JPS5864510A - Mass flowrate controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] This invention relates to mass flow controllers.

Semiconductor manufacturers typically manufacture semiconductors using diffusion furnaces that r-degrade silicon crystals or silicon polycrystalline substrates with Group III or Group V elements such as boron and phosphorous. The +y-sol agent and passivating compound are supplied by the gas stream entering the diffusion furnace. Typical gases include hydrogen, hydrogen chloride, nitrogen, oxygen, and silane. It will be appreciated that the concentration of doping materials within silicon needs to be very precisely controlled in order to obtain a semiconductor with the expected uniform electrical properties. That is, it is necessary to accurately measure the amount of gas supplied to the diffusion furnace. Additionally, more than one gas may be reacted in the furnace. In this case, precise stoichiometric proportions must be maintained for gas flow measurements.

The prior art reveals many electronic devices with bridges powered by constant current generators. A bridge typically includes a pair of resistors placed in or in a position that provides good thermal conduction to the main gas flow or branch, one resistor being located upstream of the other resistor. When current is applied to the bridge, both the upstream and downstream resistors generate heat that is transferred to the gas flowing through them. The upstream resistor is also cooled more than the downstream resistor, causing the voltage at the connection between the upstream and downstream resistors to vary. This junction voltage change is amplified and compared to a setpoint voltage to create an error signal that is fed to a servo amplifier that controls the metering valve.

U.S. Pat. No. 3,372,590 to Starling discloses a heat flow meter that uses a constant current source with a transistor 26 biased at the base by a Zener diode P connected to the base.

However, the Stirling flow meter must provide an output voltage that has a non-linear relationship with respect to the flow rate of fluid in conduit 90, as evidenced in FIG.

The environment in which mass flow controllers for diffusion furnaces must operate is typically electrically noisy, limiting the high frequency response of all control circuits while maintaining good sensitivity to the relatively slow changes experienced by the thermal detector. Then it is desirable.

A primary object of the present invention is to provide a mass flow controller having a device for adjusting the detection signal to provide a linearized signal that is substantially linear with respect to gas flow rate.

Accordingly, the present invention provides a thermal detection device that produces a detection signal representative of the gas flow rate through the tube, an amplifier device that receives and amplifies the detection signal and provides an amplified signal, and at least one variable gain element. Linear signal adjustment with 5
re apparatus, wherein the gain of the variable gain element is determined by the amplitude of the amplified signal, and the variable gain element adjusts the amplified signal such that it produces a linearized signal that is directly proportional to the flow rate of the gas. the linear signal conditioning device for adjusting;
A comparison device that compares the linearized signal with a set value signal and generates a command signal accordingly, and an amplifier that receives the command signal and controls a flow valve that measures the flow rate of the gas in response to the command signal. Provided is a mass flow controller characterized in that it has the following.

In a preferred embodiment, the mass flow controller has an upstream resistor leg and a downstream resistor leg positioned in a thermally conductive relationship to the branch conduit for thermally sensing the flow rate of gas through the conduit. It has a Zener diode biased constant current generator that supplies constant current to the bridge.

A variable gain bridge amplifier with a good C response and minimal high frequency gain is connected to the bridge to provide an amplified detection representing the relative temperature difference between the upstream and downstream arms of the bridge depending on the flow rate of gas through the branch conduit.
Create an A voltage signal. The bridge amplifier includes a feedback loop with a user adjustable impedance so that the gain can be selected by the user.

A plurality of operational amplifiers configured as precision limiters are connected in parallel with each other and receive the output signal from the bridge amplifier. Each precision limiter is adjusted during assembly to create a gradual linearization of the bridge amplified signal. A comparator with limited high frequency gain receives the setpoint signal and the incrementally linearized signal and produces a comparator output signal with an amplitude proportional to the difference between the linearized signal and the setpoint signal. give. The comparator output signal is provided to a servo amplifier that drives a solenoid control valve. A feedback loop with an IJ actance is connected to the input terminal of a comparator where the feedback signal from the amplifier is added to the linearized signal.9 Although the mass flow controller of the present invention is extremely precise, it It is difficult to keep the noise relatively low.

Other features of the invention will become apparent to those skilled in the art from reading the specification and claims in light of the accompanying drawings.

