JP3019009U - Mass flow meter - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] The present invention relates to a mass flowmeter that accurately measures the mass flow rate of a fluid flowing in a conduit. [Structure] A pair of heat-sensitive coils having a resistance value that varies depending on the temperature (t) of the fluid (G) on the outer circumference of the conduit 1 in which the fluid (G) flows in a laminar flow state. (Ru) (Rd) is wound to improve the heat conduction so that the ambient temperature (T) outside the conduit 1 can be detected, and the ambient temperature detection resistance (Rtu) (Rtd ) And a temperature difference setting resistance (Rsu) (Rsd) respectively, and a bridge circuit (Tu) (Td) is provided independently on the upstream side and the downstream side, respectively Set the temperature difference (tT) between the temperature (t) of the coil (Ru) (Rd) and the ambient temperature (T) outside the conduit 1 to be approximately equal to the value determined by the temperature difference setting resistance (Rsu) (Rsd). A control device 21 for controlling is provided, and the mass flow rate of the fluid (G) in the conduit 1 is measured by detecting the difference in energy applied to both heat sensitive coils (Ru) (Rd).

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a mass flow meter that accurately measures the mass flow rate of a fluid flowing in a conduit.

[0002]

[Prior art]

 As the mass flow meter, for example, heat-sensitive coils having a large temperature coefficient are arranged on the upstream side and the downstream side of the conduit respectively, the current value supplied to each heat-sensitive coil is kept constant, and the heat-sensitive portion is changed by flowing a fluid. The flow rate is measured by detecting the temperature distribution of the fluid (for example, Japanese Examined Patent Publication No. 56-23094), and the passing fluid is conditioned by adjusting the fluid temperature. Flow rate measurement is performed by changing the temperature of the fluid to a different temperature value and displaying the energy consumed in at least one of these temperature adjustment and temperature change steps (for example, Japanese Patent Laid-Open No. 59- 18423).

However, the former has a drawback that it lacks responsiveness because the speed at which the temperature distribution changes is affected by the heat capacity of the conduit and its coating. Also, the latter has a better response speed than the former, but since the operating principle is the same as that of the hot-wire anemometer, the zero point may change due to changes in the ambient temperature outside the conduit (1) and differences in the heat capacity of the fluid. There is a drawback that it is liable to fluctuate, and even if a temperature control circuit is provided to eliminate this drawback, the circuit configuration becomes complicated, but its effectiveness is difficult to improve.

As another conventional example, it is represented by the formula of Vu (upstream thermal coil voltage) -Vd (downstream thermal coil voltage) Vu (upstream thermal coil voltage) + Vd (downstream thermal coil voltage) There is a mass flowmeter that has a correction circuit (65) (Fig. 2) that is used. However, since (Vu + Vd) strictly changes not only with temperature change but also with flow rate change, complete temperature correction is possible. Absent. Since the temperature coefficient of the temperature setting resistors (61) (61 ') must be close to zero, both thermal coils (Ru) (Rd) are set to a constant temperature (for example, about 80 to 90 ° C), As a result, if the ambient temperature exceeds the set temperature of the heat sensitive coils (Ru) (Rd) or the difference between the two is small, noise is too large to use. Similarly, the temperature of the heat sensitive coil (Ru) (Rd) must be set considerably higher than the ambient temperature outside the conduit (1), so it is said that measurement is impossible in the case of a highly reactive fluid (G). There are restrictions.

Therefore, the temperature sensing resistors (11) and (11 ′) having temperature coefficients substantially equal to these are inserted in series with the heat sensing coil (Ru) (Rd) to insert the temperature sensing resistor (Ru) (Rd) and the temperature sensing resistor. (11) (11 ') has been devised a method of providing a constant temperature difference circuit (Tu) (Td) respectively, (Fig. 3) In this method, upstream and downstream coils (Ru) If the temperature characteristic of (Rd) is expressed by the formula, Ru = Rd = Ro (1 + αt) (1) where, the resistance value t of both coils (Ru) (Rd) at Ro = 0 ° C = both coils ( Ru) (Rd) coil temperature α = temperature coefficient of both coils (Ru) (Rd) Also, its constant temperature difference circuit (Tu) (Td) is designed to operate so that the following equation (2) is satisfied. It had been. Ru (Rd) ＝ (11) ＝ (11 ') ＝ ARo (1 ＋ αT) …… (2) where T ＝ ambient temperature outside the conduit (1) A> 1 (Ru <(11) and Rd <(11 (Because it must be ')) Substituting (1) into (2), we get t = {(A-1) / α} + AT .... (3). Therefore, since the coil temperature (t) is multiplied by (A) with respect to the rise and fall of the ambient temperature (T) outside the conduit (1), there will be no constant temperature difference and accurate mass measurement will not occur. There was a drawback that was not done.

