JPH04250316A - Mass flowmeter - Google Patents

Abstract

PURPOSE:To perform flow measurement with good accuracy by a mass flowmeter using a constant temperature control circuit not only in a small mass flow rate region, but also in a large mass flow rate region. CONSTITUTION:When Vu, Vd, represent energy given to two heat sensitive coils wound separately from each other on the outer periphery of a pipe in which a fluid flow, and (k) is a factor, the mass flow rate can be obtained based on the following expression: {(Vu+Vd)+k(Vu-Vd)}/(Vu+Vd).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter that measures the mass flow rate (hereinafter simply referred to as flow rate) of a fluid such as gas or liquid flowing in a conduit.

0002

[Prior Art] The applicant of the present application filed a patent application for the mass flowmeter on December 4, 1985.
No. 73837 (Japanese Unexamined Patent Publication No. 62-132120)], two resistors whose resistance value changes depending on the temperature of the fluid are provided independently of each other in a conduit through which a fluid flows, and the resistor Two constant temperature control circuits are provided independently of each other, and the constant temperature control circuit controls the temperatures of both resistors to be always equal and constant, and the energy given to both resistors is There is a device that uses a so-called constant temperature control circuit that measures the flow rate of the fluid flowing through the conduit based on the value obtained by dividing the difference between the two by the sum of the energies.

FIG. 2 schematically shows the configuration of the mass flowmeter according to the above patent application. In this figure, 1 is a conduit, inside which a fluid F such as gas flows. 2 is conduit 1
The sensor unit is equipped with two self-heating type thermal coils Ru and Rd (hereinafter referred to as upstream thermal coil R) as resistors wound around the outer periphery of the conduit 1 at appropriate intervals.
u, and a downstream heat-sensitive coil Rd). The heat-sensitive coils Ru and Rd are made of temperature-sensitive resistance wires with a large temperature coefficient, such as iron-nickel alloy, and are configured to detect even the slightest change in the flow rate of the fluid F flowing through the conduit 1. .

Reference numerals 3 and 4 are constant temperature control circuits including an upstream heat-sensitive coil Ru and a downstream heat-sensitive coil Rd as constituent elements of a bridge circuit (described later), and the constant temperature control circuits 3 and 4 have the same characteristics. It consists of two parts: an upstream heat-sensitive coil Ru and a downstream heat-sensitive coil Rd.
This is to control the temperature so that it is always the same and constant.

That is, the constant temperature control circuit 3 (hereinafter referred to as the upstream constant temperature control circuit 3) corresponding to the upstream thermosensitive coil Ru
) are the upstream heat-sensitive coil Ru, the resistor 5 for setting the temperature of the upstream heat-sensitive coil Ru, and the bridge resistor 6.
, 7, and a control circuit 9. The downstream constant temperature control circuit 4 corresponding to the downstream thermal coil Rd has a resistor 1 for setting the temperature of the downstream thermal coil Rd and the downstream thermal coil Rd.
0 and a bridge circuit 13 consisting of bridge resistors 11 and 12, and a control circuit 14. In addition, resistance 5~
The temperature coefficients of coils 7 and 10 to 12 are set to be sufficiently smaller than those of both heat-sensitive coils Ru and Rd.

The upstream constant temperature control circuit 3 compares the potential at its output point a and the connection point b between the bridge resistors 6 and 7, and when there is a difference between the two potentials, outputs the output to the bridge circuit 8. The downstream constant temperature control circuit 4 compares the potential at the output point c and the connection point d between the bridge resistors 11 and 12, and operates to keep the bridge circuit 8 parallel. When there is a difference in potential, the output is sent to the bridge circuit 13 and operates to keep the bridge circuit 13 parallel. Note that 15 and 16 are buffer circuits provided on the output sides of the upstream constant temperature control circuit 3 and the downstream constant temperature control circuit 4, respectively.

