JP2786813B2 - Mass flow meter converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter converter, and more particularly to a mass flow meter converter having a small detection sensitivity, for example, suitable for measuring the time difference of a straight pipe type Coriolis flow meter and capable of measuring a time difference with high sensitivity. Mass flowmeter converter.

[0002]

2. Description of the Related Art As is well known, a Coriolis flowmeter supports a measurement tube through which a fluid to be measured flows is supported at both ends, and when a central portion of the supported measurement tube is driven alternately in a direction perpendicular to a support line, a measurement is performed. This is a mass flow meter that detects a phase difference signal proportional to a mass flow rate at a symmetric position between a support portion at both ends of the tube and a central portion. Although the phase difference signal is an amount proportional to the mass flow rate, if the drive frequency is fixed, the phase difference signal can be detected as a time difference signal at the observation position of the measuring tube.

If the frequency of the alternating driving of the measuring tube is made equal to the natural frequency of the measuring tube, a constant driving frequency corresponding to the density of the fluid to be measured can be obtained, and the driving can be performed with a small driving energy. Recently, it has become common to drive the measuring tube at a natural frequency, and the phase difference signal is detected as a time difference signal.

FIG. 5 is a view for explaining an example of a time difference measurement of a conventional Coriolis mass flow meter. FIG. 5 (a)
Is a diagram showing a displacement signal of the measurement tube at the detection position of the measurement tube, a trapezoidal wave signal obtained by amplifying and shaping the detected sine wave signal, time on the horizontal axis, voltage on the vertical axis I have. In the drawing, trapezoids A, B, C, D,... And trapezoids A ₁ , B ₁ , C ₁ , D ₁ ,. The displacement signals of the measuring tubes having different phases with the voltages are shown. Each displacement signal is a continuous trapezoidal waveform having the same shape on the time axis, and the reference time indicating the phase difference time is one trapezoidal waveform A, B ,
Let T be the time between C and D, for example, the peak value C (+ E) or D (-E) of the hypotenuse CD, and the position O crossing the time axis.

[0005] In the displacement signals of the trapezoids A, B, C, D and A ₁ , B ₁ , C ₁ , D ₁ having different phases, for example, a phase difference signal will be described on the sides CD, C ₁ and D ₁ . I do.
The quadrilaterals C, C ₁ , D ₁ , D ₁ are parallelograms, and the parallel sides C
The time difference ΔT between D and C ₁ · D ₁ is a phase difference signal,
C ₁ , D · D ₁ have the same length as the time axis O · O _1, and the projection points from the points C ₁ and D ₁ to the time axis are O ₂ ,
If O ₃ , side O ₂ · O is time (T−ΔT), side O · O ₃
Indicates time (T + ΔT).

The time (T-ΔT) is shown in FIG.
+ ΔT) is shown by the pulse shown in FIG. 5D, and the time difference ΔT is conventionally each time 2M twice as long as the time pulse of the time width M of one trapezoidal wave period shown in FIG. 5B. Are subtracted from each other to obtain an average. That is, (4 (T + ΔT) −4 (T−ΔT)) / 8 = ΔT (1)

FIG. 6 shows a block diagram of a conventional mass flow meter converter for determining the time difference ΔT, and shows a pulse (T + Δ
T) and (T−ΔT) pulse width
Each of the counters 34 as the number of clocks transmitted from 1
And a calculation based on the equation (1) is performed by a CPU (Central Processing Unit) 35, and a digital value proportional to the mass flow rate is output from a terminal 36.

[0008]

