标准节流装置在满量程下30%不宜使用，量程比比较合适的也就是3：1，如果过大的话，严重影响到精度。 Many on-site craftsmen may understand that the standard throttling device of differential pressure flowmeter is not suitable for use at 30% of full scale. The ratio of ratio is more suitable is 3: 1. If it is too large, it will seriously affect accuracy. Although the range ratio of many differential pressure flowmeters can now be very large, the V cone flowmeter, which is widely used today, can achieve 13: 1, and the wedge flowmeter that is good at measuring dirty media has a larger range ratio. Can achieve 15: 1, these products directly make up for the shortcomings of the standard throttle device measuring range is small. So why is there such a small flow when the throttle device measures the flow on site? After studying the principle, you can easily find out that this is mainly determined by the flow calculation formula of the throttling device. Here are the reasons for this in detail: In flow measurement, national standards stipulate that the applicable flow ratio of the throttling device is 30% (that is, maximum flow: minimum flow = 3: 1). Here, because the differential pressure is proportional to the square of the flow, the accuracy cannot be guaranteed when the flow ratio is less than 30%. In addition, when the flow is less than 30%, Renault The number is often lower than the limit Reynolds number, and the flow coefficient α is not constant, resulting in inaccurate flow measurement.
So how to deal with this situation.
1. First negotiate with the process personnel to reduce the maximum flow rate. If the Reynolds number is large enough, you can solve it by changing the orifice plate or differential pressure. 2. Use other differential pressure flow meters. If you encounter field conditions, the parameters cannot be changed and the flow rate is changed. When the range is large, we can choose V cone flowmeter. V cone flowmeter is currently widely used. The main features are: high accuracy, large range, small pressure loss, energy saving, and For corrosive media, wedge-shaped flowmeters can be selected. The main features are: low Reynolds number lower limit, wide application range, and good stability. 首先是成本低，安装简单，更重要的是能保证现场测量效果。 3. For on-site large-caliber measurement, from the perspective of economy and installation, you can use a plug-in differential pressure flow meter, such as: Annubar averaging tube flow meter, plug-in double venturi, plug-in V cone These meters have absolute advantages when measuring large calibers. Differential pressure flow meters are first of all low-cost, simple to install, and more importantly, they can ensure on-site measurement results. No matter which type of flowmeter has its limitations, we should make up for its shortcomings by other methods. The company will continue to strive for greater breakthroughs. Differential pressure flowmeters are now facing unprecedented challenges. In the measurement of urban natural gas, gas, industrial steam, and other various media, as well as in the calculation of individual internal costing, a wide range, high accuracy, and high reliability are urgently needed. Measuring instruments. Under the premise of the company's continuous innovation and research, the differential pressure flow meter has made breakthroughs in technology. According to market reliable data surveys, the differential pressure flow meter is mature, simple in structure, and unmovable. Components, stability, reliability, wide adaptability and other advantages still occupy the top of the flowmeter list. The following describes the development process of the differential pressure flowmeter:
1. Integrated differential pressure flowmeter, which integrates throttling device, differential pressure, pressure, temperature, and calculation display into an integrated flowmeter. The flow can be displayed directly from the meter, or the instantaneous flow value can be transmitted remotely through the 4-20mA current. This is also a true differential pressure flowmeter, which contains all the necessary elements of a flowmeter. 2. Integrated differential pressure flow transmitter. The differential pressure transmitter is directly installed on the throttling device and outputs a 4-20mA electric signal representing the differential pressure signal. The flow calculation and temperature and pressure compensation are configured by the user. . To a certain extent, this configuration cannot be regarded as a flow meter. At most, it also plays a transmitting role, but it is suitable for transmitting field signals to the DCS for control. The control system performs temperature and pressure compensation. Calculate the measured flow. 3. It consists of throttling device, differential pressure transmitter, pressure transmitter, temperature transmitter and flow calculation display instrument. Also called split-type differential pressure flowmeter. I believe this configuration is no stranger to many people. This is the traditional configuration above. It was always installed when using a differential pressure flow meter, but because it is too cumbersome, the amount of use has dropped significantly in recent years.
Next, let's talk about the major factors that are mainly used in the selection of flowmeters:
选择时如果只凭以往经验，或单考虑某一因素而贸然作出决定，就可能失去选择最适合仪表的可能。 There may be multiple solutions for the instruments that can be used in a certain place of use. If the differential pressure flowmeter is selected based on past experience or a decision made only by considering certain factors, the possibility of selecting the most suitable instrument may be lost. But it is not easy to put forward the best solution by combining these factors. Here are some suggestions based on our years of accumulation for your reference when choosing a flow meter:
4. Long-term reliability
Here, due to the relationship of time, I will not elaborate on these reference factors. I believe that everyone has a certain understanding of them, because no matter which type of flowmeter these references are for, they must be considered.