X and Y are subtraction lines and addition lines provided in parallel with each other on the output sides of the upstream constant temperature control circuit 3 and the downstream constant temperature control circuit 4, and the subtraction line A subtraction circuit 17 inverts and outputs the difference (subtraction output) based on the outputs Vu and Vd, and a subtraction circuit 17 that inverts and outputs the difference (subtraction output) based on the outputs Vu and Vd, and a subtraction circuit 17 that inverts and outputs the difference between them (subtraction output) {-(Vu
-Vd)}, and the addition line Y includes an addition circuit 19 that inverts and outputs the sum (addition output) based on the outputs Vu and Vd.
Inverted addition output {-(Vu +Vd)}
and an inverting circuit 20 that inverts the .

Reference numeral 21 denotes a division circuit provided on the output side of the subtraction line X and the addition line Y, each of which has an inversion circuit 18
, 20 and the addition output (Vu + Vd) are input, and the division output (Vu - Vd) is input.
Vd )/(Vu +Vd), 22
is its output terminal.

In the mass flowmeter configured as described above, first, when the fluid F is not flowing in the conduit 1, the upstream thermal coil Ru and the downstream thermal coil Rd
are the temperature setting resistors 5, 10 of the bridge circuits 8, 13.
The temperature is set to the temperature determined by the respective values. Since the temperature setting resistors 5 and 10 have the same characteristics, the upstream heat-sensitive coil Ru and the downstream heat-sensitive coil Rd
The temperatures of will be the same. Therefore, the output Vu at the output point a of the upstream constant temperature control circuit 3 is equal to the output Vd at the output point c of the downstream constant temperature control circuit 4,
Therefore, the output signal at the output terminal will be zero, indicating that fluid F is not flowing.

Next, when the fluid F is flowing in the conduit 1, the upstream heat-sensitive coil Ru is deprived of heat by the fluid F, and the downstream heat-sensitive coil Rd is given heat from the fluid F. Therefore, the energy supply for maintaining the upstream heat-sensitive coil Ru at a predetermined temperature increases, and the output Vu at the output point a increases. On the other hand, the energy required to maintain the downstream thermosensitive coil Rd at the predetermined temperature is reduced by the amount of heat given from the fluid F, and Vd at the output point c becomes smaller.

These outputs Vu and Vd are input to the subtraction circuit 17 and the addition circuit 19 through buffer circuits 15 and 16, respectively, and are then input to the respective circuits 17 and 19.
Subtraction output from 19 - (Vu - Vd ), addition output -
(Vu +Vd) is output. These outputs are input to a division circuit 21 via inverting circuits 18 and 20, respectively, and predetermined division is performed in this division circuit 21, resulting in a division output (Vu - Vd)/(Vu
+Vd) is output. Since this output is proportional to the flow rate of the fluid F flowing within the conduit 1, the flow rate of the fluid F can be obtained by multiplying this output by a predetermined constant.

0012

[Problems to be Solved by the Invention] However, subsequent research has revealed the following. That is, as the flow rate of the fluid F in the conduit 1 increases, the difference in energy given to the upstream heat-sensitive coil Ru and the downstream heat-sensitive coil Rd, that is, the output (Vu
-Vd) is no longer proportional to the flow rate of fluid F, and as shown by curve A in Table 1 and Figure 3, the linearity between the flow rate of fluid F flowing in conduit 1 and the output decreases, and measurement errors increase. It turned out that.

[0013]

[Table 1]

The present invention has been made with the above-mentioned considerations in mind, and its purpose is to provide a mass flowmeter that can accurately measure flow rate even in areas where the flow rate of fluid has increased. It's about doing.

