JPS5815043B2 - Flow rate measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow rate measuring device, in which a plurality of flowmeters are provided in a pipe in which two or more types of fluids to be measured selectively flow, and the flow rate of the fluid to be measured is measured with the highest accuracy when measuring the flow rate. The purpose of the present invention is to provide a flow rate measuring device that can selectively output a flow rate signal from a flow meter capable of measuring the flow rate, thereby accurately measuring any fluid to be measured having different viscosity, specific gravity, etc. 3 Generally, there are multiple types of fuel oil used in thermal power plants, etc., and when these different types of oil liquid are received in one pipe, it is difficult to know which liquid to use, even though the specific gravity or viscosity differs depending on the liquid type. The disadvantage is that liquid types other than the liquid types that are suitable for measurement with this flow meter cannot be measured with high accuracy because the liquid types are also measured with a single flow meter installed in the pipe. It had

In addition, oil fluids usually have to be converted to the volume at a standard temperature (for example, 15°C), so it is necessary to measure the temperature of the fluid to be measured and correct the measured flow rate value.
This temperature correction cannot be easily performed because the correction coefficient varies depending on the specific gravity of the fluid to be measured.

For example, the temperature correction equation for petroleum is generally expressed by the following equation.

Fl5-KFt, (1)
Here, Fl5 is the volume of liquid at 15°C, Fl is t
'Volume of liquid measured in C, K is JIS, 225
This is a volume conversion coefficient set to 0.

Furthermore, according to ASTM-Rice, this volume conversion factor includes:
It is expressed as a quadratic function of temperature t as shown in the following equation.

K-1+Q1(t15)+Q2(t15
)2(2) Here, Ql and Q2 are constants (hereinafter referred to as temperature correction coefficients) determined by the specific gravity of the liquid.

If the volume conversion coefficient K is plotted with temperature and specific gravity as parameters on the horizontal axis, the result will be as shown in FIG. 1.

In other words, when the specific gravity is 0.8, it is close to a straight line;
When the specific gravity is small such as 6 or large such as 1.0, it becomes a quadratic curve.

Furthermore, as can be seen from the figure, the quadratic term Q in equation (2)
)2(t-15)2 is negative when the specific gravity is small and positive when the specific gravity is large, and the quadratic curves are upwardly convex and downwardly convex, respectively.

In addition, the conventional temperature correction device limits the target oil type at the time of manufacture, and changes the temperature correction coefficient Q1 to the volume conversion coefficient based on the specific gravity of the oil liquid. Many of them are only for one liquid type, which determines the coefficient Q1.If you want to flow different types of oil into the piping, you need to pry open the casing of the temperature correction device and adjust the internal mechanism to set the coefficient Q1. It is necessary to correct the portion related to Q2, and this adjustment work has the drawback of being extremely troublesome.

Further, there is also known a flow rate measuring device configured to change a switch each time the type of liquid changes, thereby changing the volume conversion coefficient.

However, this method assumes that the volume conversion coefficient changes proportionally to the temperature, and is configured to correct it by changing, for example, the gain of the internal arithmetic circuit, that is, the proportionality constant, depending on the type of liquid to be measured.

However, since this type of flow rate measurement device linearly approximates the volume conversion coefficient, the approximation error of the volume conversion coefficient increases as the temperature moves away from 15°C for fluids with low specific gravity or fluids with high specific gravity. This has the disadvantage that the measurement accuracy deteriorates accordingly.

In order to reduce the above approximation error, even if we increase the number of switchable proportionality constants and increase the resolution, the specific gravity of the fluid to be measured,
When the temperature ranges over a wide range, the number of switching contacts increases dramatically, which not only complicates the device configuration but also complicates operation.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIG. 2 and subsequent figures.

FIG. 2 is a schematic configuration diagram of an embodiment of the flow rate measuring device according to the present invention, and FIGS. 3 and 4 are respective implementations of a resistance-voltage conversion circuit and an A-D conversion circuit used in the above-mentioned flow rate measuring device. An example circuit diagram, FIG. 5, shows a timing chart showing the signal waveforms of the main parts of the above-mentioned A/D conversion circuit.