In the conventional mass flowmeter converter described above, the time proportional to the phase difference of the measuring tube is digitally measured as the number of clocks, but the time having a resolution corresponding to the accuracy is measured. In order to measure, the number of clocks proportional to the time difference counted at all flow rates must be set to a sufficient number of clocks to match the accuracy. In a curved tube Coriolis flowmeter where the measuring tube is an axisymmetric curved tube and the Coriolis force generated when the curved tube is driven alternately in the direction perpendicular to the symmetry axis generates around the symmetry axis, the moment around the axis is By increasing the value, a sufficiently high-sensitivity time difference signal can be detected and the time difference signal can be counted by the number of clocks.However, unlike a straight tube Coriolis flowmeter, the bending rigidity of the measurement tube is large, and thus the natural frequency is low. If it is large, the time difference signal generated by the Coriolis force is also small, and a clock oscillator that generates a high oscillation frequency (for example, 100 MHz) clock suitable for accuracy has problems in reliability and stability at present.
It is difficult to obtain a satisfactory clock oscillator at low cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mass flowmeter converter for measuring a time difference simply and accurately without using a clock transmitter having a high time resolution.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides (1) a method in which a Coriolis force acting on a measuring tube driven alternately at a constant frequency around a support point is symmetrically applied to the measuring tube. In a mass flow rate converter which detects a time difference ΔT between a pair of displacement signals detected at a position and measures a mass flow rate proportional to the time difference ΔT, the positive and negative values of the displacement signal are equal to an absolute value with respect to a reference time axis. When a pair of trapezoidal wave signals having a peak voltage is formed, and a time difference until a peak voltage position of the oblique side passes with respect to a time when an oblique side of one trapezoidal wave passes the reference time axis is represented by T. The pulse width of the other trapezoidal wave signal is equal to the leading time (T + ΔT) and the delay time (T−ΔT) of passing the peak value of the oblique side, and the leading pulse and the lagging pulse having the constant peak value are input pulses. A gate circuit that opens and closes for a predetermined time to capture the input pulse, and when the gate circuit is opened, N (N> 1) the leading and lagging pulses are simultaneously input and charged, respectively. When the gate circuit is closed, a first and second charge / discharge circuit for discharging the charged electric charge by a reference power supply, and a zero cross of a discharge voltage discharged after charging the first charge / discharge circuit is detected. First
A zero cross detection circuit, a second zero cross detection circuit for detecting a zero cross of a voltage discharged after charging the second charge / discharge circuit, and each of the zeros detected by the first and second zero cross detection circuits. A time difference detection circuit for detecting a time difference between the cross times, and outputting a mass flow rate proportional to the detected time difference. (2) In (1), the mass flow rate is input to the first charge / discharge circuit. An input pulse switching circuit that switches a leading pulse to a delay pulse input, and switches a delay pulse input to the second charging / discharging circuit to a leading pulse input; and a leading pulse input to the first charging / discharging circuit; Time delay of zero crossing time obtained by inputting a delay pulse to the second charge / discharge circuit, and a time difference obtained by inputting a delay pulse to the first charge / discharge circuit and inputting a lead pulse to the second charge / discharge circuit. Time difference of zero crossing time It is characterized in that it has a time course correction means of the charge and discharge circuit for correcting the mass flow rate which is measured in proportion to the time difference deviation.

[0011]

A negative (or positive) forward pulse having a peak value (-E) having a pulse width of time (T + .DELTA.T), and a pulse width of time (T-.DELTA.T) having a peak value equal to the leading pulse. Each of N (N> 1) negative (or positive) delay pulses is charged to a charge / discharge circuit having the same time constant. The charged charges of the charge / discharge circuit are simultaneously discharged by the same positive (or negative) reference power supply. At the time of charging, the N leading pulses and the lagging pulses are charged with an inclination according to the magnitude of the pulse width and have different charging voltages, but at the time of discharging, they are discharged with parallel discharge straight lines inclined with the same time constant. , Zero-crossing, the difference between the zero-crossing positions of the discharge straight line is the time difference ΔT due to Coriolis force
Is enlarged to 2N times.

[0012]

【Example】

Embodiment 1 (corresponding to claim 1) FIG. 1 is a circuit block for explaining Embodiment 1 of a mass flowmeter converter according to the present invention. In the drawing, reference numeral 1 denotes an input terminal of a pulse (T + ΔT); input terminal of the pulse (T-ΔT), the input terminal of the switch SW ₁ 3, the input terminal of the switch SW ₂ 4, the input terminal of the switch SW ₃ 5, the input terminal of the switch SW ₄ 6, 7, 8 , 9,10,14,
15 is a contact, 11 is a positive reference power supply, 12 and 13 are operational amplifier circuits, 16 and 17 are zero cross detection circuits, and 18 is a CPU.
(Central processing circuit).

A negative leading pulse (T + ΔT) having a pulse width of time (T + ΔT) and a constant voltage value (−E)
(Hereinafter simply referred to as (T + ΔT) pulse) input terminal 1 is driven by switch SW ₁ and simultaneously turned on.
It is connected to an integrator composed of an input resistor R ₁ , a feedback capacitor C _1, and an operational amplifier circuit 12 via a contact 7 that is turned on (closed) and turned off (opened) to form a charge / discharge circuit.

