JP2001074530A - Thermal flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regulate a regulation part in high accuracy and at a low price by setting a resistance value by combination of fixed resistance for regulation and fuses for regulation. SOLUTION: A regulating resist part 100 as a regulation part is constituted of fixed resistors 1-4 for regulation connected between connecting terminals CT1, CT2 and fuses 5-8 connected in parallel with the fixed resistors 1-4 (or in series). By this constitution, the compound resistance Rts of the regulating resistance part 100 is the compound resistance of the respective resistances R1-Rn of the fixed resistors 1-4, and by combination of connection and fusing of the fuses 5-8, an optional compound resistance Rts having the nearly same characteristic as the constituting fixed resistors 1-4 can be set. In this way, because the resistance of the regulation part can be set by cut-off of the fuse, when deregulation is required, it is enough to exchange only a fuse to be the object, and all the products are unnecessary to be abandoned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter for detecting a flow rate of a fluid by using a thermal resistor, and more particularly to an adjusting section for adjusting a flow rate characteristic thereof.

[0002]

2. Description of the Related Art Generally, in a thermal flow meter, an adjusting resistor having a resistance value obtained from a predetermined test result is soldered to an adjusting section, and the resistance value is set by laser trimming or zener zap. There is known a technology for absorbing variations in components.

[0003] For example, FIG. 7 shows Patent No. 2599854.
FIG. 1 is a circuit diagram showing a conventional thermal flow meter disclosed in Japanese Patent Application Laid-Open Publication No. H10-15095. In the figure, a thermal flow meter includes a fixed resistor 201, an adjustment resistor 202, a heat-sensitive resistor 203, and a fluid temperature sensor 20.
4 and a gain adjustment circuit including an adjustment resistor 205, a fixed resistor 206, and a differential amplifier 207. The non-inverting input terminal of the differential amplifier 207 is connected to a connection point T1 between the fixed resistor 201 and the thermal resistor 203. Connected to
The inverting input terminal is grounded via a fixed resistor 206. Further, an adjustment resistor 205 is connected between the output terminal and the inverting input terminal of the differential amplifier 207.

[0004] The thermal type flow meter is provided with a differential amplifier 208.
, A transistor 209, and a power supply 210, a non-inverting input terminal of the differential amplifier 208 is connected to the connection point T 1, and the inverting input terminal is connected to the fixed resistor 204 and the adjusting resistor 20.
2 and the output terminal thereof is connected to the base of the transistor 209. The collector of the transistor 209 is connected to the power supply 210, and the emitter is a connection point T between the thermal resistor 203 and the fluid temperature sensor 204.
3 is connected.

In such a configuration, when the voltages at the connection points T1 and T2 become equal, the circuit is in an equilibrium state. At this time, a current corresponding to the flow rate flows through the heat-sensitive resistor 203, and a fixed resistance flows through the connection point T1. A voltage equal to the terminal voltage of 201 is generated, and this voltage is used as a flow signal.

Then, in order to correct the detection variations due to the variations in the resistance values R203 and R204 of the heat-sensitive resistor 203 and the fluid temperature sensor 204, the resistance temperature coefficient, and the resistance value R201 of the fixed resistor 201, the adjustment resistors 202 and 205 respectively. By adjusting the resistance values R202 and R205, the detected flow rate characteristics can be changed equilibrium, and the detected value at a predetermined flow rate can be adjusted to the target value.

In this adjusting step, for example, as shown in FIG.
A bridge circuit including the adjustment resistor 202, the heat-sensitive resistor 203, and the fluid temperature sensor 204 is operated, and a predetermined flow rate is given to a detection tube (not shown) including the heat-sensitive resistor 203 and the fluid temperature sensor 204. And 20
5, a dummy resistor is connected, and by increasing or decreasing the dummy resistor, target resistance values of the resistance values R202 and R205 are obtained (R202 and R205 measurement). Thereafter, the power supply voltage is cut off (power supply is turned off), and the target resistance is reduced. Soldering (R
202, R205 soldering), a power supply voltage is applied again (power supply is turned on), and a series of adjustments for confirming the flow characteristics are performed. It is also known that a bridge circuit is operated by applying a power supply voltage, a predetermined flow rate is applied to a detection tube, and adjustment of the adjustment resistors 202 and 205 formed of a trimmable resistance element is performed by laser trimming.