[0006]

The present invention has been made in view of the drawbacks of the conventional example, and the object thereof is to provide a fast response speed because of the constant temperature difference method, and to It is less affected by the ambient temperature, and has a wider usable temperature range than the constant temperature type in which the heat sensitive coil is controlled to a constant temperature, and since it is not necessary to raise the temperature of the heat sensitive coil, it has an effect on the material to be measured. There is less to provide a mass flow meter.

[0007]

[Means for Solving the Problems]

 The mass flowmeter according to claim 1 has a temperature (t) of the fluid (G) on the upstream side and the downstream side of the conduit (1) on the outer periphery of the conduit (1) in which the fluid (G) flows in a laminar flow state. ), A pair of heat sensitive coils (Ru) (Rd) are wound, and the characteristics are almost the same as those of the heat sensitive coils (Ru) (Rd) in parallel with the heat sensitive coils (Ru) (Rd). The ambient temperature detection resistance (Rtu) (Rtd), which has good heat conduction and sufficient heat dissipation to detect the ambient temperature (T) outside the conduit (1), and the temperature coefficient are almost zero. Insert the temperature difference setting resistors (Rsu) (Rsd) and the temperature sensing coil (Ru) (Rd), ambient temperature detection resistor (Rtu) (Rtd) and temperature difference setting resistor (Rsu) (Rsd), respectively. A bridge circuit (Tu) (Td) including each is installed independently on the upstream side and the downstream side, and the temperature (t) of both thermal coils (Ru) (Rd) is set by the bridge circuit (Tu) (Td). Set the temperature difference (tT) from the ambient temperature (T) outside the conduit (1). A control device (21) that controls the resistance (Rsu) (Rsd) to be approximately equal to the value determined is provided, and by detecting the difference in energy applied to both thermal coils (Ru) (Rd), It is characterized in that the mass flow rate of the fluid (G) in the pipe (1) is measured.

[0008]

[Action]

 In the above configuration, when the fluid (G) does not flow in the conduit (1), the temperature difference between the upstream and downstream heat-sensitive coils (Ru) (Rd) and the ambient temperature outside the conduit (1) is the same. Since the energies for holding at are almost equal, the effects of the zero point due to changes in the ambient temperature outside the conduit (1) and differences in the fluid (G) inside the conduit (1) are offset. Further, when the fluid (G) is flowing in the conduit (1), the heat is removed from the heat sensitive coil (Ru) on the upstream side by the fluid (G).

As a result, the fluid (G) is heated and its temperature rises, but the fluid (G) flows in order to keep the ambient temperature outside the conduit (1) and the heat sensitive coil (Ru) at a predetermined temperature difference. It requires more energy than when not in use. On the other hand, the heat-sensitive coil (Rd) on the downstream side keeps a predetermined temperature difference between the ambient temperature outside the conduit (1) and the heat-sensitive coil (Rd) by receiving heat from the heated fluid (G). It requires less energy than the state in which no fluid (G) is flowing.

Since the difference in energy supplied to both the coils (Ru) and (Rd) at this time is proportional to the mass flow rate of the fluid (G) at that time, the mass flow rate is detected by detecting the difference in energy. In the present invention, the characteristics are almost the same as those of the heat sensitive coil (Ru) (Rd), the heat conduction is good so that the ambient temperature can be detected, and the heat radiation can be performed sufficiently. Temperature difference setting resistor (Rsu) (Rsd) with a very small temperature coefficient inserted in series with the temperature detection resistor (Rtu) (Rtd) (connected in parallel with the thermal coil (Ru) (Rd).) Therefore, the temperature difference between the ambient temperature (T) outside the conduit (1) and the coil temperature (t) is always kept constant regardless of the change in ambient temperature outside the conduit (1). This enables accurate mass flow measurement.

[0011]

【Example】

 Hereinafter, the present invention will be described in detail with reference to illustrated embodiments. Fig. 1 shows an example of the configuration of a mass flowmeter, where (1) is a conduit through which the fluid (G) flows in the direction of the arrow. (Ru) and (Rd) are heat-sensitive coils (hereinafter referred to as the upstream coil (Ru) and the downstream coil (Rd)) provided at two points on the conduit (1) that are appropriately separated from each other. -A temperature sensitive resistance wire with a large temperature coefficient such as nickel alloy or platinum. This is because the flow rate of the fluid (G) flowing in the conduit (1) is about 5 cc / min, and even a slight displacement of the fluid (G) is detected.