Referring now to the drawings and FIG. 1, there is shown a mass flow controller 10 embodying the present invention. Mass flow controller 10 has a constant current generator 12 connected to supply current to bridge 14 . Bridge 14 has a pair of resistors, represented by numbers 16 and 18, respectively, located in the branch pipes of the gas flow line. In this embodiment, each of the resistors 16 and 18 has a resistance of 1Ω per turn.
It consists of about 50 turns of resistance wire, wrapped around a branch pipe,
Resistor 16 is upstream of resistor 18, which conducts heat well thereto. The bridge amplifier 20 has a variable gain that can be preselected by the user by changing the impedance in the ground portion of the feedback loop 22, and the bridge 1
4 to produce an output signal proportional to the difference in resistance change of resistors 16 and 18 due to gas flowing through resistors 16 and 18. The output signal of the bridge amplifier 20 is
A linearization network 24 consisting of a plurality of precision limiting circuits is provided. Linearization network 24 provides a substantially linear voltage to comparator 26 that is directly proportional to the gas flow rate. Wiper 1
A setpoint voltage is also supplied to the comparator 26, the use of which may be selected by movement of the 1e tensiometer 28. A circuit amplifier 30 receives the output signal from the comparator 26 and provides drive current to a conventional solenoid P valve 32 that measures gas flow through the gas flow line.

Now referring to FIG. 2A, constant current generator 12 is connected at node 42 to a regulated +15V voltage source to provide a stable voltage signal from bridge 14 that ensures that the voltage signal is representative of the gas flow rate. It includes a resistor 40. IJ-y 4
4 provides a +15V voltage to the reverse biased Zener diode 1246 and to the supply rail 48 of the operational amplifier 50. Resistor 52 is connected to resistor 40. A resistor 52 powers an inverting terminal 54 of amplifier 50. Non-inverting terminal 56 of operational amplifier 50 is connected to cathode 46 of Zener diode 46 and ground lead 5.
9. The resistor 58 is connected to the resistor 58 connected to the A regulated positive voltage, held by Zener diode 46 at 6 µ below the 15 µ supply voltage, is provided to a non-inverting terminal 56 of operational amplifier 50. Output terminal 6 of operational amplifier 50
A capacitor 60 is connected in the feedback loop between the operational amplifier 2 and the inverting input terminal 50 to limit the high frequency gain of the operational amplifier and thereby prevent the output signal from the operational amplifier 50 from oscillating. Resistor 52 limits the current flowing to inverting terminal 54. A resistor 64 is connected to the output terminal 62 and the electrolytic capacitor 60 to
limits the current flowing into the base of the transistor 68
The emitter 70 of is connected to the junction of resistors 40 and 52. Collector 72 is connected to bridge 14 . The operational amplifier 50 also includes a power supply rail 74 connected across leads 75 to a -15V supply point 75&.

Bridge 14 includes resistors 16 and 1 which include two legs.
It has 8. Fixed resistor 76 is connected to resistor 16 and collector 72 of transistor 68. Fixed resistor 78 is connected to ground lead 59 and resistor 18 . Potentiometer 80 is connected between resistors 76 and 78. Potentiometer 80 is used to zero bridge amplifier 20 during the calibration stage of the structure. Wiper 82 from potentiometer 80
is connected to the inverting terminal 84 of the bridge amplifier 20. Bridge amplifier 20 includes an operational amplifier 86 having a non-inverting terminal 88 connected through a fixed resistor 90 to a junction 92 intermediate resistors 16 and 18 .

As the gas flows through the branch pipe, resistors 16 and 18
The heat produced by the gas is transferred to the gas.

Since the gas is cooler in the upstream resistor 16 than in the downstream resistor 18, the upstream resistor 16 is selectively cooled and therefore has a lower resistance, and the voltage at the junction of resistors 16 and 18 is lower than that of the resistor. The voltage at the junction of 76 and 78 is increased. The faster the gas flow, the greater the temperature difference between resistors 16 and 18. However, at very high gas flow rates, differential cooling effects are no longer detectable and a gas flow metering device other than that disclosed herein would have to be used.

The relative change in resistance of resistors 16 and 18 is determined by bridge 14
are unbalanced and operational amplifier 860 input terminals 84 and 8
8 to supply the input voltage difference. However, the voltage difference is not directly proportional to the flow rate of the gas through the branch pipe. Since the gas flow rate needs to be adjusted very precisely, the amplifier 86 is connected to bridge 1.
Amplify the differential voltage created by 4. This amplified voltage is output at the output terminal 92.