At the same time, a negative delay pulse (T) having a pulse width of time (T-.DELTA.T) and a constant voltage (-E) having a pulse width of (T-.DELTA.T).
−ΔT) (hereinafter simply referred to as a (T−ΔT) pulse) is input to the input terminal 2 via the contact 8 and the input resistor R
₂ , a feedback capacitor C ₂ and an integrator including an operational amplifier circuit 13 to form a charge / discharge circuit.

Contacts 14 and 15 driven by switches SW ₄ and SW ₅ are connected in parallel to feedback capacitors C ₁ and C ₂ of the operational amplifier circuits 12 and 13, respectively, and are turned on immediately before the charging operation. The charges of the capacitors C ₁ and C ₂ are discharged. The operational amplifier circuits 12 and 13 are connected to zero cross detection circuits 16 and 17, respectively, and the detected zero cross signals are input to the CPU 18. Here,
The resistance and the capacitance are selected as R ₁ = R ₂ and C ₁ = C ₂ .

[0016] On the other hand, between the contact 7 and the resistance R ₁ and the contact 8 and the resistance R _2, the contact 9 is driven by the switch SW _2, and the contact 10 driven by the switch SW ₃ is connected in series, A reference power supply 11 having a positive reference voltage Es is connected between the contacts 9 and 10. Next, the operation of the mass flowmeter converter configured as described above will be described with reference to FIG.

FIG. 2 is a time chart for explaining the mass flow meter converter shown in FIG. Here, the time t ₁ after the time measurement start for the description. First, the switch SW _4, SW ₅ ON the contacts 14 and 15 by the driving of (FIG. 2 (i), (h) ) and After Death charged charges the feedback capacitor C _1, C ₂ and, High switch SW ₁ The level signals (FIG. 2C) turn on the contacts 7 and 8 at the same time during the period of time t ₁ to t ₂ , and N (T + ΔT) pulses (FIG. 2).
(A)) is input to the resistor R _1, and N (T−Δ)
T) pulse (FIG. 2 (b)) is inputted to the resistor R _2. During this time, the switches SW ₂ and SW ₃ are driven to the Low level signal (FIG. 2).
(D), (e)), and the contacts 9, 8 are turned off.

Therefore, when the N (T + ΔT) pulses are input, the voltage on the straight line AB (FIG. 2 (f)) which rises in proportion to the number of input pulses from the integrator of R ₁ · C ₁ . Is output. At the same time, the input of N (T-ΔT) pulses causes the integrator of R ₂ C ₂ to output the voltage indicated by the straight line AD (FIG. 2 (f)). Clearly, the (T + ΔT) pulse is
Since the pulse width is larger than the (T-ΔT) pulse, the voltage at point B is higher than the voltage at point D.

Next, during the period of time t _{2 to} t ₃ , the switch S
Contacts 7 and 8 are turned OFF by the Low level signal W ₁ (FIG. 2 (c)), High-level signal from the switch SW _2, SW ₃ by OFF signal (FIG. 2 (d), (e) ) output by, The contacts 9 and 10 are turned on, and the reference power supply 1 of the positive reference voltage Es
3 are input to the R ₁ C ₁ and R ₂ C ₂ integrators, respectively.
The charges charged during the respective periods t _{1 to} t ₂ are discharged. Here, R ₁ = R ₂ and C ₁ = C ₂ are selected, the R ₁ C ₁ integrator is discharged according to the straight line B · C, and the R ₂ C ₂ integrator is discharged along the straight line D.
Discharge is performed according to E (FIG. 2 (f)), and each discharge straight line crosses zero-volt line at time position CE.

Since the time constant R ₁ C ₁ = R ₂ C ₂ and discharge by the reference power supply 13 having the negative reference voltage Es, a straight line B · C
, D and E are parallel, and the straight line BD and the straight line EC are proportional. The straight line EC indicates the time axis. The zero cross position C is detected as a zero cross time signal g ₁ by the zero cross detector 16, and the zero cross position E is detected by the zero cross detector 17. is detected as g _2, is output as a pulse having a pulse width g ₁ g ₂ (Fig. 2 (g)).

