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Analysis of the influence of pressure stabilizing system of regulating water flow standard device on the instrument coefficient of vortex flowmeter
时间:2020-07-29浏览量:503

通过调节水流量标准装置的稳压系统,以探求稳压系统对涡街流量计仪表系数的影响。

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.

涡街流量计是一种以直接测量封闭管道中满管流的流体流动的速度来获得流量的速度式流量计。涡街流量计由旋涡发生体、检测器、放大器及转换器组成,可与信号处理和显示部分配套使用。其工作原理为在测量管道中垂直插入一阻流体,也称旋涡发生体。随着流体的流动,当管道雷诺数达到一定值时,在发生体两侧就会交替地分离出卡门涡街。旋涡频率 f与流经发生体两侧的平均流速 v 之间的关系可表示为:

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 为旋涡频率,Hz; Sr为斯特劳哈尔数; v 为发生体两侧的平均流速,m/s; d 为发生体迎流面的宽度,m。m 为旋涡发生体两侧弓形面积与管道内横截面面积之比。

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 为管道直径,m。对于确定的测量管内径D,瞬时 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:

即测量管内径 D 和发生体迎流面宽度 d,体积流量 qV与旋涡发生体 f 成正比。若设则

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为体积流量,m3/ h; K 为涡街流量计的仪表系数,m- 3。

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

涡街流量计与节流差压式流量计相比,具有结构简单、安装方便,准确度高、量程范围宽,压力损失小、无零点漂移等优点; 但涡街流量计也有一定的局限性,若管道机械振动比较敏感,当流量或压力产生脉动时,示值大幅度偏高,影响较大等。为了验证压力波动给涡街流量计带来的影响,我们选择一套稳压系统可以进行自由切换的 DN15 ~ DN50 水流量标准装置,对某公司生产的 DN40 口径的涡街流量计进行试验。其试验条件和试验数据如下:

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:

试验条件: 环境温度: 24.5℃; 试验水温: 24.1℃;

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

相对湿度: 65%。

Relative humidity: 65%.

试验设备: DN15 ~ DN50 水流量标准装置; 准确度: 0. 1% 稳压容积: 3m3; 装置稳压时其压力波动不大于 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%.

我们选择某企业生产的性能较为稳定的一台DN40 涡街流量变送器,该流量变送器的流量范围为:4. 3 ~ 43m3/ h,准确度为 1. 0% ,按流量上限的 70%选择流量点进行试验。试验的被检流量变送器其稳压前后试验须在同一管线上进行,且不能进行重新装夹,以克服其它因素的影响。

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.

试验方案 1: 水流量标准装置的供水系统经过稳压容器 ( 3m3) 向试验台供水,此时试验压力为0. 4MPa,压力波动在 0. 1% ~ 0. 3% 之间,试验装置的直管段满足检定规程要求;

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;

试验方案 2: 水流量标准装置的供水系统不经过稳压容器,而由泵直接向试验装置供水,试验压力为0. 4MPa,试验装置的直管段满足检定规程要求。其试验结果见表 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.

通过实验表明: 从涡街流量变送器的测量原理上分析,涡街流量变送器的仪表系数应不受液体的压力、温度、粘度、密度、成分的影响。但从实际的试验的结果来看,系统的压力变化对涡街流量变器的仪表系数和线性度还是有一定的影响。分析认为是因为选择不好的企业产品,估计产品没有严格的老化、耐压等其它性能试验,仪表系数不太稳定,所以流量传感器的仪表系数会随着系统的压力变化而产生―定的变化。望今后在对此类仪表的检定/校准过程中加以考虑。

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.


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