Various problems and solutions for flowmeters in automated instrumentation engineering

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The image is in the attachment; the Word document allows you to view the image. . . . Table of Contents 1. Flow rate issues related to instruments.... 2 1.1 Problems with flow measurement and transmission.... 2 1.2 How to handle flow measurement in multiple workshops when multiple flow meters are installed in the same pipeline... 2 1.3 Vortex flow meters.... 2 1.4 Electromagnetic flow meters.... 6 1.5 Mass flow meters.... 9 1.6 Differential pressure flow measurement.... 9 1.6.1 Orba flow meter [for other gases]... 9 1.6.2 Anti-clogging composite anemometry device (used in conjunction with differential pressure transmitters) [Liaoning Focus Technology].... 13 1.7 Ultrasonic flow meters.... 14 1.7.1 Poor signal quality of ultrasonic flow meters... 14 1.8 Float flow meters.... 15 1. Flow rate issues related to instruments 1.1 Three major challenges in flow measurement and transmission. l Two flow meters were installed on the same pipeline, with different flow values, which caused problems with flow measurement in Workshop 2. There is a discrepancy between the cumulative flow value and the calculated volume value of the liquid level; the cumulative flow value for the material discharged from the tank does not match the cumulative volume value of the liquid level. Conversion between tank volume and liquid level, calibration of the head. 1.2 How to handle the issue of measuring flow in multiple workshops using multiple flow meters installed on the same pipeline. PS1: Inconsistent readings from ultrasonic flow meters and electromagnetic flow meters. Example: During calibration, it was found that there were significant discrepancies among three flow meters installed on the same pipeline. Our project involved a water treatment plant; there was one flow meter for measuring raw water, and two more flow meters inside the plant, all located on the same pipeline. Electromagnetic flow meters were used inside the plant, with pipe diameters of 1400 mm and 1200 mm respectively. An ultrasonic flow meter of the clamp-type was installed on the side where the water entered the plant. The errors produced by the two flow meters inside the plant were quite large, and these errors increased as the flow rate increased; it was not clear which meter was giving accurate readings. As a result, another ultrasonic flow meter was installed, but its readings were always somewhere between those of the two electromagnetic flow meters. If the flow rate indicated by the electromagnetic flow meters at the upstream end was 1700, then it was roughly 1200 at the downstream end, resulting in a difference of 500. The pipes were also degassed, and separate grounding was provided to ensure that the zero point did not shift. I just can’t find the cause, which is really frustrating. I’ve tried communicating with the manufacturer, but there’s still no solution. Tomorrow, when their people arrive, we’ll see what can be done. 1. Suggested solution: Different models result in varying ranges and precisions, which in turn lead to differences in errors. For instruments related to trade measurement between the two parties, to reduce disputes, it is necessary to use instruments of the same model, same specifications, and from the same manufacturer. It is also advisable for the instruments on both sides to be calibrated at the same **quality inspection and metrology institute; only those with a certification can be used. During normal operation, it is agreed that one instrument should serve as the primary one while the other acts as a backup. The common practice in the industry is to have the buyer play a primary role and the user a secondary one, with the user’s data being transmitted wirelessly to the buyer for comparison. 2. Recommended solution 1: Standardize all meters. What is reduced here is not the measurement error, but rather the inconsistency in the values obtained. As for whether the meters are accurate or not, only God knows. 2. Ultrasound devices – those notorious unreliable instruments, worthless tools, complete nonsense. Can they really be used as measuring devices? Hehe 3. I really want to test the \"accuracy\" – why isn’t a constant-speed tube used? It’s really desirable to achieve consistency; the Pitot tube is reliable and inexpensive, and fighter jets around the world rely on it. 1.3 Vortex flow meter: mechanical thread damage – 20190424 – damage to the threads of the terminal cover. For steam flow measurement, the back cover of the KROHNE vortex flow meter cannot be opened once it has been fully tightened. Upon cutting it open, it was found that the last turn of threads had been damaged; the aluminum threads are a vulnerable part, so care must be taken to prevent dust from getting in, and excessive force should be avoided. If any obstruction is detected or if the cover feels difficult to tighten, seek help from an experienced technician immediately and do not continue trying to tighten it. 1: Check whether there are any contaminants such as sand in the threads. 2: Check whether the threads are smooth and free of any damage or deformation. 3: Is the tightening process smooth with no sticking? 