JPS605885B2 - flow measuring device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a flow rate measuring device.

Differential pressure flowmeters are used as devices to measure flow rates, but differential pressure flowmeters have poor accuracy at low flow rates, so if you try to cover a wide measurement range with a single device, the accuracy will drop. This is because the flow rate is proportional to the square root value of the differential pressure, so when the differential pressure is small,
In other words, this is because the error becomes large in the small flow rate region. Therefore, it is conceivable to ensure measurement accuracy over the entire flow rate by combining signals from flow rate transmitters based on a plurality of differential pressure measurements in different measurement ranges.

One such measurement method may be to synthesize signals from flow rate transmitters with high accuracy within a predetermined measurement range by passing them through filters such as Takagi cut, bandpass, and low frequency cut. However, this method has the disadvantage that the circuit configuration becomes complicated and is not economical.

In view of the above points, the present invention has been made to solve these problems and eliminate such drawbacks.The purpose of the present invention is to eliminate setting errors with a simple configuration, and to achieve highly accurate flow rate measurement over the entire range. The object of the present invention is to provide a flow rate measuring device that can realize the following.

In order to achieve such an object, the present invention provides a plurality of flow rate transmitters that measure differential pressure, each having a different measurement range, and a method that responds to each signal from the plurality of flow rate transmitters according to each signal range. a plurality of coefficient calculators that perform calculations by multiplying by weighting coefficients, a constant signal generator that outputs the values of each boundary of the measurement range for the flow rate transmitter, and a constant signal generator that calculates the outputs from the plurality of coefficient calculators A plurality of signal selectors each compare the outputs of the signal generators and select the required signals according to the usage range, an adder synthesizes the outputs of the plurality of signal selectors, and a A subtracter is provided to obtain a flow rate signal by subtracting the output of the constant signal generator.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a flow rate measuring device according to the present invention. (see Figure 2a), that is, the signals d, g, shown in Figures 2b and c,
This shows an example of obtaining the final output j (see FIG. 2 d) at f. In the figure, OF is the throttle mechanism (orifice), and DPT, DPT2, and DPT3 are the first orifices that detect and transmit the difference between two pressures from the orifice OF.
, second and third differential pressure transmitters, EOF,, EOP2,
EOP3 is the first to third lid pressure transmitters DPT, .
The first, second, and third square root calculators which receive the outputs of DPT2 and DPT3 as inputs constitute a flow rate transmitter that measures a plurality of differential pressures each having a different measurement range.

K, , K2, and K3 are the first to third square root computing units E, respectively.
These are first, second, and third coefficient calculators (ratio calculators) that receive the outputs of OP, , EOP2, and EOP3 and calculate coefficients corresponding to the maximum flow values Q, max, Q2max, and Qmax. SG, SG2 are first and second constant signal generators that respectively output values of the boundaries of the measurement range for the flow rate transmitter, HS is a first coefficient calculator K,
The first signal selector "LS," which compares the output of the second constant signal generator K2 with the output of the first constant signal generator SG, and selects the desired high rank, compares the output of the second constant signal generator K2 with the output of the first constant signal generator signal generator SG,
The first low signal selector "HS2" selects the desired low signal by comparing the output of the
A second high signal selector selects a desired high signal by comparing the output of the constant signal selector SG2 with the output of the third coefficient calculator K3 and the output of the second constant signal generator SG2. A second low signal selector compares the low signal and selects the desired low signal.

ADD. are the first and second high signal selectors HS, HS
2 and the output of the second low signal selector LS2, ADD2 is the first constant signal generator S
A second signal adder that adds the output of G, and the output of the second constant signal generator SG2, and SUB is the first signal adder AD.
The subtracter subtracts the output of the second signal adder ADD2 from the output of the subtracter SUB, and is configured so that the final output flow rate signal, which is the output of the subtracter SUB, is obtained at the output terminal OUT. Next, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG.
First to third differential pressure transmitters DPT, , DPT different from x
2. The case of using DPT3 will be explained.