The period between the time signals g ₁ and g ₂ is a time difference signal obtained by multiplying the time difference ΔT corresponding to N (T + ΔT) −N (T−ΔT) = 2NΔT (2) by 2N,
The zero-crossing time signals g ₁ and g ₂ are converted into digital signals by the clock of the CPU 18 to which the input signals are inputted, digitally processed, and a mass flow signal proportional to the time ΔT multiplied by 2N is output.

Next, the switches SW ₂ , SW ₃ , SW ₄ , S
The operation of the W ₅ will be described. High level signal of the switch SW ₂ that ON contact 10 at time t ₂ (FIG. 2 (d)), the zero cross signal g ₂ at time g ₂ discharge linear D · E (FIG. 2 (g))
To be a Low level signal. At the same time, the zero crossing signal g ₂ is turned ON raised contact 15 up the switch SW ₅ to the High level signal (Fig. 2 (h)), (T- △ T)
The pulse side integrator charge the capacitor C ₂ to death charge. High level signal of the switch SW ₅ is lowered by the High level signal of the switch SW ₁ defining a time t ₃ when the next measurement cycle is started (FIG. 2 (c)) to the Low level signal (h).

[0023] Similarly, trailing the High level signal of the switch SW ₃ was turned ON contact 9 at time t ₂ (see FIG. 2 (e)) is a discharge linear B · C zero cross signal g ₁ (Fig. 2 (g)) It is lowered and becomes a Low level signal. At the same time, the zero cross signal g
₁ launched the switch SW ₄ to the High level signal (FIG. 2 (i)), and ON contact 14 (T + △ T) capacitor c ₁ pulse side integrator to death charge. Switch S
High level signal W ₄ is lowered to the High level signal of the switch SW ₁ defining a time t ₃ when the next measurement cycle is started (FIG. 2 (c)) by a Low level signal (FIG. 2 (i)) .

Looking at the above measurement time, as shown in FIG. 2 (j), the period of time t _{1 to} t ₂ is N (T +
△ T) is a pulse and (T-△ T) charging period for charging the pulse, a period of time t ₂ ~t ₃ is simultaneously discharges the electric charge charged (T + △ T) pulses and (T-△
T) 2N · △ T by determining pulse zero cross times g ₁ and g ₂
Is measured, and the charges of the integration capacitors c ₁ and c ₂ are discharged in the period of time g _{2 to} t ₃ to prepare for the next measurement cycle. Therefore, (T + ΔT) pulse,
(T-ΔT) 2N pulses are input and charged, and after discharging, the period of t ₁ to t ₃ in which the capacitor of the integrator is discharged and the next measurement is prepared is one measurement cycle. Hereinafter, the measurement cycle is similarly repeated.

[0025] According to the mass flowmeter converter according to the first embodiment shown in FIG. 1, the time the switch SW ₁ t ₁ ~t ₂
, N (T + ΔT) pulses and (T−ΔT) pulses are simultaneously taken in, and the drive frequency is the same even if the flow rate of the fluid to be measured changes during the period of time t _{1 to} t _2. Equal numbers of (T + ΔT) pulses and (T−ΔT)
The pulses are arithmetically processed, and a highly sensitive and accurate mass flow signal can be obtained without being affected by flow fluctuation.

In the mass flow converter according to the first embodiment, although the time constant R ₁ C ₁ = R ₂ C ₂ is selected, the resistance R
In addition, the capacitance C changes due to aging over a long period of time under the influence of temperature, and accordingly the time constant changes, and there is a risk that an error may occur in the time difference measurement result. The second embodiment relates to a detection circuit for detecting a time difference deviation caused by changes in the time constants R ₁ C ₁ and R ₂ C _2, and corrects a mass flow rate calculated based on the detected time difference deviation. It is the purpose.

[0027] Example 2 (corresponding to claim 2) FIG. 3 is a circuit block for explaining the mass flow transducer according to Example 2, in the figure, 20 is an input terminal of the switch SW _6, 21, 22 , 23, 24 are contact points, 25, 26
Is an inverter. Parts having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

The circuit block of FIG. 3, in the circuit block of FIG. 1, the contacts 23, is applied (T-ΔT) pulses between the resistor R ₁ and (T + ΔT) contact 7 lines pulse is applied It is connected to the contact 24 between the contact point 8 of the line and the resistance R ₂ that, contacts 23 and 24 are driven by a High-level signal of the switch SW ₆ is connected to the input terminal 20.