(Tu) (Td) is an upstream or downstream constant temperature difference circuit, and on the upstream side, an upstream coil (Ru), a temperature detection resistor (Rtu), a temperature difference setting resistor (Rsu), a controller ( 21) "It is an error amplifier. , And bridge resistances (12) and (13) .On the downstream side, the downstream coil (Rd), temperature detection resistance (Rtd), temperature difference setting resistance (Rsd), controller (21 ') It is an amplifier. ] And bridge resistors (12 ') and (13'). The two constant temperature difference circuits (Tu) (Td) are composed of almost the same parts, but this is because the upstream coil (Ru) and the downstream coil (Rd) are always almost the same and outside the conduit (1). This is to make a constant temperature difference from the ambient temperature. (In the figure, the numbers of components having the same function in the downstream constant temperature difference circuit (Td) are indicated by dashes.) Here, only the configuration of the upstream constant temperature difference circuit (Tu) will be described. .

That is, the upstream constant temperature difference circuit (Tu) is composed of a bridge circuit (10) and a control circuit (21) “that is, an error amplifier”, and the bridge circuit (10) has an upstream coil (10). Ru) and upstream side ambient temperature detection resistance (Rtu), temperature difference setting resistance (Rsu), bridge resistance (12) (13) and zero balance resistance (RB) if necessary. As the bridge resistors (12) and (13), those having a temperature coefficient sufficiently smaller than that of the upstream coil (Ru) are used. Here, the resistance value of the ambient temperature detection resistance (Rtu) (Rtd) changes due to the change of the ambient temperature outside the conduit (1), and the temperature of the thermal coil (Ru) (Rd) is changed to the temperature difference setting resistance (Rsu). ) (Rsd).

That is, if the temperature characteristics of the upstream side coil and the downstream side coil (Ru) (Rd) are expressed by an equation, Ru = Rd = Ro (1 + αt) (10) where both coils at Ro = 0 ° C. Resistance value of (Ru) (Rd) t = coil temperature of both coils (Ru) (Rd) α = temperature coefficient of both coils (Ru) (Rd) The constant temperature difference circuit (Tu) (Td) is It is designed to operate so that equation (11) of is satisfied. Ru ＝ Rsu ＋ Rtu ………… (11) Rd ＝ Rsd ＋ Rtd ………… (12) Ambient temperature detection resistance (Rtu) (Rtd) is almost same as upstream and downstream coil (Ru) (Rd). If the ambient temperature outside the conduit (1) and the ambient temperature detection resistance (Rtu) (Rtd) are approximately the same, then Ro (1 + αt) = Rsu + Ro (1 + αT) (13) holds. Here, T = ambient temperature outside the conduit (1) t = coil temperature Therefore, t = Rsu / (α · Ro) + T …………… (14) Rewriting this, t−T = Rsu / (α・ Ro) ……………… (14 '). In equations (14) and (14 '), the ambient temperature (T) outside the conduit (1) does not have the coefficient value (A) as in the conventional example, so the coil temperature (t) is ) It shows that it operates so that the difference between the ambient temperature (T) and Rsu / (α · Ro) is always maintained. Since the temperature difference setting resistor (Rsu) has a very small temperature coefficient, Rsu / (α · Ro) is always constant regardless of temperature.

As a result, the temperature difference between the ambient temperature (T) outside the conduit (1) and the heat sensitive coils (Ru) (Rd) is kept constant. (Au) is the connection point between the upstream coil (Ru) and the upstream ambient temperature detection resistor (Rtu), and (Ad) is the connection point in the downstream constant temperature difference circuit (Td). Point (B) is a connection point between bridge resistors (12) and (13), and a zero balance resistor (RB) that is a variable resistor is inserted, and bridge circuits (10) and (10 ') on the upstream and downstream sides are inserted. It serves to correct the minute variations in the components of and to make the output of the output circuit (50) zero.

Here, the potentials (Vu) (Vb) at the connection point (Au) and the connection point (B) are input to the control device (21). This control device (21) compares the potentials (Vu) and (Vb), and if there is a difference between the two, controls the upstream coil (Ru) so that (Vu) and (Vb) become equal. Output an output signal. This point also applies to the downstream side.

