通過調(diào)節(jié)水流量標(biāo)準(zhǔn)裝置的穩(wěn)壓系統(tǒng)，以探求穩(wěn)壓系統(tǒng)對渦街流量計儀表系數(shù)的影響。

By adjusting the pressure stabilizing system of water flow standard device, the influence of pressure stabilizing system on the instrument coefficient of vortex flowmeter is explored.

渦街流量計是一種以直接測量封閉管道中滿管流的流體流動的速度來獲得流量的速度式流量計。渦街流量計由旋渦發(fā)生體、檢測器、放大器及轉(zhuǎn)換器組成，可與信號處理和顯示部分配套使用。其工作原理為在測量管道中垂直插入一阻流體，也稱旋渦發(fā)生體。隨著流體的流動，當(dāng)管道雷諾數(shù)達(dá)到一定值時，在發(fā)生體兩側(cè)就會交替地分離出卡門渦街。旋渦頻率 f與流經(jīng)發(fā)生體兩側(cè)的平均流速 v 之間的關(guān)系可表示為:

Vortex flowmeter is a kind of velocity flowmeter which can obtain the flow rate by directly measuring the flow velocity of full pipe flow in closed pipe. Vortex flowmeter is composed of vortex generator, detector, amplifier and converter. It can be used with signal processing and display. Its working principle is to insert a blocking fluid vertically into the measuring pipe, also known as vortex generator. With the flow of fluid, when the Reynolds number reaches a certain value, the Karman vortex street will be separated alternately on both sides of the generator. The relationship between the vortex frequency f and the average velocity V flowing through both sides of the generator can be expressed as follows:

式中: f 為旋渦頻率，Hz; Sr為斯特勞哈爾數(shù); v 為發(fā)生體兩側(cè)的平均流速，m/s; d 為發(fā)生體迎流面的寬度，m。m 為旋渦發(fā)生體兩側(cè)弓形面積與管道內(nèi)橫截面面積之比。

Where: F is the vortex frequency, Hz; Sr is the Strouhal number; V is the average velocity on both sides of the generator, M / S; D is the width of the upstream surface of the generator, M. M is the ratio of the arcuate area on both sides of the vortex generator to the cross-sectional area of the pipe.

式中: D 為管道直徑，m。對于確定的測量管內(nèi)徑D，瞬時 量 ( m3/s) 有:

Where: D is the pipe diameter, M. For the determined inner diameter D of measuring tube, the instantaneous quantity (m3 / s) is as follows:

即測量管內(nèi)徑 D 和發(fā)生體迎流面寬度 d，體積流量 qV與旋渦發(fā)生體 f 成正比。若設(shè)則

In other words, the inner diameter of the tube D and the width of the upstream surface D of the generator are measured, and the volume flow rate QV is directly proportional to the vortex generator F. If set, then

式中: qV為體積流量，m3/ h; K 為渦街流量計的儀表系數(shù)，m- 3。

Where: QV is the volume flow rate, m3 / h; K is the instrument coefficient of vortex flowmeter, m-3.

渦街流量計與節(jié)流差壓式流量計相比，具有結(jié)構(gòu)簡單、安裝方便，準(zhǔn)確度高、量程范圍寬，壓力損失小、無零點漂移等優(yōu)點; 但渦街流量計也有一定的局限性，若管道機械振動比較敏感，當(dāng)流量或壓力產(chǎn)生脈動時，示值大幅度偏高，影響較大等。為了驗證壓力波動給渦街流量計帶來的影響，我們選擇一套穩(wěn)壓系統(tǒng)可以進(jìn)行自由切換的 DN15 ～ DN50 水流量標(biāo)準(zhǔn)裝置，對某公司生產(chǎn)的 DN40 口徑的渦街流量計進(jìn)行試驗。其試驗條件和試驗數(shù)據(jù)如下:

Compared with throttling differential pressure flowmeter, vortex flowmeter has the advantages of simple structure, convenient installation, high accuracy, wide range, small pressure loss and no zero drift. However, vortex flowmeter also has certain limitations. If pipeline mechanical vibration is more sensitive, when the flow or pressure produces pulsation, the indication value will be greatly higher and the influence will be greater. In order to verify the influence of pressure fluctuation on vortex flowmeter, we choose a set of water flow standard device from DN 15 to DN50, which can be switched freely by pressure stabilization system, to test the vortex flowmeter with diameter of Dn40 produced by a company. The test conditions and data are as follows:

試驗條件: 環(huán)境溫度: 24.5℃; 試驗水溫: 24.1℃;

Test conditions: ambient temperature: 24.5 ℃; test water temperature: 24.1 ℃;

相對濕度: 65%。

Relative humidity: 65%.

