In the history of the development of flow measurement and testing technology, flow and device verification technology are the two major themes of flow measurement. At present, what hinders the development of flow measurement technology is the lag between flow meter verification technology and flow device.
The main reason is that people are not paying enough attention and the measures are not effective enough; the objective reason is that the construction of a high-accuracy, large-range flow standard device requires huge manpower and material resources, and it is not a short-term effort.
Over the years, through practice and investigation, it has been discovered that the device established with the original standard and standard meter method has expanded the measurement limit and promoted the development of flow measurement technology.
The purpose of the flowmeter verification is to determine whether the main characteristics of the flowmeter in actual use meet the technical requirements, but the verification of the flowmeter is generally required to be carried out under specific conditions, so the following problems will occur:
(1) The influence of the physical properties of the verification medium on the characteristics of the flowmeter;
(2) The influence of the flow characteristics of the fluid on the characteristics of the flowmeter;
(3) Traceability and consistency of flow value.
Only by solving these problems, can the metering characteristics of the flowmeter verified in the laboratory be transformed into the characteristics of the flowmeter on-site. In this regard, the majority of engineering and technical personnel for flow measurement and testing are still making continuous efforts.
There are several verification methods for flow meters:
(1) Direct measurement method: A measurement method that compares the quantity to be inspected with the standard quantity. The flow meter is calibrated on the flow standard device, and the flow standard amount on the device is compared with the displayed value of the tested flow meter.
(2) Indirect measurement method: A method to determine the measured value by measuring other quantities that have a functional relationship with the measured value. For example, the throttling differential pressure flowmeter adopts the verification of the geometric size of the throttling device and the relevant parameters of the fluid to determine the flow value, which is an indirect measurement method.
(3) Comprehensive measurement method: use similar models to simulate and verify the actual fluid first, and then use similar principles to calculate. When the throttling device has a large pipe diameter DN >1000mm, or larger pipe diameter, large flow, special media, and flow under special conditions, it is difficult to use direct or indirect methods to verify this method.
The verification of the gas turbine flowmeter is divided into normal pressure verification and high-pressure verification according to the pressure at the time of verification. Under normal conditions of use, verification is generally performed under normal pressure, but sometimes it is also under high pressure if required by the customer or for other purposes.
Since gas turbine flow meters have a large measurement range, the standard meter method is usually used to verify gas turbine flow meters. The standard devices involved generally include velocity flow meters, critical flow meters, mass flow meters, and positive displacement flow meters. , By them alone or in combination to complete the measurement of each flow point within the range of the gas turbine flowmeter. For turbine flow meters with smaller calibers (DN80 and below), bell-jar type gas standard devices can also be used for verification.
A turbine flow meter is a flow measuring instrument. The power of the flowing fluid drives the turbine blades to rotate, and the rotation speed of the turbine is approximately proportional to the volume flow. The volume of fluid passing through the flow meter is based on the number of revolutions of the turbine wheel.