Next, (50) is an output circuit, which is the potential (Vu) of the connection point (Au) of the upstream constant temperature difference circuit (Tu) and the connection point (Ad) of the downstream constant temperature difference circuit (Td). The potential (Vd) of each is input, and the difference between the two is output. The output signal (K) of this output circuit (50) is used to keep the upstream coil (Ru) and the downstream coil (Rd) at the same temperature and to maintain a constant temperature difference from the ambient temperature outside the conduit (1). (Not shown) represents the difference in energy supplied to the coils (Ru) and (Rd) respectively, and the magnitude of the output signal (K) is the mass flow rate of the fluid (G) flowing in the conduit (1). Is proportional to. In the mass flowmeter configured as described above, when the fluid (G) is not flowing in the conduit (1), the upstream coil (Ru) and the downstream coil (Rd) are connected via the bridge circuit (10). The energy from the power supply is only given to the coils, and the temperature of both coils (Ru) (Rd) is determined by the temperature difference setting resistors (Rsu) (Rsd) and the ambient temperature outside the conduit (1). Holds in sum with (T).

The ambient temperature detection resistors (Rtu) (Rtd) of the upstream and downstream constant temperature difference circuits (Tu) (Td) have the same characteristics, so that the conduits (1) of the coils (Ru) (Rd) are provided. The temperature difference from the outside ambient temperature (T) is almost equal. Therefore, the potential (Vu) at the point (Au) and the potential (Vd) at the point (Ad) are almost equal, the output signal (K) from the output circuit (50) becomes zero, and the fluid (G) flows. Indicates that not. However, as described above, the condition of each component varies so that it does not become exactly zero. Therefore, the ratio of the zero balance resistance (RB) is changed to achieve zero balance.

Next, when the fluid (G) is flowing in the conduit (1), the upstream coil (Ru) is deprived of heat by the fluid (G), and the heated fluid (G) flows to the downstream side. Although coming in, the amount of heat absorbed is smaller than that on the upstream side because the temperature difference between the downstream coil (Rd) and the fluid (G) is small. For this reason, the amount of heat taken away is complemented to maintain the temperature difference between the temperature of the upstream coil (Ru) and the ambient temperature outside the conduit (1) at a constant temperature difference of, for example, about 10 ° C. The energy supply at the point becomes large, and as a result, the potential at the point (Au) increases.

On the other hand, the downstream coil (Rd) also maintains a predetermined temperature difference from the ambient temperature outside the conduit (1), but the amount of heat taken by the fluid (G) is so small (the amount of heat taken by the upstream side). Therefore, the amount of energy supplied from the power supply is small, and as a result, the potential at the point (Ad) drops. Therefore, there is no difference in the voltage (Vu) (Vd) input to the output circuit (50). (Vu)-(Vd) is obtained as the output signal (K). Since (Vu)-(Vd) is proportional to the mass flow rate of the fluid (G) flowing in the conduit (1), multiplying this by a constant gives the mass flow rate of the fluid (G). To be

(60) is a temperature detection amplifier that detects and amplifies the voltage (Vt) of the temperature detection resistor (Rtu), and (70) detects the voltage (Vi) of the temperature difference setting resistor (Rsu). The voltage (Vi) that is detected and amplified by the temperature difference setting amplifier that amplifies is represented by the product of the bridge current (i) that passes through the temperature difference setting resistor (Rsu) and this resistance value. The temperature detection amplifier (60) and the temperature difference setting amplifier (70) are provided on either the upstream side or the downstream side.

The temperature detection resistance voltage (Vi) and the temperature difference setting resistance voltage (Vt) detected and amplified by the temperature detection amplifier (60) and the temperature difference setting amplifier (70) are sent to the correction circuit (80). On, the calculation of (Vt) / (Vi) = (Rtu) / (Rsu) is performed and the temperature difference setting resistance (Rsu) takes a constant value regardless of the ambient temperature outside the conduit (1). (1) The ambient temperature outside the conduit (1) is calculated from (Rtu) which changes with the ambient temperature outside. This ambient temperature signal enables more precise temperature correction calculation.

In the present embodiment, the correction circuit (80) is composed of the A / D conversion circuit (81), the CPU (82) and the D / A conversion circuit (83), but of course it is not limited to this. Instead, it is possible to process with a logic circuit method or an analog method.