First, the relationship between the input of the differential pressure transmitter (differential pressure △P) and the flow rate Q is shown by the following equation 1. Then, when Qimax>Q, △Pimax》△P, so the differential pressure transmitter The relative error of will increase and the measurement accuracy will deteriorate.

For this reason, ``In low-flow castles, the second
and the signals of the third reed pressure transmitters DPT2 and DPT3 are calculated. Above [1]
} From the relationship of the formula, the first to third differential pressure transmitters DPT, DP
The outputs from T2 and DPT3 are sent to the first to third square root calculators E.
OP, , EOP2, and EOP3 are respectively operated to obtain signals a, b, and c.

(See Figure 2a) In addition, in Figure 2a, "signal a is K
, = 1, they are also signals x, x', x'', which will be described later.Then, these signals a, b, c are the flow rate expansion values Q, max,
Coefficients corresponding to Q2max and Q3max are multiplied by first, second and third coefficient calculators K, , K2 and K3, respectively, to obtain signals x, x' and x''.

Note that the constant Ki at this time is determined by the following equation {21]. Ki=Qimax/Qmax
■However, Qmax is the maximum value of the measurement range.
Next, the signal x obtained by the first coefficient calculator K,
is the maximum flow rate Q2ma by the first high signal selector HS.
It is compared with the output k of the first constant signal generator SG, which corresponds to
When x, x<k, d=k. (See Figure 2b)
On the other hand, the signal x′ obtained by the second coefficient calculator K2
The first low signal selector is the first constant signal generator S
It is compared with the output k of G, to obtain an output signal e.

That is, when x'≧k, e=k, and when x'<k, e=x'. (See Figure 2c) Hereinafter, the second high signal selector HS2 converts the signal e from the first low signal selector to the output 1 of the second constant signal generator SG2 corresponding to the maximum flow rate Q3max. is compared to obtain a signal f.

(See FIG. 2c) Also, the second low signal selector LS2 compares the output x'' of the third coefficient calculator K3 with the output 1 of the second constant signal generator SG2 to obtain a signal g. (See Figure 2b) The signals d, f, and g obtained in this way are
A signal h is obtained by the signal adder ADD. On the other hand, the signals k,1, which are the outputs of the first and second constant signal generators SG, SG2, corresponding to the maximum flow values Q2max and Qmax, respectively, are added by a second signal adder ADD2,
Get signal i. (See Figure 2 d) Since the output signal b of the first signal adder ADD is a signal obtained by adding the bias amount i to the flow rate signal, the subtracter SUB performs the calculation h-i. , a flow rate signal i, which is the final output, is obtained at the output end PUn. (Refer to Fig. 4d) By the above operation, the first, second and third differential pressure transmitters DPT, D
Signals within highly accurate ranges of PT2 and DPT3 are selected and used. In this way, after multiplying the signal from each transmitter by a weighting coefficient according to each signal range, a signal according to the usage range is selected by combining and using a signal selector outside the usage range of each signal. It is possible to measure the flow rate with high accuracy over the entire desired measurement range.

FIG. 3 is a block diagram showing another embodiment of the present invention.
This figure shows an example of a case where the signals ', g, and f' shown in FIG. 4 are obtained instead of the signals d, g, and f in the embodiment shown in the figure, and these are synthesized.

In FIG. 3, the same reference numerals as in FIG.
B2 is a first low signal selector; a second subtracter HS;
is a first high signal selector which obtains a signal d' by comparing the signal obtained by the first subtracter SUB, with the output of the third constant signal generator SG3, and HS2 is a second subtracter SUB2. a second high signal selector, LS, which obtains a signal f' by comparing the signal obtained by LS with the output of the third constant signal generator SG3;
2 is the signal obtained by the third coefficient calculator K3 and the second
The second low signal selector ADD obtains the signal g' by comparing the output of the constant signal generator SG2 with the output of the constant signal generator SG2.
S, signal b' from second high signal selector HS2, signal f' from second low signal selector LS2, and signal g from second low signal selector LS2.
A signal adder SUB that adds the signals is a third subtracter that subtracts the output of the constant signal generator 2×SG3 from the signal obtained by the signal adder ADD to obtain the flow rate signal j.

