渦街流體振動現(xiàn)象應(yīng)用于測量的研究開始于20世紀(jì)50年代，到20世紀(jì)80年代基于不同檢測方法的渦街流量計發(fā)展異常迅速，目前已躋身通用流量計之列。

The application of vortex flow vibration phenomenon in measurement began in 1950s. In 1980s, vortex flowmeter based on different detection methods developed rapidly, and now it has become one of the general flow meters.

渦街流量計在投入使用之前，需要根據(jù)其所測介質(zhì)是液體或氣體選擇相應(yīng)的標(biāo)定系統(tǒng)標(biāo)定，從而確定儀表系數(shù)、測量范圍、精度以及電路參數(shù)。針對DN300渦街流量計在液體介質(zhì)中的使用，我們選擇了3臺送往開封國家水大流量計量站進(jìn)行標(biāo)定，確定了其儀表系數(shù)、測量范圍及電路參數(shù)。

Before the vortex flowmeter is put into use, it is necessary to select the corresponding calibration system according to the measured medium is liquid or gas, so as to determine the instrument coefficient, measurement range, accuracy and circuit parameters. In view of the application of DN300 vortex flowmeter in liquid medium, three sets of DN300 vortex flowmeter were selected and sent to Kaifeng national water flow metering station for calibration, and the instrument coefficient, measurement range and circuit parameters were determined.

1 工作原理

Working principle

渦街流量計是根據(jù)“卡門渦街”原理研制成的一種流體振蕩型流量儀表。在流動的液體中插入一個斷面為非流線型柱狀物體時，在柱體后部兩側(cè)會產(chǎn)生兩列交錯排列的旋渦，如圖1所示。旋渦分離的頻率與流速成正比，與柱體的寬度成反比，可以用公式（1）表示：

Vortex flowmeter is a kind of fluid oscillation flow meter developed according to the principle of "Karman vortex street". When a non streamline cylinder is inserted into the flowing liquid, two rows of vortices will be generated on both sides of the back of the cylinder, as shown in Fig. 1. The frequency of vortex separation is directly proportional to the velocity of flow and inversely proportional to the width of the cylinder

f=St×U/d……公式                （1）

f=St×U/d…… Formula (1)

式中：

Where:

f：  旋渦分離頻率

f: Vortex separation frequency

St：斯特勞哈爾數(shù)（無量綱常數(shù)）

ST: Strouhal number (dimensionless constant)

U： 柱體側(cè)面的流速

U: Velocity on the side of the cylinder

d： 柱體的迎流面寬度

d: Width of upstream surface of cylinder

由公式（1）可見，通過測量旋渦的分離頻率便可測出流體流速，再由流速求出體積流量，進(jìn)而得到公式（2）

It can be seen from formula (1) that the fluid velocity can be measured by measuring the separation frequency of vortices, and then the volume flow rate can be calculated from the velocity, and then formula (2) can be obtained

f=Q×K……公式                   （2）

f=Q×K…… Formula (2)

式中：

Where:

K：儀表系數(shù)m-3。

K: The instrument coefficient is m-3.

Q：體積流量（m3/h）

Q: Volume flow (m3 / h)

渦街流量計的電路將壓電晶體元件（傳感器）檢測到的旋渦分離頻率經(jīng)放大、整形處理后。以頻率信號輸出，或進(jìn)一步變換成與流量成比例的4～20mADC信號輸出，如圖2所示。

The circuit of vortex flowmeter amplifies and reshapes the vortex separation frequency detected by piezoelectric crystal element (sensor). It is output by frequency signal, or further transformed into 4 ~ 20mADC signal output proportional to flow rate, as shown in Fig. 2.

2 預(yù)期目標(biāo)

2 expected objectives

本次是對DN300渦街流量計的標(biāo)定，我們制定了以下目標(biāo)

This is the calibration of DN300 vortex flowmeter, we set the following objectives

（1）按量程比7：1、精度1.0級、重復(fù)性0.3%以下的指標(biāo)標(biāo)定合格；

(1) According to the range ratio of 7:1, accuracy level 1.0, repeatability less than 0.3%, the calibration is qualified;

（2）取得其在水標(biāo)定時電路參數(shù)的設(shè)定值；

(2) The setting value of the parameters in the water mark timing circuit is obtained;

（3）在滿足量程比7：1、精度1.0級的條件下，通過對電路參數(shù)的調(diào)整，尋找其盡可能低的下限流量。

(3) Under the condition that the range ratio is 7:1 and the accuracy is 1.0, the lower limit flow can be found by adjusting the circuit parameters.

3 分析及調(diào)整

3 Analysis and adjustment

3.1 中小口徑渦街流量計水標(biāo)定

3.1 water calibration of small and medium diameter vortex flowmeter

數(shù)據(jù)如表1所示。

The data are shown in Table 1.

表1 中小口徑渦街流量計水標(biāo)定數(shù)據(jù)

Table 1 water calibration data of small and medium diameter vortex flowmeter

3.2 電路參數(shù)的設(shè)定

3.2 setting of circuit parameters

對于應(yīng)力式渦街流量計，介質(zhì)流過旋渦發(fā)生體產(chǎn)生的旋渦強(qiáng)度與升力ρU2（ρ為介質(zhì)密度，U為流速）成比例關(guān)系。對同一種介質(zhì)，測量的流量范圍的不同，信號強(qiáng)弱就不同，大口徑的渦街流量計產(chǎn)生的旋渦強(qiáng)度比小口徑的渦街流量計產(chǎn)生的旋渦強(qiáng)度大，因此大口徑的渦街流量計電荷放大器的放大率（K1）可調(diào)得比小口徑的渦街流量計電荷放大器的放大率小。渦街流量計優(yōu)質(zhì)次標(biāo)定時，其儀表系數(shù)和流量范圍都是未知的，流量范圍對應(yīng)的頻率也是未知的。此時帶通濾波器通頻帶（K2、K3）應(yīng)設(shè)得較寬，我們設(shè)定上下限頻率比為30：1左右。由于標(biāo)定裝置的流場穩(wěn)定，干擾少，因此電壓放大器的放大率（GB）以及施密特觸發(fā)器的觸發(fā)門限（SB）可按常規(guī)設(shè)置。

