JPH0153403B2 - - Google Patents
Info
- Publication number
- JPH0153403B2 JPH0153403B2 JP56212524A JP21252481A JPH0153403B2 JP H0153403 B2 JPH0153403 B2 JP H0153403B2 JP 56212524 A JP56212524 A JP 56212524A JP 21252481 A JP21252481 A JP 21252481A JP H0153403 B2 JPH0153403 B2 JP H0153403B2
- Authority
- JP
- Japan
- Prior art keywords
- zero
- excitation
- signal
- output
- positive
- 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
Links
- 230000005284 excitation Effects 0.000 claims description 43
- 238000005070 sampling Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 239000012530 fluid Substances 0.000 description 5
- 230000010354 integration Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000005279 excitation period Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000003990 capacitor Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000004043 responsiveness Effects 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
- G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
- G01F1/60—Circuits therefor
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Volume Flow (AREA)
Description
【発明の詳細な説明】
本発明は、低周波励磁方式の電磁流量計の改良
に関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a low frequency excitation type electromagnetic flowmeter.
一般に電磁流量計は、流体の流れ方向に対して
垂直に磁界を与え、同時に流体流路中の電気的信
号の変化を検出し、これに基づいて流体の流量を
計測するように構成されている。最近の電磁流量
計は、交流励磁方式や直流励磁方式に比して零点
の安定性にすぐれている台形波励磁や方形波励磁
などと呼ばれている低周波励磁方式のものが多く
用いられている。この種の低周波励磁方式の電磁
流量計において、特に電磁流量計発信器の励磁コ
イルに定常値が負・零・正・零の順で繰り返す励
磁電流を供給し、電磁流量計発信器から与えられ
る励磁電流の定常値が負・零・正・零の各期間の
信号電圧ea1、ea2、ea3、ea4を用いて、信号処理
回路で実質的に(ea1+ea2)−(ea3+ea4)なる演
算を行うものは、電気化学的な直流電圧や回路に
基づくオフセツト電圧成分および励磁電流の切換
えに伴うノイズ成分の影響を除去し、流量成分に
関連した出力を得ている。ところでこの方式の電
磁流量計においても、電気化学的な直流電圧が変
動しオフセツト電圧成分が変化するとその影響を
もろに受け、出力変動はまぬがれ得なかつた。し
かもオフセツト電圧は、数百mVにも達し、流量
成分のスパン(1〜10mV)に対し非常に大き
く、かつその過渡変化は直線と見倣すことができ
ない。そこで、信号電圧ea2とea3にそれぞれ係数
を乗じた後(ea4−3ea2+3ea2−ea1)なる演算を
行えば、オフセツト電圧成分の2次変動まで除去
できる。しかし実験によればオフセツト電圧成分
は正および負方向に振れるが、その振れは−1V
〜+1Vていどを越えることがなく、その電位変
化は変曲点を必ずもつていることが確認された。
このためオフセツト電圧成分を2次式近似で除去
する場合には、電位変化の変曲点で大きな誤差が
生ずる。また電磁流量計における励磁電流の最小
値は、信号処理回路の入力換算ノイズとの比によ
つて決定され、入力換算ノイズはほぼベクトル加
算されるため、(ea1+ea2−ea3−ea4)なる演算を
行うものと(ea4−3ea3+3ea2−ea1)なる演算を
行うものとの比は
√12+12+12+12:√12+32+32+12
=2:4.47
となり、後者の演算を行うものの方が同一の大き
さの流量信号を得るための励磁電流の大きさが
2.24倍となり、消費電力は5倍も大きくなる。 Generally, an electromagnetic flowmeter is configured to apply a magnetic field perpendicular to the direction of fluid flow, simultaneously detect changes in electrical signals in the fluid flow path, and measure the fluid flow rate based on this. . Many modern electromagnetic flowmeters use low-frequency excitation methods, such as trapezoidal wave excitation and square wave excitation, which have superior zero point stability compared to AC excitation and DC excitation methods. There is. In this type of low-frequency excitation type electromagnetic flowmeter, in particular, an excitation current is supplied to the excitation coil of the electromagnetic flowmeter transmitter with a steady value that repeats in the order of negative, zero, positive, and zero. Using the signal voltages e a1 , e a2 , e a3 , and e a4 for each period in which the steady-state value of the excitation current is negative, zero, positive, and zero, the signal processing circuit essentially calculates (e a1 +e a2 )−( e a3 + e a4 ) is used to remove the effects of electrochemical DC voltage, offset voltage components based on circuits, and noise components associated with excitation current switching, and obtain outputs related to flow rate components. . By the way, even in this type of electromagnetic flowmeter, when the electrochemical direct current voltage fluctuates and the offset voltage component changes, it is affected by the fluctuations, and output fluctuations cannot be avoided. Moreover, the offset voltage reaches several hundred mV, which is extremely large compared to the span of the flow rate component (1 to 10 mV), and its transient change cannot be regarded as a straight line. Therefore, by multiplying the signal voltages e a2 and e a3 by coefficients and then performing the following calculation (e a4 -3 e a2 +3 e a2 - e a1 ), even the quadratic fluctuation of the offset voltage component can be removed. However, according to experiments, the offset voltage component swings in the positive and negative directions, but the swing is -1V.
