1 General Things to Note When Using Liquids The conductivity should have the conductivity required for the measurement and the conductivity distribution should be substantially uniform. Therefore, the flow sensor installation should avoid the place where the conductivity is not uniform, for example, the liquid is added near the upstream, and the liquid addition point is preferably located downstream of the sensor.
The sensor tube must be filled with liquid when in use (except for non-full tube type). When mixed, the distribution should be roughly uniform.
The liquid should be at the same potential as the ground and must be grounded. For example, when the process pipe is made of an insulating material such as plastic, the liquid is transported to cause rubbing static electricity and the like, causing a potential difference between the liquid and the ground.
2 flow sensor installation
1) Installation location Generally, the electromagnetic flowmeter sensor housing protection is extremely IP65 (dust-proof and dust-proof grade specified in GB4208), and all the following requirements are imposed on the installation site.
1) When measuring the mixed phase fluid, select the place that will not cause phase separation; when measuring the two-component liquid, avoid the downstream of the mixture that has not been uniformly mixed; when measuring the chemical reaction pipeline, it should be installed downstream of the fully completed reaction section;
2) Avoid changing the inside of the measuring tube into negative pressure as much as possible;
3) Choose a place with small vibration, especially for integrated instruments;
4) Avoid large motors and large transformers nearby to avoid electromagnetic field interference;
5) It is easy to realize the place where the sensor is grounded separately;
6) Avoid high concentrations of corrosive gases in the surrounding environment as much as possible;
7) The ambient temperature is in the range of -25/-10~50/600 °C, and the integral structure temperature is also subject to electronic components, and the range is narrower;
8) The relative humidity of the environment is in the range of 10% to 90%;
9) Avoid direct sunlight as much as possible;
10) Avoid rain and immersion without being immersed in water.
If the degree of protection is IP67 (dust-proof and flood-proof) or IP68 (dust-proof and snorkel-proof), the above requirements 8) and 10) are not required.
(2) The length of the straight pipe is required to obtain the normal measurement accuracy. The electromagnetic flowmeter 90o elbow, T-shaped pipe, concentric reducer, and full-opening valve are usually considered as far from the electrode center line (not the sensor inlet end connection surface). For straight pipe lengths of 5d diameter, 10D for different opening valves; (2~3)D for downstream straight pipe or no requirement; however, prevent the butterfly valve disc from protruding into the measuring tube of the sensor. The lengths of the upstream and downstream straight pipe sections proposed by various standards or verification procedures are also inconsistent. As shown in Table 2, the requirements are higher than usual. This is due to the requirement to ensure that the current 0.5-level precision instrument is achieved.
Spoiler name standard or verification procedure number
ISO 6817
ISO 9104
JIS B7554
ZBN 12007
JJG 198
Upstream bend, tube, full open gate, taper
10D or manufacturer regulations
10D
5D
5D
10D
The reducer can be regarded as a straight tube and other various valves
10D
Downstream types are not required to ask for 5D
Not required 2D 2D
If the valve can be opened, it should be installed at an angle of 45o from the electrode axis and the additional error can be greatly reduced.
(3) Installation position and flow direction Sensor installation direction can be horizontal, vertical or inclined, without restriction. However, it is preferred to measure the solid-liquid two-phase fluid vertically and to flow from bottom to top. This can avoid the disadvantages of severe local wear of the lower half of the lining during horizontal installation and solid phase precipitation at low flow rates.
When installing horizontally, make the electrode axis parallel to the horizon, not perpendicular to the horizon, because the electrode at the ground is easily covered by the deposit, and the top electrode is easily wiped by the occasional bubbles in the liquid to cover the surface of the electrode, causing the output signal to fluctuate. . In the piping system shown in Figure 5, c and d are suitable positions; a, b, and e are unsuitable positions, liquid may not be filled at b, gas may accumulate at a and e, and short pipe may not be filled after sensor at e The discharge port is preferably as shown in the shape of f. It is also unsuitable for the solid-liquid two-phase flow c.
(4) Bypass pipe, easy to clean connection and preset inlet hole In order to check and adjust the zero point when the process pipe continues to flow and the sensor stops flowing, a bypass pipe should be installed. However, large-diameter pipe systems are often difficult to handle due to investment and location constraints. It is difficult to correct the measured value according to the degree of electrode contamination or to determine a pollution level that does not affect the measured value. In addition to the above, the use of non-contact electrodes or instruments with a scraper to remove the electrodes of the device can solve some problems. In addition, if it is necessary to remove the inner wall attachments, it can be removed in place without removing the sensor as shown in Figure 6.
For pipes with a pipe diameter greater than 1.5 to 1.6 m, the pipe is placed on the pipe near the EMF, so that the inner wall of the sensor measuring pipe is cleaned when the pipe system stops running.