4: 2019/5/8【Low steam flow measurement value】【The client, who was on night shift, noticed that the steam flow rate remained constant at 10 t/h; they informed the automation team, which in turn told the instruments that the measurement range was too low.】 We ran another 1 kilometer to the site to change the range; fortunately, it supported 475, and thankfully we had a car. 】In general, while ensuring the accuracy of the instrument and keeping the current value far away from 4 mA, it is advisable to increase the measurement range as much as possible, so as to avoid having to adjust parameters later on in case the steam flow rate becomes too high; especially for instruments whose parameters cannot be changed at 475.【2019/10/5】Vibration interference causes false readings even when there is no medium present. Model: Cronus vortex flow meter VFM1091GF13A0100100013. Parameters: Measurement medium: saturated steam; measurement type: mass, ρ=3.6672 kg/m3; pressure compensation: 0.6 MPa. Phenomenon: No steam present, yet the flow rate is occasionally displayed as 0.6–3.8 t/h. Solution: Use the up and down buttons to check the vortex frequency; when there is actually no flow, the vortex frequency is around 7–8 Hz, which clearly indicates external vibration interference, resulting from the instrument’s high sensitivity. Press Enter for 2 seconds then release to enter the menu ； Use the up and down arrows and the Enter key to select menus and change values; set the GAIN parameter to 5 (it was originally 9, as the sensitivity was too high) ； Hz immediately shows 0.0hz, which is normal ； On the second day, Party A reported that there was still occasional traffic, but it was much better than before; this time the AMPLIFY value was changed to 3 (it was originally 5, which is the charge amplification factor) ； It should work; we’re observing. Note: Both AMPLIFY and GAIN are sensitivity-related coefficients; the higher their values, the greater the sensitivity, and the more susceptible it is to external interference. 2019/11/25【The flow rate reading is extremely high; it does not reflect the actual flow rate at all】Location: Thioerythrin extraction, Class 1 explosion-proof area ； Time: 20:10 Model: VFM1091G415A0101100013 Range: 0–4000 L/h Manufacturer: KROHNE Medium: purified water Diameter: DN15 Installation: Installed in a straight pipe section; purified water flows from bottom to top. A length of 10D in front and 5D behind is sufficient; no pump is required, and there is no vibration. Phenomenon: When the manual valve upstream of the flow meter is opened, the instantaneous flow rate shows around 587,383 L/h; the exact value is not clear, but it’s approximately 580,000 L/h ； The vortex frequency is around 216 Hz ； When the valve is closed, the flow rate displays 0.0 L/h. Analysis: The valve is closed; flow rate cannot be measured; external vibration interference has been ruled out ； In fact, there was no vibration either ； The valve is open, and the flow rate exceeds the range. At that time, the vortex street frequency was 216 Hz, which seemed a bit high; I suspected there might be debris inside the pipeline ； The DN15 vortex flow meter is relatively light in weight; it was installed at a height of 1.5 meters. I removed the vortex flow meter myself and found a burr in the middle of the pipe – it was 2 cm long (the pipe had a DN25 diameter, while the vortex flow meter itself had a diameter of 15 mm), with a thickness of 1 mm. It was a leftover edge from cutting the pipe, and it was positioned right in the middle of the pipe. I immediately suspected that this burr was the cause of the problem. I broke off the burr with my hand and removed it. Flow meter reinstallation ； Water is allowed to flow in by opening the valve, but the reading is still above the range – just as before. I suspect there might be a problem with the operational amplifier on the circuit board (it’s just a guess), but I have taken the circuit board apart and rotated the direction of the LCD screen; therefore, I think that when the direction of the LCD screen was changed, the cable connecting the LCD screen to the circuit board might have been twisted, thereby damaging some electronic components. Indeed, the cable was pressing tightly against the circuit board at that time ； Then, after removing the circuit board, it was found that there was a surface-mount resistor of type 103 on the screw, and this resistor was connected to both the screw and a pin on the circuit board ； It might affect the current within the circuit ； The multimeter showed that the resistance is 995Ω, which is approximately 10kΩ. At this point, it was also found that there were indeed two locations on the circuit board where surface-mount resistors should be, and they appeared to have signs of being damaged. At that time, two possibilities were suspected: one was that two patch resistors had fallen off ； This causes the internal signals to be amplified ； 2 is the circuit that is attached to the screw and connected to the circuit board, affecting the internal signals ； Once I finished thinking about it, the lid had been opened many times, and the other one could no longer be found at all. First, it’s necessary to determine where the resistor fell from, and then contact the manufacturer to find a solution. So I opened the circuit board of another good vortex flow meter and found that