It was confirmed that the potential never exceeded ~+1V, and that the potential change always had an inflection point.
Therefore, when the offset voltage component is removed by quadratic approximation, a large error occurs at the inflection point of potential change. In addition, the minimum value of the excitation current in an electromagnetic flowmeter is determined by the ratio to the input conversion noise of the signal processing circuit, and since the input conversion noise is almost vector-added, (e a1 +e a2 −e a3 −e a4 ) and those that perform the operation (e a4 −3e a3 +3e a2 −e a1 ) are √1 2 +1 2 +1 2 +1 2 :√1 2 +3 2 +3 2 +1 2 =2: 4.47, and the one that performs the latter calculation requires less excitation current to obtain the same flow rate signal.
The power consumption is 2.24 times larger, and the power consumption is 5 times larger.
本発明は、電磁流量計発信器から与えられる励
磁電流の定常値が負・零・正・零・負・零・正・
零の各期間の信号電圧をそれぞれea1、ea2、ea3、
ea4、ea5、ea6、ea7、ea8としたとき、信号処理回
路で実質的に(ea6−3ea5+2ea4+2ea3−3ea2+
ea1)または(ea8−3ea7+2ea6、2ea5−3ea4+ea3)
なる演算を行い、少ない消費電力でオフセツト電
圧成分の3次変動まで除去できる低周波励磁方式
の電磁流量計を実現したものである。 In the present invention, the steady-state value of the excitation current given from the electromagnetic flowmeter transmitter is negative, zero, positive, zero, negative, zero, positive,
The signal voltages in each period of zero are e a1 , e a2 , e a3 ,
When e a4 , e a5 , e a6 , e a7 , e a8
e a1 ) or (e a8 −3e a7 +2e a6 , 2e a5 −3e a4 +e a3 )
This calculation has been carried out to realize a low frequency excitation type electromagnetic flowmeter that can eliminate even third-order fluctuations in offset voltage components with low power consumption.
第1図は本発明電磁流量計の一実施例を示す接
続図である。図において、1は励磁回路で、直流
定電流源11と、定電流源11からの電流を切換
えるスイツチ12,13とを有している。2は電
磁流量計発信器で、励磁コイル21、流体が流れ
るパイプ22および電極23,24を備えてい
る。3は信号処理回路で、電磁流量計発信器2の
電極23,24間に誘起する電圧eaを増幅する交
流増幅器31と、交流増幅器31の出力電圧ebが
加えられる直列接続された6個のサンプルホール
ド回路32a〜32fと、これらサンプルホールド
回路32a〜32fの出力ec1〜ec6が各々係数器3
3a〜33fを介して加えられる演算回路34と、
演算回路34の出力edを反転するインバータ35
と、演算回路34の出力edとインバータ35の出
力efとを切換えるスイツチ36と、スイツチ36
で選択されたedまたはefをサンプルホールドする
サンプルホールド回路37および、励磁回路1の
スイツチ12,13を制御するパルスP1a,P1b
と、サンプルホールド回路32a〜32fのサンプ
リングを制御するパルスP2a〜P2fと、切換スイツ
チ36を制御するパルスP3および、サンプルホ
ールド回路37のサンプリングを制御するパルス
P4を第2図に示す如きタイミングで発生するタ
イミングパルス発生回路38とを有している。そ
して係数器33a〜33fの係数K1〜K6はそれぞ
れK1=K6=1、K2=K5=3、K3=K4=2に選
ばれており、演算器34で、(ec1−3ec2+2ec3+
2ec4−3ec5+ec6)なる加減演算を行うようになつ
ている。 FIG. 1 is a connection diagram showing an embodiment of the electromagnetic flowmeter of the present invention. In the figure, reference numeral 1 denotes an excitation circuit which includes a DC constant current source 11 and switches 12 and 13 for switching the current from the constant current source 11. Reference numeral 2 denotes an electromagnetic flowmeter transmitter, which includes an exciting coil 21, a pipe 22 through which fluid flows, and electrodes 23 and 24. 3 is a signal processing circuit, which includes an AC amplifier 31 that amplifies the voltage e a induced between the electrodes 23 and 24 of the electromagnetic flowmeter transmitter 2, and six circuits connected in series to which the output voltage e b of the AC amplifier 31 is applied. The sample and hold circuits 32 a to 32 f and the outputs e c1 to e c6 of these sample and hold circuits 32 a to 32 f are respectively input to the coefficient multiplier 3.