FIG. 9 is a circuit diagram showing a conventional thermal flow meter disclosed in Japanese Patent Application Laid-Open No. 5-313613. This thermal type flow meter adopts an adjustment circuit using a memory function of a zener zap and a polysilicon phase for setting an adjustment resistor, and a terminal for selecting a memory state of a zener zap and a polysilicon phase is a sensor device. It is provided outside.

In the figure, adjusting resistors Ra to R connected in series are connected.
c, Zener diodes Da to
Dc is selected by an external electric signal and short-circuited, that is, an “L” voltage is applied to the terminal X, and the terminals Ya to
The zener zap is performed by applying the “H” voltage to Yc to adjust the characteristics.

[0010]

However, the conventional thermal flowmeter as described above has the following problems. That is, first, in a conventional thermal flow meter that solders a dummy resistor, it is necessary to apply power again to check the flow characteristics. However, there is a problem in that the length of the manufacturing process increases and the number of manufacturing steps increases.

In addition, laser trimming requires a large-scale trimming facility, and the trimming resistor is apt to lack initial stability due to the heat generated during trimming and the state of the trimming end face treatment, which tends to cause an error. . In addition, if the memory state of the zener zap and the polysilicon phase is selected from the outside of the sensor device, the adjustment is performed only once, and if the readjustment is required, the entire product must be discarded. was there.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional problems, and has as its object to provide a thermal type flow meter capable of adjusting an adjusting section with high accuracy and at low cost. .

[0013]

According to a first aspect of the present invention, there is provided a thermal flow meter having an adjusting section for adjusting a flow characteristic, wherein the adjusting section comprises an adjusting means and an adjusting means. And a fuse provided for the means.

According to a second aspect of the present invention, in the thermal flow meter according to the first aspect, the fuse is electrically blown.

According to a third aspect of the present invention, in the thermal flowmeter according to the first aspect, the fuse is thermally blown.

A thermal flowmeter according to a fourth aspect of the present invention is the thermal flowmeter according to any one of the first to third aspects, wherein the adjusting means and the fuse are connected in series.

A thermal flow meter according to a fifth aspect of the present invention is the thermal flow meter according to any one of the first to third aspects, wherein the adjusting means and the fuse are connected in parallel.

According to a sixth aspect of the present invention, there is provided a thermal flow meter having an adjusting section for adjusting a flow characteristic, wherein the adjusting section is provided for an adjusting means and the adjusting means. And a switch.

According to a seventh aspect of the present invention, there is provided a thermal flow meter according to the sixth aspect, wherein the adjusting means and a switch are connected in series.

According to an eighth aspect of the present invention, there is provided a thermal flow meter according to the sixth aspect, wherein the adjusting means and a switch are connected in parallel.

According to a ninth aspect of the present invention, there is provided a thermal flow meter according to any one of the first to eighth aspects, wherein the adjusting means comprises:
R, 2R, 4R,..., 2 ^{n -1} R (R is an arbitrary resistance value, n is the number of resistors used).

According to a tenth aspect of the present invention, in the thermal flow meter according to any one of the first to eighth aspects, the adjusting means is a discrete component.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a circuit diagram showing Embodiment 1 of the present invention. In the figure, an adjustment resistor unit 100 as an adjustment unit having a combined resistance value Rts includes fixed resistors 1 to 3 connected as adjustment means connected between connection terminals CT1 and CT2.
4 and fuses 5 to 8 connected in parallel to these fixed resistors 1 to 4, respectively. The fixed resistors 1, 2, 3, and 4 have resistance values R1, R2, R3, and Rn, respectively, and their combined resistance value is equal to the combined resistance Rts of the adjustment resistor unit 100.

In FIG. 1, if the connections and blow states of the fuses 5 to 8 are D1 to Dn, the combined resistance value Rts at that time is represented by the following equation.

