How to choose the right flow meter according to the performance of the flow meter
2024-03-28
The selection of flowmeters should deeply understand the knowledge of the fluid characteristics of various flowmeters, and at the same time, choose according to the specific situation of the site and the surrounding environmental conditions. Next, let me tell you how to choose the right flowmeter according to the fluid characteristics.
Flowmeter performance requirements Flowmeter performance mainly includes: measuring flow (instantaneous flow) or total (cumulative flow); Accuracy requirements; Repeatability; Linearity; Flow range and range degree; Pressure loss; Output signal characteristics and flowmeter response time, etc.
(1) Flow measurement or total flow measurement includes two kinds, namely instantaneous flow and cumulative flow. For example, the total amount of crude oil in the pipeline of sub-transmission station belongs to the trade handover or the continuous matching production of petrochemical pipelines or the process control of the production process needs to be measured, and occasionally supplemented by the observation of instantaneous flow. In some workplaces, flow control requires instantaneous flow measurement. Therefore, the selection should be made according to the needs of on-site measurement.
(2) The accuracy level of the flow meter is specified in a certain flow range, if used under a specific condition or a relatively narrow flow range, for example, only in a small range of changes, at this time its measurement accuracy will be higher than the specified accuracy level. For trade accounting, storage and transportation handover and material balance, if the measurement accuracy is required to be high, the durability of the accuracy measurement should be considered, generally used in the above cases of the flow meter, the accuracy level is 0.2. In such workplaces, standard metering equipment (such as volume tubes) is generally equipped on site to carry out online testing of the flowmeter used.
(3) Repeatability is determined by the principle of the flow meter itself and the manufacturing quality, and is an important technical indicator in the use of the flow meter, which is closely related to the accuracy of the flow meter. Generally, in the measurement performance requirements of the verification regulations, the flowmeter not only has the accuracy level, but also the repeatability is specified, which is generally stipulated as follows: the repeatability of the flowmeter shall not exceed the maximum allowable error of 1/3 ~ 1/5 specified in the corresponding accuracy level. However, in practical applications, the repeatability of the flowmeter will often be affected by changes in fluid viscosity and density parameters, and sometimes these parameter changes have not reached the degree of need for special correction, which will be mistaken for the poor repeatability of the flowmeter. In this case, a flowmeter that is not sensitive to changes in this parameter should be selected.
(4) The output of the linear degree flowmeter mainly has two linear and nonlinear square roots. Generally speaking, the nonlinear error of the flowmeter is not listed separately, but is included in the error of the flowmeter. For generally wide flow range, the output signal is pulse, used as a total integration flowmeter, linearity is an important technical indicator, if a single instrument coefficient is used in its flow range, when the linearity difference will reduce the accuracy of the flowmeter. With the development of computer technology, the flow range can be segmtioned and the flow meter coefficient curve can be fitted with the least square method to correct the flow meter, so as to improve the accuracy of the flow meter and expand the flow range.
(5) The upper limit flow rate and flow range The upper limit flow rate is also called the full degree flow rate or maximum flow rate of the flowmeter. When we choose the diameter of the flowmeter, it should be configured according to the flow range used in the pipeline under test and the upper and lower flow limit of the selected flowmeter, and it can not be simply matched according to the pipe diameter. Generally speaking, the maximum flow rate of the design pipeline fluid is determined according to the economic flow rate. If the selection is too low, the pipe diameter is thick, and the investment will be large; If it is too high, the transmission power is large and the operating cost is increased.
(6) Range degree Range degree is the ratio of the upper limit flow rate and the lower limit flow rate of the flowmeter, the larger the value, the wider the flow range. Linear instruments have a wide range, generally 1:10. The range of the nonlinear flowmeter is small, only 1:3. Flowmeters generally used for process control or trade handover accounting, if the flow range is required to be wide, do not choose a small range of flowmeters. In fact, the key to the wide range is to have a low lower limit flow rate to meet the measurement needs. Therefore, a wide range flowmeter with low lower flow rate is more practical.
(7) Pressure loss Pressure loss generally refers to the flow sensor due to the static or active detection elements set in the flow channel or change the flow direction, resulting in an unrecoverable pressure loss with flow, the value of which can sometimes reach tens of thousands of kpa. Therefore, the flowmeter should be selected according to the piping system pumping capacity and flowmeter inlet pressure to determine the maximum flow allowable pressure loss. Improper selection will restrict the fluid flow and produce excessive pressure loss, which will affect the flow efficiency. Some liquids (high vapor pressure hydrocarbon liquids) should also pay attention to excessive pressure drop may cause cavitation phenomenon and liquid phase vaporization, reduce measurement accuracy and even damage the flow meter.
(8) The output signal characteristics of the flowmeter output and display can be divided into: ① flow (volume flow or mass flow); ② Total quantity; ③ Average flow rate; ④ point flow rate. Some flowmeters output analog quantities (current or voltage), others output pulse quantities. Analog output is generally considered to be suitable for process control, and is more suitable for connecting with control loop units such as regulating valves. Pulse volume output is suitable for total volume and high accuracy flow measurement. The pulse output of long distance signal transmission has higher transmission accuracy than that of analog output. The mode and amplitude of the output signal should also have the ability to adapt to other equipment, such as control interfaces, data processors, alarm devices, break protection loops and data transmission systems.
(9) Response time Applied to pulsating flow situations, attention should be paid to the response of the flow meter to the step change of the flow. Some applications require the flow meter output to follow the flow of the fluid, while others require a slower response output to obtain the overall average value. Instantaneous response is often expressed as a time constant, or response frequency, with values ranging from a few milliseconds to a few seconds for the former and below hundreds of Hz for the latter. The availability of display instruments may significantly increase response times. It is generally believed that the asymmetric dynamic response of flowmeter will accelerate the increase of flow measurement error when the flow rate increases or decreases.
If you still have questions about how to select the flow meter, please contact Aister Instrument flow meter manufacturer.
(1) Flow measurement or total flow measurement includes two kinds, namely instantaneous flow and cumulative flow. For example, the total amount of crude oil in the pipeline of sub-transmission station belongs to the trade handover or the continuous matching production of petrochemical pipelines or the process control of the production process needs to be measured, and occasionally supplemented by the observation of instantaneous flow. In some workplaces, flow control requires instantaneous flow measurement. Therefore, the selection should be made according to the needs of on-site measurement.
(2) The accuracy level of the flow meter is specified in a certain flow range, if used under a specific condition or a relatively narrow flow range, for example, only in a small range of changes, at this time its measurement accuracy will be higher than the specified accuracy level. For trade accounting, storage and transportation handover and material balance, if the measurement accuracy is required to be high, the durability of the accuracy measurement should be considered, generally used in the above cases of the flow meter, the accuracy level is 0.2. In such workplaces, standard metering equipment (such as volume tubes) is generally equipped on site to carry out online testing of the flowmeter used.
(3) Repeatability is determined by the principle of the flow meter itself and the manufacturing quality, and is an important technical indicator in the use of the flow meter, which is closely related to the accuracy of the flow meter. Generally, in the measurement performance requirements of the verification regulations, the flowmeter not only has the accuracy level, but also the repeatability is specified, which is generally stipulated as follows: the repeatability of the flowmeter shall not exceed the maximum allowable error of 1/3 ~ 1/5 specified in the corresponding accuracy level. However, in practical applications, the repeatability of the flowmeter will often be affected by changes in fluid viscosity and density parameters, and sometimes these parameter changes have not reached the degree of need for special correction, which will be mistaken for the poor repeatability of the flowmeter. In this case, a flowmeter that is not sensitive to changes in this parameter should be selected.
(4) The output of the linear degree flowmeter mainly has two linear and nonlinear square roots. Generally speaking, the nonlinear error of the flowmeter is not listed separately, but is included in the error of the flowmeter. For generally wide flow range, the output signal is pulse, used as a total integration flowmeter, linearity is an important technical indicator, if a single instrument coefficient is used in its flow range, when the linearity difference will reduce the accuracy of the flowmeter. With the development of computer technology, the flow range can be segmtioned and the flow meter coefficient curve can be fitted with the least square method to correct the flow meter, so as to improve the accuracy of the flow meter and expand the flow range.
(5) The upper limit flow rate and flow range The upper limit flow rate is also called the full degree flow rate or maximum flow rate of the flowmeter. When we choose the diameter of the flowmeter, it should be configured according to the flow range used in the pipeline under test and the upper and lower flow limit of the selected flowmeter, and it can not be simply matched according to the pipe diameter. Generally speaking, the maximum flow rate of the design pipeline fluid is determined according to the economic flow rate. If the selection is too low, the pipe diameter is thick, and the investment will be large; If it is too high, the transmission power is large and the operating cost is increased.
(6) Range degree Range degree is the ratio of the upper limit flow rate and the lower limit flow rate of the flowmeter, the larger the value, the wider the flow range. Linear instruments have a wide range, generally 1:10. The range of the nonlinear flowmeter is small, only 1:3. Flowmeters generally used for process control or trade handover accounting, if the flow range is required to be wide, do not choose a small range of flowmeters. In fact, the key to the wide range is to have a low lower limit flow rate to meet the measurement needs. Therefore, a wide range flowmeter with low lower flow rate is more practical.
(7) Pressure loss Pressure loss generally refers to the flow sensor due to the static or active detection elements set in the flow channel or change the flow direction, resulting in an unrecoverable pressure loss with flow, the value of which can sometimes reach tens of thousands of kpa. Therefore, the flowmeter should be selected according to the piping system pumping capacity and flowmeter inlet pressure to determine the maximum flow allowable pressure loss. Improper selection will restrict the fluid flow and produce excessive pressure loss, which will affect the flow efficiency. Some liquids (high vapor pressure hydrocarbon liquids) should also pay attention to excessive pressure drop may cause cavitation phenomenon and liquid phase vaporization, reduce measurement accuracy and even damage the flow meter.
(8) The output signal characteristics of the flowmeter output and display can be divided into: ① flow (volume flow or mass flow); ② Total quantity; ③ Average flow rate; ④ point flow rate. Some flowmeters output analog quantities (current or voltage), others output pulse quantities. Analog output is generally considered to be suitable for process control, and is more suitable for connecting with control loop units such as regulating valves. Pulse volume output is suitable for total volume and high accuracy flow measurement. The pulse output of long distance signal transmission has higher transmission accuracy than that of analog output. The mode and amplitude of the output signal should also have the ability to adapt to other equipment, such as control interfaces, data processors, alarm devices, break protection loops and data transmission systems.
(9) Response time Applied to pulsating flow situations, attention should be paid to the response of the flow meter to the step change of the flow. Some applications require the flow meter output to follow the flow of the fluid, while others require a slower response output to obtain the overall average value. Instantaneous response is often expressed as a time constant, or response frequency, with values ranging from a few milliseconds to a few seconds for the former and below hundreds of Hz for the latter. The availability of display instruments may significantly increase response times. It is generally believed that the asymmetric dynamic response of flowmeter will accelerate the increase of flow measurement error when the flow rate increases or decreases.
If you still have questions about how to select the flow meter, please contact Aister Instrument flow meter manufacturer.
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