an arithmetic circuit 34 added via 3a to 33f ;
an inverter 35 that inverts the outputs e and d of the arithmetic circuit 34;
, a switch 36 that switches between the output e d of the arithmetic circuit 34 and the output e f of the inverter 35;
A sample and hold circuit 37 samples and holds e d or e f selected in , and pulses P 1a and P 1b that control switches 12 and 13 of the excitation circuit 1.
, pulses P 2a to P 2f that control the sampling of the sample and hold circuits 32 a to 32 f , a pulse P 3 that controls the changeover switch 36, and a pulse that controls the sampling of the sample and hold circuit 37.
It has a timing pulse generation circuit 38 which generates P4 at the timing shown in FIG. The coefficients K 1 to K 6 of the coefficient units 33 a to 33 f are respectively selected as K 1 = K 6 = 1, K 2 = K 5 = 3, and K 3 = K 4 = 2. , (e c1 −3e c2 +2e c3 +
2e c4 −3e c5 +e c6 ).
このように構成した本発明の動作を第2図の波
形図を参照して以下に説明する。まずスイツチ1
2,13は第2図に示す如き駆動パルスP1a,P1b
で制御され、P1aがオンとなつている期間T1に定
電流源11からの電流Iwを正方向に励磁コイル2
1に流し、P1bがオンとなつている期間T3に定電
流源11からの電流Iwを逆方向に切換えて励磁コ
イル21に流し、P1a,P1bが共にオフとなつてい
る期間T2,T4には励磁コイル21に電流を流さ
ない。よつて励磁コイル21には第2図に示すよ
うに定常値が正の励磁期間T1と負の励磁期間T3
および零の休止期間T2,T4があり、定常値が
正・零・負・零の順で繰り返す励磁電流Iwが供給
される。なお、励磁電流Iwはスイツチ12,13
で切換えられたとき、定電流源11は有限の出力
電圧しか供給できぬから励磁コイル21のインダ
クタンスと抵抗による時定数で実際には立上り、
立下りの部分で遅れを伴つたのち定常値となるが
図では省略してある。電磁流量計発信器2の電極
23,24間には励磁電流Iwに応じた誘起電圧ea
が発生する。誘起電圧eaには第2図に示すよう
に、パイプ22を流れる流体の流量Fに比例した
流量成分Vsの外に、電気化学的な直流電位や回
路によるオフセツト電圧成分Voと、励磁電流の
切換えに伴うノイズ成分Veとが重畳されている。
その結果第2図に示す励磁電流の定常値が負・
零・正・零・負・零・正・零・負の各期間に発生
する誘起電圧eaを一定間隔Δtでサンプリングし
た信号電圧ea1、ea2、ea3、ea4、ea5、ea6、ea7、
ea8、ea9はそれぞれ次式で与えられる。なおオフ
セツト電圧成分Voはテーラ展開して3次式近似
で示してある。 The operation of the present invention configured in this way will be explained below with reference to the waveform diagram of FIG. 2. First, switch 1
2 and 13 are drive pulses P 1a and P 1b as shown in FIG.
During the period T1 when P1a is on, the current Iw from the constant current source 11 is controlled in the positive direction by the exciting coil 2.
1, and during the period T3 when P 1b is on, the current Iw from the constant current source 11 is switched in the opposite direction and flows through the excitation coil 21, and during the period when both P 1a and P 1b are off. No current is applied to the excitation coil 21 at T 2 and T 4 . Therefore, as shown in FIG. 2, the excitation coil 21 has an excitation period T1 in which the steady value is positive and an excitation period T3 in which the steady value is negative.
There are rest periods T 2 and T 4 of zero, and an excitation current I w whose steady value repeats in the order of positive, zero, negative, and zero is supplied. Note that the excitation current I w is connected to the switches 12 and 13.
When the constant current source 11 can only supply a finite output voltage, the voltage actually rises due to the time constant due to the inductance and resistance of the excitation coil 21.
After a delay in the falling part, it reaches a steady value, but this is omitted in the figure. An induced voltage e a corresponding to the exciting current I w is generated between the electrodes 23 and 24 of the electromagnetic flowmeter transmitter 2 .
occurs. As shown in Fig. 2, the induced voltage e a includes a flow rate component V s proportional to the flow rate F of the fluid flowing through the pipe 22, an offset voltage component V o due to the electrochemical DC potential and the circuit, and an excitation voltage component V s . A noise component V e accompanying current switching is superimposed.
As a result, the steady value of the excitation current shown in Figure 2 is negative.
Signal voltages e a1 , e a2 , e a3 , e a4 , e a5 , e obtained by sampling the induced voltage e a generated in each period of zero, positive, zero, negative, zero, positive, zero, and negative at regular intervals Δt. a6 , e a7 ,
e a8 and e a9 are each given by the following equations. Note that the offset voltage component V o is shown by Taylor expansion and cubic equation approximation.
ea1=−Vs−Ve+VoO
ea2=+Ve+VoO+Vo1+Vo2+Vo3
ea3=Vs+Ve+VoO+2Vo1+22Vo2+23Vo3
ea4=−Ve+VoO+3Vo1+32Vo2+33Vo3
ea5=−Vs−Ve+VoO+4Vo1+42Vo2+43Vo3
ea6=+Ve+VoO+5Vo1+52Vo2+53Vo3
ea7=Vs+Ve+VoO+6Vo1+62Vo2+63Vo3
ea8=−Ve+VoO+7Vo1+72Vo2+73Vo3
ea9=−Vs−Ve+VoO+8Vo1+82Vo2+83Vo3
(1)
信号処理回路3では、まず電磁流量計発信器2
からの誘起電圧eaを増幅器31で増幅し、第2図
に示す如きタイミングで発生するサンプリングパ
ルスP2aによつて、信号電圧ea1〜ea9に相当する増
幅器31の出力が順次サンプルホールド回路32
aにホールドされる。サンプルホールド回路32a
のホールド値ec1は第2図に示す如きタイミング
で発生するサンプリングパルスP2bによつてサン
プルホールド回路32bにホールドされる。同様
にサンプルホールド回路32b〜32eのホールド
値ec2〜ec5は、第2図に示す如きタイミングで発
生するサンプリングパルスP2c〜P2fによつてそれ
ぞれサンプルホールド回路32c〜32fにホール
ドされる。したがつて、サンプルホールド回路3
2aに信号圧ea6に関連した電圧がホールドされた
時点では、サンプルホールド回路32b〜32fに
はea5〜ea1にそれぞれ関連した電圧がホールドさ
れ、サンプルホールド回路32aにea7に関連した
電圧がホールドされた時点では、サンプルホール
ド回路32b〜32fにはea6〜ea2にそれぞれ関連
した電圧がホールドされる。これらサンプルホー
ルド回路32a〜32fのホールド電圧ec1〜ec6は
それぞれ係数器33a〜33fを介して演算回路3
4で(ec1−3ec2+2ec3+2ec4−3ec5+ec6)なる演
算が行われる。その結果演算回路34の出力端に
はサンプルホールド回路32aに信号電圧ea6に相
当する増幅器31の出力がホールドされたときの
演算結果ed1と、信号電圧ea7に相当する増幅器3
1の出力がホールドされたときの演算結果ed2と、
信号電圧ea8に相当する増幅器31の出力がホー
ルドされたときの演算結果ed3と、信号電圧ea9に
相当する増幅器31の出力がホールドされたとき
の演算結果ed4を順次繰り返す波形の電圧edが得
られる。そしてed1〜ed4は増幅器31のゲインを
kとするとそれぞれ次式で与えられる。 e a1 = −V s −V e +V oO e a2 = +V e +V oO +V o1 +V o2 +V o3 e a3 =V s +V e +V oO +2V o1 +2 2 V o2 +2 3 V o3 e a4 = −V e +V oO +3V o1 +3 2 V o2 +3 3 V o3 e a5 = -V s -V e +V oO +4V o1 +4 2 V o2 +4 3 V o3 e a6 = +V e +V oO +5V o1 +5 2 V o2 +5 3 V o3 e a7 =V s +V e +V oO +6V o1 +6 2 V o2 +6 3 V o3 e a8 = -V e +V oO +7V o1 +7 2 V o2 +7 3 V o3 e a9 = -V s -V e +V oO +8V o1 +8 2 V o2 +8 3 V o3 (1) In the signal processing circuit 3, first the electromagnetic flowmeter transmitter 2
An amplifier 31 amplifies the induced voltage e a from the amplifier 31, and the outputs of the amplifier 31 corresponding to signal voltages e a1 to e a9 are sequentially applied to the sample and hold circuit by the sampling pulse P 2a generated at the timing shown in FIG. 32
It is held at a . Sample hold circuit 32 a
The hold value e c1 is held in the sample and hold circuit 32b by the sampling pulse P2b generated at the timing shown in FIG. Similarly, the hold values ec2 to ec5 of the sample and hold circuits 32b to 32e are transferred to the sample and hold circuits 32c to 32f , respectively, by sampling pulses P2c to P2f generated at the timing shown in FIG. will be held. Therefore, sample hold circuit 3
At the time when the voltage related to the signal pressure e a6 is held in 2 a , the voltages related to e a5 to e a1 are held in the sample hold circuits 32 b to 32 f , and the voltages related to the signal pressure e a7 are held in the sample hold circuit 32 a . At the time when the voltages related to e a6 to e a2 are held, the sample and hold circuits 32 b to 32 f hold the voltages related to e a6 to e a2 , respectively. The hold voltages e c1 to e c6 of these sample and hold circuits 32 a to 32 f are sent to the arithmetic circuit 3 via coefficient units 33 a to 33 f , respectively.
4, the calculation (e c1 -3e c2 +2e c3 +2e c4 -3e c5 +e c6 ) is performed. As a result, the output terminal of the arithmetic circuit 34 contains the arithmetic result e d1 when the output of the amplifier 31 corresponding to the signal voltage e a6 is held in the sample and hold circuit 32 a , and the output of the amplifier 3 corresponding to the signal voltage e a7 .
The calculation result e d2 when the output of 1 is held,
A voltage with a waveform that sequentially repeats the calculation result e d3 when the output of the amplifier 31 corresponding to the signal voltage e a8 is held and the calculation result e d4 when the output of the amplifier 31 corresponding to the signal voltage e a9 is held. e d is obtained. And e d1 to e d4 are respectively given by the following equations, assuming that the gain of the amplifier 31 is k.
ed1=k(ea6−3ea5+2ea4+2ea3−3ea2+ea1)=4
kVs(2)
ed2=k(ea7−3ea6+2ea5+2ea4−3ea3+ea2)=
−4k(Vs+2Ve)(3)
ed3=k(ea8−3ea7+2ea6+2ea53ea4+ea3)=−4
kVs(4)
ed4=k(ea9−3ea8+2ea7+2ea6−3ea5+ea4)=4
k(Vs+2Ve)(5)
よつて演算回路34の出力には、サンプルホール
ド回路32aに励磁電流の定常値が正または負の
ときの信号電圧に相当する増幅器31の出力がホ
ールドされた時点では励磁電流の切換えに伴うノ
イズ成分Veが重畳されているが、定常値が零の
ときの信号電圧に相当する増幅器31の出力がホ
ールドされた時点では3次式近似のオフセツト電
圧成分VoO〜Vo3が除去されるとともに励磁電流
の切換えに伴うノイズ成分Veも除去され流量成
分Vsのみを得ることができる。そこで第2図に
示すタイミングで発生するパルスP3で切換スイ
ツチ36を駆動し、演算回路34の出力がed1の
ときはインバータ35を介して取り出し第2図に
示すタイミングで発生するサンプリングパルス
P4で演算回路34の出力ed1とインバータ35を
介して取り出すed3をサンプルホールド回路37
に交互に与える。その結果サンプルホールド回路
37の出力端には流量成分Vsに関連した出力電
圧epが得られる。 e d1 = k(e a6 −3e a5 +2e a4 +2e a3 −3e a2 +e a1 )=4
kV s (2) e d2 = k(e a7 −3e a6 +2e a5 +2e a4 −3e a3 +e a2 )=
−4k(V s +2V e )(3) e d3 =k(e a8 −3e a7 +2e a6 +2e a5 3e a4 +e a3 )=−4
kV s (4) e d4 = k(e a9 −3e a8 +2e a7 +2e a6 −3e a5 +e a4 )=4
k (V s + 2V e ) (5) Therefore, the output of the amplifier 31 corresponding to the signal voltage when the steady value of the excitation current is positive or negative is held in the sample and hold circuit 32 a as the output of the arithmetic circuit 34. At the time when the output of the amplifier 31, which corresponds to the signal voltage when the steady-state value is zero, is held, the noise component V e due to switching of the excitation current is superimposed, but when the output of the amplifier 31 is held, the offset voltage component approximates to the cubic equation. While V oO to V o3 are removed, the noise component V e accompanying the switching of the excitation current is also removed, and only the flow rate component V s can be obtained. Therefore, the selector switch 36 is driven by the pulse P3 generated at the timing shown in FIG. 2, and when the output of the arithmetic circuit 34 is e d1 , the sampling pulse generated at the timing shown in FIG. 2 is taken out via the inverter 35.
