One, the principle of flowmeter
selection choose the principle of flow meter
was first to deep understanding of the fundamentals of the structure of the flow meter and flow characteristics of knowledge, even at the same time, according to the specific situation and investigation surrounding environment conditions.
Also want to consider the economic factors.
In general, the main choice from the following five aspects: (1) meter performance requirements;
(2) flow characteristics;
3. Installation requirements;
(4) environmental conditions;
The price of 5 meter.
1, the performance requirements of flowmeter flowmeter performance mainly includes: measuring flow (
The instantaneous flow)
The cumulative flow)
Flow range and scope;
The pressure loss;
Output signal characteristics and the response time of the flowmeter, etc.
Measuring flow or total flow measurement includes two kinds, namely the instantaneous flow and cumulative flow, such as the transfer station pipeline crude oil belongs to trade or ratio of petrochemical pipeline for continuous production or the process of the production process control and so on need to measure total, or by observation of instantaneous flow rate.
In some workplaces to control flow is equipped with the instantaneous flow measurement.
Therefore, to undertake choosing according to the needs of field measurement.
Some meter such as volumetric flowmeter, turbine flowmeter, etc. , its measurement principle is based on mechanical counting or pulse frequency, total output directly by its high accuracy, suitable for measuring the total, if equipped with the corresponding transmission device can also be output flow.
Electromagnetic flowmeter, ultrasonic flowmeter based on measurement of fluid velocity of flow is deduced, the response is fast, suitable for process control, if match with integrating function also can get the total.
The provisions of the accuracy of flowmeter accuracy level is within the scope of a certain flow, if used in a specific condition or the flow of the narrow scope, for example, change only in a small scope, its measurement accuracy is higher than specified level of accuracy.
Such as turbine flowmeter metering of the oil barrel distribution, under the condition of the valve is fully open to use, basic constant flow, its accuracy may be from zero.
Level 5 to 0.
Accounting for trade, storage and transportation and material balance if required measurement accuracy is high, should consider the durability of the accuracy of measurement, the flowmeter is commonly used in the above case, the accuracy of grade of 0.
In the workplace is typically the site equipped with metrology standard equipment (
Such as the volume tube)
The flowmeter to use online detection.
Tense in recent years because of the crude oil and the high requirements for crude oil metering unit, put forward implement coefficient of crude oil metering transition, namely except for flow meter once every six months after the cycle test, trade transfer both sides talks things over every 1 or 2 months for flowmeter calibration flow coefficient is determined, according to the daily flowmeter measurement data with flowmeter to handover flow coefficient to calculate the data, in order to improve the accuracy of flow meter, also known as the zero error of transition.
Accuracy degree is generally determined according to maximum permissible error of the meter.
The factory provide prospectus of flowmeter are given.
It is important to note that the percentage of error is refers to the relative error or reference error.
Relative error of measured values, the percentage of commonly used & other;
Reference error is refers to the percentage of measuring upper limit or range, commonly used & other;
Many manufacturers did not indicate the specification.
For example, flow meter is commonly used reference error, error of electromagnetic flowmeter in some models also have use reference.
Meter if not simply measuring the total, but the application in the fluid flow control system, the detection of flowmeter accuracy should be determined as required by the control accuracy of the whole system.
Because of the whole system not only has the traffic detection error, also contains a signal transmission, control and operation of error and various influencing factors.
Existing in the operating system, for example, about 2% of back to the poor, the accuracy of the measuring instrument used to determine the high (
Level 5 or above)
Is not economic and reasonable.
In terms of the instrument itself, between the sensor and secondary instrument accuracy should also be appropriate to match, for example designed velocity-equalizing tube without actual calibration error as in & plusmn;
~ ± 5%;
Deserve to go up 4%, 0.
2% ~ 0.
5% high accuracy differential pressure gauge is not significant.
Another problem is the verification procedures or factory prospectus of flowmeter specified level of accuracy refers to the maximum permissible error of the meter.
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