Amplifier 86 is constructed as a differential amplifier with resistor 94 connected between ground lead 59 and non-inverting terminal 88. An electrolytic capacitor 96 is connected in parallel with resistor 94. The electrolytic capacitor 96 and resistor 94 are
They provide a low impedance ground path for high frequency noise that would otherwise be amplified by operational amplifier 86.

It is recognized that the diffusion furnace environment in which the present invention operates is electrically noisy. It is important to remove this noise as much as possible. An electrolytic capacitor 98 having the same capacitance as the electrolytic capacitor 96 and a resistor 100 having the same resistance as the resistor 94 are connected in parallel with each other, and the feedback roots between the inverting terminal 84 and the output terminal 92 of the operational amplifier 86 are connected in parallel with each other. 101. Electrolytic capacitor 98 and resistor 100 also limit the high frequency response or bandwidth of operational amplifier 86 to prevent spurious noise signals from being amplified. Feedback loop 101 also includes a portion of fixed resistor 102 and potentiometer 104. Potentiometer 10 in feedback loop 101
The amount of resistor 4 is controlled by the user's selection of the location of tap 106 so that the user can select the desired amount of relative gain from bridge amplifier 20. Potentiometer 104 is connected to a fixed resistor 108 which is also connected to ground air 59.

The electrical circuit response is much faster than the thermal response of the bridge 14. The relatively slow response of bridge 14 is due to temperature lag within Sezza resistors 16 and 18. That is, when the gas flow rate changes, terminal 84
The voltage difference across 88 and 88 does not change immediately. An electrolytic capacitor 110 is connected to capacitor 98 and resistor 100 to compensate for temperature lag. Resistor 112
is connected to the electrolytic capacitor 110 and the ground lead 59. The combination of electrolytic capacitor 110 and resistor 112 provides a time variation to the signal provided by operational amplifier 86 and compensates for the temperature leg of bridge 14 .

A ground or common lead 113 is connected to lead 59. A pair of filter capacitors 114 and 11
5 is connected between the common lead 113 and the power supply lead 116, which is connected to the lead 75 and terminated at a point 75a. Another pair of filter capacitors 11
7 and 118 are the common lead 113 and the adjusted +i
+15 connected at point 120 to a suitable voltage source of 5VDC.
v power supply IJ-[19. Lee r1
19 is also connected to the lead 42. capacitor 11
4 and 117 are electrolytic capacitors. Lee P122
Connected to beam -+yr5 and -1 to resistor 124.
Supply 5V voltage. Resistor 124 and ground - IS59
A Zener diode 126 is connected between the voltage and the voltage to provide a regulated -6VDC pressure to the supply lead 128.

Supply IJ-P 128 powers supply lead 129 which powers linearization network 24 . Linearization network 24 includes four precision limiting circuits.

The first precision limiting circuit 130, which is also called a 25-chi precision limiter, has a non-inverting terminal 134 that is grounded and an inverting terminal 13.
IJ-)' 9
3 and resistor 140 to receive current from resistor 138 . Resistor 140 beam
A voltage of -6v is supplied from P129. resistor 138
is supplied with an output signal from bridge amplifier 20. Feedback resistor 142 is connected to the connection point between inverting terminal 136 and resistor 138. Diode 144 is resistor 142
and output terminal 1 of the operational amplifier 132.
46 and the connection point between diode P148.

Diode 148 is connected to the connection point between inverting terminal 136 and resistor 140 . In this embodiment, the resistor 13
8 and 142 are each 100Ω resistors,
Further, the resistor 140 is a resistor of 499Ω. Amplifier 132 inverts the bridge amplified signal when it exceeds 1.25V. At 1.25 V or less,
Point diode 144 is reverse biased and diode v 148 is forward biased to keep resistor 142 at ground, effectively removing the amplifier from the circuit so that no output signal is provided.

The cutoff point of the gain curve of amplifier 132 is 1 in this example.
．． It is 25V.

The output signal from bridge amplifier 20 is selected to vary between Ov and +5v over the entire range of gas flows of interest. That is, the cutoff point of amplifier 132 is approximately 2
This occurs at a flow amplitude of 5 inches.