[0015]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, two resistors whose resistance value changes depending on the temperature of the fluid are provided independently of each other in a conduit through which a fluid flows, and Two constant temperature control circuits each including the resistor are provided independently from each other, and the temperature of both the resistors is always equal to each other by the constant temperature control circuit, and
In a mass flow meter that measures the mass flow rate of fluid flowing through the conduit based on the energy given to both resistors, the energy given to both resistors is determined by coefficients Vu and Vd. When k is {(Vu −Vd )+k(Vu −Vd )
The mass flow rate is obtained based on the formula: 2 }/(Vu +Vd).

[0016]

[Operation] Subtraction power (Vu
-Vd) plus the amount k(Vu -Vd)2, divided by (Vu +Vd),
The linearity between the flow rate and the output is improved, and the flow rate can be accurately measured not only in a region where the fluid flow rate is small, but also in a region where the fluid flow rate is increased.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows the configuration of a mass flowmeter according to the present invention, and in this figure, the same reference numerals as those shown in FIG. 2 are the same or equivalent parts.

The major difference between the mass flowmeter shown in FIG. 1 and the conventional one shown in FIG. 2 is that (
Vu −Vd )+k(Vu −Vd )2 is outputted, and this output becomes one input of the division circuit 21.

That is, in FIG. 1, 23 is a squaring circuit interposed between the subtraction circuit 17 and the inversion circuit 18, which squares the subtraction output {-(Vu −Vd)} of the subtraction circuit 17. , squared output (Vu - Vd)2. 24 is an addition/inversion circuit interposed between the inversion circuit 18 and the division circuit 21 for adding, inverting and outputting the result;
} and the squared output (Vu - Vd) 2 are inverted by the inverting circuit 18
By adding the output {-(Vu −Vd)2} obtained through
(Vu - Vd)2 is output. in this case. The magnitude of the coefficient k is determined by the resistance 25 in the addition and inversion circuit 24,
It can be set arbitrarily by selecting the size of resistor 26 appropriately, for example, the ratio of the resistance values of resistors 25 and 26 is set to 1:
When it is set to 5, k becomes 0.2.

According to the mass flowmeter having the above configuration,
In the division circuit 21, the output of the subtraction line
Vu −Vd )+k(Vu −Vd )2 and (Vu +Vd ) which is the output of the addition line Y are input, and by dividing the former by the latter, the division circuit 21 outputs {(Vu −Vd )+k (Vu −Vd )2 }/
(Vu +Vd) is output, and this output is shown in Table 2.
As shown by curve B in FIG. Therefore, it is possible to accurately measure the flow rate not only in a small flow rate area but also in a large flow rate area.

[0022]

[Table 2]

In the above-described embodiment, the heat-sensitive coils Ru and Rd are of the self-heating type, but it goes without saying that they may be of the indirect heating type.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
Subtraction power (Vu −Vd
) by adding the amount k(Vu - Vd)2 and dividing it by (Vu + Vd), the linearity between the flow rate and the output is improved, not only in the region where the fluid flow rate is small, but also in the region where the fluid flow rate is small. Even in a region where the flow rate has increased, the flow rate can be measured with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a mass flowmeter according to the present invention.

FIG. 2 is a block diagram showing the configuration of a conventional mass flowmeter.

FIG. 3 is a flow rate-output characteristic diagram of a mass flowmeter.

[Explanation of symbols]

1... Conduit, 3, 4... Constant temperature control circuit, F... Fluid, Ru
, Rd...Heat-sensitive coil (resistor), Vu, Vd...Energy given to the resistor.

Claims (1)

[Claims] 1. Two resistors whose resistance value changes depending on the temperature of the fluid are provided independently of each other in a conduit through which a fluid flows, and two constant temperature control circuits each including the resistors are provided independently of each other. The constant temperature control circuit controls the temperature of both resistors so that they are always equal and constant, and the mass flow rate of the fluid flowing through the conduit is controlled based on the energy given to both resistors. In the mass flowmeter to be measured, when the energies given to both the resistors are Vu and Vd, and the coefficient is k, {(Vu - Vd) + k(Vu - Vd)2
}/(Vu + Vd).