JPH06229800A - Mass flow sensor with abnormality diagnosis function and abnormality diagnosis method - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a mass flow controller having a function of diagnosing whether or not there is an abnormality such as clogging of a sensor unit at any specified flow rate within the entire flow rate control range. [Structure] Two resistors whose electric resistance changes according to temperature are provided in a conduit through which a fluid flows, and a difference ΔR between the electric resistances of the two resistors is measured, and the inside of the conduit is measured based on the difference ΔR between the electric resistances. In a flow meter for measuring the mass flow rate of a fluid, a means for measuring a sensor voltage applied to both resistors in advance and a difference ΔR between electric resistances stepwise over the entire flow rate range, and storing these as a reference sensor signal. Difference in electrical resistance ΔR
Means for reading the reference sensor signal corresponding to the above from the storage means, means for comparing the read reference sensor signal and the actual sensor voltage applied to both resistors at this time with consideration of the allowable amount, and this comparison. Display means for displaying an abnormal signal according to the result is provided.

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 for measuring a mass flow rate and a mass flow controller for controlling a mass flow rate of a fluid used in a semiconductor manufacturing process, and more particularly, it has a function of self-diagnosing whether or not an abnormality occurs in a flow rate sensor section. And a mass flow meter and a mass flow controller.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing an example of a conventional mass flow controller. In this mass flow controller, a fluid inflow path 50, a bypass flow path 51 in which the fluids in the inflow path 50 are separately flowed in parallel, a sensor flow path 52, and the fluids in the bypass flow path 51 and the sensor flow path 52 join. The outflow passage 53, a flow rate control valve 54 provided in the middle of the outflow passage 53, an amplifier circuit 56 for amplifying the detection signal of the sensor section 55, the amplified detection signal and a preset mass flow rate setting signal 57 are provided. It comprises a comparison control unit 58 for comparing and outputting a drive signal to the flow rate control valve 54.

The sensor section 55 has a coil 62 wound around the outer peripheral surface of a thin stainless steel tube 52 having an inner diameter of about 0.5 mm, and a coil 63 wound downstream of the coil 62. The bridge circuit 60 is composed of 62, the coil 63, and other resistance elements, usually two.

Further, this mass flow controller may take out the amplified detection signal from the sensor section 55 as an output signal and display the mass flow rate outside.

In recent years, with the progress of semiconductor manufacturing processes, the kinds of fluids flowing to the mass flow controller have been increasing and diversifying. When a corrosive gas or a gas that is easily decomposed by heat is flown through the mass flow controller for a long period of time, the gas decomposes in the stainless steel thin tube used for the sensor part of the mass flow controller, and solid matter When the solidified substance adheres to the inner wall of the thin tube or a substance that reacts with other gas reacts with the thin tube, the thin tube may be clogged.
As a result, the sensitivity of the sensor part changes, the pressure loss of the sensor part increases, and the flow rate of the sensor part decreases even though there is sufficient fluid in the bypass flow path. It happens that you increase the amount. However, conventionally, since the mass flow controller does not have a means for detecting clogging of the thin tube of the sensor section, it is the actual situation that this abnormality is discovered only after the state of the semiconductor manufacturing process changes.

Due to such a problem, a mass flow controller having an abnormality diagnosis function by the following method has recently been proposed.

For example, one method is as follows:
As disclosed in Japanese Patent No. 4 publication, a sensor tube for flow rate measurement and a sensor tube for checking with a large inner diameter are provided separately, and the output signal values of both sensor parts are compared by a comparator, and the difference is constant. When the value exceeds the value, it is determined that an abnormality such as clogging has occurred in the sensor tube for flow rate measurement and an alarm is issued.

Another method is disclosed in JP-A-63-484.
As disclosed in Japanese Patent Laid-Open No. 22-22, the control circuit is provided with a valve opening setting means for setting the valve opening of the control valve to a constant value, and when diagnosing whether there is an abnormality, the valve opening setting means is switched to the diagnostic circuit. The control valve is temporarily fixed to a predetermined valve opening according to the reference value input by, and after obtaining a predetermined flow rate, the reference value and the actual output signal of the flow rate sensor are compared, and depending on the difference between the two, There was a method of judging the presence or absence of abnormality.