2nd precision limiter 150 also called 50q6 precision limiter
is a non-inverting input terminal 154 connected to the ground lead 59.
and an operational amplifier 152 having an inverting input terminal 156 connected to a connection point between resistors 158 and 160. Resistor 162 connects input terminal 156 and resistor 15
Amplifier 152 between the connection point with 8 and diode 164
connected in the feedback loop. Diode r164 is connected to the output terminal 166 of operational amplifier 152.

Diode 168 connects diode 164 and output terminal 166
connected to the connection point. Diode 168 is connected to the connection point between resistor 160 and inverting input terminal 156. Resistor 158 receives the bridge amplified signal from lead 93. Resistor 160 beam - adjusted from P129 -
Receives a voltage of 6v.

In this example, resistors 158 and 162 are each e!
It is a resistor of A100xΩ, but resistor 169 is 249
is a resistor of Ω. Operational amplifier 152 inverts the bridge amplified signal as long as the bridge amplifier output voltage exceeds +2.50V. The bridge amplified signal is +2.
When less than 50 V, diode P164 is
168 is reverse biased to the blocked state while forward biased, thereby removing the output signal from operational amplifier 152 and effectively removing it from the circuit.

That is, the gain curve cutoff point of the precision limiter 150 is +2.
50 V, which corresponds to an ideal gas flow rate of 50 volts in this example.

The third N-tight limiter 170, also called a 75-chi precision limiter, has a non-inverting input terminal 174 that is grounded, and a resistor 17.
Inverting input terminal 176 connected to the connection point between 8 and 180
It is equipped with an operational amplifier 172 having the following functions. Feedback resistor 18
2 is connected to the connection point between the resistor 178 and the inverting terminal 176.

Diode 184 is connected to resistor 182. The output terminal 186 of the operational amplifier 172 is a diode)'184.
It is connected to the. Diode 188 is diode-v18
4 and the output terminal 186. Diode 188 is connected to the connection point between resistor 180 and inverting input terminal 176. Resistor 178 receives the bridge amplified signal from lead 93, while resistor 180 receives the regulated -6■ voltage from lead 129. As long as the bridge amplifier voltage exceeds +3.75 V, operational amplifier 172 inverts bridge amplifier 46.

When the bridge amplifier voltage is less than +3.75 V, diode 184 is reverse biased and diode 18
8 is forward biased so that operational amplifier 172 provides no output signal, effectively removing it from the circuit. That is, the gain curve cutoff point of precision limiter 170 is 75% of the maximum voltage.
+3.75 V, which corresponds to +3.75 V. A cut-off point of 3.75 V and a unity inverting gain factor of 100KΩ resistor 178.
100Ω resistor 182 and 165Ω resistor 1
80 resistances.

In order to obtain the correct coefficients over the entire range of flow rates in question (171), an operational amplifier 200 made as an inverting amplifier with unity gain is provided here in this example from a corresponding voltage of O~5 There is.

Resistor 202 is connected between Lee P93 and the inverting terminal 204 of operational amplifier 200. operational amplifier 200
also includes a non-inverting terminal 206 and an output terminal 208. Feedback resistor 210 connects inverting terminal 204 and output terminal 2
08. In this embodiment, resistor 2
02 and 210 are the same 100Ω resistors. The amplified signal is sent from output terminal 208 through resistor 212 to summing point 213 .

Thus, amplifiers 132, 152, 172 and 200
It is recognized that all provide a unit gain inversion function. The only difference between each amplifier is that the gain curve
at +1.25 V and at amplifier 152 at +2.50 V.
V and +3.75 V at amplifier 172. The complete 0.00 to 5.00 V range is covered by amplifier 200.

The resistance value of the output resistor connected to each output terminal of each precision circuit is selected to provide gradual linear compensation. In this embodiment, the output resistor from each precision limiting circuit is a fully inverting operational amplifier 2 depending on the polarity of the voltage being modified.
Used to power the input or output side of the 00. In this example, flows of 25 inches, 50% and 75 inches [t! ,
Although points have been selected for calibration, it will be appreciated that additional precision limiters can be added in parallel to obtain as many adjustment or calibration points along the flow curve as desired.

