JP3749324B2 - Unit weighing device - Google Patents
Unit weighing device Download PDFInfo
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- JP3749324B2 JP3749324B2 JP33701696A JP33701696A JP3749324B2 JP 3749324 B2 JP3749324 B2 JP 3749324B2 JP 33701696 A JP33701696 A JP 33701696A JP 33701696 A JP33701696 A JP 33701696A JP 3749324 B2 JP3749324 B2 JP 3749324B2
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- Prior art keywords
- capacitor
- thermistor
- temperature coefficient
- temperature
- oscillation
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Description
【０００１】
【発明の属する技術分野】
本発明は、温度、湿度、風速、風量又は気圧などの測定に使用される単位計量装置に係り、特に、発振周波数を決定する素子としてサーミスタとコンデンサを用いたＲＣ発振回路を具備する電子式の単位計量装置に関する。
【０００２】
【従来の技術】
この種の単位計量装置は、測定する温度等を発振周波数に変換してそれを発振用アンプで増幅して出力するＲＣ発振回路と、当該ＲＣ発振回路から出力される発振周波数を記憶装置に予め記憶させた温度値等に対応する周波数と比較演算して温度等の表示値を算出し、その表示値を表示器へ出力する信号処理回路とを具備している。
【０００３】
図３は、従来装置の一例として示すサーミスタ温度計の回路図であって、温度センサとなるサーミスタ２、発振定数用コンデンサ３及び発振用アンプ４とから成るＲＣ発振回路１と、信号処理回路５とを具備し、発振用アンプ４としては、シュミットインバーターＩＣ等のデジタルＩＣを用いたものが一般的である。
【０００４】
【発明が解決しようとする課題】
しかし、ＲＣ発振回路１のコンデンサ３として一般的に用いられるのは、フィルムコンデンサやセラミックコンデンサ、積層セラミックコンデンサ等であるが、これらは周囲温度の変化に対する温度係数が大きい。
このため、図３に示す従来装置においては、被測定物の温度が一定であっても周囲温度の影響でＲＣ積が変化して、信号処理回路５による演算表示の精度を維持することができず、図４のグラフに示すように温度ドリフトによる測定誤差を生ずることとなる。
なお、これを回避するために、サーミスタ２とは別個に周囲温度測定用のサーミスタを設けたり、温度により信号が変化する電子部品を信号処理回路５内などに付加して表示値を補正するなどの手段が提案されているが、それらは何れも簡易な手段とは言えない。
【０００５】
そこで本発明は、コストの嵩まない簡易な回路構成により、周囲温度の変化に対してＲＣ積を一定に維持して温度ドリフトによる測定誤差を実用上無視し得る程度に抑制して、、測定精度を高めることを技術的課題としている。
【０００６】
【課題を解決するための手段】
上記の課題を解決するために、本発明は、発振周波数を決定する素子としてサーミスタとコンデンサを用いたＲＣ発振回路を具備する単位計量装置において、前記ＲＣ発振回路のサーミスタと直列又は並列に、前記コンデンサの温度係数特性と反比例した特性を有するリニア温度係数抵抗が接続されていることを特徴とする。
【０００７】
本発明によれば、コンデンサの温度係数特性と反比例した特性を有するリニア温度係数抵抗が接続されているので、ＲＣ回路に周囲温度の変化に対する温度係数の大きなコンデンサが用いられている場合でも、周囲温度の変化に対応してコンデンサの温度係数が変化しても、リニア温度係数抵抗によりＲＣ積が一定に維持されるので、温度ドリフトによる測定誤差を事実上無視し得る程度に抑制することができる。
したがって、ＲＣ発振回路にサーミスタと直列又は並列にリニア温度係数抵抗を接続するだけの簡易な構成によって測定精度が高められる。
【０００８】
【発明の実施の形態】
以下、本発明の実施形態を図面によって具体的に説明する。
図１は本発明による単位計量装置の一例を示す回路図、図２はその装置の作用効果を示すグラフである。なお、図３に示す従来装置との共通部分については同一符号を付して説明する。
【０００９】
次に、図１は本発明による単位計量装置の他の例を示す回路図、図２はその装置の作用効果を示すグラフである。
図１に示す装置は、ＲＣ発振回路１のサーミスタ２と直列又は並列に、コンデンサ３の温度係数特性と反比例した特性を有するリニア温度係数抵抗７が接続されている。
このリニア温度係数抵抗７は、被測定物の温度が一定であればＲＣ発振回路１の発振周波数が常に一定になるように、サーミスタ２とコンデンサ３のＲＣ積を一定にするよう補正するもので、それによって、周囲温度の変化により温度センサとなるサーミスタ２の入出力特性が変動する温度ドリフトが防止される。
【００１０】
すなわち、ＲＣ発振回路１に、周囲温度の変化に対してＲＣ積が一定になるようなリニア温度係数抵抗７を付加するのみの簡易な手段によって、温度ドリフトによる測定誤差を図２のグラフに示すとおり実用上無視し得る程度に抑制することができる。
なお、リニア温度係数抵抗７としては、被測定温度におけるサーミスタ２の抵抗をＲとし、周囲温度が０℃のときのコンデンサ３の容量値をＣ０（ｐＦ）、リニア温度係数抵抗の抵抗値をＲ０（Ω）とし、また、周囲温度が５０℃のときのコンデンサ３の容量値をＣ５０（ｐＦ）、リニア温度係数抵抗の抵抗値Ｒ５０（Ω）とするならば、Ｃ０Ｒ０＝Ｃ５０Ｒ５０となるものを選択すれば良い。
また、リニア温度係数抵抗７の代わりに、コンデンサ３の温度係数特性とは反比例した特性を有するコンデンサを、コンデンサ３に対して直列又は並列に接続することにより、ＲＣ積を一定にして同様の効果を得ることができる。
なお、本発明は、温度の測定に用いる単位計量装置に限らず、湿度、風速、風量又は気圧などの測定に用いる単位計量装置にも適用できる。
【００１１】
【発明の効果】
本発明によれば、発振周波数を決定する素子としてサーミスタとコンデンサを用いたＲＣ発振回路に、抵抗やコンデンサを付加するだけの極めて簡易な構成によって、単位計量装置の測定精度を高めることができるという大変優れた効果がある。
【図面の簡単な説明】
【図１】本発明による単位計量装置の一例を示す回路図。
【図２】図１の構成を有する本発明装置の作用効果を示すグラフ。
【図３】従来装置の構成を示す回路図。
【図４】従来装置の欠点を図２に示す本発明装置の作用効果と対比して示すグラフ。
【符号の説明】
１・・・・・ＲＣ発振回路
２・・・・・サーミスタ
３・・・・・コンデンサ
４・・・・・発振用アンプ
５・・・・・信号処理回路
６・・・・・チューニング用可変抵抗
７・・・・・リニア温度係数抵抗
８ａ・・・・シールドケーブル
８ｂ・・・・シールドケーブル
８ｃ・・・・配線
９・・・・・抵抗
１０・・・・・コンデンサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a unit weighing device used for measuring temperature, humidity, wind speed, air volume, or atmospheric pressure, and more particularly, an electronic type comprising an RC oscillation circuit using a thermistor and a capacitor as elements for determining an oscillation frequency. It relates to a unit weighing device.
[0002]
[Prior art]
This type of unit weighing device converts an oscillation frequency to be measured into an oscillation frequency, amplifies it with an oscillation amplifier and outputs it, and an oscillation frequency output from the RC oscillation circuit in a storage device in advance. A signal processing circuit is provided for calculating a display value such as temperature by comparing with a frequency corresponding to the stored temperature value and outputting the display value to a display.
[0003]
FIG. 3 is a circuit diagram of a thermistor thermometer shown as an example of a conventional device, and includes an RC oscillation circuit 1 including a thermistor 2 serving as a temperature sensor, an oscillation constant capacitor 3 and an oscillation amplifier 4, and a signal processing circuit 5. In general, the oscillation amplifier 4 uses a digital IC such as a Schmitt inverter IC.
[0004]
[Problems to be solved by the invention]
However, generally used as the capacitor 3 of the RC oscillation circuit 1 are a film capacitor, a ceramic capacitor, a multilayer ceramic capacitor, and the like, which have a large temperature coefficient with respect to a change in ambient temperature.
For this reason, in the conventional apparatus shown in FIG. 3, even if the temperature of the object to be measured is constant, the RC product changes due to the influence of the ambient temperature, and the accuracy of calculation display by the signal processing circuit 5 can be maintained. First, as shown in the graph of FIG. 4, a measurement error due to temperature drift occurs.
In order to avoid this, a thermistor for measuring the ambient temperature is provided separately from the thermistor 2, or an electronic component whose signal changes with temperature is added to the signal processing circuit 5 to correct the display value. Although these means have been proposed, none of them is a simple means.
[0005]
Therefore, the present invention has a simple circuit configuration that does not increase the cost, keeps the RC product constant with respect to changes in ambient temperature, and suppresses measurement errors due to temperature drift to a level that can be ignored in practice. Increasing accuracy is a technical issue.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a unit weighing device including an RC oscillation circuit using a thermistor and a capacitor as elements for determining an oscillation frequency, in series or in parallel with the thermistor of the RC oscillation circuit. characterized in that the linear temperature coefficient resistor is connected with a characteristic which is inversely proportional to the temperature coefficient characteristics of the capacitor.