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to FIG. 4.

First, the outputs from the first to third differential pressure transmitters DPT, to DPT3 are calculated by the first to third square root calculators EOP, to EOP3, respectively, as in the case of FIG. 1, and the L signal a
, b, c are obtained. (See Figure 4) Then, this signal a,
b, c are maximum flow values Q, max, Q2max, Q3ma
Signals x, x', x'' are obtained by multiplying the coefficients corresponding to x by the first to third coefficient calculators K, to K3, respectively.
(see figure) Next, the signal x output from the first coefficient calculator K is processed by the first subtracter SUB to x-m (constant signal generator SG,
(output of one SG3) and its output is introduced into a first high signal selector HS. On the other hand, the signal output from the second coefficient calculator K2 is compared with the output k of the first constant signal generator SG by the first low signal selector LS, and its output is sent to the second subtracter SUB. the first low signal selector LS,
-n (outputs of the constant signal generators SG2-SG3) is calculated, and the output thereof is introduced into the second high signal selector HS2. Hereinafter, the first high signal selector HS,
The signal from the subtractor SUB, is sent to the third constant signal generator SG.
It is compared with the output o of 3B to obtain the output d'. (See FIG. 4) Also, the signal from the second subtractor SUZ is compared with the output o of the third constant signal generator SG3B by the second high signal selector HS2 to obtain an output r. (See Figure 4) Also,
The second low signal selector LS2 selects the third coefficient calculator K3.
The signal x'' from is compared with the output 1 of the second constant signal generator SG2 to obtain the output g. The signal adder ADD adds the signal to obtain the desired signal.
The third subtractor SUB3 calculates the signal -P (output of the constant signal generator 2×SG3) to obtain the flow rate signal j. In addition, in the embodiment shown in FIG. 3, when each signal [(a, b, c) to j] is 1 to 5 V or 4 to 2 hA, IV or 4
Drive zero signal like mA (commonly called getting geta waku)
Indicates the case where the

Therefore, if the o% equivalent signal is OV or skin A, the third
Since SG3=B=0, the constant signal generator SG3 of
In this case, the number of constant signal generators can be reduced, and the third subtracter SUB3 at the final stage is also unnecessary. FIG. 5 is a block diagram showing still another embodiment of the present invention. In FIG. 5, the same reference numerals as in FIGS. 1 and 3 indicate corresponding parts, and LS and 2 are the signals b and c obtained by the second and third square root calculators EOP2 and EOP3, respectively. first and second low signal selectors for selecting a desired low signal by comparing the output k of the constant signal generator SG, respectively;
SG4 is a fourth constant signal generator. In the flow measuring device configured in this way, the first to third differential pressure transmitters D
The outputs from PT, .about.DPT8 are operated by first to third square root computing units EOP, .about.EOP3, respectively, to obtain signals a, b, and c.

(See Figure 6) ``Then, this signal a is the maximum flow rate Q,
The required signal is obtained by multiplying the coefficient corresponding to max by the first coefficient calculator K, and the signals b and c are respectively connected to the first and second low signal selectors, A coefficient corresponding to the maximum value Q2max.Qmax is multiplied by the second and third coefficient calculators K2 and K3 to obtain the respective required signals.The signal output from the first coefficient calculator K is sent to the first subtracter. SUB, the signal -r (constant signal generator SG2 - SG
4) and its output is introduced into the first high signal selector HS.