In Figure 2, oil supply pipe 1 has two pipes, one for high viscosity and one for low viscosity.
The flowmeters 2 and 3 of the stand are connected in series with each other, and in this embodiment, the flowmeter 2 for high viscosity is used for high viscosity oil liquid with a specific gravity of 1.0, and the flowmeter 3 for low viscosity is used for example The measurement target is a low viscosity oil liquid of 0.6.

For the flowmeters 2 and 3, a positive displacement flowmeter such as a roots meter, another turbine meter, a vortex flowmeter, etc., are used, each of which can measure the oil liquid to be measured with the highest accuracy.

The flow rate measured by the flowmeter 2゜3 is measured by the pulse transmitter 2.
It is supplied from the az3a into the temperature correction device 5 via the flow meter switching device 4.

For example, a resistance temperature detector 6 (resistance value R1) is provided in the supply pipe 1 as a temperature detector for measuring the temperature of the fluid to be measured. The temperature t is supplied into the temperature correction device 5.

The temperature correction device 5 is supplied with the flow rate pulse signals from the flowmeters 2 and 3 and the temperature signal from the temperature measuring resistor 6, and corrects the flow rate pulse signals to a flow rate pulse signal at a reference temperature of 15°C. , resistance-voltage conversion circuit 7, frequency division circuit 8
, an adder circuit 10, and the like.

The flow meter switching device 4 constitutes a flow rate signal receiving section which is a main part of the present invention, and is supplied with flow rate pulse signals from the flow meters 2 and 3, and is designated by an oil type selection command from an oil type selector 9. Only the flow rate pulse signal measured by the flow meter corresponding to the selected oil type is selectively supplied to the frequency dividing circuit 8.

Since the oil type selector 9 measures two types of oil in this embodiment, it has a two-point selector switch, and by operating the selector switch, it issues an oil type selection command to the flow meter switch 4. At the same time, one of the two built-in oil type selection circuits 9a and 9b corresponding to the selected oil type is connected to the resistance-voltage conversion circuit 7.

The resistance-voltage conversion circuit 7 converts the change in resistance value according to the temperature t measured by the resistance temperature detector 6 into a voltage signal, and converts a temperature correction coefficient according to the oil type selected by the oil type selector 9 into a voltage signal. Q1. Q2 accurately corrects the temperature of the volume conversion coefficient K.

The frequency dividing circuit 8 divides the frequency of the flow rate pulse signal selectively output from the flow meter switching device 4, and sends the frequency-divided pulse signal to the addition circuit 10 and the A-D conversion circuit 11 at a ratio of 9:1. supply

That is, in the case of this embodiment, the flow rate signal F0 is 1 as described later.
A 9-pulse signal (0,9Ft) is supplied each time a 0 pulse is input, and the remaining 1-pulse signal (0,9Ft) is supplied to the A-D converter circuit 11.
, IFt).

The A-D conversion circuit 11 receives the pulse signal (
0, IF, ) is supplied, and based on this signal, the output voltage signal E of the resistance-voltage conversion circuit 7 as described later.

is converted from analog to digital, and a correction pulse signal accompanying temperature correction is supplied to the addition circuit 10.

The adder circuit 10 receives the reference pulse signal (0
, 9Ft) and a correction pulse signal from the A/D conversion circuit 11, and adds these to output a flow rate pulse signal F15 converted to the reference temperature.

Here, it can be expressed as a temperature correction equation obtained from equation (IX2) above.

The first term of this equation (4) corresponds to the reference pulse signal supplied from the frequency divider circuit 8 to the adder circuit 10 in FIG. It corresponds to the supplied correction pulse signal.

In FIG. 3, the resistance-voltage conversion circuit 1 includes a constant voltage circuit 12,
A feedback system is constructed in which the voltage addition/subtraction circuit 13, voltage-current conversion circuit 14, temperature detection circuit 15, etc. are forward-facing elements, and the oil type selection circuit 9a or 9b of the oil type selector 9 is a backward-facing element.

