JPS6346821Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a flowmeter that outputs a flow rate signal according to a flow rate larger or smaller than a reference value in accordance with the flow direction of a fluid to be measured. This is an attempt to eliminate many errors.

For example, in an ultrasonic flowmeter, as shown in Figure 1, a pipe 1 in which the fluid to be measured is flowing in a full state.
1, the transducer 12 and 1 are connected via the piping.
3 are provided facing each other. The diameter of the pipe 11 is D,
If the angle between the plane perpendicular to the piping and the propagation path 14 of the ultrasonic wave between the transducers 12 and 13 is θ, the sound speed of the ultrasonic wave in the fluid to be measured is C, and the flow velocity of the fluid to be measured is v, then From the transducer 12 to the transducer 1 when the propagation direction of the ultrasonic wave is in the forward direction of the flow velocity of the fluid to be measured.
The propagation time T of the ultrasonic waves up to 3 is T ₁ =D/cosθ/C+vsinθ (1). The propagation time of the ultrasonic wave when it is propagated in the opposite direction to the flow of the fluid to be measured, that is, the propagation time T ₂ from the transducer 13 to the transducer 12 is T ₂ =D/cosθ/C−vsinθ...(2 ) becomes. From these two equations, the flow velocity v can be found as v=D/sin2θ(1/T ₁ -1/T ₂ ) (3). When the fluid flows in the opposite direction to the state shown in FIG. 1, the sign of the flow velocity v changes. Therefore, in a flowmeter that calculates equation (3), not only the flow velocity but also the flow direction can be determined. In other words, this flowmeter can measure flow rates in both forward and reverse directions.

However, such flowmeters necessarily include a point where the flow rate is zero, so when the flow velocity is very low, the direction of the flow may fluctuate due to fluid vibrations, etc., making the flow rate unstable and causing the reading to become inaccurate. The drawback was that it was difficult to see. In order to avoid this drawback, this variation has conventionally been removed using the principle shown below. That is, as shown in FIG. 2, the flow rate signal V _i from the terminal 16 is compared with the zero flow rate voltage from the power supply 17 in the comparator 15 which is given hysteresis characteristics by positive feedback, and the output terminal of the comparator 15 is 18, a signal indicating the direction of flow is detected. The input/output characteristics of this comparator 15, that is, the flow rate v
As shown in Figure 3, the comparator output _Vout for
is a low level, and it remains at a low level even when v becomes smaller than this and reaches zero, and only when the flow direction is reversed and the flow rate v becomes even smaller than -V ₀ .
Vout becomes a high level, and conversely, when the flow rate v increases, it becomes a high level only when it exceeds _V0 . In this way, unless the flow rate v changes by more than ±V ₀ , the output indicating the flow direction will not change, and therefore, it is possible to eliminate fluctuations in the flow direction indication near the zero flow rate.

However, for example, as shown in Figure 4A, the flow rate v is
If the flow direction continues to decrease from a state larger than V ₀ and does not become smaller than -V ₀ even if the flow direction is reversed at time _{t 0} , the flow direction detector shown in FIG. It remains pointing to the previous flow direction. Also, as shown in Figure 4B, if the steady flow rate is small and a relatively large flow rate flows in the opposite direction for a short period of time from time t ₀ to t ₁ , an instruction is given in the opposite direction to the steady flow direction. This results in a large flow rate error.

The purpose of this device is to generate a flow rate signal that stably indicates the correct flow direction even if the flow direction oscillates at a small flow rate, and to output a flow rate signal that correctly indicates the changed state even if the flow direction changes at a small flow rate. Our objective is to provide a flowmeter that

According to this invention, the flow rate signal from the flow rate detection section is periodically integrated by the integrating means. An average flow rate calculation means performs calculations on each of the integration results to obtain an average flow rate signal for each integration period, which is output as a flow rate signal. Since errors based on changes in flow direction occur in a range where the flow rate is small, a means is provided to detect when the flow rate is larger than a predetermined value, and this output indicates that if the flow rate is larger than the predetermined value, the averaged flow rate signal is detected. Instead, it is also possible to directly output the flow rate signal from the flow rate detection section.

Figure 5 shows an example of a flowmeter based on this invention.
The flow rate detection unit 21 is, for example, an ultrasonic flowmeter, and its output terminal 22 receives a voltage flow rate signal V _i that is proportional to the flow rate and whose sign (polarity) changes depending on the flow direction.
appears. This flow rate signal is integrated by an integrating circuit 23. The integrating circuit 23 includes an operational amplifier 24, an input integrating resistor 25, and an integrating capacitor 26. connected across the integrating capacitor 26
The FET switch 27 is turned on at regular intervals Δt by the output of the timer 28, and the integration circuit 23 is reset, which is repeated.

The integral output of the integrating circuit 23 is sampled and held in the sample and hold circuit 29 immediately before its reset. That is, the output of the operational amplifier 24 is sampled and held in the capacitor 32 through the FFT analog switch 31 immediately before the switch 27 is turned on. The integrated value held in this capacitor 32 is supplied to an average calculation circuit 34 through a buffer circuit consisting of an operational amplifier 33. Average calculation circuit 34
is used to calculate the time average of the integrated value of the flow rate signal at the terminal 22 during the integration period of Δt, and includes, for example, an operational amplifier 35, an input resistor 36, and a negative feedback resistor 37. By selecting the resistance value of , the amplifier is configured with a gain of 1/Δt. The calculated output is used as a flow rate output signal of the flow meter.