試驗設(shè)備: DN15 ～ DN50 水流量標(biāo)準(zhǔn)裝置; 準(zhǔn)確度: 0. 1% 穩(wěn)壓容積: 3m3; 裝置穩(wěn)壓時其壓力波動不大于 0. 1% ～0. 3% 。

Test equipment: water flow standard device of DN 15-dn50; accuracy: 0.1% stabilized volume: 3m3; pressure fluctuation of the device shall not be greater than 0.1% - 0.3%.

我們選擇某企業(yè)生產(chǎn)的性能較為穩(wěn)定的一臺DN40 渦街流量變送器，該流量變送器的流量范圍為:4. 3 ～ 43m3/ h，準(zhǔn)確度為 1. 0% ，按流量上限的 70%選擇流量點進(jìn)行試驗。試驗的被檢流量變送器其穩(wěn)壓前后試驗須在同一管線上進(jìn)行，且不能進(jìn)行重新裝夾，以克服其它因素的影響。

We choose a Dn40 vortex flow transmitter with stable performance produced by an enterprise. The flow range of the flow transmitter is 4.3 ~ 43M3 / h, and the accuracy is 1.0%. The flow point is selected according to 70% of the upper flow limit for test. The tested flow transmitter must be tested on the same pipeline before and after voltage stabilization, and can not be re clamped to overcome the influence of other factors.

試驗方案 1: 水流量標(biāo)準(zhǔn)裝置的供水系統(tǒng)經(jīng)過穩(wěn)壓容器 ( 3m3) 向試驗臺供水，此時試驗壓力為0. 4MPa，壓力波動在 0. 1% ～ 0. 3% 之間，試驗裝置的直管段滿足檢定規(guī)程要求;

Test scheme 1: the water supply system of the water flow standard device supplies water to the test bench through a pressure stabilizing container (3m3). At this time, the test pressure is 0.4MPa and the pressure fluctuation is between 0.1% and 0.3%. The straight pipe section of the test device meets the requirements of the verification regulation;

試驗方案 2: 水流量標(biāo)準(zhǔn)裝置的供水系統(tǒng)不經(jīng)過穩(wěn)壓容器，而由泵直接向試驗裝置供水，試驗壓力為0. 4MPa，試驗裝置的直管段滿足檢定規(guī)程要求。其試驗結(jié)果見表 1 ～ 表 3。

Test scheme 2: the water supply system of the water flow standard device does not pass through the pressure vessel, but directly supplies water to the test device by the pump. The test pressure is 0.4MPa, and the straight pipe section of the test device meets the requirements of the verification regulation. The test results are shown in table 1-3.

通過實驗表明: 從渦街流量變送器的測量原理上分析，渦街流量變送器的儀表系數(shù)應(yīng)不受液體的壓力、溫度、粘度、密度、成分的影響。但從實際的試驗的結(jié)果來看，系統(tǒng)的壓力變化對渦街流量變器的儀表系數(shù)和線性度還是有一定的影響。分析認(rèn)為是因為選擇不好的企業(yè)產(chǎn)品，估計產(chǎn)品沒有嚴(yán)格的老化、耐壓等其它性能試驗，儀表系數(shù)不太穩(wěn)定，所以流量傳感器的儀表系數(shù)會隨著系統(tǒng)的壓力變化而產(chǎn)生―定的變化。望今后在對此類儀表的檢定/校準(zhǔn)過程中加以考慮。

The experimental results show that: from the measurement principle of vortex flow transmitter, the instrument coefficient of vortex flow transmitter should not be affected by liquid pressure, temperature, viscosity, density and composition. However, from the actual test results, the pressure change of the system still has a certain influence on the instrument coefficient and linearity of the vortex flow converter. The analysis shows that it is because of the poor selection of enterprise products, it is estimated that there is no strict aging, withstand voltage and other performance tests on the products, and the instrument coefficient of the flow sensor is not stable, so the instrument coefficient of the flow sensor will change with the pressure change of the system. It is hoped that this kind of instrument will be considered in the process of verification / calibration in the future.