[0007]
According to the present invention, since a linear temperature coefficient resistor having a characteristic inversely proportional to the temperature coefficient characteristic of the capacitor is connected, even when a capacitor having a large temperature coefficient with respect to a change in ambient temperature is used in the RC circuit, Even if the temperature coefficient of the capacitor changes in response to a change in temperature, the RC product is maintained constant by the linear temperature coefficient resistance, so that measurement errors due to temperature drift can be suppressed to a level that can be virtually ignored. .
Therefore, the measurement accuracy is enhanced by a simple configuration in which a linear temperature coefficient resistor is simply connected to the RC oscillation circuit in series or in parallel with the thermistor.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a circuit diagram showing an example of a unit weighing device according to the present invention, and FIG. 2 is a graph showing the operational effects of the device. It should be noted that common portions with the conventional apparatus shown in FIG.
[0009]
Next, FIG. 1 is a circuit diagram showing another example of the unit weighing device according to the present invention, and FIG. 2 is a graph showing the operational effects of the device.
In the apparatus shown in FIG. 1, a linear temperature coefficient resistor 7 having a characteristic inversely proportional to the temperature coefficient characteristic of the capacitor 3 is connected in series or in parallel with the thermistor 2 of the RC oscillation circuit 1.
The linear temperature coefficient resistor 7 corrects the RC product of the thermistor 2 and the capacitor 3 to be constant so that the oscillation frequency of the RC oscillation circuit 1 is always constant if the temperature of the object to be measured is constant. Thereby, temperature drift in which the input / output characteristics of the thermistor 2 serving as a temperature sensor fluctuate due to a change in ambient temperature is prevented.
[0010]
That is, the measurement error due to the temperature drift is shown in the graph of FIG. 2 by a simple means simply by adding the linear temperature coefficient resistor 7 that makes the RC product constant with respect to the change in the ambient temperature. As can be practically ignored.
As the linear temperature coefficient resistor 7, the resistance of the thermistor 2 at the measured temperature is R, the capacitance value of the capacitor 3 is C 0 (pF) when the ambient temperature is 0 ° C., and the resistance value of the linear temperature coefficient resistor is If the capacitance value of the capacitor 3 is C 50 (pF) and the resistance value R 50 (Ω) of the linear temperature coefficient resistor is R 0 (Ω), and the ambient temperature is 50 ° C., then C 0 R 0 What should be set to be = C 50 R 50 may be selected.
Further, by connecting a capacitor having a characteristic inversely proportional to the temperature coefficient characteristic of the capacitor 3 instead of the linear temperature coefficient resistor 7 in series or in parallel to the capacitor 3, the RC product is made constant and the same effect is obtained. Can be obtained.
In addition, this invention is applicable not only to the unit measuring device used for the measurement of temperature, but also to the unit measuring device used for measuring humidity, a wind speed, air volume, or atmospheric pressure.
[0011]
【The invention's effect】
According to the present invention, it is possible to increase the measurement accuracy of the unit weighing device with an extremely simple configuration in which a resistor and a capacitor are added to an RC oscillation circuit using a thermistor and a capacitor as elements for determining an oscillation frequency. There is a very good effect.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of a unit weighing device according to the present invention.
FIG. 2 is a graph showing the effect of the device of the present invention having the configuration of FIG.
FIG. 3 is a circuit diagram showing a configuration of a conventional apparatus.
FIG. 4 is a graph showing the disadvantages of the conventional apparatus in comparison with the effects of the apparatus of the present invention shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... RC oscillation circuit 2 ... Thermistor 3 ... Capacitor 4 ... Oscillation amplifier 5 ... Signal processing circuit 6 ... Variable for tuning Resistor 7 ... Linear temperature coefficient resistor 8a ... shielded cable 8b ... shielded cable 8c ... wiring 9
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP33701696A JP3749324B2 (en) | 1996-12-17 | 1996-12-17 | Unit weighing device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP33701696A JP3749324B2 (en) | 1996-12-17 | 1996-12-17 | Unit weighing device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10176959A JPH10176959A (en) | 1998-06-30 |
| JP3749324B2 true JP3749324B2 (en) | 2006-02-22 |
Family
ID=18304680
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP33701696A Expired - Fee Related JP3749324B2 (en) | 1996-12-17 | 1996-12-17 | Unit weighing device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3749324B2 (en) |
-
1996
- 1996-12-17 JP JP33701696A patent/JP3749324B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10176959A (en) | 1998-06-30 |
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