Rts = R1 × D1 + R2 × D2 + R3 × D3 +... + Rn × Dn (1)

However, in the above formula (1), D1 to Dn
Is 1 for the connection state (short) of the fuse and 0 for the blown state (open). In other words, it is possible to set an arbitrary resistance value having substantially the same characteristics as the fixed resistance that constitutes it. In particular, generally, for example, a metal film resistor or a thin film resistor that is a discrete component having excellent temperature characteristics and accuracy is fixed. When used for resistors, the temperature characteristics and accuracy of these metal film resistors or thin film resistors can be reproduced.

For example, when the fixed resistance and the fuse are combined in six sets, the combined resistance value Rt of the adjustment resistance unit 100 is determined.
s will now be described with reference to FIG. 2. Now, the resistance value of the n-th fixed resistor that is configured is Rn = R1 × 2 ^(n−1), and R
When 1 = 1 kΩ, the resistance values of the first to sixth fixed resistors are R1 = 1 kΩ, R2 = 2 kΩ, and R3 =
R4 = 8 kΩ, R5 = 16 kΩ, R6 = 32 kΩ
Becomes At this time, there are ²⁶ types of combined resistance values Rts based on the combination of the resistance values of R1 to R6.
As shown in FIG. Further, the resistance value that can be taken by Rts by the combination of Dn is as shown in FIG. 3, and it can be seen that excellent linearity is shown.

As a method of blowing the fuse, an excessive current may be applied to the fuse to electrically blow the fuse. When the fuse is electrically disconnected, the contact terminal may be provided outside the sensor. Further, the fuse may be spot-heated and thermally blown. In the case of this thermal fusing, since an input of an electric signal is unnecessary, an excessive current does not flow through the resistor immediately after the fusing.

As described above, in the present embodiment, since the adjusting section of the thermal flow meter is performed by cutting the fuse, the adjusting process can be simplified and the reliability of the adjusting section can be improved. When readjustment is required, only the target fuse need be replaced, and there is no need to discard the entire product.

Embodiment 2 FIG. In the present embodiment, the fuses 1-4 used in the first embodiment are replaced with switches J1 and J2.
2, J3, and Jn. Therefore, as a circuit configuration, the fuses 1 to 4 include the switches J1, J2, and Jn.
3, except that it is replaced with Jn. Now, the switches J1, J2, J3, Jn are turned on,
Assuming that the off state is D1 to Dn, the combined resistance value Rts of the adjustment resistance unit 100 is expressed by the following equation, as in the first embodiment.

Rts = R1 × D1 + R2 × D2 + R3 × D3 +... + Rn × Dn (2)

However, in the above formula (2), D1 to Dn
Is 1 for the ON state (short) of the switch and 0 for the OFF state (open). That is, in this case as well, as in the first embodiment, an arbitrary resistance value having substantially the same characteristics as the fixed resistor that is configured can be set. Further, since the resistance value can be set by turning on and off the switch, readjustment is possible.

As described above, in this embodiment, since the adjusting section of the thermal flow meter is operated by switching, the adjusting process can be simplified and the reliability of the adjusting section can be improved. When readjustment is required, the readjustment can be performed without requiring replacement of parts.

Embodiment 3 FIG. 4 is a circuit diagram showing a third embodiment of the present invention. In the figure, the combined resistance value Rt
An adjusting resistor 101 as an adjusting unit having p is connected in parallel to a mother resistor 18 connected between the connection terminals CT1 and CT2 via a fixed resistor 17, and has fixed resistors 9 to 12 and fuses 13 to 12 as adjusting means. 16. The fixed resistor 9 and the fuse 13, the fixed resistor 10 and the fuse 14, the fixed resistor 11 and the fuse 15, and the fixed resistor 12 and the fuse 16 are connected in series, respectively, and a plurality of these series circuits are connected in parallel to the mother resistor 18. Fixed resistors 9, 10,
11 and 12 are resistance values R9, R10, R11, respectively.
And Rm, and their combined resistance value is the adjustment resistance part 1
01 is equal to the combined resistance Rtp.

Now, referring to FIG.
If the connection and fusing state of D are D13 to Dm, the combined resistance value Rtp at that time is represented by the following equation.

