JPS61128123A - Mass flow meter - Google Patents

Abstract

PURPOSE:To accelerate response speed by eliminating zero-point variation, by installing heat-sensitive coils changing their resistance value according to liquid temperature on upper and lower reach of a pipe passing the fluid, controlling temperature of both coils and detecting a difference of given energies. CONSTITUTION:A pipe 1 allows passage of fluid G, such as gas, etc. in the direction of an arrow. Two points set apart by a proper distance in the pipe 1, heat-sensitive coils Ru, Rd are placed, these coils Ru, Rd being of temperature sensitive resistance wires of high temperature coefficient, such as those of Fe, Ni-alloys, etc. Constant temperature circuits Tu, Td are provided with coils Ru, Rd respectively, made of the same component parts and coils Ru, Rd are so made that they are always alike and held at the constant temperature. Thus, a difference of energies supplied to the circuits Tu, Td from the DC power sources 40, 40' is detected and a signal proportional to a mass flow rate flowing in the pipe 1 is obtained by an output current K of an output circuit 50. Thus, the mass flow rate of rapid response can be measured by eliminating variation of zero points.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a claw flowmeter for measuring the mass flow rate of a fluid flowing in a conduit.

<Prior art> As the mass flowmeter, for example, heat-sensitive coils with large temperature coefficients are arranged on the upstream and downstream sides of a conduit, and the current value supplied to each heat-sensitive coil is held constant to allow fluid to flow. A device that performs /i1Em measurement by detecting the temperature distribution of the heat-sensitive part that changes depending on the temperature (for example,
6-23094 Publication No. 114j), the passing fluid is conditioned by adjusting the fluid temperature, and the temperature of the fluid is changed to a different temperature value in the heat exchange action when the fluid passes,
There is a method (for example, Japanese Unexamined Patent Publication No. 18423/1983) that measures the flow rate by displaying the energy expended in at least one of the temperature adjustment and temperature change steps.

However, the former has the disadvantage of lacking Ei properties because the speed at which the temperature distribution changes is affected by the heat capacity of the conduit and its covering. In addition, although the latter has a better response speed than the former, the operating principle is the same as that of a hot wire anemometer, so the zero point is likely to change due to changes in ambient temperature or the lack of heat capacity of the fluid. Even if a temperature control circuit is provided to eliminate this drawback, there is a point where it is difficult to increase its effectiveness despite the complexity of the circuit configuration.

<Problems to be Solved by the Invention> The present invention has been made with the above-mentioned considerations in mind, and an object of the present invention is to provide a mass flowmeter whose zero point does not fluctuate and whose response speed is fast. .

<Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention provides heat-sensitive coils whose resistance value changes depending on the temperature of the fluid on the upstream and downstream sides of the conduit through which the fluid flows, Further, a constant temperature circuit including each of the heat-sensitive coils is provided independently, and the temperature of both heat-sensitive coils is controlled to be always equal and constant by the constant-temperature circuit, and the difference in energy given to both heat-sensitive coils is reduced. The sensing measures the mass flow rate of fluid in the conduit.

According to the configuration described above, when no fluid is flowing in the conduit, the energy needed to maintain the upstream and downstream thermal coils at the same temperature is equal, so changes in ambient temperature The interference of the fluid in the conduit and the zero point are canceled out by each other. Furthermore, when fluid flows in the conduit, heat is taken away from the upstream thermosensitive coil by the fluid. As a result, the fluid is heated and becomes wetter, but in order to maintain the heat-sensitive coil at a predetermined temperature, more energy is required than when no gas is flowing. On the other hand, since the heat-sensitive coil on the downstream side receives heat from the heated fluid, less energy is required to maintain the heat-sensitive coil at a predetermined temperature compared to when no gas is flowing. . Since the difference in energy supplied to both coils that occurs at this time is proportional to the mass flow rate of the fluid at that time, the mass flow rate can be measured by detecting the difference in energy.

<Example> Hereinafter, one embodiment of the present invention will be described based on the drawings.

The drawing shows an example of the configuration of a mass flowmeter, and numeral 1 denotes a conduit through which a fluid G such as gas flows, and the fluid G flows in the direction of the arrow. Ru
* Rd is a heat-sensitive coil (hereinafter referred to as the first coil Ru and second coil Rd) installed at two appropriately spaced points on the conduit l, and is made from a temperature-sensitive resistance wire with a large temperature coefficient such as an iron-nickel alloy. Become. This is because the flow rate of the fluid G flowing through the conduit 1 is 1 Occ/min, and even the slightest displacement thereof can be detected.

