An electromagnetic flowmeter is a standard flow measurement instrument. With the rapid development of modern fine chemical technology, more and more widely used in petrochemical, paper, metallurgy, environmental protection, food, and other industrial fields. An electromagnetic flowmeter is used for fluid monitoring of complex industrial pipeline systems, real-time monitoring of the system’s raw materials and finished products, providing the basis for automated system control.
As the electromagnetic flowmeter distribution, its operating environment is more complex, its installation process is likely to affect its working conditions and the chance of failure, thus affecting the operation of the entire instrument control system. Therefore, our analysis of the principle of electromagnetic flowmeter, installation process research, commissioning technology, and continuous summary and update.
1. Selection of the Electromagnetic flowmeters
1.1 Size selection
When choosing an electromagnetic flowmeter, we usually use the nature of the fluid, the flow rate, and other factors to determine its selection diameter.
Generally speaking, when the pipeline flow rate is 0.5 ~ 1.5m / s for the economic flow rate, if the fluid medium on the sidewall abrasiveness is small, we recommend a long-term flow rate greater than 3m / s, but should be less than 7m / s, when you can choose less than the diameter of the flow meter.
1.2 Selection of lining materials
Electromagnetic flow meters are mainly used to measure the flow of fluid substances. Different lining materials should be selected according to the corrosive, abrasive, temperature, and condensation characteristics of the material to be measured.
The lining materials generally used in electromagnetic flowmeters and their characteristics are described below.
1.2.1 Natural rubber
which is resistant to temperatures ranging from -10 to 70 degrees Celsius, with good resistance to abrasion and insulation and average corrosion resistance.
which has better elasticity and is more resistant to wear than natural rubber but is less resistant to cold.
1.2.3 Polyurethane rubber
which can be used at lower temperatures than natural rubber, up to -252℃.
which is more resistant to high temperatures and wear than natural rubber and has pretty good oil resistance but is less flexible.
PTFE, a type of plastic, has excellent resistance to acids and alkalis but is less resistant to the corrosion of non-conventional substances such as fluorine, oxygen, and ozone, and negative pressure, and is less resistant to wear tear.
1.3 The selection of electrode material
When choosing the electromagnetic flowmeter, we should be based on precision requirements, the measured corrosive, price affordability to the electrode material selection. The electrode of the electromagnetic flowmeter is mounted on the pipe’s inner wall, which is in direct contact with the measured material, so we should select according to the corrosiveness of the rhythmic material.
Materials generally used in the manufacture of electrodes include: titanium (Ti), strong acid-resistance; button (Ta), high measurement accuracy; pincer-Yi (Pt-Yi) alloy, strong corrosion-resistance; Hastelloy C (HC), they can be used for high-temperature hypochlorite, sulphuric acid, nitric acid measurement; 316L, general corrosion resistance, but the low price.
1.4 Selection of other parameters
The choice of electromagnetic flowmeter should also consider the protection level, connection flange and cable, and other factors. Electromagnetic flowmeter connection flange selection should be determined according to the pipeline, especially for the corrosive fluid pipeline, which does not allow arbitrary field processing of the pipeline welding, so we should be careful to choose.
2. Electromagnetic flowmeter wiring and commissioning
When we connect the electromagnetic flowmeter before, we should confirm its installation orientation, the direction is accurate, and to clean the site, no accumulation of dust before wiring. The wiring of the electromagnetic flowmeter includes the connection of the power supply line, the input/output signal line, the sensing signal line, and the working earth line. The integrated wiring is shown in the diagram.
In the above wiring process, we should pay attention to the wiring of the following types of lines.
2.1.1 Input / output signal
Most of the electromagnetic flowmeter can be programmed through the external PLC, detection, and communication bus to accept the central control system input instructions, so the electromagnetic flowmeter set up a signal input contact, the measured value of the critical alarm instructions, and other access points. The outgoing signal can be connected via an analog issue or combined with the outgoing signal via the RS-232 communication interface to the PC.
2.1.2 Sensor connections
Suppose the sensor and the flowmeter are mounted in a separate unit. In that case, a connection is also required between the flowmeter and the sensor for passing the sensed current through the measurement terminal of the flowmeter (actually a magnetic pole and voltage measurement unit), which is used to measure the various parameters to be measured.
2.1.3 Grounding line
As the operating current of the electromagnetic flowmeter is very small, it is very susceptible to interference from changes in the external electric field. So its power supply and signal lines must be matched with grounding lines to ensure the accuracy of the measurement data and to eliminate frequent oscillations in the measurement process.
2.2.1 Before commissioning, inspection, and preparation
Electromagnetic flowmeter in the commissioning before, we should be a thorough inspection of the pipeline and flowmeter, including pipeline debris and other clean-up. The oily media pipeline also needs to be dry treatment.
Commissioning before the inspection also includes the review of the electrical circuit. First of all, the grounding of the line should be tested to ensure that the grounding is reliable before other lines can be tested and inspected to avoid the capacitive effect of the line, the storage of electricity, or measuring power to produce destructive results the instrument. In addition, insulation resistance and earth resistance tests should also be carried out.
2.2.2 Water commissioning
Whether the instrument is measuring aqueous media, mixed liquids, or oily press, we should simulate the measuring medium’s temperature, pressure, and flow rate before commissioning. If abnormalities occur during the water test or parameters are missing, the instrument should be tested individually or sent out for calibration.
2.2.3 System commissioning
Electromagnetic flowmeter in a single function through the water test, control the host of various preparatory commissioning is completed, the system can be commissioned. Oily medium pipelines need to be dried before the measured medium can be passed into the system operation.
To improve the performance of the electromagnetic flowmeter in the industrial pipeline control system, we need to use the professional method in the instrument selection, installation process adjustment, testing, and other aspects of the summary. We can improve the industrial pipeline control system in the electromagnetic instrument installation. The commissioning success rate has accumulated some technical experience. For the industrial pipeline control system to a higher degree of integration, automation provides a practical experience.