(5) Installation of fluoroplastic lining sensors for negative pressure piping systems shall be applied with caution to negative pressure piping systems; positive pressure piping systems shall be protected against negative pressure, such as piping with liquid temperatures above room temperature, shutting off the upstream and downstream shut-off valves of the sensor. After the operation, the fluid cooling contraction will form a negative pressure, and a negative pressure prevention valve should be installed near the sensor, as shown in Fig. 7. There are manufacturers that PTFE and PFA plastic linings can be used in negative pressure piping systems. The absolute pressures used at 200C, 1000C, and 1300C must be greater than 27, 40, and 50KPa, respectively.
(6) The grounding sensor must be grounded separately (grounding resistance 100Ω or less). In principle, the grounding should be on the sensor side and the converter grounding should be at the same grounding point. If the sensor is installed on the cathodic corrosion protection pipe, in addition to the grounding of the sensor and the grounding ring, it is also necessary to use a thicker copper wire (16mm2) over the two connecting flanges of the sensor jumper pipe to make the cathodic protection current between the sensors. isolation.
Sometimes the stray current is too large. If the leakage current of the electrolytic cell along the electrolyte affects the normal measurement of the EMF, the method of electrically isolating the flow sensor from the process connected thereto can be adopted. This method can also be used on cathodic protection lines where the cathodic protection current affects EMF measurements.
3. Converter installation and connection cable integrated EMF No separate installation of the converter; separate converter installed near the sensor or instrument room, the choice of room is larger, the environmental conditions are better than the sensor, the protection level is IP65 or IP64 (dustproof Splash level). The requirements for the installation site are the same as those of 3), 4), 6), 8), 9), and 10) in (1) of Section 7.2. The ambient temperature is limited by the electronic components, and the temperature range is higher than that specified in 7). Narrower.
The distance between the converter and the sensor is limited by the conductivity of the measured medium and the type of signal cable, ie the distributed capacitance of the cable, the cross-section of the conductor and the number of shields. Use the signal cable attached to the instrument (or the specified model) from the manufacturer. When the conductivity is low and the transmission distance is long, a three-layer shielded cable is also specified. The general instrument "Instruction Manual" gives the corresponding transmission distance range for different conductivity liquids. Single-layer shielded cables are used for industrial water or acid-base fluids with a distance of 100m.
In order to avoid interference signals, the signal cable must be worn separately in the grounding protection steel tube. The signal cable and power cable cannot be installed in the same steel pipe. There is also a length of straight pipe section upstream of the sensor, but its length is lower than most other flow meters.
The sensor tube must be filled with liquid when in use (except for non-full tube type). When mixed, the distribution should be roughly uniform.
The liquid should be at the same potential as the ground and must be grounded. For example, when the process pipe is made of an insulating material such as plastic, the liquid is transported to cause rubbing static electricity and the like, causing a potential difference between the liquid and the ground.
2 flow sensor installation
1) Installation location Generally, the electromagnetic flowmeter sensor housing protection is extremely IP65 (dust-proof and dust-proof grade specified in GB4208), and all the following requirements are imposed on the installation site.
1) When measuring the mixed phase fluid, select the place that will not cause phase separation; when measuring the two-component liquid, avoid the downstream of the mixture that has not been uniformly mixed; when measuring the chemical reaction pipeline, it should be installed downstream of the fully completed reaction section;
2) Avoid changing the inside of the measuring tube into negative pressure as much as possible;
3) Choose a place with small vibration, especially for integrated instruments;
4) Avoid large motors and large transformers nearby to avoid electromagnetic field interference;
5) It is easy to realize the place where the sensor is grounded separately;
6) Avoid high concentrations of corrosive gases in the surrounding environment as much as possible;
7) The ambient temperature is in the range of -25/-10~50/600 °C, and the integral structure temperature is also subject to electronic components, and the range is narrower;
8) The relative humidity of the environment is in the range of 10% to 90%;
9) Avoid direct sunlight as much as possible;
10) Avoid rain and immersion without being immersed in water.
If the degree of protection is IP67 (dust-proof and flood-proof) or IP68 (dust-proof and snorkel-proof), the above requirements 8) and 10) are not required.
(2) The length of the straight pipe is required to obtain the normal measurement accuracy. The electromagnetic flowmeter 90o elbow, T-shaped pipe, concentric reducer, and full-opening valve are usually considered as far from the electrode center line (not the sensor inlet end connection surface). For straight pipe lengths of 5d diameter, 10D for different opening valves; (2~3)D for downstream straight pipe or no requirement; however, prevent the butterfly valve disc from protruding into the measuring tube of the sensor. The lengths of the upstream and downstream straight pipe sections proposed by various standards or verification procedures are also inconsistent. As shown in Table 2, the requirements are higher than usual. This is due to the requirement to ensure that the current 0.5-level precision instrument is achieved.
