JPH0663801B2 - Flow rate measurement circuit - Google Patents
Flow rate measurement circuitInfo
- Publication number
- JPH0663801B2 JPH0663801B2 JP63272936A JP27293688A JPH0663801B2 JP H0663801 B2 JPH0663801 B2 JP H0663801B2 JP 63272936 A JP63272936 A JP 63272936A JP 27293688 A JP27293688 A JP 27293688A JP H0663801 B2 JPH0663801 B2 JP H0663801B2
- Authority
- JP
- Japan
- Prior art keywords
- temperature
- flow rate
- circuit
- heater
- temperature sensor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Description
【発明の詳細な説明】 〔産業上の利用分野〕 本発明は流量測定回路に関し、特に、自動的に感度を補
正する自動感度補正回路に関するものである。Description: TECHNICAL FIELD The present invention relates to a flow rate measuring circuit, and more particularly to an automatic sensitivity correction circuit for automatically correcting sensitivity.
マイクロブリッジを使用した流量測定回路は、上流側温
度センサと下流側温度センサとの間に配置されたヒータ
抵抗に電流を流して発熱させ、上流側温度センサと下流
側温度センサの出力信号の差により流量を測定する。こ
の回路を第４図に示す。第４図において、ＲＨはヒータ
抵抗、ＲＲは基準抵抗、ＲＵは上流側温度センサ、ＲＤ
は下流側温度センサ、１および２は演算増幅器である。
第４図(a)はヒータ制御回路で、ヒータ抵抗ＲＨの温度
上昇を一定に保つようにフィードバック制御を行なう。
このとき基準抵抗ＲＲは周囲温度の測定を行なう。第４
図(b)は温度センサ回路で、上流側，下流側の２つの温
度センサＲＵ，ＲＤによって発生する電圧ＶＤ，ＶＵの
差を演算増幅器２でＡ倍に増幅して流量信号Ｘとする。
Ｘは次のように表わせる。A flow rate measurement circuit using a microbridge causes heat to flow by passing a current through a heater resistor arranged between the upstream temperature sensor and the downstream temperature sensor, and the difference between the output signals of the upstream temperature sensor and the downstream temperature sensor. To measure the flow rate. This circuit is shown in FIG. In FIG. 4, RH is a heater resistance, RR is a reference resistance, RU is an upstream temperature sensor, and RD.
Is a downstream temperature sensor, and 1 and 2 are operational amplifiers.
FIG. 4 (a) shows a heater control circuit which performs feedback control so as to keep the temperature rise of the heater resistance RH constant.
At this time, the reference resistance RR measures the ambient temperature. Fourth
FIG. 2B shows a temperature sensor circuit in which the difference between the voltages VD and VU generated by the two temperature sensors RU and RD on the upstream side and the downstream side is amplified by A times by the operational amplifier 2 to obtain the flow rate signal X.
X can be expressed as follows.
Ｘ＝Ａ（ＶＤ−ＶＵ）・・・・・(1) ここで、（ＶＤ−ＶＵ）はヒータ温度上昇ＴＲに比例す
るため、ＸもＴＲに比例する。すなわち、(1)式は、 Ｘ＝ｋ・ＴＲ・・・・・(2) と表わせる。X = A (VD-VU) (1) Since (VD-VU) is proportional to the heater temperature rise TR, X is also proportional to TR. That is, the equation (1) can be expressed as X = k · TR (2).
ところが、ヒータ抵抗ＲＨは常に基準抵抗ＲＲより高温
になるため、抵抗値の経年変化がヒータ抵抗ＲＨと基準
抵抗ＲＲとで異なり、ヒータ抵抗ＲＨの方が劣化が早
い。第５図に示すヒータ抵抗ＲＨの温度特性のグラフに
おいて、初期特性を直線Ｌ１で示し、劣化の進んだ特性
を直線Ｌ２で示すと、第４図の回路ではヒータ抵抗の抵
抗値が一定となるように制御されるため、ヒータ抵抗Ｒ
Ｈの温度は初期に点Ａで示すＴＡであったものが、後に
点Ｂで示すＴＢになってしまう。このため、感度特性が
変化し、流量信号Ｘの値が変わってしまうという欠点が
あった。However, since the heater resistance RH is always higher than the reference resistance RR, the aging change of the resistance value is different between the heater resistance RH and the reference resistance RR, and the heater resistance RH is deteriorated earlier. In the graph of the temperature characteristic of the heater resistance RH shown in FIG. 5, if the initial characteristic is shown by the straight line L1 and the deteriorated characteristic is shown by the straight line L2, the resistance value of the heater resistance becomes constant in the circuit of FIG. Heater resistance R
The temperature of H was initially TA indicated by point A, but changed to TB indicated by point B later. Therefore, there is a drawback that the sensitivity characteristic changes and the value of the flow rate signal X changes.
