The principle of type selection of flow meter
Flow meter according to the need of production requirements, from the medium of the flow characteristics and the reality of flows, considering the safety of the measurement. Accuracy and economy, reasonable choose and take pressure rotor of measuring instrument of form and specifications.
First to ensure the safe and reliable measuring way, that is, not in the running accident caused by the failures of the mechanical strength and electrical circuit; Second instrument flow meter in normal production and living failure cases such as does not affect the safety of the production system. , therefore, the general preference in standard throttle device, and don't choose insert flowmeter non-standard devices such as low level of structure strength of the target flowmeter and the turbine flowmeter, etc.
Environmental conditions on the flow type and its vital role, flammable and explosive occasions should choose explosion-proof instrument flow meter; In order to guarantee the service life of the meter and the accuracy, and model selection of the flow meter of vibration control requirements; Selection when must give full consideration to the physical and chemical properties of measured medium. The degree of pressure gauges should be slightly more than the working pressure of measured medium, generally choose 1.25 times, in order to make sure no disclosure or an accident.
Scale range (a common traffic), maximum flow rate, the choice of the main is the maximum range of choice. Is too small easy to overload, damage the instrument; Too much impedes the accuracy of the measurement. General optional for the actual operation of 1.2 ~ 1.3 times that of the maximum flow rate.
Installed on the pipeline operation contact instrument for a long time, should also be cary the flow measurement device of capacity loss. In general, not in the same production line should choose pressure loss of the multiple large measuring, such as throttling.
By the fluid properties and flow formula illuminates the flowmeter types used by different operating conditions and selection should pay attention to matters. For incompressible fluids, such as water, is not to need to consider when measuring the flow temperature pressure compensation; For compressible fluids, such as steam, flue gas, effects of temperature, pressure compensation should be fully considered. So when designing compressible fluid flow, city traffic increases the pressure and temperature of sensor design, press for temperature compensation.
Selection guidelines:
One, the determination of diameter: sensor size is different, its measuring range is different, and each kind of caliber of its measuring range and with the type of measured medium and condition of the change of temperature and pressure changes. For saturated steam, determine the condition of either of the temperature and pressure and flow range, roughly determine the calibre of the sensor; For superheated steam, determine the condition of temperature and pressure, through the magnetic density and flow range roughly determine the sensor size. For gas and liquid level, when the condition is not in the table of the medium or used for other medium, the flow measurement range is affected by medium density and viscosity.
Second, determine the appropriate configuration:
1, determine to use remote or scene shows;
2, choose remote transmission type, if it is saturated steam, win select automatic temperature compensation density or pressure automatic compensation density; If it is a superheated steam, colleagues should choose to temperature and pressure compensation density; According to the actual situation to determine whether other media need to compensation; If required measurement accuracy is not high, the constant temperature or pressure, optional fixed pressure or temperature compensation, also can be fixed density compensation.
3, choice of intelligent flow totalizer.especially should consider whether you need a communication interface.
4, choose, intelligent flow totalizer.especially should consider whether to need to provide meter box, will be placed among them, the intelligent flow totalizer.especially set parameter adjust to prevent.
5,, no matter choose which kinds of intelligent flow totalizer.especially should consider whether to need to configure the backup power supply, so that all of a sudden power failure meter can be measured normal.
6, choose remote transmission type, no process should consider whether to need to wireless traffic monitoring system, realize real-time monitoring and management of the pipeline flow.
7, if the medium to be measured is flammable and explosive substances or measuring flammable and explosive gas environment, should choose the explosion-proof type sensor and explosion-proof type measuring system.
Three, selection of vortex flowmeters, for example:
Example 1: industrial pipe diameter for DN100, medium for saturated steam, gas is about 0.5 t/h, gauge pressure is 0.4 MPa, please select a meter diameter.
Solution: according to the table press pressure is 0.5 MPa to 0.4 MPa know, Chad temperature 152 ℃, the DN100 flow range is 0.4 to 3.5 t/h, can fully meet the demands, so choose the diameter for the DN100 vortex flow sensor. If gas is about 0.3 t/h - 2 t/h, should choose diameter for DN80 vortex flow sensor, then the DN100 reducing to DN80 process piping.
Example 2: the process piping diameter as the DN100, medium for superheated steam, gas is about 0.5 t/h - 2.8 t/h, gauge pressure is 0.5 Mpa, the temperature is 220 ℃, please select a meter diameter.
Solution: according to the pressure and temperature, pressure is 0.5 Mpa, the temperature is 220 ℃ when the density is 2.66, the DN100 flow range is 0.40 to 3.50 t/h, can fully meet the demands, so choose the diameter for the DN100 vortex flow sensor. If gas is about 0.3 to 2.0 t/h, should choose diameter for DN80 vortex flow sensor, the process piping should be shrink tube processing.