[0009]

However, in the former method of the above-mentioned conventional techniques, the checking sensor also changes with time at the same time, and it is necessary to mechanically add the checking sensor tube and the sensor section. Therefore, there is a problem in that the mass flow controller itself becomes large and assembly is complicated.

Further, in the latter method, a predetermined reference value (valve driving signal) is given to the control valve to fix it to a predetermined valve opening, and this reference value is compared with the output signal of the sensor. It is not possible to diagnose the presence or absence of abnormality. That is, since it is premised that the flow rate is constant, the diagnostic operation is not performed at a flow rate other than the predetermined flow rate determined by the reference value, for example, the flow rate currently controlled.

The causes of the deterioration of the accuracy of the mass flow controller are a span drift in which the slope of the graph showing the relationship between the flow rate of the sensor section and the output signal changes, and a zero point drift. In other words, as described above, it is not possible to calibrate the relationship of the flow rate sensor output over the other entire flow rate range by diagnosing or calibrating at only one point. That is, although it is necessary to diagnose whether or not there is an abnormality with as many control flow rates as possible, the above-mentioned prior art cannot flexibly deal with the detailed designation of the diagnostic flow rate. In addition, the flow rate range that can be diagnosed was limited.

In view of the above, the present invention solves the above-mentioned problems and allows an arbitrary designated flow rate (diagnostic flow rate) within the entire flow rate control range.
It is an object of the present invention to provide a mass flow controller having a function capable of diagnosing whether or not there is an abnormality such as clogging of a sensor section.

[0013]

According to the present invention, a mass flow controller and a mass flow meter are provided with a diagnostic function for self-diagnosis of presence / absence of abnormality. This is to measure the flow rate sensor voltage corresponding to the flow rate output signal in advance over the entire flow rate setting range in advance, and to store these as a reference sensor signal, and a reference sensor signal corresponding to the flow rate output value in use. Reading means, comparing means for comparing the read reference sensor signal with the sensor voltage actually output from the flow rate sensor at this time by considering the allowable amount, and an abnormal signal is displayed according to the comparison result. The display means is provided.

[0014]

In normal use of the mass flow controller, the comparison control section compares and controls the separately set mass flow rate setting signal and the flow rate output signal detected by the flow rate sensor, and outputs the valve drive signal to the flow rate control valve. . Here, if the flow sensor starts to become clogged, the sensitivity of the sensor will decrease,
The pressure loss of the flow rate sensor increases and the flow rate flowing to the bypass side increases. Since the comparison control unit increases the valve drive signal so as to eliminate the deviation between the flow rate setting signal and the flow rate output signal, the flow rate increases more than necessary.

At this time, the heat radiation of the sensor pipe is larger than that in the initial state due to clogging, and the upstream and downstream resistors constantly flow a constant current, so that the temperature, that is, the resistance value is in the initial state. It is lower than that. Therefore, the voltage applied to both resistors is lower than that in the initial state.

According to the present invention, the difference ΔR between the electric resistances of both resistors corresponding to the flow rate output signal and the voltage applied to both resistors at the initial stage are stored. This extracted voltage is compared with the voltage actually applied to both resistors at this time, and an alarm is generated when the voltage exceeds the allowable range.

Further, according to the present invention, even when the control flow rate is changed,
It is possible to freely set the flow rate value for diagnosing the presence or absence of an abnormality.The reference sensor voltage corresponding to the flow rate output signal at this time is extracted, and this is compared with the actual sensor voltage. In case of failure, the alarm is displayed by a lamp or sound.

Here, the reference characteristic data consisting of the difference ΔR between the electric resistances of the two resistors corresponding to the flow rate output signal and the reference sensor voltage is taken stepwise over the entire flow rate range and stored in series. At the time of diagnosis, the reference sensor voltage corresponding to the flow rate output value at this time can be extracted even if an arbitrary value is selected as the flow rate set value. Further, even for a flow rate value that is not stored or a flow rate value below the decimal point, the corresponding reference sensor voltage can be obtained by linear interpolation calculation, and can be repeatedly diagnosed over the entire flow rate range. Further, since it is not affected by the pressure change, the diagnosis can be performed even when the pressure difference between the inlet and the outlet changes.