On the other hand, the signal output from the second coefficient calculator K2 is sent to the second subtracter S.
The signal -s (the output of the constant signal generators SG and SG4) is operated by UB2, and the output thereof is introduced into the second high-intensity signal selector HS2. Hereinafter, the first high signal selector HS.
The signal from the first subtractor SUB is compared with the output t of the fourth constant signal generator SG4 to obtain the output d.

(See FIG. 6) Also, the signal from the second subtracter SUB2 is compared with the output t of the fourth constant signal generator SG4 by the second high signal selector HS2 to obtain an output f.

(See FIG. 6) The signals d and f thus obtained and the signal g from the third coefficient calculator K3 are added by a signal adder ADD to obtain a desired signal.

This signal is processed by the third subtractor SUB3 on the signal -u (output of the constant signal generator 2×SG4), and the output terminal O
A flow rate signal i, which is the final output, can be obtained from the UT. In the embodiment shown in FIG. 5, similarly to the embodiment shown in FIG.
When the value is 0, the constant signal generator 2×SG4 and the third subtracter SUB3 at the final stage are unnecessary. Although the present invention has been described above using an example in which flow rate is measured using three transmitters (low, middle, and high range) within a desired measurement range, the present invention is not limited to this, and the present invention is not limited to this. It is possible to provide a plurality of flow rate transmitters each using differential pressure measurement, each having a different measurement range depending on the flow rate, and a plurality of signal converters corresponding to the plurality of flow rate transmitters. Further, when Q skin ax=Q, max, the coefficient calculator K is not necessary, and the devices shown in the blocks shown in the figure do not need to be separate.
For example, a device in which a coefficient calculator and a subtracter are integrated is put into practical use. As is clear from the above description, according to the present invention, a constant signal generator that outputs each boundary value of a measurement range for a flow rate transmitter and a plurality of coefficient calculators are provided without using complicated means. a plurality of signal selectors that respectively compare the outputs from the constant signal generators with the outputs of the constant signal generators and select the desired signals according to the range of use;
With this simple configuration including an adder that combines the outputs of multiple signal selectors, setting errors can be completely eliminated, and it is possible to completely eliminate setting errors. This method automatically selects signals in each measurement range using an analog method using a combination of analog calculators, so the signal from the flow transmitter with high accuracy in each predetermined measurement range can be selected by Takagi cut, Achieving highly accurate flow rate measurement over the entire range by a simple combination of a signal selector and an analog computing unit without using complicated means of synthesis through filters such as band passes and low-frequency cuts. ``The practical effects are extremely large.''

Furthermore, it is extremely effective in that the cost can be reduced by simplifying the configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the flow rate measuring device according to the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of FIG. 3, FIG. 5 is a block diagram showing still another embodiment of the present invention, and FIG. 6 is an explanatory diagram of the operation of FIG. 5. DOT, ~DOT8...Differential pressure transmitter, EOP, ~E
OP3...square root calculator, K, ~K3...coefficient calculator, H
S. , HS2...High signal selector, B,, LS2
...Low signal selector, ADD, ADD,, ADD2...
...Signal adder "SUB, SUB, ~SUB...
...Subtractor "SG.~SG4...Constant signal generator. Figure 1 Figure 2 Snake diagram Dimensions ○ Fuji Figure 5

Claims (1)

[Claims] 1 Multiple flow rate transmitters that measure differential pressure, each with a different measurement range, and multiple coefficient calculations that calculate each signal from the multiple flow rate transmitters by multiplying them by a weighting coefficient that corresponds to each signal range. a constant signal generator that outputs values at each boundary of a measurement range for the flow rate transmitter; and a constant signal generator that compares the outputs from the plurality of coefficient calculators with the outputs of the constant signal generator, respectively, to determine the range of use. a plurality of signal selectors that respectively select desired signals according to the signal; an adder that combines the outputs of the plurality of signal selectors; and a flow rate signal by subtracting the output of the constant signal generator from the output of the adder. A flow measuring device characterized in that it comprises a subtractor for obtaining.