, the integration circuit can be made resistant to noise.

[Brief explanation of drawings]

FIG. 431 is a circuit diagram of a preferred example according to the present invention, and FIG. 2 is a time chart illustrating the operation of the example shown in FIG. 6...Resistor, 7...Operation amplifier, 12...Comparator, 14.15.17.18...Analog switch, 16...Capacitor, 26...D type fritz flop . 11 Patent Attorneys Hajime Imamura

Claims (3)

[Claims] (1) In order to time-divide the supplied voltage, an integrating circuit with a capacitor, a comparator circuit that compares the integrated voltage output from this integrating circuit with a reference voltage, and the connection of the capacitor of the integrating circuit are reversed. and an inversion command circuit that outputs a command signal to the inversion circuit to invert the connection of the capacitor of the integration circuit according to the comparison result signal output from the comparison circuit when the integrated voltage crosses the reference voltage. voltage frequency converter. (2) The integrating circuit consists of an operational amplifier and a capacitor, and the inverting circuit consists of a first analog switch connected to one input terminal of the operational amplifier and one terminal of the capacitor, and one input terminal of the operational amplifier. a second analog switch connected to the input terminal and the other terminal of the capacitor; a third analog switch connected to the output terminal of the operational amplifier and one terminal of the capacitor; and the output terminal of the operational amplifier and the capacitor. 2. The voltage frequency converter according to claim 1, comprising: the other terminal of the voltage frequency converter; and a fourth analog switch connected to the voltage frequency converter. (3) The reversal command circuit alternately turns on and off the first and fourth analog switches and the second and third analog switches.
The voltage frequency converter according to claim 2, wherein the voltage frequency converter is configured to output the off signal as a command signal for reversing the connection of the capacitor.