At P4 , the output e d1 of the arithmetic circuit 34 and e d3 taken out via the inverter 35 are sampled and held by the sample hold circuit 37.
Give alternately. As a result, at the output of the sample-and-hold circuit 37, an output voltage e p is obtained that is related to the flow rate component V s .
このように本発明においては、励磁電流の切換
えに伴なうノイズ成分Veおよびオフセツト電圧
成分の3次変動まで除去できるので、オフセツト
電圧成分が変曲点を持つような変動を示す場合に
も有効に除去できる。この場合に、信号処理回路
3の入力換算ノイズは(12+32+22+22+32+12)
1/2=5.29となるが、流量成分Vsが4倍されるの
で、その信号対雑音比は5.29/4=1.32となる。
これに対して、オフセツト電圧の2次変動まで除
去する場合には既述のようにその入力換算ノイズ
は4.47であり流量成分は2倍になるので、その信
号対雑音比は4.47/2=2.24となる。従つて、本
発明の演算によればオフセツト電圧の3次変動ま
で除去しながら信号対雑音比が2次変動まで除去
する場合に比べてかなり低下していることがわか
る。また、本発明によれば、オフセツト電圧成分
の2次変動まで除去する場合に比べて同一の大き
さの流量信号を得るのに必要な励磁電流は59%
(=1.32/2.24)でよく、消費電力は35%にも減
少させることができる。さらに、この方式は流量
変動に対して、積算誤差を生じない特質も有して
おり、ランプ状の流量変化に対するオフセツトも
生じない。 In this way, in the present invention, it is possible to remove the noise component V e and the third-order fluctuations in the offset voltage component that occur when switching the excitation current, so even when the offset voltage component exhibits fluctuations that have an inflection point, it is possible to eliminate them. Can be effectively removed. In this case, the input equivalent noise of the signal processing circuit 3 is (1 2 +3 2 +2 2 +2 2 +3 2 +1 2 )
1/2 = 5.29, but since the flow rate component V s is multiplied by 4, the signal-to-noise ratio is 5.29/4 = 1.32.
On the other hand, when removing even the second-order fluctuations in the offset voltage, the input equivalent noise is 4.47 and the flow rate component is doubled, as described above, so the signal-to-noise ratio is 4.47/2 = 2.24. becomes. Therefore, it can be seen that according to the calculation of the present invention, the signal-to-noise ratio is considerably lower than when even the second-order fluctuations are removed while even the third-order fluctuations of the offset voltage are removed. Furthermore, according to the present invention, the excitation current required to obtain a flow signal of the same magnitude is 59% compared to the case where even the quadratic fluctuation of the offset voltage component is removed.
(=1.32/2.24), and power consumption can be reduced by as much as 35%. Furthermore, this method has the characteristic that no integration error occurs in response to flow rate fluctuations, and no offset occurs in response to ramp-like flow rate changes.