Further, an input terminal 20 is connected to an inverter 25.
Is turned on, the contacts 21 and 22 are turned on by the Low level signal of the switch SW _{6, and} an inverter 26 is further connected to the inverter 25.
It is driven by a high level signal of ₅ .

One side of the contact 21 is connected between the contacts 7 and 23 to which the (T + ΔT) pulse is inputted, and the other side is connected between the resistor R ₂ of the (T−ΔT) pulse line and the contact 24. Connected to. Similarly, one side of the contact 22 is (T−Δ
T) is connected between the contacts 8 and 24 to which the pulse is input, and the other side is connected between the resistor R ₁ of the (T + ΔT) pulse line and the contact 23.

[0031] In the circuit block diagram shown in FIG. 3, in a normal period of time difference measurement, the contacts 23 and 24 at the High level signal of the switch SW ₆ is turned ON, the same operation as the mass conversion circuit shown in FIG. 1 A time difference signal g ₂ g ₁ proportional to the mass flow rate as shown in FIG. 2 (g) is detected.

However, at the time of the time difference test for checking whether the time constants R ₁ C ₁ and R ₂ C ₂ are changing with time, the signal of the switch SW ₆ is set to a low level signal, and the contacts 23 and 24 are turned off. , 22 are turned on, the N (T + ΔT) pulses applied to the input terminal 1 are converted to a time constant R
N (T-ΔT) pulses applied to the input terminal 2 are input to an integrator having a time constant of R ₁ C ₁ , which is input to an integrator of ₂ C _2. The time difference signal at the time is compared.

FIG. 4 is an output voltage characteristic for explaining the operation of the mass flow meter operation circuit shown in FIG.
4A shows an output voltage characteristic based on a time difference signal at the time of measurement of a normal time difference signal, and FIG.

FIG. 4 (a) is a diagram showing a time difference signal in the normal flow measurement, the N input to the input terminal 1 (T + ΔT) pulses of constant R ₁ C ₁ when the period t ₁ The signal is input to the integrator and charged in proportion to the number N of input pulses according to the straight line A ₁ · B ₁ until the period t ₂ . On the other hand, N (T-ΔT) pulses simultaneously input to the input terminal 2 are also charged according to the straight line A ₁ D ₁ with the time constant R ₂ C ₂ during the same period, and the switches SW ₁ , SW ₂ , SW ₃ are switched. by being discharged in accordance with each linear _{B 1 · C 1, D 1} · E 1 by the reference power source 11, measurement time difference _{E 1 · C 1 = 2N ·} ΔT = ΔT 1 is measured.

Next, the time difference signal ΔT ₂ at the time of inspection shown in FIG.
T) A pulse is input to an integrator having a time constant R ₂ C ₂ and a straight line A ₂
A charging voltage according to D ₂ is output, and N (T-ΔT) pulses input to the input terminal 2 are input to an integrator having a time constant R ₁ C ₁ at the same time, so as to form a straight line A ₂ .B ₂ The corresponding charging voltage is output. During the next period from t _{2 to} g ₃ , the reference power source 11 discharges according to the parallel straight lines D ₂ · E ₂ and B ₂ · C, and the measurement time difference E ₂ C ₂ = 2NΔT = ΔT ₂ is measured.

If the time constant R ₁ C ₁ = R ₂ C ₂ , the measurement time difference ΔT ₁ = ΔT ₂ and the time constant R ₁ C ₁ and the time constant R
Time course of ₂ C ₂ is determined not. However, the time constant R
_{If 1} C ₁ -R ₂ C ₂ = ΔTε, the measurement time difference ΔTε is detected as twice as large, and becomes | ΔT ₁ −ΔT ₂ | = 2 | ΔTε | (3). An error occurs.
From this, ΔTε is calculated in the CPU 18 and the mass flow rate is corrected.

As described above, according to the mass flow meter conversion circuit of the second embodiment, in addition to the effects of the first embodiment, errors due to temperature change and time-dependent change of a time constant, which is a main part of time difference measurement, are measured. In addition, since the correction is added, it is possible to measure the mass flow rate with high accuracy, high reliability and high reliability.