The constant voltage circuit 12 provides a reference voltage E, 8, and the voltage addition/subtraction circuit 13 receives the reference voltage E8° and the output voltage E.

is applied via the feedback resistor Rf.

Assuming that the gain of the oil type selector 9, that is, the feedback gain determined by the value of the feedback resistor Rf, is 1,
The output voltage Es of the voltage addition/subtraction circuit 13 is Es-Es50/1Eo(5).

In the compound top on the right side of equation (5), 10 represents the case of positive feedback, and - represents the case of negative feedback.

If the conversion coefficient (gain) of the voltage-current conversion circuit 14 is 2, its output current 8 is expressed as I,=2B8 (6).

Also, the resistance-voltage conversion coefficient (gain) of the temperature detection circuit 15
When Eo is set to 3, the output voltage Eo is expressed as Eo=3I5R, (7).

Here, R1 is the resistance value of the temperature measuring resistor 5, and the resistance-voltage conversion coefficient 3 can be set to a desired value by varying the value of the gain adjustment resistor Of.

Here, R8 and ■8 are deleted from the above formula (5X6X7) to obtain E.

To summarize, Eo = K2 to 3E
88Rt (8) Expressed as 1K, 1, 2, 3R0, and considering that K1, 2, and 3R1 are sufficiently small compared to 1, expand the right side and ignore expansion terms of order 3 or below. Then, 1KiKiR83R%+ to 2 and 3E88Rt to Eo-±
It is expressed as (9).

In this way, the resistance-voltage generating circuit 1 generates an output voltage E expressed by a quadratic equation of the resistance value Rt1 of the resistance temperature detector 6, that is, the temperature t.
.

Output. The slope of the tangent to the volume conversion coefficient at 15°C is determined by 3, which is the resistance-voltage conversion coefficient of the temperature detection circuit 15, and the curvature of the quadratic curve is determined by 1, which is the addition/subtraction coefficient of the feedback voltage.

Therefore, the gain adjustment resistor G1- of the temperature detection circuit 15 and each oil type selection circuit 9a of the oil type selector 9 are adjusted according to the type of liquid.
, 9b may be adjusted by adjusting the feedback resistance Rf'x.

In the case of this embodiment, two types of oil liquids are to be measured: a high viscosity liquid (specific gravity 1.0) and a low viscosity liquid (specific gravity 0.6), and as shown in FIG. The volume conversion coefficients in the case of 0 and 0.6 are respectively downwardly convex and upwardly convex with respect to the temperature t.

Therefore, in the case of a high viscosity liquid, Eo = 1KiKiR88R% + 2 = 3B, 8Rt
(10); In the case of low viscosity liquid, 1KiKiR88R%+ to 23Es5Rt for Eo--
(It is necessary to use it properly as 1υ.

Therefore, the oil type selection circuit 9a for high viscosity liquids has negative feedback, and the oil type selection circuit 9b for low viscosity liquids has positive feedback, and the gain adjustment resistor Gf and feedback resistor Rf of each oil type selection circuit '9a, 9b. By setting each to a predetermined value, accurate temperature correction according to the oil type becomes possible.

For example, when a high viscosity oil is flowing through the oil supply pipe 1, the operator operates switch 9st of the oil type selector 9,
The oil type selection circuit 9a for high viscosity liquid has a resistance-voltage conversion coefficient of 7.
Connect with negative feedback.

In addition, when a low viscosity liquid is flowing in the oil supply pipe 1,
The operator operates the switch 9s and selects the oil type selection circuit 9b.
is connected to the resistance-voltage conversion circuit 1 in a positive feedback state.

In this way, the temperature correction device 5 has an oil type selector 9 provided with oil type selection circuits 9a and 9b according to the liquid type of the fluid to be measured, and temperature correction is performed by each oil type selection circuit 9a and 9b. is 2
Since it is highly accurate due to the following curve approximation, the flow rate pulse signal Ft from the flow meter switching device 4 can be converted into a flow rate pulse signal at the reference temperature with extremely high accuracy.

Further, when the operator operates the oil type selector 9 according to the type of fluid to be measured flowing through the pipe 1, the flowmeter selector 4
selectively supplies the flow rate signal of the flowmeter 2 or 3 designated by the operator to the frequency dividing circuit 8.