Tu and Td are the first coil Ru and the second coil Rd
Constant temperature circuits (hereinafter referred to as first constant temperature circuits Tu
, the second constant temperature circuit Td), both constant temperature circuits w!
rTu and Td are included in the same part, and the first coil Ru
The first and second coils Rd are always kept at the same and constant temperature. (In the figure, the second constant temperature circuit T
A dash is added to the numbers of the components of the d-sword. ) Here, only the configuration of the first constant temperature circuit Tu will be explained. That is, the first constant temperature circuit Tu is composed of a bridge circuit io, a control circuit 20, a switching element 30, and a DC power supply 40, and the bridge circuit Bto is composed of a first coil Ru,
It consists of a temperature setting resistor 11 of this first coil Ru and bridge resistors 12 and 13. Said resistor 11.12.13
A coil whose temperature coefficient is sufficiently smaller than that of the first coil Tu is used. Au (Ad in the second constant temperature circuit 1i1GTd) and B are 1g1 coil Ru and Ru, respectively.
At the connection point between the resistor 11 and the bridge resistors 12 and 13, the potentials vA and vB are input to the control circuit 20.

The control circuit 20 includes, for example, an operational amplifier 21 and an oscillation prevention capacitor 22, and the operational amplifier 21 compares the potentials vA and vB and outputs a signal P when there is a difference between them.

The switching element 30 is made of a transistor, for example,
Switching control is performed based on the signal P.

Next, 50 is the potential V of the connection point Au of the first constant temperature circuit Tu.
, and the potential V at the connection point Ad of the second constant temperature circuit Td, respectively, and output the difference between the two, and the output circuit is composed of an operational amplifier 51 and an invidanos circuit 52 for increasing the input impedance. . This output circuit 50
In order to rub the first coil Ru and the second coil Rd at the same temperature and at a constant temperature, the output signal of
The magnitude of this output signal is proportional to the mass flow rate of the fluid G flowing through the four pipes 1.

In the mass flowmeter configured as described in E, when the fluid G is not flowing in the conduit 1, the first coil Ru, IW2
Direct current 'aff is applied to the coil Rd via the bridge circuit 10.
The energy from fi, 40 + 40' is given n
, and both coils Ru and Rd have resistances of 11.11
′ is maintained at a temperature determined by ’ respectively. Since the characteristics of the resistors 11 and 11' of the first constant temperature circuit Tu and the second constant temperature circuit Td are the same, both the coils Ru
+ The temperatures of Rd become equal. Therefore, the potential V at the point Au and the potential V at the point Ad are equal to each other, and the output circuit 5
The output signal from 0 becomes zero, indicating that the fluid G is not flowing.

Next, when fluid G is flowing in conduit 1, coil 31 is heated by fluid G, and conversely, coil 2 is heated by coil R.
d is given heat by the fluid G.

Therefore, in order to maintain the %t coil Ru at a predetermined temperature, the energy supply from the DC power supply 40 becomes large, and as a result,
The potential at point Au increases. In the case where the second coil Rd is maintained at a predetermined temperature, the energy from the DC power supply 40' is reduced by the amount of heat given from the fluid G, and as a result, the potential at the point Ad decreases. Therefore, a difference occurs between the voltages VI and v2 input to the output circuit 50, and V and -V2 are obtained as output signals. And said V,
Since -V is proportional to the mass flow rate of the fluid G flowing in the conduit 1, the mass flow rate of the fluid can be obtained by multiplying this by the constant factor.

<Effects of the Invention> As explained above, in the present invention, changes in temperature distribution are not detected, and the temperature of the heat-sensitive coils provided at two points on the conduit is always controlled to be equal and constant. Since it detects the difference in the energy given to both coils at the time, it is not affected by external factors such as conduits, so the S zero speed is fast and it is not affected by changes in ambient temperature or 41! Zero point fluctuations due to the fluid type in P are canceled out, resulting in a highly accurate mass flowmeter. In addition, since a complicated temperature control circuit or the like is not required, the structure can be reduced to 1 m 113, and the cost can be reduced.

[Brief explanation of drawings]

The drawing is a schematic configuration diagram of a quality microflow meter according to the present invention. 1 ・-411v, Ru, Rd-thermal coil, T
u, Td...Constant fan degree circuit, G-...Gas voluntary procedure amendment December 22, 1980 Patent No. 249861 2, Title of invention Mass flow meter 3, Person making the amendment Relationship to the case Patent applicant Mr. Pa Manao Name Representative Masao Horiba Principal agent

Claims (1)

[Claims] Heat-sensitive coils whose resistance value changes depending on the temperature of the fluid are provided on the upstream and downstream sides of the conduit through which the fluid flows, and further, constant temperature circuits each containing the heat-sensitive coils are independently provided,
The constant temperature circuit controls the temperatures of both heat-sensitive coils so that they are always equal and constant, and the mass flow rate of the fluid in the conduit is measured by detecting the difference in energy applied to both heat-sensitive coils. A mass flow meter characterized by: