1. Requirements for straight pipe sections
Inlet/outlet straight pipe section: inlet should be ≥10×DN; outlet should be ≥5×DN
2. Grounding point requirement
In order to make the instrument work reliably, improve the measurement accuracy, free from external parasitic potential / the sensor should have good grounding, the grounding resistance is less than 10. (If the metal pipe is well grounded, no special grounding device is required) 3.3 Pair installation Location requirements as shown
Insert the electromagnetic flowmeter according to the situation of the pipeline in the field. If the flowmeter without the ball valve is installed, it should be installed on the pipeline without overpressure (that is, the flowmeter without the ball valve can be installed without pressure), and the hole is opened in the pipeline. Diameter 50, ready to weld the connecting welded pipe to the opening of the pipe; for occasions requiring constant flow loading or unloading or no media spillage, a ball valve must be installed, that is, a plug-in electromagnetic flowmeter with a ball valve structure is selected; With a diameter of 50, it is ready to weld the connecting welded pipe to the opening of the pipe.
Measuring range : Recommended range: 0.5m/s to 10m/s continuously adjustable. Maximum use range: continuously adjustable from 0.2m/s to 15m/s
Signal output: 1, the switch quantity can be set to: pulse output (up to 1000HZ); high/low flow alarm; empty pipe alarm; flow direction indication;
Fault alarm; 2, current output: 4-20mA output
Configuration method: 1. Field configuration through three manual keys. 2. Field configuration via remote control. 3. Perform on-site configuration through the handheld communicator.
Memory: The memory that the EEPROM does not disappear, no battery saving.
Vortex flowmeter common fault
1. The measurement range of the vortex flowmeter is large, generally 10:1, but the lower limit of measurement is limited by many factors: Re>10000 is the most basic condition for the operation of the vortex flowmeter. In addition, it is also responded by the vortex. The signal, the vortex frequency f is also small, and it also makes signal processing difficult. The upper limit of measurement is the frequency response of the sensor and the frequency limit of the circuit. Therefore, the flow rate range must be calculated and calculated according to the flow rate of the fluid. The environmental conditions on the site are complicated. In addition to the conditions such as ambient temperature, humidity, and atmosphere, electromagnetic interference should also be considered.
2, vibration is also a big enemy of this type of instrument. Therefore, care should be taken to avoid mechanical vibrations, especially the lateral vibration of the pipe (perpendicular to the pipe axis and the vertical vortex generating body axis). This effect cannot be suppressed and eliminated in the design of the flowmeter structure. Since the vortex signal is equally sensitive to the influence of the flow field, it is not suitable for the length of the straight pipe section to ensure the flow conditions necessary for stabilizing the vortex street. Even the capacitive and ultrasonic type with strong anti-vibration performance guarantees that the fluid is a fully developed one-way flow, which is not negligible.
The medium temperature also has a great influence on the performance of the vortex flowmeter. For example, the pressure stress type vortex flowmeter cannot be used for a long time at 300 °C, because its insulation resistance is rapidly reduced from 10-100 MΩ at normal temperature to 1-101 Ω, and the output signal is also small, resulting in deterioration of measurement characteristics. In the measurement system, the sensor and the converter should be installed separately to avoid long-term high temperature affecting the reliability and service life of the instrument. The vortex flowmeter is a relatively new type of flowmeter. It is in the development stage and is not very mature. If it is not properly selected, the performance will not work well. Only after reasonable selection and correct installation, it is necessary to carefully and regularly maintain during the use process, accumulate experience, improve the predictability of system failure and the ability to judge and deal with problems, so as to achieve satisfactory results.
Ultrasonic flowmeter measurement principle
When the ultrasonic beam propagates in the liquid, the flow of the liquid will cause a small change in the propagation time, and the change in the propagation time is proportional to the flow velocity of the liquid, and its relationship conforms to the following expression.
θ is the angle between the sound beam and the direction of flow of the liquid
M is the number of linear travels of the sound beam in the liquid
D is the inner diameter of the pipe
Tup is the propagation time of the sound beam in the positive direction
Tdown is the propagation time of the sound beam in the reverse direction
Let the speed of sound in the stationary fluid be c, the velocity of the fluid flow be u, and the propagation distance be L. When the sound wave is in the same direction as the fluid flow direction (ie, the downstream direction), the propagation velocity is c+u; otherwise, the propagation velocity is cu. Two sets of ultrasonic generators and receivers (T1, R1) and (T2, R2) are placed at two places separated by L. When T1 is in the forward direction and T2 transmits ultrasonic waves in the reverse direction, the time required for the ultrasonic waves to reach the receivers R1 and R2 respectively is t1 and t2, then
Since the flow velocity of the fluid in the industrial pipeline is much smaller than the sound velocity, that is, c>>u, the time difference between the two is ▽t=t2-t1=2Lu/cc. Thus, the propagation velocity of the acoustic wave in the fluid is known. When it is known, the flow rate u can be obtained by measuring the time difference ▽t, and the flow rate Q can be obtained. The method of measuring the flow using this principle is called the time difference method. In addition, a phase difference method, a frequency difference method, or the like can be used.