As described above, there is flexibility in setting the flow rate value for diagnosis, and it is possible to diagnose whether or not there is an abnormality with the flow rate that is currently being controlled in the in-line state.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a main part of a mass flow controller with an abnormality diagnosis function according to an embodiment. The mass flow controller with an abnormality diagnosing function of the present embodiment comprises a mass flow controller portion A (shown by ...), a diagnostic function portion B (shown by-), and a console portion C (shown by -...-). The diagnostic function part B is provided in the controller part A (however, it partially overlaps with the diagnostic function part B in FIG. 1).
And a console portion C are added. However, it is not limited that these components are provided integrally or close to each other.

First, the mass flow controller portion A will be described. In FIG. 1, a fluid to be measured, for example, a gas body flows from an inlet of a mass flow controller through an inflow passage 1 and is branched at a predetermined ratio to a bypass flow passage 2 and a sensor flow passage 31 that are divided in parallel. Further, the gas that has passed through the bypass flow passage 2 and the sensor flow passage 31 merges again and flows through the outflow passage 4, and the outflow passage 4
The flow rate is controlled by a flow rate control valve 5 provided in the middle of the flow, and the fluid flows out from the outlet.

The sensor flow path 31 is provided with a sensor section 3 for outputting a mass flow rate signal according to the flow rate. Normally, the upstream coil 32 and the downstream coil 33 have the same electric resistance value,
The same amount of heat is generated when a constant current is passed. When the gas flows through the sensor flow path 31, the gas takes away the amount of heat generated in the upstream coil 32, and the downstream coil 33 is heated by the gas whose temperature has risen. As a result, the temperature of the downstream coil 33 becomes higher than that of the upstream coil 32, and accordingly, the electric resistance value also differs. When this difference is taken out as an unbalanced voltage via the bridge circuit 6, the mass flow rate of the gas flowing in the sensor flow path 31 has a relationship with this unbalanced voltage. Therefore, the mass flow rate is detected by detecting the unbalanced voltage. Can be measured.

The detected unbalanced voltage e is applied to the amplifier circuit 7 and A
It is amplified through the / D converter 8 and becomes a mass flow rate signal f, which is input to the comparison unit 11. On the other hand, the mass flow rate setting signal g corresponding to the desired control flow rate is externally input to the comparison unit 11 via the a contact of the changeover switch 14. Therefore, the comparison unit 11 compares the mass flow rate signal f detected by the sensor unit with the mass flow rate setting signal g, and the signal h proportional to the difference.
Is output to the valve drive voltage determination circuit 12. In the valve drive voltage determination circuit 12, PID control is performed by a built-in valve drive voltage determination program based on the signal h and the current drive signal, and a valve drive signal (hereinbelow, referred to as voltage) V is output. Then, it is input as a drive voltage to the actuator of the flow rate control valve 5 via the D / A converter 13, and as a result, the flow rate control valve 5 is driven and the valve opening changes so as to reduce the above difference. In this way, the flow rate control valve 5 is controlled so that the valve opening degree is adjusted and the control flow rate according to the mass flow rate setting signal g is maintained.

Next, the mass flow controller portion A
The bridge circuit 6 therein will be described in detail with reference to FIG.

The bridge circuit 6 has a Wheatstone bridge formed by connecting four resistors of constant resistors 42 and 43 having the same resistance value and sense coils 32 and 33. At the connection point between the constant resistance 42 and the upstream side sense coil 32, the constant current source V _cc (for example, +15 V) to the current limiting resistance 41
A current I ₀ is supplied via The current I flows into the series body of the sense coils 32 and 33 and the series body of the constant resistances R ₂ and R ₃ separately into the split currents I ₁ and I ₂ , respectively.
₁ and I ₂ join at the connection point between the constant resistance 43 and the downstream side sense coil 33, and are flown to the ground through the current control transistor 44. Assuming that the resistance values of the constant resistors 42 and 43 are R ₂ and R ₃ and the resistance values of the sense coil are R ₄ and R ₅ , the actual values thereof are, for example, 5 kΩ and R ₄ for R ₂ and R _3.
And R ₅ is, for example, 50Ω at zero flow rate.