Rtp = 1 / (D13 / R9 + D14 / R10 + D15 / R11 +... + Dm / Rmn) (3)

However, in the above equation (3), D13 to D13
m is 1 for the connection state (short) of the fuse and 0 for the blown state (open). That is, in this case as well, an arbitrary resistance value having substantially the same characteristics as the fixed resistance constituting the resistor can be set. In particular, a metal film resistor or a thin film, which is a discrete component generally having excellent temperature characteristics and accuracy, can be set. If a resistor is used as a fixed resistor, the temperature characteristics and accuracy of these metal film resistors or thin film resistors can be reproduced.

For example, when the fixed resistance and the fuse are combined in six sets, the combined resistance value Rt of the adjustment resistance unit 101 is determined.
p will now be described with reference to FIG. 5, where the resistance value of the n-th fixed resistor is Rm = R9 × 2 ^(n−1), and R
When 9 = 10 kΩ, the resistance values of the first to sixth fixed resistors are R9 = 10 kΩ and R10 = 20 k, respectively.
Ω, R11 = 40 kΩ, R4 = 80 kΩ, R13 = 16
0 kΩ and R14 = 320 kΩ. At this time, R9 ~
The combined resistance value Rtp based on the combination of the resistance values of R14 is ²⁶ types, and the values are as shown in FIG.

The Rtp by the combination of Dn
Can be taken as shown by the characteristic of “R18: none” in FIG. 6 when the mother resistor 18 is not provided.

On the other hand, as shown in FIG. 4, when the mother resistor 18 is present, the resistance value that can be taken by Rtp by the combination of Dn is, for example, R18 = 10 kΩ, and “R18 = 10 kΩ” in FIG. It is as follows. That is, the characteristic of “R18 = 10 kΩ” in FIG.
The resistance value that can be taken by the combined resistance of Rtp // R18 in the case of is shown. 6, the linearity of the adjustment resistance value is improved when the mother resistor 18 is present. Therefore, in order to make the adjustment resistance value linear, the configuration including the mother resistor R18 is included. It is understood that it is preferable to set

As described above, in the present embodiment, since the adjusting section of the thermal type flow meter is performed by cutting the fuse, the adjusting process can be simplified and the reliability of the adjusting section can be improved. When readjustment is required, only the target fuse need be replaced, and there is no need to discard the entire product. Furthermore, in the present embodiment, when the fuse is blown electrically, an excessive current does not easily flow through the resistor after the fuse is blown, so that the current at the time of blowing can be easily set.

Embodiment 4 In the present embodiment, the fuses 13 to 16 used in the third embodiment are connected to the switch J1.
3, J14, J15, and Jm. Therefore, the same circuit configuration as that of FIG. 4 may be used except that the fuses 13 to 16 are replaced with switches J13, J14, J15, and Jm. Now, switches J13 and J
Assuming that the on / off states of 14, J15, and Jm are D13 to Dm, the combined resistance value Rtp of the adjustment resistance unit 101 is expressed by the following equation, as in the third embodiment.

Rtp = 1 / (D13 / R9 + D14 / R10 + D15 / R11 +... + Dm / Rmn) (4)

However, in the above equation (4), D13 to D13
m is 1 for the ON state (short) of the switch and 0 for the OFF state (open). That is, in this case as well, as in the third embodiment, an arbitrary resistance value having substantially the same characteristics as the fixed resistor can be set. Further, since the resistance value can be set by turning on and off the switch, readjustment is possible.

As described above, in the present embodiment, since the adjusting section of the thermal flow meter is operated by switching, the adjusting process can be simplified and the reliability of the adjusting section can be improved. When readjustment is required, the readjustment can be performed without requiring replacement of parts.

When each of the above embodiments is applied to, for example, the above-described thermal flow meter having the configuration shown in FIG. 7 or FIG. 9, the connection terminals CT1 and CT2 are connected to each of the adjustment resistors. What is necessary is just to connect between terminals.

[0047]

As described above, according to the first aspect of the present invention, in the thermal type flow meter having the adjusting section for adjusting the flow characteristics, the adjusting section comprises an adjusting means and an adjusting means. With the provision of the fuse provided in this manner, the adjustment process can be simplified and the reliability of the adjustment unit can be improved, so that an inexpensive and high-precision thermal flow meter can be obtained.