In this embodiment, the correction coefficients from resistors 214 and 218 are added together to a summing point 213 which is passed through a lead 222 to an inverting input terminal 224 of an operational amplifier 226.
I think it can be recognized that it is connected to Operational amplifier 226 also has a non-inverting input terminal 228 that is connected to ground 59 and also to an output terminal 230 that is connected to feedback resistor 232 . Feedback resistor 232 is IJ-)? 234 to operational amplifier 22
6 is connected to the inverting terminal 224 of No. 6. Feedback resistor 23
It will be appreciated that the selection of the resistance values of resistors 214 and 218, along with the value of 2, determines the gain for the respective voltages supplied to summing point 213 through these resistors. Although in this example resistors 214 and 218 are connected to the amplifier 2000 Å power while resistor 216 is connected to the input of amplifier 226, the calibration measurements may otherwise be made using different I think it would be acceptable to require a connection combination.

The signal provided from amplifier 200 to resistor 213 is inverted by operational amplifier 226 and added to the signal from resistor 216.

The output detection terminal 236 is connected to the output terminal 230 and
A 0Ω resistor 238 is connected to an output lead 236 that externally monitors the output from linearization network 24. The linearized voltage signal is applied through a resistor 240 to an inverting input terminal 242 of a comparator consisting of an operational amplifier 246. Operational amplifier 246 also includes a non-inverting terminal 248 and an output terminal 250. Capacitor 252 is connected between input terminal 242 and output terminal 250. The external voltage set point signal is passed through lead 254 to resistor 256.
IJ −v 2 connected to the input terminal 248 through
Served in 5 g. Resistor 256 and ground IJ-)?
A filter network including a resistor 262 and a capacitor 264 connected in series with 59 selectively directs the high frequency noise signal to ground and also outputs a DC set point signal to the non-inverting input terminal 248 of operational amplifier 246. The high frequency response of operational amplifier 246 is limited by providing only

The signal from comparator 246 is provided to a resistor 270 connected between output terminal 250 and servo amplifier 30. That signal is NPN) Rangie'! ' 272 is supplied to the base 274. The collector 276 and emitter 278 of transistor 272 are PNP power transistor 2
80 and connected to the Darlington structure. A base 282 of transistor 280 is connected to collector 276. Emitter 284 is connected to a power supply lead. The collector 286 has an oscillation suppression capacitor 288
is connected to the emitter 278 of transistor 272 through. Bias resistor 290 is connected to the junction of emitter 278 and capacitor 288. Transistor protection diode 292 is connected between base 274 and emitter 278 of transistor 272 to prevent reverse bias damage to the base-emitter junction of transistor 272.

Power is provided to transistor 280 through emitter 284 from a power supply line 294 connected to a regulated +12 VDC external voltage source.

A filter capacitor 296 is connected between emitter 284 and ground lead 59 to remove high frequency signals from the servo amplifier supply line. Collector 286 is connected to feedback loop 298 as well as valve control lead 300 . reverse biased diode v302
The valve control circuit 300 is also connected to the diode 302.
A pair of terminals are provided, respectively represented by numerals 304 and 306, located on opposite sides of the terminal.

The control valve 32 is a well-known electromagnetic solenoid control valve used to control gas flowing into the diffusion furnace.

It will be appreciated that the amount of current passing through the emitter-collector junction of transistor 280 determines the amount of valve opening of control valve 32 connected to terminals 304 and 306.

The signal provided by comparator 246 is connected to transistor 272.
controls the amount of current flowing through power transistor 280. Additionally, the current flow supplied to the flow control valve 32 determines the flow rate of the gas through the mains. To minimize or prevent damage to power transistor 280, when the magnetic field surrounding solenoid P collapses when power is removed, diode p3o2 is reverse biased to conduct a 'fit current through itself. Oscillation suppression capacitor 310
is connected between diode 302 and resistor 290 and performs the same function as capacitor 288.

Feedback loop 298 includes a capacitor 320 connected in series with a resistor 322. Resistor 322 is connected to comparator 2460 inverting input terminal 242. Since comparator 246 may be more responsive than desired to high frequency components provided through resistor 240, a capacitor 252 is included in feedback loop 298 to limit the bandwidth or high frequency gain of operational amplifier 246. Thus, it is desirable to use feedback loop 298 to control the amount of power provided directly to control valve 32 such that the valve regulates relatively slowly. This is desirable because thermal lag exists in other parts of the system. Feedback roof 298 with capacitor 320 connects comparator 246, transistor 2
72 and transistor 280 as one amplifier with a 12 dB per octave gain curve rolloff. A capacitor 320 is added to the feedback loop to prevent the circuit from oscillating around the roll-off cutoff point.