The current I flowing through this bridge is controlled so as to always have a constant value. That is, the voltage corresponding to the voltage drop in the current limiting resistor 41 is input to the non-inverting input terminal of the operational amplifier 45, and the voltage corresponding to the constant zener voltage of the zener diode 46 is the inverting input terminal of the operational amplifier circuit 45. Is input to the output terminal of the operational amplifier 45, which is applied to the base of the current control transistor 44. As a result, the voltage drop at the current limiting resistor 41 is controlled to be constant, that is, the current I flowing through the bridge is controlled to be constant.

In such a structure, the unbalanced voltage e generated between the connection point of the constant resistors 42 and 43 of the bridge and the connection point of the sense coils 32 and 33 is used for the flow rate control as described above. Further, the voltage drops e ₀ and e _{1 of} the sense coils 32 and 33 are taken out and input to the diagnostic function unit B described later.

The voltage e of the sense coils 32 and 33 is
_{Between 0} , e ₁ and the above-mentioned unbalanced voltage e, R ₂ = R ₃
Under the condition of, the relation of e = (e ₁ −e ₀ ) / 2 is established. 3 and 4 show how these voltages e ₀ , e ₁ and e change with the flow rate.

Although e decreases when the sensor pipe is clogged, the mass flow controller is always positioned at the target value because feedback control is performed by the control circuit. Therefore, even if e is monitored, the abnormal flow rate cannot be monitored. On the other hand, the voltages at e ₀ and e ₁ decrease due to the clogging of the pipe, as shown in FIG. In this embodiment, abnormality detection is performed by monitoring e ₀ and e ₁ .

Next, the diagnostic function portion B will be described with reference to FIGS. 1 and 5, and FIG. 5 is a schematic flow chart for setting the reference characteristic data in the initial state.

First, for each mass flow controller using the diagnostic function section B, the flow rate output signal corresponding to each flow rate set value and the voltage drops e ₀ and e ₁ in the sense coil in the initial state have a one-to-one correspondence. The obtained reference characteristic data is obtained. At this time, the changeover switch 14 is changed over from the a-contact to the b-contact, and the setting signal automatic generation circuit 15 is changed. The setting signal generation circuit 15 has a built-in program for performing the flow rate setting stepwise over the entire flow rate range from 0% to 120% with a margin. This allows each flow rate setting value i% to be generated stepwise at an arbitrary interval (for example, 1% interval), and the flow rate setting signal ki is generated corresponding to this flow rate setting value i%. . This signal k is substantially the same as the mass flow rate setting signal g described above, but k has a corresponding signal over the entire flow rate range from k0 to k120 (5b in FIG. 5).
Then, the generated flow rate setting signal ki is input to the reference data writing unit 16 and the comparison unit 11. Comparison unit 11
Then, as already described, the valve drive voltage Vi is output via the valve drive signal determination circuit 12 in comparison with the mass flow rate signal f from the sensor unit 3, whereby the valve 5 is driven and the flow rate set value i%. To achieve a flow rate equal to.

In this state, the reference data writing unit 16
However, the voltage drops e _0i and e _1i of the sense coils 32 and 33 are converted into amplifiers 17 ₀ and 17 ₁ and A / D conversion circuits 18 ₀ and 18.
Take in via ₁ . (5c, 5d in FIG. 5). Then, the reference data writing unit 16 receives the flow rate setting signal ki from the flow rate signal automatic generation unit 15 and the fetched sense coil voltage drop e.
_0i and e _1i are written in the memory 19 in a one-to-one correspondence (5e in FIG. 5).

The above operation corresponds to 0 to 120% and k0
Up to k120 (5f, 5 in FIG. 5)
g) and 121 sets of reference characteristic data and the sense coil voltage drop e _{0 · 0} ~e _{0 · 120} and e _{1 · 0} ~e _{1 · 120} were respectively is stored in the memory 19. FIG. 3 can be obtained from this reference characteristic data. Although the allowable error range is also shown in FIG. 3 in addition to the diagram of this reference characteristic data, the present invention essentially compares the reference value shown by the solid line with the actual measurement value at the sensor unit during operation and compares them. The presence or absence of abnormality is determined by checking whether this difference is within the allowable range shown by the diagonal lines. Moreover, this can be performed separately for the upstream side sensor and the downstream side sensor.