[0024]

[Effect of device]

 The mass flowmeter according to the present invention has a pair of heat-sensitive coils whose resistance value changes according to the temperature of the fluid on the outer circumference of the conduit through which the fluid flows in a laminar flow state. The temperature sensing resistor is installed in parallel with the heat sensing coil and has substantially the same characteristics as the heat sensing coil to improve heat conduction so that the ambient temperature outside the conduit can be detected, and sufficient heat dissipation can be performed. A temperature difference setting resistor having a temperature coefficient of substantially zero is inserted, and a bridge circuit including the heat sensitive coil, the ambient temperature detecting resistor, and the temperature difference setting resistor is provided independently on the upstream side and the downstream side, respectively. The bridge circuit is provided with a control device for controlling the temperature difference between the temperature of both heat sensitive coils and the ambient temperature outside the conduit to be substantially equal to the value determined by the temperature difference setting resistance, and is provided to both heat sensitive coils. Energy Since the mass flow rate of the fluid in the conduit is measured by detecting the difference, the response speed is increased because the temperature distribution of the upstream and downstream coils is not changed, and the In order to maintain a constant temperature difference between the upstream and downstream coils with respect to the ambient temperature, there is little influence of the ambient temperature outside the conduit, and compared to the constant temperature type in which the upstream and downstream coils are controlled to a constant temperature. Therefore, the usable temperature range can be widened. In addition, there is no need to raise the temperature of the upstream side coil and the downstream side coil, so there are various advantages that the influence on the substance to be measured can be reduced. Furthermore, since the temperature difference setting resistors with a temperature coefficient of almost zero are inserted in parallel with the heat-sensitive coil, the ambient temperature in Eq. As a result of operating to keep the difference between the ambient temperature and Rsu / (α · Ro) at all times, the temperature difference between the ambient temperature outside the conduit and the temperature of the heat-sensitive coil is kept exactly constant. The fluid flowing in the conduit is measured by a measuring member outside the conduit until the laminar flow is maintained, so it is optimal for ultra-precision measurement of a very small amount of fluid to be measured. If a temperature correction circuit that calculates the ambient temperature by calculating the resistance value, which is the quotient of the terminal voltage of the ambient temperature detection resistor and its current, is provided, the ambient temperature signal can be obtained and a more accurate temperature can be obtained. It has the advantage that it can also be corrected.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional example.

FIG. 3 is a schematic configuration diagram of another conventional example.

[Explanation of symbols]

 (1) ... Conduit (G) ... Fluid (Rtu) (Rtd) ... Ambient temperature detection resistance (Rsu) (Rsd) ... Temperature difference setting resistance (12) (13) ... Bridge resistance (21) ... Control device (50) … Output circuit

Claims (2)

[Scope of utility model registration request] 1. A pair of heat-sensitive coils, whose resistance value changes depending on the temperature of the fluid, are wound around the outer circumference of a conduit in which the fluid flows in a laminar flow state, and the heat-sensitive coil is provided with the heat-sensitive coil. In parallel, the characteristics are almost the same as those of the heat-sensitive coil, the heat conduction is good so that the ambient temperature outside the conduit can be detected, and the ambient temperature detection resistance and the temperature coefficient of which the heat dissipation can be sufficiently performed are almost zero. A temperature difference setting resistor is inserted into each of the heat sensitive coils, a bridge circuit including the ambient temperature detecting resistor and a temperature difference setting resistor is independently provided on each of the upstream side and the downstream side, and both heat sensitive coils are provided by the bridge circuit. By installing a control device that controls the temperature difference between the temperature of the pipe and the ambient temperature outside the conduit to be approximately equal to the value determined by the temperature difference setting resistance, and detecting the difference in energy applied to both heat sensitive coils. A mass flowmeter, wherein the mass flow rate of the fluid in the conduit is measured. 2. A pair of heat-sensitive coils whose resistance values change according to the temperature of the fluid are wound around the outer circumference of a conduit in which the fluid flows in a laminar flow state, and the heat-sensitive coil is provided with the heat-sensitive coil. In parallel, the characteristics are almost the same as those of the heat-sensitive coil, the heat conduction is good so that the ambient temperature outside the conduit can be detected, and the ambient temperature detection resistance and the temperature coefficient of which the heat dissipation can be sufficiently performed are almost zero. A temperature difference setting resistor is inserted into each of the heat sensitive coils, a bridge circuit including the ambient temperature detecting resistor and a temperature difference setting resistor is independently provided on each of the upstream side and the downstream side, and both heat sensitive coils are provided by the bridge circuit. By installing a control device that controls the temperature difference between the temperature of the pipe and the ambient temperature outside the conduit to be approximately equal to the value determined by the temperature difference setting resistance, and detecting the difference in energy applied to both heat sensitive coils. In the mass flowmeter characterized by measuring the mass flow rate of the fluid in the conduit, the ambient temperature outside the conduit is calculated by calculating the resistance value which is the quotient of the terminal voltage of the ambient temperature detection resistance and its current. A mass flowmeter characterized by having a temperature correction circuit for calculating the temperature.