关于流量计的校准问题

beiwei5du

各位蒲友：
针对于一般的流量计（比如涡街流量计）的校准是否必须使用后期要测量的溶剂进行校准？？？比如我有多个涡街流量计，使用到甲醇，乙醇，DMF，丙酮等溶剂进行计量（要求准确度相对比较高），那么在送外校准是否必须使用分别的溶剂进行校准吗？？？

hongwei2000

如果是检定肯定是不可能的
如果是自校的话
建议考虑
因为不同溶剂的黏度不同

beiwei5du

hongwei2000 发表于 2016-9-29 13:39
如果是检定肯定是不可能的
如果是自校的话
建议考虑

Flowmeter calibration: Five best practices you need to know

A flowmeter measures the rate that fluid or gas moves through it.  Test and measurement professionals use them in a wide variety of applications where accurate flow measurements are critical, including (but not limited to) HVAC, energy and utilities, water management, aerospace, agriculture and the pharmaceutical industry. In applications like these, it’s important to calibrate the flowmeters that make the measurements.  Regular calibrations assure you that the flowmeter’s measurements are as accurate as their specifications say they are.

Even the most rugged flowmeters can fall out of calibration. All instruments’ performance degrades over time; parts wear out or break. Flowmeters can be affected by corrosion or dirt within the media that flows through them. They may also be damaged by impact, variations in the process, or by improper installation.

Standard best practices in calibration apply to flowmeter calibration as they do for all test equipment; flow calibration also has some specific best practices to keep in mind:

1.       The standard that you use to calibrate a flowmeter must be accurate enough to perform the calibration. The general rule of thumb is that your standard should be four times more accurate than the unit under test (UUT); however, this can vary depending on the requirements of the calibration.
2.       Your standard should be traceable to a recognized standard. Traceability provides an unbroken chain of documentation that shows how the measurements it makes compare to even more accurate standards. Traceable measurements help you prove that your measurements are what your flowmeter says they are, within specific ranges.
3.       The rate of flow between the UUT and the calibration standard must be in a steady state. Since the flow rate of the standard and the UUT are compared in real time during calibration, the system flow rate should not vary with time.
4.       All media measured by the calibration standard must also be measured by the flowmeter at the same time. In other words, there should not be any leaks or significant temperature changes in intermediary volumes that might affect the measurement.
5.       You should perform the calibration under conditions that are typical of the flowmeter’s actual operation. For example, the viscosity, density or heat content of the liquid being measured can affect the flowmeter based on its operating technology. It is important to match the calibration with the flowmeter’s application.

To learn more about flow calibration:
Read “Flowmeter Calibration Landscape: A look at today’s calibration techniques & best practices” in Flow Control Magazine.

Read the Fluke Calibration application note, “Four steps to more effective gas flow calibration.”

Read “Flow Calibration Basics” and “Selecting a Solution” on the Fluke Calibration web site.


同时我在另一份资料中也看到“be sure that it is calibrated for the liquid in use”，确实像hongwei老师所说，这个在官方校验不是很可能，但是内部的校准规程应该有相应的规定比较好！

beiwei5du

The Importance of Calibration Fluid and Conditions 3.1 Fluid properties
All flow meters interact in some way with the flowing fluid. The nature of this interaction is affected by the properties ofthe fluid or the velocity distribution of the fluid passing through the device. Changes in this interaction alter the ability ofthe device to give an accurate representation of the quantity. The magnitude of the error is different for different metertypes and fluids.
For this reason it is desirable to calibrate using the same fluid and pipework configuration within which the meter willnormally operate. This is clearly not often possible; the meter has to be installed in a test laboratory, or calibration standardhas to be installed in the process application. In either case some degree of disturbance to the meter is inevitable. Thebest economic compromise must be established in choosing the calibration. This will be based on the final duty of themeter, the required uncertainty and knowledge of the meter performance.
For some meters, for example orifice plates,the performance can be related to Reynolds number. This allows a calibration to be carried out in a fluid different to themeter’s operating fluid. The relationship may even allow a liquid calibration to be applied to a meter for a gas duty bymatching Reynolds numbers(通过相应的雷诺系数进行模拟）.For other meter types, such as turbine meters（涡街流量计））, the choice ofcalibration fluid is particularly important. Turbine meters areviscosity sensitive, and the figure opposite shows some typicalcalibration results from a turbine meter using water and threepetroleum products. Because of this sensitivity to viscosity it isimportant to calibrate these meters using a fluid as close to theviscosity of working fluid as is practicable（所以针对这类流量计的校准，尽量使用与工作流体连读相近的流体进行校准，很多时候对于涡街流量计采取on-site 校准的方式了）. For this reason, amongothers, fiscal meters for oil are often calibrated on site using adedicated pipe prover.



上文选自《good practice guide: the calibration of flow meters》http://www.tuvnel.com/_x90lbm/The_Calibration_of_Flow_Meters.pdf供大家参考！

hongwei2000

beiwei5du 发表于 2016-9-29 16:04
Flowmeter calibration: Five best practices you need to know

我只是经验之谈
毛细管黏度计也好、移液管也好
不同黏度的液体流出时间肯定不同
如果只是拿水去做完全就失去了意义
因为我们的物料的属性和水可能差得太多