本発明はこのような点に鑑みてなされたものであり、そ
の目的とするところは、出力流量の値がヒータ抵抗の特
性変化の影響を受けないような流量測定回路に得ること
にある。The present invention has been made in view of the above points, and an object thereof is to obtain a flow rate measuring circuit in which the value of the output flow rate is not affected by the characteristic change of the heater resistance.
このような目的を達成するために本発明は、上流側温度
センサと下流側温度センサの周力信号からヒータの上昇
温度を示す上昇温度信号を出力する上昇温度算出回路
と、上流側温度センサと下流側温度センサの出力信号か
ら温度差を示す温度差信号を出力する温度差回路と、上
昇温度により温度差を割って流量を得る割算回路と、ヒ
ータを断続する制御回路とを設けるようにしたものであ
る。In order to achieve such an object, the present invention provides a rising temperature calculation circuit that outputs a rising temperature signal indicating a rising temperature of a heater from the circumferential force signals of the upstream temperature sensor and the downstream temperature sensor, and an upstream temperature sensor. A temperature difference circuit that outputs a temperature difference signal indicating a temperature difference from the output signal of the downstream temperature sensor, a division circuit that divides the temperature difference by the rising temperature to obtain a flow rate, and a control circuit that disconnects the heater are provided. It was done.
本発明による流量測定回路においては、自動的に感度が
補正される。In the flow rate measuring circuit according to the present invention, the sensitivity is automatically corrected.
第１図は本発明による流用測定回路の一実施例を示す回
路図である。同図において、３は割算回路、Ｕ１〜Ｕ３
は演算増幅器、４は制御回路、Ｓ１，Ｓ２はスイッチ、
Ｒ１，Ｒ２は抵抗、Ｃ１はコンデンであり、演算増幅器
Ｕ１〜Ｕ３は上昇温度信号を出力する上昇温度算出回路
を構成し、演算増幅器２は温度差信号を出力する温度差
回路を構成する。なお、第１図において第４図と同一部
分又は相当部分には同一符号が付してある。FIG. 1 is a circuit diagram showing an embodiment of a diversion measuring circuit according to the present invention. In the figure, 3 is a division circuit, U1 to U3.
Is an operational amplifier, 4 is a control circuit, S1 and S2 are switches,
R1 and R2 are resistors and C1 is a condenser. The operational amplifiers U1 to U3 form a rising temperature calculation circuit that outputs a rising temperature signal, and the operational amplifier 2 forms a temperature difference circuit that outputs a temperature difference signal. In FIG. 1, the same or corresponding parts as those in FIG. 4 are designated by the same reference numerals.
演算増幅器２は温度差Ｘを示す温度差信号を割算回路３
へ出力し、演算増幅器Ｕ１〜Ｕ３は上昇温度Ｙを示す上
昇温度信号を割算回路３へ出力する。The operational amplifier 2 divides the temperature difference signal indicating the temperature difference X into a division circuit 3
Then, the operational amplifiers U1 to U3 output the rising temperature signal indicating the rising temperature Y to the division circuit 3.
温度センサＲＵ，ＲＤからの出力電圧は流量に対して第
２図に示すように変化するが、基準電圧VONに対する温
度センＲＵとＲＤの出力電圧の偏差ΔＶＤ（曲線ＳＤ）
とΔＶＵ（曲線ＳＵ）の比は一定とみなせるので、第１
図の抵抗Ｒ１とＲ２の抵抗値ｒ１とｒ２の比を ｒ１／ｒ２＝ΔＶＤ／ΔＶＵ・・・・・(3) となるように選べば、温度センサＲＵ，ＲＤからの出力
電圧を加算することにより、流量にかかわらず、基準電
圧VONの値を求めることができる。Although the output voltage from the temperature sensors RU and RD changes as shown in FIG. 2 with respect to the flow rate, the deviation ΔVD (curve SD) between the output voltages of the temperature sensors RU and RD with respect to the reference voltage V ON .