Spoiler name standard or verification procedure number
ISO 6817
ISO 9104
JIS B7554
ZBN 12007
JJG 198
Upstream bend, tube, full open gate, taper
10D or manufacturer regulations
10D
5D
5D
10D
The reducer can be regarded as a straight tube and other various valves
10D
Downstream types are not required to ask for 5D
Not required 2D 2D
If the valve can be opened, it should be installed at an angle of 45o from the electrode axis and the additional error can be greatly reduced.
(3) Installation position and flow direction Sensor installation direction can be horizontal, vertical or inclined, without restriction. However, it is preferred to measure the solid-liquid two-phase fluid vertically and to flow from bottom to top. This can avoid the disadvantages of severe local wear of the lower half of the lining during horizontal installation and solid phase precipitation at low flow rates.
When installing horizontally, make the electrode axis parallel to the horizon, not perpendicular to the horizon, because the electrode at the ground is easily covered by the deposit, and the top electrode is easily wiped by the occasional bubbles in the liquid to cover the surface of the electrode, causing the output signal to fluctuate. . In the piping system shown in Figure 5, c and d are suitable positions; a, b, and e are unsuitable positions, liquid may not be filled at b, gas may accumulate at a and e, and short pipe may not be filled after sensor at e The discharge port is preferably as shown in the shape of f. It is also unsuitable for the solid-liquid two-phase flow c.
(4) Bypass pipe, easy to clean connection and preset inlet hole In order to check and adjust the zero point when the process pipe continues to flow and the sensor stops flowing, a bypass pipe should be installed. However, large-diameter pipe systems are often difficult to handle due to investment and location constraints. It is difficult to correct the measured value according to the degree of electrode contamination or to determine a pollution level that does not affect the measured value. In addition to the above, the use of non-contact electrodes or instruments with a scraper to remove the electrodes of the device can solve some problems. In addition, if it is necessary to remove the inner wall attachments, it can be removed in place without removing the sensor as shown in Figure 6.
For pipes with a pipe diameter greater than 1.5 to 1.6 m, the pipe is placed on the pipe near the EMF, so that the inner wall of the sensor measuring pipe is cleaned when the pipe system stops running.
(5) Installation of fluoroplastic lining sensors for negative pressure piping systems shall be applied with caution to negative pressure piping systems; positive pressure piping systems shall be protected against negative pressure, such as piping with liquid temperatures above room temperature, shutting off the upstream and downstream shut-off valves of the sensor. After the operation, the fluid cooling contraction will form a negative pressure, and a negative pressure prevention valve should be installed near the sensor, as shown in Fig. 7. There are manufacturers that PTFE and PFA plastic linings can be used in negative pressure piping systems. The absolute pressures used at 200C, 1000C, and 1300C must be greater than 27, 40, and 50KPa, respectively.
(6) The grounding sensor must be grounded separately (grounding resistance 100Ω or less). In principle, the grounding should be on the sensor side and the converter grounding should be at the same grounding point. If the sensor is installed on the cathodic corrosion protection pipe, in addition to the grounding of the sensor and the grounding ring, it is also necessary to use a thicker copper wire (16mm2) over the two connecting flanges of the sensor jumper pipe to make the cathodic protection current between the sensors. isolation.
Sometimes the stray current is too large. If the leakage current of the electrolytic cell along the electrolyte affects the normal measurement of the EMF, the method of electrically isolating the flow sensor from the process connected thereto can be adopted. This method can also be used on cathodic protection lines where the cathodic protection current affects EMF measurements.
3. Converter installation and connection cable integrated EMF No separate installation of the converter; separate converter installed near the sensor or instrument room, the choice of room is larger, the environmental conditions are better than the sensor, the protection level is IP65 or IP64 (dustproof Splash level). The requirements for the installation site are the same as those of 3), 4), 6), 8), 9), and 10) in (1) of Section 7.2. The ambient temperature is limited by the electronic components, and the temperature range is higher than that specified in 7). Narrower.
The distance between the converter and the sensor is limited by the conductivity of the measured medium and the type of signal cable, ie the distributed capacitance of the cable, the cross-section of the conductor and the number of shields. Use the signal cable attached to the instrument (or the specified model) from the manufacturer. When the conductivity is low and the transmission distance is long, a three-layer shielded cable is also specified. The general instrument "Instruction Manual" gives the corresponding transmission distance range for different conductivity liquids. Single-layer shielded cables are used for industrial water or acid-base fluids with a distance of 100m.
In order to avoid interference signals, the signal cable must be worn separately in the grounding protection steel tube. The signal cable and power cable cannot be installed in the same steel pipe. There is also a length of straight pipe section upstream of the sensor, but its length is lower than most other flow meters.
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