Error Analysis of Oval Gear Flow Meter and Positive Displacement Flow Meter

Abstract: The error analysis information of the oval gear flow meter and the positive displacement flow meter is provided by the excellent flow meter and flow meter production and quotation manufacturers. Error analysis of oval gear flowmeter and positive displacement flowmeter: Positive displacement flowmeter is the most accurate type of flowmeter among flowmeters. Its basic principle is to use mechanical measuring elements to continuously divide the fluid into a single known flowmeter. body. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the error analysis article for oval gear flowmeters and positive displacement flowmeters. Error analysis of oval gear flowmeter and positive displacement flowmeter: Positive displacement flowmeter is the most accurate type of flowmeter among flowmeters. Its basic principle is to use mechanical measuring elements to continuously divide the fluid into a single known flowmeter. Volume fraction, the total volume of fluid is measured based on the number of times the chamber is continuously filled and drained with fluid for that volume fraction. The flow range of the positive displacement flowmeter is related to the type of the measured medium (mainly determined by the viscosity of the fluid), the characteristics of use (continuous work or intermittent work), the measurement accuracy and other factors. In the field of industrial flow measurement, positive displacement flowmeters, differential pressure flowmeters and float flowmeters are listed as the three most widely used flowmeters, and are often used in the total measurement of expensive media (oil, natural gas, etc.). Positive displacement flowmeters include oval gear flowmeters, dual rotor flowmeters, waist wheel flowmeters, scraper flowmeters, piston flowmeters, etc. The same positive displacement flowmeter, for the type of medium, is used for higher viscosity fluids , its flow range is large (mainly the lower limit flow can be extended to a lower value); for the characteristics of use, when it is used for intermittent measurement, its flow range is large (mainly, the upper limit flow can be larger than that in continuous operation); for Measurement accuracy, when used for low-accuracy measurement, its flow range is large, and when used for high-accuracy measurement, the flow range is small. This can also be clearly seen from the flowmeter characteristic curve. In order to maintain the good performance and long service life of the instrument, the maximum flow rate should preferably be selected at 70%-80% of the maximum flow rate of the instrument. Due to the large volume of the general positive displacement flowmeter, it will generate large noise when the flow is large, so it is generally suitable for small and medium flow measurement. Combined with the performance of the positive displacement flowmeter, when it is necessary to measure a large flow, a flowmeter with a 45-degree combined waist wheel structure can be used; when low noise work is required, a dual-rotor flowmeter can be used. The oval gear flowmeter positive displacement flowmeter is one of the flowmeters with the highest measurement accuracy. The measurement accuracy given by the manufacturer on the product sample refers to the basic error obtained under the laboratory reference conditions. In actual use, due to the deviation of the field conditions, additional errors will inevitably be brought, and the actual error should be the basic error. and a composite of additional errors. Therefore, measures should be taken according to the problems that may arise in the field when selecting the instrument. The major influences of site conditions on the measurement accuracy are the influence of the viscosity of the measured medium and the influence of temperature. The influence of fluid viscosity on the error characteristics of the flowmeter is one of the factors that has a greater influence on the error of the flow rate. When the actual viscosity of the fluid used is quite different from the fluid viscosity at the time of laboratory verification, the corresponding viscosity correction should be carried out. If there is no significant change in parameters other than fluid viscosity, viscosity correction can be performed with . Regarding the error characteristics of the above-mentioned flowmeters, what are the obvious differences compared with other types of flowmeters? Users should pay attention to the following points in the process of installing and using positive displacement flowmeters such as oval gear flowmeters: ① The fixed displacement of the fixed displacement volumetric flowmeter is an important factor to ensure the accuracy of the volumetric flowmeter. Therefore, the size and physical properties of the fixed displacement element are the influencing factors. a. Temperature. As the temperature rises, the volumetric expansion of the fixed displacement element material increases. For example, a flowmeter made of aluminum has a greater effect on temperature than a flowmeter made of other materials. Typically, each increase in 10°C F temperature, the error increases by 0.02%. b. Wear. With the increase in use time, wear increases the fixed displacement. But usually this wear is slow and predictable. c. Viscosity. The viscosity of the liquid will form a film on the surface of the detection element, and as the film thickness increases, the fixed displacement will decrease until the film thickness no longer increases (due to the friction of the parts). d. Coating and Precipitation. Similar to the principle that viscosity causes a thin film on the surface of the detection element, coatings and deposits also reduce the fixed displacement of the detection element. For some crude oil containing paraffin oil whose working temperature is close to the melting point temperature, the thickness variation will be large. ②In the positive displacement flowmeter, there is a gap between the moving part and the stationary part,This is called a capillary seal. Different fluid differential pressures cause fluid loss from the fixed displacement detection element, which is an important factor causing errors. a. Flow rate. As the differential pressure of the fluid increases, the flow rate increases, and therefore, the drift increases, as shown in Curve 1 in Figure 2-79. In addition, as the differential pressure increases, the friction within the component and the torque of the driving component increase, as shown in curve 2 of Figure 2-79. Therefore, there is an optimal flow rate that minimizes drift.

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