The ratio of ΔVU (curve SU) can be regarded as constant, so
If the ratio of the resistance values r1 and r2 of the resistors R1 and R2 in the figure is selected to be r1 / r2 = ΔVD / ΔVU (3), add the output voltages from the temperature sensors RU and RD. Thus, the value of the reference voltage V ON can be obtained regardless of the flow rate.
制御回路４により一定周期でスイッチＳ１をオフにし、
ヒータ抵抗ＲＨをオフにする。このとき演算増幅器Ｕ１
に現れる直線Ｌ３の電圧VOFFをスイッチＳ２をオンにし
てコンデンサＣ１に充電する。次に、測定状態に戻る
と、スイッチＳ１がオン、スイッチＳ２がオフになり、
演算増幅器Ｕ１に現れる電圧VONとコンデンサＣ１，演
算増幅器Ｕ２が保持している電圧VOFFとの差が演算増幅
器Ｕ３にて演算される。すなわち、演算増幅器Ｕ３の出
力信号値（上昇温度）Ｙは、 Ｙ＝VON−VOFF・・・・・・(4) となる。演算増幅器２の出力信号値（温度差）Ｘは、
(1)式で示したようにＸ＝Ａ（ＶＤ−ＶＵ）で表わせる
が、(2)式で示したように温度差は上昇温度ＴＲすなわ
ちＹに比例するので、割算回路３でＸ／Ｙを計算するこ
とにより、その出力信号値（流量値）Ｚにはヒータ温度
上昇による変動分が含まれなくなる。The control circuit 4 turns off the switch S1 at regular intervals,
Turn off the heater resistance RH. At this time, the operational amplifier U1
The voltage V OFF of the straight line L3 appearing at is charged to the capacitor C1 by turning on the switch S2. Next, when returning to the measurement state, the switch S1 is turned on and the switch S2 is turned off,
The difference between the voltage V ON appearing at the operational amplifier U1 and the voltage V OFF held by the capacitor C1 and the operational amplifier U2 is calculated by the operational amplifier U3. That is, the output signal value (rising temperature) Y of the operational amplifier U3 is Y = V ON -V OFF (4). The output signal value (temperature difference) X of the operational amplifier 2 is
Although X = A (VD-VU) can be expressed as shown in the equation (1), the temperature difference is proportional to the rising temperature TR, that is, Y as shown in the equation (2). By calculating / Y, the output signal value (flow rate value) Z does not include the variation due to the heater temperature rise.
第３図は本発明の第２の実施例を示す回路図で、デジタ
ル回路による実施例である。第３図においては、ヒータ
抵抗ＲＨを断続して第１図と同様の機能を実現してい
る。すなわち、温度差Ａ（ＶＤ−ＶＵ）と２つの温度セ
ンサの出力値ＶＤ，ＶＵをマルチプレクサ（ＭＵＸ）５
でＡ／Ｄ変換器６に取り込み、演算装置７で上昇温度の
値Ｙ＝VON−VOFFを演算することにより、ヒータ温度上
昇を補正した流量値Ｚを得ることができる。FIG. 3 is a circuit diagram showing a second embodiment of the present invention, which is an embodiment using a digital circuit. In FIG. 3, the heater resistance RH is interrupted to realize the same function as in FIG. That is, the temperature difference A (VD-VU) and the output values VD and VU of the two temperature sensors are given to the multiplexer (MUX) 5
Then, the flow rate value Z in which the heater temperature rise is corrected can be obtained by fetching it into the A / D converter 6 and calculating the rise temperature value Y = V ON −V OFF by the arithmetic unit 7.
以上説明したように本発明は、上流側温度センサと下流
側温度センサの出力信号からヒータの上流温度および温
度差を算出し、上昇温度により温度差に割って流量を得
ることにより、ヒータの上昇温度による流量誤差を除去
できるので、ヒータの特性変化の影響を受けない流量測
定回路を得ることができる。As described above, the present invention calculates the upstream temperature and the temperature difference of the heater from the output signals of the upstream temperature sensor and the downstream temperature sensor, and divides the temperature difference by the rising temperature to obtain the flow rate, thereby increasing the heater temperature. Since the flow rate error due to the temperature can be removed, it is possible to obtain a flow rate measuring circuit that is not affected by the heater characteristic change.
また、例えばゴミの付着によりヒータ抵抗の放熱状態が
変わっても感度が変化しなくなる効果がある。Further, there is an effect that the sensitivity does not change even if the heat radiation state of the heater resistance changes due to adhesion of dust, for example.