For the stress vortex flowmeter, the vortex intensity generated by the medium flowing through the vortex generator is proportional to the lift force ρ U2 (ρ is the medium density and u is the velocity). For the same medium, the signal strength varies with the flow range measured. The vortex intensity generated by the large diameter vortex flowmeter is larger than that generated by the small diameter vortex flowmeter. Therefore, the amplification ratio (K1) of the charge amplifier of the large caliber vortex flowmeter can be adjusted to be smaller than that of the charge amplifier of the small caliber vortex flowmeter. The instrument coefficient and flow range of vortex flowmeter are unknown, and the corresponding frequency of flow range is also unknown. At this time, the passband (K2, K3) of the band-pass filter should be set wider. We set the upper and lower frequency ratio as about 30:1. Since the flow field of the calibration device is stable and there is little interference, the amplification rate (GB) of the voltage amplifier and the trigger threshold (sb) of the Schmidt trigger can be set as usual.

結(jié)合表1估計DN300的渦街流量計的流量范圍可能在300～1800m3/h。選擇1000m3/h進(jìn)行標(biāo)定，得到系數(shù)K為0.0442。根據(jù)公式f=Q×K計算出估算的流量上下限對應(yīng)的頻率上下限。

Combined with table 1, it is estimated that the flow rate range of DN300 vortex flowmeter may be 300 ~ 1800m3 / h. When 1000m3 / h is selected for calibration, the coefficient K is 0.0442. According to the formula F = q × K, the upper and lower limits of the frequency corresponding to the upper and lower limits of the estimated flow are calculated.

在標(biāo)定時應(yīng)遵循一個原則：工作頻率范圍盡可能多地落到帶通濾波器設(shè)定的通頻帶內(nèi)。因此根據(jù)計算得到的頻率上下限，重新設(shè)置濾波器通頻帶。由于濾波器通頻帶的設(shè)定是通過調(diào)整K2、K3每一位開關(guān)決定一個濾波電容是否并聯(lián)到電路中來實現(xiàn)的，而對于K2、K3的開關(guān)組合非常多，調(diào)整要逐步摸索，使濾波器截止頻率接近計算得到的上下限頻率。標(biāo)定時當(dāng)流量上升到某一個值時，渦街流量計的輸出頻率突然大幅度下降，這就是濾波器上限頻率太小造成的。此時調(diào)整K3，選擇較小的電容并聯(lián)值，提高上限截止頻率。受設(shè)備能力的限制，流量上限只能到1500m3/h，因此按300～1500m3/h流量范圍進(jìn)行標(biāo)定。在300～1500m3/h流量范圍內(nèi)取5點標(biāo)定[2]，得到表2所示的數(shù)據(jù)：

In calibration, a principle should be followed: the working frequency range should fall into the passband set by the band-pass filter as much as possible. Therefore, according to the calculated frequency upper and lower limits, the filter passband is reset. Because the filter pass band is set by adjusting each bit switch of K2 and K3 to determine whether a filter capacitor is connected in parallel to the circuit, and for the switch combination of K2 and K3, adjustment should be gradually explored to make the filter cut-off frequency close to the calculated upper and lower limit frequency. During calibration, when the flow rate rises to a certain value, the output frequency of vortex flowmeter suddenly drops sharply, which is caused by the low upper limit frequency of filter. At this time, K3 is adjusted to select a smaller capacitor parallel value to increase the upper cut-off frequency. Due to the limitation of equipment capacity, the upper limit of flow can only reach 1500m3 / h, so it is calibrated according to the flow range of 300-1500m3 / h. In the range of 300-1500m3 / h flow rate, five points are selected for calibration [2], and the data shown in Table 2 are obtained

從表2中可以看出，基本誤差和重復(fù)性都在要求的范圍之內(nèi)，但量程比不到7：1。這時通過降低下限流量的方法來增大量程比，將流量范圍調(diào)整為220～1500m3/h。由于流量范圍的調(diào)整使輸出頻率大小及信號強(qiáng)弱發(fā)生改變，此時要對電路中帶通濾波器的通頻帶重新設(shè)置。對于優(yōu)質(zhì)次標(biāo)定的渦街流量計，這是需要反復(fù)進(jìn)行的工作。在滿足所產(chǎn)生的旋渦強(qiáng)度的要求以及***低雷諾數(shù)（20000）限制時，低的流量下限是追求的目標(biāo)之一。而DN300渦街流量計到流量下限220m3/h時產(chǎn)生的頻率為3Hz左右，非常接近壓電晶體熱效應(yīng)產(chǎn)生的頻率。因此在調(diào)低

As can be seen from table 2, the basic error and repeatability are within the required range, but the range ratio is less than 7:1. At this time, the range ratio is increased by reducing the lower flow rate, and the flow range is adjusted to 220 ~ 1500m3 / h. Due to the adjustment of the flow range, the output frequency and signal strength change, so the passband of the band-pass filter should be reset. For the vortex flowmeter with high quality and sub calibration, this work needs to be repeated. In order to meet the requirements of vortex intensity and the low Reynolds number (20000) limit, low flow limit is one of the goals. The frequency of DN300 vortex flowmeter is about 3Hz when it reaches the lower flow limit of 220m3 / h, which is very close to the frequency of piezoelectric crystal thermal effect. So it's going down