It will therefore be appreciated that the present invention provides a mass flow control circuit that is sensitive to relatively small changes in gas flow rate through a tube. The linearization network provides linear corrections at multiple points along the flow curve to ensure that the voltage supplied to comparator 246 is directly proportional to the flow rate of gas through the tube. Comparator 246 has a fast response to any change in the amount of error signal in the flow rate of gas through the tube. Capacitances 252 and 320 limit the high frequency gain of amplifier 246 and the circuit amplifier, forcing the control valve to adjust its position relatively slowly to prevent overshooting of the control valve.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the mass flow control circuit, FIG. 2A is a schematic diagram of a part of the mass flow control circuit, and FIG. 2B is a schematic diagram of another part of the mass flow control circuit. 10... Mass flow controller, 12... Constant current generator,
14... Bridge, 20... Bridge amplifier, 22
゜101.298... Feedback loop, 24... Linearization circuit network, 26... Comparator, 30... Zapo amplifier,
32...control valve, 46.1.26, 144.148,
164°168.184,188,292,302...
・Diode, 50,86,132,152,172°200.226,230,232.246...Operation amplifier, 68.272.280...Transistor, 13
0, 150, 170... Precise limit circuit agent
Asamura Akira Procedural Amendment (Voluntary) December 1, 1981 Dear Commissioner of the Japan Patent Office1, Indication of the case 1982 Patent Application No. 1573632, Name of the invention Mass flow controller3, Person making the amendment Case and Relationship between patent applicant 4, agent name (6669) Akira Asamura 5, date of amendment order 6, Showa year, month, day 6, number of inventions increased by amendment 8, content of amendment as shown in the attached sheet a Location 1 Sowing n 1 It's sunny l Mountain 1 SI - It's raining 1
) Procedural amendment (method) % formula % 1. Indication of the case Showa Sz year patent application No. 15 ri θz3 No. 2. Name of the invention 3. Person making the amendment Relationship with the case Patent applicant 4. Agent 5. Date of amendment order July 1939 ηguchi 6, the number of inventions increased by the amendment 7, φ, n' of the application subject to the amendment
Mr. Hiroyuki: One letter of appointment and one copy of drawings each. i (No change in '17) 8. Details of amendments as attached.

Claims (6)

[Claims] (1) Heat that creates a detection signal representing the flow rate of gas through the tube. a detection device, an amplifier device that receives and amplifies the detection signal and supplies an amplified signal, and a linear signal conditioning device having at least one variable gain element, the gain of the variable gain element being equal to the amplification signal. the linear signal conditioning device for adjusting the amplified signal to produce a linearized signal determined by the amplitude of the signal, the variable gain element being directly proportional to the flow rate of the gas; It is characterized by comprising a comparison device that compares it with a set value signal and generates a command signal accordingly, and a servo amplifier that receives the command signal and controls a gas flow valve that measures the flow rate of the gas accordingly. mass flow controller. (2) In the mass flow controller according to claim (1), the heat detection device includes a bridge having a pair of resistors, and the first resistor is located in the upstream portion of the tube. a second
A resistor is placed in a position for good heat conduction in the downstream part of the tube, and a voltage is applied in the bridge such that the differential cooling of the resistor created by the gas flow creates the detection signal. The mass flow controller is characterized in that the mass flow controller is configured to change the mass flow rate. (3) In the mass flow controller according to claim (2), the bridge is supplied with current from a constant current generator to minimize errors in detecting the flow rate of the gas. The mass flow controller characterized in that: (4) In the mass flow controller according to claim (1), (2), or (3), the variable gain element has at least one diode connected in the feedback loop. The mass flow controller is an operational amplifier. (5) The mass flow controller according to claim (4), wherein the operational amplifier has a second diode connected therein to a second feedback loop, and the operational amplifier has a first amplitude range. the amplified signal within the first
The mass flow controller generates a signal having an amplitude, and generates a signal having a second amplitude in response to the amplified signal within a second amplitude range. (6) The mass flow controller according to any one of claims (1) to (5), wherein the amplifying device is a differential amplifier. .