JP2869128B2 - Gas mass flow meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a gas mass flowmeter that generates a pressure fluctuation in a fluid flow path and uses a flow rate whose frequency is proportional to the flow rate.

[Conventional technology]

Since the pulsation frequency is proportional to the flow rate, the overflow meter measures the flow rate, that is, the volume flowing per unit time from that frequency, or measures the integrated flow rate by integrating the number of pulsations.

This vortex flow meter does not require a fluid pressure sensor and temperature sensor, and a complicated arithmetic circuit measures the mass flow rate of unnecessary gas. It is disclosed as prior art.

[Problems to be solved by the invention]

In the above prior art, since the mass flow rate is measured by the vortex flow meter, there is a problem that it is not possible to correctly calculate even a small flow rate.

Therefore, an object of the present invention is to provide a gas mass flowmeter capable of solving this problem.

[Means for solving the problem]

In order to achieve the above object, a gas mass flowmeter of the present invention is a fluidic flowmeter, which includes a pressure / voltage conversion element and a filter for removing unnecessary signals, and a first rectifier circuit that passes only a positive voltage. A second rectifier circuit that passes only a negative voltage, a crosspoint detection circuit that detects a crosspoint of an electric signal, first and second integration circuits that integrate outputs of the first and second rectifier circuits, A calculation / control circuit for calculating and controlling the signal of the cross point detection circuit, wherein a mass flow rate is obtained by integrating the absolute value of the electric signal from the filter for one cycle.

[Action]

When the electric signal obtained by the pressure-voltage conversion element (1) is represented by F (t) as a function of time t, its absolute value | F (t)
The integral value during the period T of | Becomes On the other hand, the frequency of the pulsation is 1 / T, since this frequency is proportional to the flow rate Q, when the proportional constant and K _1, a _{1 / T = K 1 Q ···} (2).

The pulsating pressure detected by the pressure-voltage conversion element is a pressure difference when a fluid pulsates, and is a kind of pressure loss in a fluid circuit. Proportional. In this case, the pulsation pressure F
Since the average value of (t) can be considered as a so-called pressure loss, K ₂ is a proportional constant I will show you.

From equation (3) and equation (2), Get. Since Qρ on the right side of the equation (4) is the mass flow rate, the mass flow rate Qρ is obtained by multiplying the integral value of the equation (1) by a coefficient of K ₁ / K ₂ .

〔Example〕

In FIG. 1, reference numeral 1 denotes a pressure / voltage conversion element, which converts a pressure difference between the pressures of the pressure detection ports 3b and 3c in FIG. 2 into an electric signal. In FIG. 2, reference numeral 2 denotes a flow path, and reference numeral 3 denotes a fluidic element provided in the flow path 2. Fluid flowing from the arrow A to the nozzle portion 3a flows alternately with arrows B and C to generate pulsation. The pulsating pressure is taken out from the pressure detection ports 3b and 3c, and the pressure difference between the two pressure detection ports 3b and 3c is converted into an electric signal by the pressure / voltage conversion element 1. This electric signal is filtered out of unnecessary high-frequency components by the filter 4 shown in FIG. 1, and becomes an output voltage F (t) as shown in FIG. The filter 4 is a so-called low-pass filter. In FIG. 1, 5 is a first rectifier circuit that removes a negative voltage from the output voltage F (t) of the filter 4 and passes only a positive voltage, and 6 is a positive voltage of the output voltage F (t) of the filter 4. A first rectifier circuit that removes only the negative voltage, and 7 and 8 are first and second integration circuits that integrate the outputs of the rectifier circuits 5 and 6, respectively, 9
Are the cross points t ₁ , t of the output voltage F (t) of the filter 4
_2, t ₃ ... cross point detection circuit for detecting a (see FIG. 3), 10 in the arithmetic and control circuit, from the cross point detection circuit 9 the cross point t _1, t _2, t ₃ for each ... in First and second integrating circuits 7, 8 based on the output short pulse signal
In addition to controlling the integration time, that is, determining the integration start time and the end time, the integral values of those integration circuits are taken in, and the mass flow rate is calculated by multiplying by the proportional constant.

The output voltage F (t) of the filter 4 is calculated by the first integrating circuit 7
A positive voltage by, i.e. half a period, are integrated from time t ₀ to t _1, and then the second negative voltage by the integrating circuit 8, i.e. the next half cycle, been integrated from time t ₁ to t ₂ both component value Are added by the arithmetic and control circuit 10. The result of the addition is given assuming that the cycle of the output voltage F (t) is T. Becomes

The frequency of the pulsation generated by the fluidic element 3 is the same as the frequency of the output voltage F (t) of the filter 4. That is, the reciprocal 1 / T of the cycle T of the output voltage F (t). This frequency in proportion to the flow rate Q, a proportionality constant is K _1, the _{1 / T = K 1 Q ···} (2).

The pulsating pressure detected by the pressure / voltage conversion element 1 is a pressure difference when the fluid pulsates (vibrates) and is a kind of pressure loss in the fluid circuit. Generally, the pressure loss of the fluid circuit is the flow rate Q
Is proportional to the product of the density of the fluid and the square of. Since the average value of the pulsating pressure F (t) is considered to be a so-called pressure loss, K ₂ is defined as a proportional constant. I will show you.

From equation (3) and equation (2), Get. Qρ on the left side of the equation (4 ′) is a mass flow rate, and indicates that the arithmetic and control circuit 10 can obtain the mass flow rate.

Having described the measurement in one period from the time t ₀ of FIG. 3 to t _2, as well during the next cycle to obtain the mass flow rate also words from time t ₂ to t ₄ in the above description It is also possible to obtain an integrated mass flow rate by further integrating the values obtained in each of these periods.

〔The invention's effect〕

Since the present invention is configured as described above, there is an advantage that a small flow rate can be measured and a mass flow meter having a wide measurement range can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a fluidic element portion of a fluidic flow meter, and FIG. 3 is a diagram showing an output voltage waveform of a filter 4 in FIG. . 1 pressure / voltage conversion element, 3 liquid crystal element, 3b, 3c pressure detection port, 4 filter, 5,6 rectifier circuit, 7,8 integration circuit, 9 Crosspoint detection circuit, 10 ... Calculation and control circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-128817 (JP, A) JP-A-51-131349 (JP, A) JP-A-58-30620 (JP, A) 189518 (JP, A) JP-A-62-108115 (JP, A) JP-A-62-128325 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1/20 G01F 1 / 32

Claims (1)

(57) [Claims] 1. A fluidic flow meter, comprising: a filter for removing a pressure / voltage conversion element and an unnecessary signal; a first rectifier circuit for passing only a positive voltage; a second rectifier circuit for passing only a negative voltage; A cross point detection circuit for detecting a cross point of a signal, first and second integration circuits for integrating outputs of the first and second rectifier circuits, and a calculation for calculating and controlling a signal of the cross point detection circuit A gas mass flow meter comprising a control circuit, wherein a mass flow rate is obtained by integrating an absolute value of an electric signal from the filter for one cycle.