Therefore, according to the above-mentioned configuration device, it is possible to measure the fluid to be measured with the most accurate flow meter according to the liquid type, and the correction by the temperature correction device 5 can be made even more effective.

As shown in FIG. 4, the A-D conversion circuit 11 includes a triangular wave generation circuit 16, a comparison circuit 17, a reference voltage generation circuit 18, a gate circuit 19, a high frequency oscillation circuit 20, a frequency division circuit 21, a memory circuit 22, and a timing circuit 23. It is composed of etc.

The triangular wave generation circuit 16 receives the pulse signal (
0, IF, ), a triangular wave signal Et shown in FIG. 5 is generated and supplied to the comparison circuit 17.

The comparison circuit 11 receives the output voltage E from the resistance-voltage conversion circuit 14 .

is supplied. This output voltage E.

is compared with the triangular wave signal E□ in the comparison circuit 17 using the reference voltage signal Ek supplied from the reference voltage generation circuit 18 as a reference, and its magnitude is converted into the pulse width of the time width signal Ew.

The signal Ew is used as a gate signal for the gate circuit 19.

The gate circuit 19 is configured to allow the high frequency pulse signal from the high frequency oscillation circuit 20 to pass therethrough only while being supplied with the gate signal Ew.

In the case of this embodiment, the output pulse E of the gate circuit 19 is set to be 0 pulse when the volume conversion coefficient K is 0.9, 1000 pulses when K is 1.0, and 2000 pulses when K is 1.1. It is.

The pulses output from the gate circuit 19 are supplied to the frequency dividing circuit 21, and the frequency dividing circuit 21 counts the number of pulses of the pulse signal E2, and divides the frequency into one pulse every time the number of pulses reaches 1000 pulses, for example. The corrected pulse signals E, / are outputted, and the fractions are stored in memory and added at the next calculation.

The memory circuit 22 stores the corrected pulse signals E,/ from the frequency dividing circuit 21, and when the timing circuit 23 supplies the corrected pulse signals E,'(=(0 ,1+Q1(t-15)+Q2(t-
i 5) JFt).

Here, consideration is given to the addition command signal from the timing circuit 23 so that the output signal of the memory circuit 22 does not overlap with the output signal of the frequency dividing circuit 8.

In the above embodiment, the fluid to be measured flowing through the pipe 1 is not limited to oil liquid, but may be any other liquid, and there may be any number of types of fluid to be measured for the - pipe. Accordingly, a flow meter most suitable for measuring each fluid to be measured may be provided in the piping 1.

As described above, the flow rate measuring device according to the present invention includes a plurality of flowmeters provided in a pipe through which two or more types of fluids to be measured flow, and selects the output of the - flowmeter depending on the type of fluid to be measured. Because the structure allows for the flow of multiple fluids with different viscosities, specific gravity, etc. in the piping, each fluid can be measured with the most accurate flowmeter, which allows for It has features such as being able to measure the flow rate of the fluid to be measured with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing how the volume conversion coefficient changes with temperature change when the specific gravity of the fluid to be measured is taken as a parameter, and FIG. 2 is a schematic configuration diagram of an embodiment of the flow rate measuring device according to the present invention. 3 and 4 are circuit diagrams of one embodiment of the resistance-voltage conversion circuit and the A-D conversion circuit used in the above-mentioned flow rate measuring device, respectively, and FIG. 5 shows the signals of the main parts of the above-mentioned A-D conversion circuit. 5 is a timing chart showing waveforms. 2...Flowmeter for high viscosity, 3...Flowmeter for low viscosity, 6...Resistance temperature sensor, 9...
Oil type selector.

Claims (1)

[Claims] A plurality of flow meters provided in a pipe through which 12 or more types of fluids to be measured selectively flow, a flow rate signal receiving section to which flow signals measured by the respective flow meters are supplied, and the flow rate signal receiving section. An oil type selector that selectively outputs a flow rate signal suitable for the type of measured fluid to be measured from among the plurality of flow rate signals received by the flow meter.