[0038]

As is apparent from the above description, the converter according to the present invention has the following effects. (1) Effects corresponding to claim 1: N (T + Δ)
T) pulse and (T-ΔT) pulse are taken in at the same time, the integrators having the same time constant are charged, then discharged simultaneously by the reference power supply, and the time difference of the zero cross voltage is measured. A signal is detected, a highly sensitive time difference measurement is measured without using a special clock pulse, and an accurate high-sensitivity mass flow is measured without fluctuation even if there is some flow fluctuation. (2) Effects corresponding to claim 2: N (T + Δ
(T) and (T−ΔT) pulses are input to an integrator having the same time constant for charging and discharging, and the (T + ΔT) pulse and the (T−ΔT) pulse are different from each other during normal measurement and inspection. It is switched to input to the integrator on the side.
It is detected whether or not a time difference of ΔTε occurs in the time difference of 2NΔT obtained by the switching, and when the difference occurs, correction is performed. Can output a mass flow rate measurement signal.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram for explaining a mass flow meter converter according to a first embodiment of the present invention.

FIG. 2 is a time chart for explaining the mass flow meter converter shown in FIG. 1;

FIG. 3 is a circuit block diagram illustrating a mass flow converter according to a second embodiment.

FIG. 4 is an output voltage characteristic for explaining the operation of the mass flow meter operation circuit shown in FIG. 3;

FIG. 5 is a diagram for explaining an example of a time difference measurement of a conventional Coriolis mass flow meter.

FIG. 6 shows a block diagram of a conventional mass flow meter converter for determining a time difference ΔT.

[Explanation of symbols]

1 ... Pulse (T + ΔT) input terminal, 2 ... Pulse (T−
Input terminal of ΔT), 3 ... input terminal of the switch SW _1, 4
... input terminal of the switch SW _2, the input terminals of 5 ... switch SW _3, the input terminal of the 6 ... switch SW _4, 7,8,9,1
0, 14, 15: contacts, 11: reference power supply, 12, 13, ...
Operational amplification circuit, 16, 17 ... Zero cross detection circuit, 18 ...
CPU (Central Processing Unit), 20 input terminals of switch 6, 21, 22, 23, 24 contacts, 25, 26 inverters.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01F 1/84

Claims (2)

(57) [Claims] 1. A Coriolis force acting on a measuring tube driven alternately at a constant frequency around a support point is detected as a time difference ΔT between each pair of displacement signals detected at symmetric positions of the measuring tube. In a mass flow rate converter for measuring a mass flow rate proportional to a time difference ΔT, the displacement signal is a pair of trapezoidal wave signals having positive and negative peak voltages having the same absolute value with respect to a reference time axis, and the hypotenuse of one trapezoidal wave signal Is the time when the peak voltage position on the oblique side passes with respect to the time when the oblique side passes the reference time axis, and T is the advance time (T + Δ) when the oblique side peak value of the other trapezoidal wave signal passes.
T) having a pulse width equal to the delay time (T-ΔT), and a leading and lagging pulse having a constant peak value as input pulses, and a gate circuit that opens and closes for a predetermined time to capture the input pulse; When the gate circuit is opened, the N (N> 1) advance and delay pulses are simultaneously input and charged, respectively, and when the gate circuit is closed, the charged charge is discharged by the reference power supply. A first and a second charge / discharge circuit, a first / zero cross detection circuit for detecting a zero cross of a discharge voltage discharged after the first charge / discharge circuit is charged, and a discharge / discharge after the second charge / discharge circuit is charged. A second zero cross detection circuit for detecting a zero cross of the detected voltage, and a time difference detection circuit for detecting a time difference between the respective zero cross times detected by the first and second zero cross detection circuits. Time difference Mass flowmeter converter and outputs a mass flow rate that example. 2. An input pulse switching circuit for switching a lead pulse input to the first charge / discharge circuit to a delay pulse input, and switching a delay pulse input to the second charge / discharge circuit to a lead pulse input; A first pulse is input to the first charge / discharge circuit, a time difference between zero cross times obtained by inputting a delay pulse to the second charge / discharge circuit, and a delay pulse is input to the first charge / discharge circuit, (2) A charging / discharging circuit with time-dependent change correction means for correcting a mass flow rate measured in proportion to a time difference from a time difference of a zero crossing time obtained by inputting a pulse to a charge / discharge circuit. The mass flow meter converter according to claim 1.