In this embodiment, if the flow rate of any flow exceeds a predetermined value, the flow rate signal at the terminal 22 is directly used as the flow meter output. Therefore, the flow rate signal V _i at the terminal 22 is set to an absolute value |V _i | by the absolute value circuit 38 . In other words, when the flow rate signal V _i is positive, it is supplied to the adding circuit including the operational amplifier 42 through the resistor 39, and when the flow rate signal V _i is negative, it is made positive by the polarity reversing circuit including the operational amplifier 41, and the operational amplifier 42. The output of the absolute value circuit 38 is compared with the reference voltage V ₀ of the power supply 44 by a comparator 43, and if the absolute value output |V _i | is larger than V ₀ , the output of the comparator 43 switches the switch 45
is switched to the contact a side, and the flow rate signal V _i of the terminal 22
is output to the output buffer circuit 46 through the switch 45. When the absolute value output |V _i | is smaller than the reference voltage V ₀ , the switch 45 is switched to the contact b side by the output of the comparator 43, and the average calculation circuit 34
The output of the switch 45 is output to the output buffer circuit 46. The output of the output buffer circuit 46 becomes the flowmeter output.

As described above, according to the configuration shown in FIG. 5, even if the flow direction changes more than once during one integration time Δt, the sum of the flow rates in one direction during that period Δt , the difference between the sum of the flow rates in the other direction is obtained as the output of the integrating circuit 23, and this value is equal to the sum of the flow rates in the other direction.
Since this is the total flow rate that flowed in time t, the average flow rate in that time Δt is the value obtained by dividing the integral value that is the output of the sample and hold circuit by Δt, and this is output from the average calculation circuit 34. Therefore, even if the flow direction oscillates or the flow direction changes but the flow rate after the change is small, it is possible to obtain a flow rate signal in the correct flow direction, and by appropriately selecting the time Δt, the flow direction can be determined. A stable output can be obtained without vibration.

Furthermore, according to the embodiment shown in FIG. 5, an instantaneous flow rate signal can be obtained when the flow rate is large, and if the flow direction is suddenly reversed during time Δt and the flow rate is large, the reverse signal can be obtained. When the switch 45 is switched, the signal at the terminal 22 is outputted, and a correct measurement is performed.

The example shown in FIG. 5 can also be implemented by a microcomputer. For example, when the system is started as shown in Fig. 6, the contents of the buffer memory M are first cleared in step _S1 , and the flow rate signal V _{i is cleared} in step _S2 .
, and check whether its absolute value |V _i | is smaller than V ₀ . If ｜V _i ｜＞V ₀ , step S ₂
Set V _i as the flowmeter output and return to step _S1 . If |V _i |<V ₀ in step _S2 , move to step _S4 ,
Add V _i to the contents of buffer memory M. Next, in step _S5 , it is checked whether the contents of the counter C that counts clocks has reached a certain value, that is, whether △t has elapsed.
Returning to _S2 , if the result is Δt, proceed to step _S6 , divide the contents of the buffer memory M by Δt, obtain the average flow rate, and return to step _S1 as the flow meter output.

If a microcomputer is used in the detection unit 21, this microcomputer is used to
The operations shown in the figure only need to be performed, and almost no special hardware is required.

The flow rate signal is not limited to one whose polarity changes depending on the flow direction; with a constant value V _Q as a reference, the larger the flow in the positive direction, the greater the output than V _Q , and the larger the flow in the negative direction, the greater the output V _Q. This idea can also be applied to smaller flow rate signals.
In this case, in Figure 5, V _Q is applied to the reference input side of the operational amplifier of the integrating circuit, and instead of the absolute value circuit,
The switch 45 may be connected to the b side by detecting that it is outside the range of V _Q ±△V. Furthermore, this idea can be applied not only to ultrasonic flowmeters but also to flowmeters that can detect flow in the forward and reverse directions, such as electromagnetic flowmeters.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the flow mass and the transducer of an ultrasonic flowmeter, Figure 2 is a connection diagram showing the flow direction detector of a conventional flowmeter, and Figure 3 is the same as shown in Figure 2. 4 is a diagram showing the flow rate over time to explain the problems with conventional flowmeters; FIG. 5 is a connection diagram showing an example of a flowmeter according to this invention; FIG. 6 is a diagram showing input/output characteristics of the detector; The figure is a flowchart showing an example of the operation when this invention is configured using a microcomputer. 21...Flow rate detection section, 23...Integrator circuit, 28
...Timer, 29...Sample hold circuit, 3
4...Average calculation circuit, 38...Absolute value circuit, 43
... Comparator, 46 ... Output buffer circuit.

Claims (1)

[Scope of utility model registration request] a flow rate detection means for detecting a flow rate signal according to the flow direction of the fluid to be measured with a reference value as a boundary; and a comparison detection means for detecting whether the flow rate signal is within a predetermined range including the reference value. , an integrating means for integrating the flow rate signal for a certain period of time at a predetermined period and outputting this integrated voltage; and a holding means for sampling and holding this integrated voltage for a certain period of time;
An averaging circuit that averages the sampled and held integrated voltage over the certain period of time and outputs an average flow rate signal; and an output of the comparing and detecting means are input; A flowmeter comprising: a selection means for outputting the flow rate signal as it is and for outputting the average flow rate signal when the flow rate signal is within the predetermined range.