JPH0574844B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of Description] The present invention relates to a flow rate control device for open channels such as agricultural canals and tunnels, and in particular, by reducing the flow delay time of open channels. This invention relates to an open channel flow rate control device that can stabilize the water level of water.

[Background of the invention]

In agricultural canals, etc., as shown in Fig. 7, water in a reservoir 1 is guided by gravity to a regulating tank 5 via a flow rate regulating valve 2 and an open channel 4, and from there further flows down to consumers. . The water level in the regulating water tank 5 needs to be controlled so as not to fluctuate too much in order to provide a stable supply of water to consumers. Therefore, the inflow flow rate Q ₀ to the open channel 4 and the outflow flow rate Q _a to the consumers (the total flow rate if there are multiple consumers) are detected by the flow rate detectors 3 and 7, and the valve 2 is adjusted according to the difference between them. Feedback control is performed to adjust the opening degree, that is, the inflow flow rate _Q0 . However, when the open channel 4 is long, a large flow delay time is required from when the flow rate Q ₀ at the position of the valve 2 changes until the flow rate at the inlet of the water tank 5 changes accordingly. The feedback control may become unstable, and undesirable fluctuations such as hunting may occur in the water level of the water tank 5. A conventional technique for solving this problem is disclosed in Patent No. 873851, in which when a difference occurs between the inflow flow rate Q ₀ and the outflow flow rate Q _a , the opening degree of the valve 2 is slightly changed. Wait until the effect appears on the aquarium side,
In addition, a method of slightly changing the opening degree is used to prevent hunting and the like. However, this has the disadvantage that the response time becomes longer and temporary water level fluctuations in the aquarium become larger.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an open channel flow rate control device that is capable of performing stable and quick response control by reducing the flow delay time of an open channel.

[Summary of the invention]

In the present invention, water is stored in an open channel in an amount that changes depending on the flow rate (this is called the storage amount), and one of the major factors in the flow delay time is the amount of water stored when the flow rate changes. Focusing on the fact that this is to follow changes, when changing the flow rate, a large flow rate change is applied until the change in storage amount is compensated for, and then normal control is performed so that the inflow flow rate follows the outflow flow rate. It is characterized by the fact that it is designed to be carried out.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail, and first, prior to working examples, the amount of storage in an open channel will be described. 6th
The figure is an explanatory diagram thereof, where L is the length from the valve 2 in FIG. 7 to the inlet of the water tank 5, and the horizontal axis represents the position along the open channel. Moreover, the vertical axis shows the water level EL when taken with an appropriate horizontal plane as a reference. The bottom of the open channel 4 is a straight line AB, and the water level is EL2 at the inlet (position of valve 2) and the water level EL1 at the outlet (water tank inlet). When water is flowing down at a certain flow rate Q ₁ , the water head is a straight line DC, and the water level at the inlet is
EL5, the water level at the exit is EL3. Therefore, the storage amount V ₁ at this flow rate Q ₁ is proportional to the rectangle ABCD if the open channel 4 has a uniform cross section along the water flow direction. From this state, when the flow rate becomes constant at Q ₂ (>Q ₁ ), the water head in the open channel becomes a straight line EF, and as a result, the storage volume changes by V ₂ , that is, by an amount proportional to the rectangle CDEF. The present invention reduces the delay time by supplying an amount of water corresponding to the change in the stored amount to the open channel in as short a time as possible.

FIG. 1 shows an embodiment of the device of the present invention, in which the difference between the open channel inflow Q ₀ detected by the detector 3 and the demand Q _a detected by the detector 7 during steady state is determined by the subtractor. The control signal calculated by 8 and calculated (proportional, integral, etc.) by the adjustment part 9 is sent to the opening adjustment part 1.
4, and thereby the valve 2 is adjusted so that the water level H in the regulating tank is controlled to be constant. The opening meter 15 detects the actual opening of the valve 2 and feeds it back to the adder/subtractor 13 with the opposite polarity so that it matches the command value. Furthermore, water level detector 6
The detected water level is input to a water level correction section 10, and its output is added to the output of the adjustment section 9 by an adder 11. Details of this water level correction section 10 will be described later. The storage amount calculation circuit 12, which is a feature of the present invention, inputs the detected inflow amount Q ₀ and the demand amount Q _a , and calculates the change in the storage amount when the amount of change in Q _a exceeds a predetermined value. A control signal for flowing the changed amount into the open channel 4 in a short time is output, and this signal is applied to the adder/subtractor 13. Although the open channel 4 in FIG. 1 is shown to be horizontal, it is assumed that it has an inclination such that the water flows downward to the right. This also applies to FIG.