なお上述では、励磁電流の定常値が負・零・
正・零・負・零の各期間の信号電圧を用いる(2)式
の演算結果と正・零・負・零・正・零の各期間の
信号電圧を用いる(4)式の演算結果を交互に出力す
る場合を例示したが、いずれか一方を出力するよ
うにしてもよい。ただし実施例のように交互に出
力する場合の方が応答性を2倍よくできる利点が
ある。また上述では、増幅器31の出力ebをサン
プルホールド回路32aに直接与える場合を例示
したが、第3図に示すように増幅器出力ebを積分
器39で一定時間積分した後サンプルホールド回
路32aに与えるようにしてもよい。この場合積
分時間Tsを商用電源周期の整数倍に選べば電源
周波数ノイズの影響を除去できる。なお第3図に
おいては、積分器39として抵抗RIと、演算増
幅器OPと、OPの帰還回路に接続された積分用コ
ンデンサCIと、入力積分時間Tsを制御するタイ
ミングスイツチTSおよび積分値をリセツトする
リセツトスイツチRSを有し、TSおよびRSはタ
イミングパルス発生器38からのパルスP5,P6
によつて駆動されるものか例示されている。また
信号処理回路3は第4図に示すようにデイジタル
演算を行うマイクロプロセツサ40を用いて構成
してもよい。第4図においては、積分器39の出
力eiがA/D変換器41でデイジタル信号に変換
されてマイクロプロセツサ40に与えられ、マイ
クロプロセツサ40で(2)式または(4)式に相当する
デイジタル演算を行い流量成分Vsに相当するデ
イジタル値を出力し、D/A変換器42でアナロ
グ信号に変換した後サンプルホールド回路37に
ホールドして、この出力端に流量成分Vsに関連
した出力電圧epを得るものが例示されている。な
お第4図において積分器39で基準電圧erをパル
スP7で駆動されるスイツチTS′を介して与え、er
を一定時間だけ積分した値をA/D変換器41で
デイジタル信号に変換後マイクロプロセツサ40
に与えて、スパン調整等を行うようにしてもよ
い。さらに上述では励磁電流Iwとして矩形波の場
合を例示したが、台形波や商用交流電源を周波数
変換した後整流して得た波形のもの等必要に応じ
て種々の波形のものを用いることができる。 Note that in the above, the steady value of the excitation current is negative, zero,
The calculation results of equation (2) using signal voltages in each period of positive, zero, negative, and zero, and the calculation results of equation (4) using signal voltages in each period of positive, zero, negative, zero, positive, and zero, are Although the case in which the signals are output alternately has been illustrated, it is also possible to output either one of them. However, the case where output is performed alternately as in the embodiment has the advantage that the responsiveness can be twice as good. Furthermore, in the above description, the case where the output e b of the amplifier 31 is directly applied to the sample and hold circuit 32 a has been illustrated, but as shown in FIG. You may also give it to a . In this case, if the integration time T s is selected to be an integral multiple of the commercial power supply cycle, the influence of power supply frequency noise can be removed. In Fig. 3, the integrator 39 includes a resistor RI, an operational amplifier OP, an integrating capacitor CI connected to the feedback circuit of OP, a timing switch TS that controls the input integration time Ts , and resets the integral value. TS and RS are pulses P 5 and P 6 from timing pulse generator 38.
The following is an example of what is driven by. Further, the signal processing circuit 3 may be constructed using a microprocessor 40 that performs digital calculations as shown in FIG. In FIG. 4, the output e i of the integrator 39 is converted into a digital signal by the A/D converter 41 and given to the microprocessor 40, which then converts it into equation (2) or (4). A corresponding digital calculation is performed to output a digital value corresponding to the flow rate component V s , which is converted into an analog signal by the D/A converter 42 and then held in the sample hold circuit 37 . An example is shown that yields an associated output voltage e p . In FIG. 4, the reference voltage e r is applied to the integrator 39 via the switch TS' driven by the pulse P7 , and e r
The A/D converter 41 converts the value integrated over a certain period of time into a digital signal, and then the microprocessor 40
It may also be possible to perform span adjustment, etc. by giving the Furthermore, although the above example uses a rectangular wave as the excitation current Iw , it is possible to use various waveforms as necessary, such as a trapezoidal wave or a waveform obtained by converting the frequency of a commercial AC power source and then rectifying it. can.
このように本発明においては、電磁流量計発信
器の励磁コイルに定常値が零・負・零・正の順で
繰り返す励磁電流を供給する励磁回路と、電磁流
量計発信器から与えられる励磁電流の定常値が
負・零・正・零・負・零・正・零の各期間の信号
電圧をea1、ea2、ea3、ea4、ea5、ea6、ea7、ea8と
したとき実質的に(ea6−3ea5+2ea4+2ea3−3ea2
+ea1)または(ea8−3ea7+2ea6+2ea5−3ea4+
ea3)なる演算を行う信号処理回路とを有してい
るので、良好な信号対雑音比を有しながらオフセ
ツト電圧成分の3次変動まで除去することがで
き、また少ない消費電力で励磁電流の切り換えに
伴なうノイズ成分を除去できる低周波励磁方式の
電磁流量計を実現することができる。 In this way, the present invention includes an excitation circuit that supplies an excitation current whose steady value repeats in the order of zero, negative, zero, and positive to the excitation coil of the electromagnetic flowmeter transmitter, and an excitation current that is supplied from the electromagnetic flowmeter transmitter. The signal voltages during each period in which the steady - state value of Then, practically (e a6 −3e a5 +2e a4 +2e a3 −3e a2
+e a1 ) or (e a8 −3e a7 +2e a6 +2e a5 −3e a4 +
Since it has a signal processing circuit that performs calculations such as e a3 ), it is possible to eliminate even third-order fluctuations in the offset voltage component while maintaining a good signal-to-noise ratio, and it can also reduce the excitation current with low power consumption. It is possible to realize a low-frequency excitation type electromagnetic flowmeter that can eliminate noise components associated with switching.
