The choice of electromagnetic flowmeter is mainly the correct choice of the transmitter, and the converter only needs to be matched with it.
Choice of caliber and range
The diameter of the transmitter is usually the same as that of the piping system. If the piping system is to be designed, the diameter can be selected according to the flow range and flow rate. For electromagnetic flowmeters, the flow rate is suitable for 2 - 4m / s. In special cases, such as solid particles in the liquid, in consideration of wear, the optional flow rate is ≤ 3m / s, for easy to manage the fluid. Available flow rate ≥ 2m / s. After the flow rate is determined, the transmitter diameter can be determined according to qv= D2.
The range of the transmitter can be selected according to two principles: one is that the full scale of the meter is greater than the expected maximum flow value; the other is that the normal flow is greater than 50% of the full scale of the meter to ensure a certain measurement accuracy.
Temperature and pressure selection
There are certain restrictions on the fluid pressure and temperature that the electromagnetic flowmeter can measure. When used, the pressure used must be lower than the working pressure specified by the flowmeter. At present, the working pressure specifications of domestically produced electromagnetic flowmeters are:
Less than 50mm caliber, working pressure is 1.6MPa; 900 mm caliber, working pressure is 1 MPa;More than 1000mm caliber, working pressure is 0.6MPa.
If there are special requirements on the pressure resistance of the transmitter, you can negotiate with the manufacturer.
The operating temperature of the electromagnetic flowmeter depends on the lining material used, which is generally 5 - 70 ° C. Such as special treatment, can exceed the above range, such as the wear-resistant corrosion-resistant electromagnetic flowmeter produced by Tianjin Automation Instrument No.3. The transmitter allows the measured medium temperature to be -40 to 130 °C.
Selection of lining material and electrode tree material
The lining material and electrode material of the transmitter must be correctly selected according to the physical and chemical properties of the medium. Otherwise, the instrument will be damaged quickly due to the corrosion of the lining and the electrode, and the corrosive medium will easily cause an accident if it leaks. Therefore, the electrode and the lining material must be carefully selected according to the specific measurement medium in the production process.
Ultrasonic Flowmeter Introduction and Features
Definition:
Ultrasonic flow meters are meters that measure the flow by detecting the effect of fluid flow on the ultrasound beam (or ultrasound pulse).
Principle:
According to the principle of signal detection, ultrasonic flowmeter can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method and frequency difference method), beam offset method, Doppler method, cross correlation method, spatial filtering method. And noise law, etc.
Ultrasonic flowmeter is the same as electromagnetic flowmeter. It is an unobstructed flowmeter because it does not have any obstruction parts. It is a kind of flowmeter suitable for solving difficult flow measurement problems, especially in large-diameter flow measurement. The advantage is that it is one of the fastest growing types of flow meters.
Features:
Unique signal digital processing technology makes the meter measurement signal more stable, anti-interference ability and more accurate measurement.
No mechanical transmission parts are not easy to damage, maintenance-free and long life.
The circuit is more optimized and integrated; the power consumption is low and the reliability is high.
Intelligent standard signal output, friendly man-machine interface, multiple secondary signal output, for you to choose.
Pipe-type small pipe diameter measurement is economical and convenient, and the measurement accuracy is high.
Ultrasonic flowmeter common problems (1)
1. The ultrasonic flowmeter probe is used for a period of time, and irregular alarms may occur. This problem is more common when there are more impurities in the transport medium. Solution: Clean the probe regularly (recommended once a year).
2. When the ultrasonic flowmeter transport medium contains liquid impurities such as water, the flow metering tube is prone to effusion, and the freezing of the pressure tube may occur when the temperature is low, especially in the northern regions in winter. Solution: Purge or electrify the pressure tube
3, the ultrasonic flowmeter is very strict on the requirements of the pipeline, there can be no abnormal noise, otherwise it will affect the measurement error.
During the propagation of ultrasonic waves, their strength is attenuated due to obstruction or absorption by impurities in the medium and medium. Whether it is an ultrasonic flowmeter or an ultrasonic level gauge, there is a certain requirement for the received sound wave intensity, so various attenuations are suppressed.
4. What is the instantaneous flow fluctuation?
The signal strength is large, and the measured fluid fluctuation is large.
Solution: Adjust the probe position, improve the signal strength, and ensure the signal strength is stable. If the fluid fluctuation is large, the position is not good. Re-select the point to ensure the 5D working condition after the first 10D.