According to the second aspect of the present invention, since the fuse is electrically blown, when readjustment is required, only the target fuse may be replaced, and the entire product is discarded. The effect is that there is no need.

According to the third aspect of the present invention, since the fuse is thermally blown, when readjustment is required, only the target fuse may be replaced, and the entire product is discarded. The effect is that there is no need.

According to the fourth aspect of the present invention, since the adjusting means and the fuse are connected in series, when the fuse is electrically blown, an excessive current hardly flows through the resistor after the fuse is blown. There is an effect that the current can be easily set.

According to the fifth aspect of the present invention, since the adjusting means and the fuse are connected in parallel, there is an effect that the adjusting step can be simplified.

According to the sixth aspect of the present invention, there is provided a thermal type flow meter having an adjusting section for adjusting a flow rate characteristic.
Since the adjusting unit includes the adjusting unit and the switch provided for the adjusting unit, the adjusting process can be simplified and the reliability of the adjusting unit can be improved. There is an effect that it can be obtained.

According to the seventh aspect of the present invention, since the adjusting means and the switch are connected in series, when the readjustment is required, the readjustment can be performed without replacing the parts. effective.

According to the eighth aspect of the present invention, since the adjusting means and the switch are connected in parallel, when the re-adjustment is required, the re-adjustment can be performed without replacing parts. effective.

According to the ninth aspect of the present invention, the adjusting means is provided with R, 2R, 4R,..., 2 ^{n- 1} R resistors (R is an arbitrary resistance value, and n is the number of resistors used). , There is an effect that excellent linearity of the adjustment resistance value can be obtained.

According to the tenth aspect of the present invention, since the adjusting means is a discrete component, there is an effect that the temperature characteristic and accuracy of the discrete component can be reproduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing Embodiments 1 and 2 of the present invention.

FIG. 2 is a diagram showing a combination example of resistance values according to the first and second embodiments of the present invention.

FIG. 3 is a diagram showing linearity of a combined resistance based on a combination of resistance values in the first and second embodiments of the present invention.

FIG. 4 is a circuit diagram showing Embodiments 3 and 4 of the present invention.

FIG. 5 is a diagram showing an example of a combination of resistance values according to the third and fourth embodiments of the present invention.

FIG. 6 is a diagram illustrating linearity of a combined resistance based on a combination of resistance values according to the third and fourth embodiments of the present invention.

FIG. 7 is a circuit diagram showing an example of a conventional thermal flow meter.

FIG. 8 is a view for explaining an adjustment step in a conventional thermal flow meter.

FIG. 9 is a circuit diagram for setting an adjustment resistance in a conventional thermal flow meter.

[Explanation of symbols]

1-4, 9-12 fixed resistance, 5-8, 13-16 fuse, 18 mother resistance, 100, 101 adjustment resistance part,
J1 to Jn, J13 to Jm switches.

Claims (10)

[Claims] 1. A thermal flow meter having an adjusting unit for adjusting a flow characteristic, wherein the adjusting unit includes an adjusting unit and a fuse provided for the adjusting unit. Thermal flow meter. 2. The thermal flow meter according to claim 1, wherein said fuse is electrically blown. 3. The thermal flowmeter according to claim 1, wherein said fuse is thermally blown. 4. The thermal flow meter according to claim 1, wherein the adjusting means and the fuse are connected in series. 5. The thermal flow meter according to claim 1, wherein said adjusting means and said fuse are connected in parallel. 6. A thermal flowmeter having an adjusting section for adjusting a flow characteristic, wherein the adjusting section includes an adjusting means and a switch provided for the adjusting means. Thermal flow meter. 7. The thermal flow meter according to claim 6, wherein said adjusting means and a switch are connected in series. 8. The thermal flow meter according to claim 6, wherein said adjusting means and a switch are connected in parallel. 9. The method according to claim 8, wherein the adjusting means comprises R, 2R, 4R,.
The thermal flow meter according to any one of claims 1 to 8, wherein the thermal flow meter is constituted by ^2n- 1R resistors (R is an arbitrary resistance value, and n is the number of resistors used). 10. The thermal flow meter according to claim 1, wherein said adjusting means is a discrete part.