さらに、ヒータ抵抗を直接電源に接続すれば、電源電圧
が低くても十分な電力を供給でき温度上昇を高くとれる
ため、温度センサの出力値が増大し、流量信号のＳ／Ｎ
比が向上する効果がある。Further, if the heater resistance is directly connected to the power supply, sufficient power can be supplied even if the power supply voltage is low and the temperature rise can be increased, so that the output value of the temperature sensor increases and the S / N of the flow rate signal is increased.
This has the effect of improving the ratio.
第１図は本発明による流量測定回路の一実施例を示す回
路図、第２図はヒータオンオフにおける温度センサの特
性を示すグラフ、第３図は本発明の第２の実施例を示す
回路図、第４図は従来の流量測定回路を示す回路図、第
５図は一般的なヒータ電源の制御方法を説明するための
グラフである。 ２，Ｕ１〜Ｕ３……演算増幅器、３……割算回路、４…
…制御回路、ＲＨ……ヒータ抵抗、ＲＵ……上流側温度
センサ、ＲＤ……下流側温度センサ、Ｓ１，Ｓ２……ス
イッチ、Ｒ１，Ｒ２……抵抗、Ｃ１……コンデンサ。FIG. 1 is a circuit diagram showing an embodiment of a flow rate measuring circuit according to the present invention, FIG. 2 is a graph showing characteristics of a temperature sensor when a heater is on and off, and FIG. 3 is a circuit diagram showing a second embodiment of the present invention. FIG. 4 is a circuit diagram showing a conventional flow rate measuring circuit, and FIG. 5 is a graph for explaining a general heater power source control method. 2, U1 to U3 ... Operational amplifier, 3 ... Division circuit, 4 ...
... Control circuit, RH ... Heater resistance, RU ... Upstream temperature sensor, RD ... Downstream temperature sensor, S1, S2 ... Switch, R1, R2 ... Resistor, C1 ... Capacitor.
Claims (1)
力信号からヒータの上昇温度を示す上昇温度信号を出力
する上昇温度算出回路と、前記上流側温度センサと下流
側温度センサの出力信号から温度差を示す温度差信号を
出力する温度差回路と、前記上昇温度により前記温度差
を割って流量を得る割算回路と、前記ヒータを断続する
制御回路とを備えた流量測定回路。1. A rising temperature calculation circuit for outputting a rising temperature signal indicating a rising temperature of a heater from output signals of an upstream temperature sensor and a downstream temperature sensor, and an output signal of the upstream temperature sensor and a downstream temperature sensor. A flow rate measurement circuit including a temperature difference circuit that outputs a temperature difference signal indicating a temperature difference, a division circuit that divides the temperature difference by the rising temperature to obtain a flow rate, and a control circuit that connects and disconnects the heater.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63272936A JPH0663801B2 (en) | 1988-10-31 | 1988-10-31 | Flow rate measurement circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63272936A JPH0663801B2 (en) | 1988-10-31 | 1988-10-31 | Flow rate measurement circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02120621A JPH02120621A (en) | 1990-05-08 |
| JPH0663801B2 true JPH0663801B2 (en) | 1994-08-22 |
Family
ID=17520829
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP63272936A Expired - Lifetime JPH0663801B2 (en) | 1988-10-31 | 1988-10-31 | Flow rate measurement circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0663801B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1742025A2 (en) | 2005-07-08 | 2007-01-10 | Hitachi, Ltd. | Thermal type flow measuring apparatus |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3493116B2 (en) * | 1996-05-24 | 2004-02-03 | 株式会社リコー | Flow measurement device and flow measurement method |
| EP1418408B1 (en) | 2001-08-14 | 2014-07-09 | Hitachi, Ltd. | Thermal flow sensor |
| JP4793621B2 (en) * | 2005-02-17 | 2011-10-12 | 横河電機株式会社 | Thermal flow meter |
| JP4811636B2 (en) * | 2005-02-18 | 2011-11-09 | 横河電機株式会社 | Thermal flow meter |
| JP5178261B2 (en) * | 2008-03-19 | 2013-04-10 | アズビル株式会社 | Thermal flow meter |
-
1988
- 1988-10-31 JP JP63272936A patent/JPH0663801B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1742025A2 (en) | 2005-07-08 | 2007-01-10 | Hitachi, Ltd. | Thermal type flow measuring apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02120621A (en) | 1990-05-08 |
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