The data reading section 20 has a reference voltage drop value e corresponding to a certain flow rate value x when it is set in a diagnostic mode described later.
_It has a function to read _0x and e _1x . More specifically,
As described later, the flow rate set value k before and after the flow rate value x at that time
The reference voltage drop value corresponding to is read. Then, based on this, linear interpolation is performed to calculate reference voltage drop values e _0x , e _1x corresponding to the flow rate value x. If displayed a voltage drop value e0, the relationship between e ₁ and the flow rate setting signal k from the data reading unit 20 to the external monitor 22 also it becomes easier to monitor with this monitor.

The comparing unit 21 compares the reference voltage drop value output from the data reading unit 20 in the diagnostic mode with the actual voltage drop value from the sensor, and when it determines that there is an abnormality, it outputs the result. It is output to the monitor 22.

The allowable error setting unit 24 is to set the allowable error ε which is added when the comparison unit 25 makes the above comparison. As the allowable error ε, for example, a measurement error allowed for each mass flow controller, or a value calculated from a fixed amount that is usually determined for the full-scale flow rate is often used, but there is no particular focus on this and the range of the control flow rate, etc. It can be variably set (5h in FIG. 5). Further, the memory 25 is a place for storing the set allowable error ε (5i in FIG. 5).

All the above functions are configured and processed in the microcomputer.

The monitor 22 is equipped with an alarming device such as a buzzer, a visually appealing device such as a lamp, or an alarm device having both functions in order to give an alarm when an abnormality judgment result is received.

Next, the operation for diagnosing the presence or absence of abnormality in the diagnosis mode will be described with reference to FIGS. 1 and 6. FIG. 6 shows an outline of a flow chart in the case of diagnosis.

The allowable error is preset from the console. The normal changeover switch 14 is located in the operation mode on the contact a side. In this case, when the mass flow controller unit A functions and a desired flow rate, for example, a flow rate of 65% is desired, a mass flow rate setting signal corresponding to this flow rate is set. The flow rate is controlled as described above based on g.

Upon receipt of the flow rate setting signal q, the reference data detecting section 20 selects the reference flow rate setting values stored in the memory 19 from the reference flow rate setting values q%, and the closest values Q _j and Q _{j + 1} above and below the flow rate setting value q%. (6b in FIG. 6), the reference flow rate set value Q
Reference voltage drop values e _0j , e _{0j + 1} , e corresponding to _j , Q _{j + 1
1j} and e _{1j + 1} are read from the memory 19. Next, the reference voltage drop values e _0q and e _1q for the flow rate setting signal kq are obtained by linear interpolation (6c in FIG. 6) and output to the comparison unit 21. If the flow rate setting signal kq is stored in advance at the time of the above-described initialization, the flow rate setting signal k
The reference voltage drops e _0q and e _1q corresponding to _q are directly read and output to the comparison unit 21. At this time, the flow rate setting signal q is also input to the comparison unit 11.

On the other hand, the actual voltage drops e ₀ ′ and e ₁ ′ detected by the sensor unit 3 are input to the comparison unit 21 (6 in FIG. 6).
d, 6g), and compared with the reference voltage drop values e _0q , e _1q . When this comparison is made (e ₀ ′, e ₁ ′) = (e _0q ,
e _1q ), it is determined to be normal, and (e ₀ ′, e ₁ ′)
When ≠ (e _0q , e _1q ), it may be determined that there is an abnormality, but it is desirable to add the allowable amount ± ε as described above, and the allowable error ± ε input from the memory 25 is taken in, (E _0q , e _1q ) −ε ≦ (e ₀ ′, e ₁ ′) ≦
(E _0q , e _1q ) + ε is determined (6e, 6 in FIG. 6).
h). Therefore, if it is out of this range, the abnormal signal P is output to the monitor 22 to give an alarm. Also,
Even if it is out of range, set the timer (6 in Fig. 6).
j, 6l) For a few seconds, for example, when the same state continues for 5 seconds (6k, 6m in FIG. 6), an alarm is displayed for the first time (6n in FIG. 6), and a warning message is displayed on the monitor 22 until then. It may be performed. Furthermore, if the above comparison is within the range, a normal signal O is output to the monitor 22 and OK.
You may make it display. As described above, it is possible to self-diagnose whether or not there is an abnormality in the sensor unit.