FIG. 2 shows an embodiment of the storage amount calculation circuit 12,
An explanatory diagram of the operation is shown in FIG. At the current time t<t ₁ , the demand Q _a , the inflow into the open channel 4 Q ₀ (or q ₀ ), and the inflow into the water tank 5 Q ₁ (or q ₁ ) are determined by normal control. are all approximately the same value, Q ₁ . At time _t1 , the demand Q _a changes as shown in FIG. 3, and when the amount of change exceeds a predetermined value, the change detector 16 shown in FIG. , 172. As a result,
Q _a −Q ₀ (or q ₀ ) is calculated by the subtracter 18 and input to the storage amount calculator 20 . Storage amount calculator 20
The calculations are as follows. Now, when the average flow velocity in the steady state of the open channel 4 is v, the slope is I, the diameter depth is R, and the roughness coefficient is n, Equation (1), which is well known as Manning's formula, holds true.

v = (1/n) R ^2/3・I ^1/2 ...(1) If the steady flow rate is Q and the water flow cross-sectional area of the open channel is A (uniform along the open channel), then Q = Since v・A, equation (1) is transformed into Q・n/I ^1/2 =A・R ^2/3 (2). Furthermore, the diameter depth R is as follows, assuming that the cross section of the water passage in the now open channel is a rectangle with width b and height h: R=b・h/(b+2h)...(3), and A=b・h... (4). Note that the diameter depth R varies depending on the shape of the water passage cross section, but is given by a formula that includes the height h of the water passage cross section. In equations (2), (3), and (4), the constants are n, I, and b, and if these are set in the constant setting device 19 in advance, the steady flow rate Q and the height h of the water flow cross section (the sixth If the relationship with the water level (in the figure) is given, and the change in flow rate ΔQ is given, then the change in water level h, Δh, can be found. Therefore, if the output of the subtractor 18 is regarded as the change in flow rate ΔQ, then the change in water level h due to this change Δh, and therefore the change in storage amount V ₂
=Δh・b・L (L is the open channel length) can be calculated. In this way, the storage amount calculator 20 calculates the amount of change in the storage amount.
V ₂ is calculated, and a command to flow a flow rate Q ₃ determined by Q ₃ =V ₂ /τ for the time τ set in the timer 21 is output. On the other hand, the timer 21 is connected to the change detector 16 at time _t1 in FIG.
Depending on the output, the output is turned on and the arithmetic unit 20
output Q ₃ from , and after τ time t ₂ =
When t ₁ +τ is reached, the output is turned off and the arithmetic unit 20
Force the output _Q3 to 0. As a result, in the case of the conventional device that does not include the storage amount calculation section 12, t>t ₁
In this case, the inflow flow rate into the open channel 4 has a value of Q ₂ as shown in Q ₀ in Fig. 3, but in the present invention, t ₁ < t < t ₂
During this time, as shown at q ₀ in FIG. 3, an inflow flow rate Q ₃ is further added to this Q ₂ . Therefore, in the conventional case, the flow rate flowing into the water tank 5 reaches the target value Q ₂ at time t ₃ (>t ₂ ) as shown in Fig. 3 Q ₁ .
However, in the present invention, the third
As shown in q ₁ in the figure, at time t ₂ , which is sufficiently smaller than t ₃ ,
It is possible to set q ₁ = Q ₂ , and the flow time delay can be significantly shortened.

Note that the flow rate control described above is to balance the flow rate in and out of the adjustment tank 5, so once the water level in the adjustment tank 5 fluctuates due to measurement error or other causes, this will remain unchanged. The water level correction unit 10 is provided for this purpose, and examples of its configuration are shown in FIGS. 4 and 5. The fourth of these
The figure shows a method of adding a correction amount so that the aquarium water level becomes the target water level.
The subtractor 24 calculates the deviation ΔH between H ₀ and the aquarium water level detected by the water level meter 6, and if the deviation ΔH is greater than the value set in the constant dead zone 25, the multiplier 26 multiplies ΔH by the coefficient K. , this is output as a flow rate correction amount. On the other hand, in Fig. 5, when the water tank water level is not between the water levels H _H and H _L set by the water level setters 27 and 28, the output from either the comparator 29 or 30 is output from the contact 29.
a or 30a is turned on, and the output circuit 29b or 3
A flow rate control signal of a constant magnitude from 0b to -k or k is output. These are applied to the adder 11 in FIG. 1, and the control valve 2 is opened/closed by that amount (or a little more) to change the inflow amount Q ₀ and reduce the water level deviation ΔH.

〔Effect of the invention〕

As is clear from the above embodiments, according to the present invention, it is possible to rapidly follow the change in open channel storage amount, so the flow delay time is reduced, and the control effect waiting time is reduced.
This has the effect of enabling small and stable control of water tank water level fluctuations, flow rate adjustment valve operating frequency, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a diagram showing an embodiment of the storage amount calculation section, FIG. 3 is an explanatory diagram of the operation of the embodiment of FIG. 1, and FIGS.
The figure shows a configuration example of a water level correction circuit diagram, FIG. 6 is an explanatory diagram of storage amount, and FIG. 7 is an explanatory diagram of an open channel system. 2...Inflow rate adjustment valve, 3...Inflow rate detector, 4...Open channel, 5...Adjustment water tank, 7...Demand amount detector, 12...Storage amount calculation circuit, 16...Flow rate change detection Section, 19...Constant setting section, 20...Storage amount calculator, 21...Timer, 17, 22...And gate.

Claims (1)

[Claims] 1. An open channel flow rate control device that controls the opening degree of a valve provided at the inlet of the open channel using an opening control signal corresponding to the demand flow taken out to the consumer from a regulating water tank provided at the outlet of the open channel. a change detection means for detecting a change and outputting a change signal when the amount of change in the demand flow exceeds a predetermined value; and a preset time from the time when the change signal is received. a timekeeping means that turns on its output only for the specified time; and a storage amount correction signal obtained by dividing the change in the open channel storage amount corresponding to the amount of change in the demand flow rate by the set time, and outputs the signal from the timekeeping means. an open channel flow rate control device, comprising: storage amount calculation means that outputs an output so as to be added to the opening control signal only while the opening control signal is on.