The electromagnetic flowmeter has a large measuring range, usually 20:1~50:1, and the optional flow range is wide; the diameter of the electromagnetic flowmeter is wider than other types of flowmeters, from a few millimeters to 3 meters; the positive and negative two-way flow can be measured. The pulsating flow rate can also be measured as long as the pulsation frequency is much lower than the excitation frequency; the meter output is linear in nature; it is easy to select the material type of the fluid contact member, and can be applied to corrosive fluids and the like. Since the electromagnetic flowmeter measures much more with suspended solids or dirt than other flow meters, the probability of failure of the inner wall adhesion layer is relatively high. If the electrical conductivity of the adhesion layer is close to the liquid conductivity, the instrument can output the signal normally, but only change the flow area to form a hidden fault of the measurement error; if it is a high conductivity adhesion layer, the electromotive force between the electrodes will be short-circuited; if it is an insulating adhesion layer The surface of the electrode is insulated to disconnect the measuring circuit. The latter two phenomena will make the meter inoperable.
Vortex flowmeter installation requirements for straight pipe sections:
It is very important that the vortex flowmeter installation meets the requirements for straight pipe sections. Its detailed requirements are as follows:
The flowmeter has certain requirements on the upstream and downstream straight pipe sections at the installation point, otherwise it will affect the measurement accuracy.
If there is a tapered pipe upstream of the installation point of the flowmeter, there should be a straight pipe section of not less than 15D (D is the pipe diameter) upstream of the flowmeter, and a straight pipe section of not less than 5D in the downstream.
If there is a diverging pipe upstream of the installation point of the flowmeter, the upstream of the flowmeter shall have a straight pipe section of not less than 18D (D is the pipe diameter), and the downstream shall have a straight pipe section of not less than 5D.
If there is a 90° elbow or down joint upstream of the installation point of the flowmeter, there should be a straight pipe section of not less than 20D upstream of the flowmeter, and a straight pipe section of not less than 5D downstream.
If there is a 90° elbow on the same plane upstream of the installation point of the flowmeter, there should be a straight pipe section of not less than 25D upstream of the flowmeter, and a straight pipe section of not less than 5D downstream.
The flow regulating valve or pressure regulating valve should be installed as far as possible downstream of the flowmeter 5D. If it must be installed upstream of the flowmeter, the upstream of the flowmeter should have a straight pipe section of not less than 25D, and the downstream should have a straight pipe section of not less than 5D. .
If there is a piston type or plunger type pump in the upstream of the flow meter, a piston type or a Roots type fan and a compressor, the upstream of the flow meter should have a straight pipe section of not less than 25D, and the downstream should have a straight pipe section of not less than 5D.
Special attention: If the valve is installed near the upstream of the installation point of the vortex flowmeter, the valve is continuously opened and closed, which has a great influence on the service life of the flowmeter, and it is very easy to cause permanent damage to the flowmeter. The flowmeter should be avoided to be installed on the very long pipelines in overhead. After a long time, the leakage of the flowmeter can easily cause the leakage of the flowmeter to the flange. If it has to be installed, it must be in the upstream and downstream of the flowmeter. Pipe fastening devices are provided separately.
Several problems of steam metering and their solutions
Steam is one of the important energy sources for enterprise production. It is the main heat energy for urban central heating and an important indicator for economic accounting. Therefore, the accuracy of steam metering is particularly important.
In order to solve the problem of heating for employees, the company has updated the original boiler equipment, adding 4 new boilers (2 sets of 25t/h, and another 2 sets of 35t/h). The DCS realizes the automatic control of the boiler system, and the product is saturated steam.
Analysis of problems and influencing factors
Starting from the boiler ignition operation in November 2010, the steam flow often shows the maximum value, and the differential pressure signal measured by the differential pressure transmitter exceeds 20 mA. The same is true when the load is low and the actual flow is small. In this case, steam flow measurement does not provide a safety reference for boiler operation, and it cannot be used for cost accounting.
In response to this phenomenon, the design of the project uses a V-cone flowmeter, equipped with an intelligent differential pressure transmitter, and the measurement signal is sent to the DCS for calculation and display.