[0043]

As described above, according to the mass flow controller with an abnormality diagnosing function of the present invention, since the flow rate value to be diagnosed can be set arbitrarily and at any time, it is possible to confirm whether or not there is an abnormality in the sensor unit such as clogging. Has spread and can be flexibly dealt with, making it easier to use. In particular, it is suitable for a mass flow controller used in a semiconductor manufacturing process in which there is a change in pressure or the control flow rate is changed relatively frequently.

[Brief description of drawings]

FIG. 1 is a block diagram of a mass flow controller with an abnormality diagnosis function of the present invention.

FIG. 2 is a diagram showing a bridge circuit of a mass flow controller.

FIG. 3 is a diagram showing how the sense coil voltages ₀ and e ₁ change with respect to the flow rate.

FIG. 4 is a diagram showing how the sense coil voltages ₀ and e ₁ change with respect to the flow rate.

FIG. 5 is a flowchart for setting reference characteristic data in an initial state.

FIG. 6 is a flowchart for diagnosing an abnormality in a use state.

FIG. 7 is a block diagram showing a conventional mass flow controller.

[Explanation of symbols]

 2 Bypass flow path 3 Sensor section 5 Flow control valve 11 Comparison section 12 Valve drive voltage determination circuit 14 Changeover switch 15 Flow rate signal automatic generation circuit 16 Reference data writing section 19 Memory 20 Reference data reading section 21 Comparison section 22 Monitor

Claims (4)

[Claims] 1. A conduit in which a fluid flows, two identical resistors whose electric resistance changes according to temperature are contacted and wound in series, and a constant current circuit keeps a constant current flowing through both resistors. Keep and measure the difference ΔR between the electric resistances of the two resistors,
In a flowmeter for measuring the mass flow rate of a fluid in the conduit based on the difference ΔR in electric resistance, a difference ΔR between the sensor voltage and the electric resistance applied to the resistors in advance over the entire flow range is stepwise. Means for measuring and storing these as reference sensor signals, means for reading out the reference sensor signal corresponding to the electric resistance difference ΔR from the storage means in use, the read reference sensor signal, and the both A mass flow with an abnormality diagnosing function, which is provided with a means for comparing the actual sensor voltage applied to the resistor with an allowable amount, and a display means for displaying an abnormal signal according to the comparison result. Sensor. 2. The reading means has a correcting means for obtaining a reference sensor signal at the electric resistance difference ΔR by linear interpolation calculation based on the reference sensor signal stored in the storing means, and the reference from the correcting means is provided. 2. The mass flow sensor with an abnormality diagnosing function according to claim 1, wherein a sensor signal and the sensor voltage actually output are compared by taking an allowable amount into consideration. 3. A fluid flow conduit is provided with two identical resistors whose electrical resistance changes according to temperature, which are connected in series and wound in series, and a constant current circuit keeps the current flowing through both resistors constant. Keep and measure the difference ΔR between the electric resistances of the two resistors,
In a flowmeter for measuring the mass flow rate of a fluid in the conduit based on the difference ΔR in electric resistance, a difference ΔR between the sensor voltage and the electric resistance applied to the resistors in advance over the entire flow range is stepwise. By measuring and using these as reference sensor signals, the reference sensor signal corresponding to the electric resistance difference ΔR is read out in use, and the read reference sensor signal and the actual sensor applied to both resistors at this time. An abnormality diagnosing method for a mass flow sensor with an abnormality diagnosing function, which compares the voltage with an allowable amount and displays an abnormal signal according to the comparison result. 4. A reference sensor signal corresponding to the electric resistance difference ΔR is obtained from the stored reference sensor signal by linear interpolation calculation, and the obtained reference sensor signal and the actually output sensor voltage are allowed. 4. The method for diagnosing an abnormality of a mass flow sensor according to claim 3, further comprising: