Vortex flow meter is mainly used for industrial piping medium fluid flow measurement, vortex flow meter is widely used in petroleum, chemical, metallurgical, thermal, textile, paper and other industries of superheated steam and saturated steam, compressed air and gas, water and liquid measurement and control. Temperature and pressure affect a lot of the volume of saturated steam and superheated steam.
1. Preset the steam density
Firstly, the working parameters of steam -- temperature and pressure were determined. The density of steam under working state was determined by vortex shedding flow meter according to working parameters, and the density was taken as the only density of steam in the future flow measurement process. In the work, the actual change of steam is no longer compensated or corrected, which is called Preset the steam density calculation compensation method.
The accuracy of steam flow measurement can be guaranteed if the working temperature and pressure are consistent with the preset values at design time. If the parameters deviate or even deviate greatly in actual working conditions, the accuracy of the vortex steam flow meter will become very poor.
Preset the steam density, the measurement method adopted at the initial stage of the development of automatic detection technology, has a large error in measurement results, which can be used as a rough measurement.
2. Online density compensation method
The wide application of microelectronics technology in flow instruments has been realized. The calculation function, compensation and correction function, accumulation function, historical data storage function, digital filtering function, output function and digital communication function of vortex street flow meter can be easily realized. The on-line density compensation has been widely used as an essential basic function of steam flow meter. The following article introduces the classification of steam density compensation:
a.Online density compensation for saturated steam.
Vortex flow meter can realize integrated temperature and pressure compensation, and there is a strict correspondence between the temperature and pressure of saturated steam. The density of saturated vapor is unique under certain temperature and pressure. According to the temperature or pressure value of saturated steam, the real-time density value can be obtained by looking up the table method or formula calculation method (IFC1967 or iapw-1997).
In flow measurement, vortex flow meter can choose temperature compensation or pressure compensation to realize saturated vapor flow measurement. Some brand vortex flow meter has built-in temperature or pressure sensor to detect the temperature or pressure value and then the intelligent flow meter calculate the compensation.
If the built-in temp or pressure compensation vortex meter is expensive, you can also choose pressure sensor or temperature sensor (RTD sensor) to realize temperature and pressure compensation.
b.Online density compensation for superheated steam
Superheated steam is a kind of steam with special quality obtained by reheating saturated steam. It breaks the strict correspondence between temperature and pressure inherent in saturated steam. The superheated steam can be regarded as a single medium in the flow measurement process of vortex street flow meter. Under different temperature and pressure, then density is different. If we want to realize compensation of superheated vapor ,we should get accurate steam temperature and pressure value. We can have external temperature sensor (such as RTD temperature sensor) and pressure transmitters, equip together with flow computer to calculate accurate mass flow measurement of superheated steam.
Some brand vortex shedding flow meters can even have built-in temperature sensor and pressure detector, which will save a lot installation work for the users in steam flow measurement.