第1図は本発明電磁流量計の一実施例を示す接
続図、第2図はその動作説明のため波形図、第3
図および第4図は本発明電磁流量計の他の実施例
を示す接続図である。
1…励磁回路、2…電磁流量計発信器、21…
励磁コイル、23,24…電極、3…信号処理回
路、31…交流増幅器、32a〜32f…サンプル
ホールド回路、34…演算器、37…サンプルホ
ールド回路、39…積分器、40…マイクロプロ
セツサ、41…A/D変変器、42…D/A変換
器、38…タイミングパルス発生器。
Fig. 1 is a connection diagram showing one embodiment of the electromagnetic flowmeter of the present invention, Fig. 2 is a waveform diagram for explaining its operation, and Fig. 3 is a waveform diagram for explaining its operation.
4 and 4 are connection diagrams showing other embodiments of the electromagnetic flowmeter of the present invention. 1... Excitation circuit, 2... Electromagnetic flow meter transmitter, 21...
Excitation coil, 23, 24... Electrode, 3... Signal processing circuit, 31... AC amplifier, 32 a to 32 f ... Sample hold circuit, 34... Arithmetic unit, 37... Sample hold circuit, 39... Integrator, 40... Micro programmer. 41...A/D converter, 42...D/A converter, 38...timing pulse generator.
Claims (1)
零・負・零・正の順で繰り返す励磁電流を供給す
る励磁回路と、電磁流量計発信器から与えられる
励磁電流の定常値が負・零・正・零・負・零・
正・零の各期間の信号電圧をea1、ea2、ea3、ea4、
ea5、ea6、ea7、ea8としたとき実質的に(ea6−
3ea5+2ea4+2ea3−3ea2+ea1)または(ea8−3ea7
+2ea6+2ea5−3ea4+ea3)なる演算を行い、オフ
セツト電圧成分の3次変動まで除去して流量信号
を得る信号処理回路とを有する電磁流量計。1. An excitation circuit that supplies an excitation current to the excitation coil of the electromagnetic flowmeter transmitter, whose steady value repeats in the order of zero, negative, zero, and positive;・Positive・Zero・Negative・Zero・
The signal voltages in each period of positive and zero are e a1 , e a2 , e a3 , e a4 ,
When e a5 , e a6 , e a7 , e a8 , essentially (e a6 −
3e a5 +2e a4 +2e a3 −3e a2 +e a1 ) or (e a8 −3e a7
+2e a6 +2e a5 -3e a4 +e a3 )) and removes even third-order fluctuations in offset voltage components to obtain a flow rate signal.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP21252481A JPS58115324A (en) | 1981-12-29 | 1981-12-29 | Electromagnetic flowmeter |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP21252481A JPS58115324A (en) | 1981-12-29 | 1981-12-29 | Electromagnetic flowmeter |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS58115324A JPS58115324A (en) | 1983-07-09 |
JPH0153403B2 true JPH0153403B2 (en) | 1989-11-14 |
Family
ID=16624091
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP21252481A Granted JPS58115324A (en) | 1981-12-29 | 1981-12-29 | Electromagnetic flowmeter |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPS58115324A (en) |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS57149919A (en) * | 1981-03-13 | 1982-09-16 | Yokogawa Hokushin Electric Corp | Electromagnetic flow meter |
-
1981
- 1981-12-29 JP JP21252481A patent/JPS58115324A/en active Granted
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS57149919A (en) * | 1981-03-13 | 1982-09-16 | Yokogawa Hokushin Electric Corp | Electromagnetic flow meter |
Also Published As
Publication number | Publication date |
---|---|
JPS58115324A (en) | 1983-07-09 |
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