there were also 2 empty resistor slots in the same location; at that moment I felt relieved, as the 103 resistor hadn’t been displaced – it was likely an extra resistor that was left over from the manufacturing process. This leads to the suspicion that it is affected by the first scenario. The resistor has been removed, and it seems that the circuit should be working properly. The circuit board was reinstalled, power was supplied, and the valve was opened; yet the flow rate remained extremely high. Therefore, the problem isn’t related to the circuit. I checked the parameters several times but couldn’t find any related to the flow coefficient. So the next morning I called the manufacturer, who said to go to the level 5 menu and check the K coefficient for 5.1 to see if it differed from the value indicated on the flow rate label. The way to access this menu is {press ESC}{press ENT}{release ESC}{release ENT}. After entering the level 5 menu, it was confirmed that the K coefficient differed from the value on the label by at least two orders of magnitude ； Flow meter K=1.79999E3; Nameplate K=3.87944E5 ； One is a little over 1,000, and the other is over 380,000 – there’s a huge difference ； After changing the K coefficient, the valve was opened and water was supplied; everything worked normally. 2020-04-15【Inaccurate measurement of steam by vortex flow meters】With Croni vortex flow meters used for measuring steam, there were issues such as no flow detected during testing, and the total flow rate of the branch steam streams being greater than the flow rate of the main steam stream. At the same time, there have been multiple instances of the flow meter freezing when saving parameters. Process parameters: Medium: Saturated steam ； Temperature: 165 degrees, Pressure (absolute pressure): 0.6 MPa ； Density: 3.685 kg/m3 (this is the parameter under ideal conditions; it is also the value set by the manufacturer at the time of production. In reality, the density and pressure of steam are not 0.6, nor is the density 3.685 kg/m3) ； However, the vortex flow meter calculates the mass flow rate by multiplying the volume flow rate by a density value of 3.685; as a result, the calculation is inaccurate. The steam pressure in the workshop is around 0.3 MPa, which is lower than that in the main steam pipeline, and the density is also lower. This leads to an overestimation of the steam flow rate in the workshop’s branch pipes, such that the total value is much higher than that of the steam in the main pipeline. Workshop: Bottleneck technical improvement project; Location: Main steam pipeline ； Model: VFM1091G/E/1/3/A/0/1/0/1/1/0/0/0/1/3 ； Diameter: DN200 ； Range: 0-15 t/h; cut-off at 0.2 t/h. Process parameters for the main pipe: Medium: saturated steam ； Temperature: 165 degrees, Pressure (absolute): 0.6 MPa ； Density: 3.685 kg/m3. Process parameters upon entering the workshop: Medium: Saturated steam ； Temperature: 150 degrees, pressure (absolute) 0.45 Mpa ； (Refer to the steam density table) Density: 2.242 kg/m3; a coefficient K is defined artificially; it is assumed that K is the coefficient by which the steam density decreases as pressure drops; K = 2.242/3.685 = 0.608 ； Tag number: Branch 01 ； Model: VFM1091G/D/1/3/A/0/1/0/1/1/0/0/0/0/1/3; Diameter: DN150; Range: 0-10t/h; Cutting capacity at 0.2t/h; Port number: Branch 02 ； VFM1091G/B/1/3/A/0/1/0/1/1/0/0/0/1/3; Diameter: DN100; Range: 0-5t/h; Cutting capacity at 0.2t/h: Branch line 03 ； VFM1091G/B/1/3/A/0/1/0/1/1/0/0/0/1/3; Diameter: DN100; Range: 0-5t/h; Cutting capacity at 0.2t/h: Branch line 03 ； VFM1091G/A/1/3/A/0/1/0/1/1/0/0/0/1/3; Diameter: DN80; Range: 0-4t/h; Cutting capacity: 0.2t/h ； Main pipe flow rate: 4.5 t/h; the total flow rate of the branch pipes is around 9 t/h ； Analysis: The branch pipe flow is still calculated based on the density of the main pipe, which is actually on the high side ； The branch pipe pressure has been reduced to a relative pressure of around 0.35 Mpa at the steam distribution package, with an absolute pressure of around 0.45 Mpa. At that time, the flow rate in the workshop was estimated based on the conditions on site: file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image004.png file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image006.png, which is roughly similar to the density value obtained from tables (2.242 for saturated steam at 150 degrees). file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image008.png Summary: During the testing process, the steam pressure was unstable and on the low side; at the start of testing, the steam flow rate could not be measured stably, and there were significant variations in the actual density and pressure of the steam. There was a large difference between the steam density in the workshop and that in the main steam pipeline. Moreover, the density parameter used in the Coriolis vortex flow meter did not take temperature and pressure into account, with a fixed value of 3.865; as a result, the total amount of steam in the workshop was greater than the flow rate in the main steam pipeline. 2021-05-14|19:21:17【Vortex flow meter – The meter reading decreases when the valve is opened, and it increases when the valve is closed】file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image010.jpg Model: VFM1091G/4/1/3/A/0/1/0/1/1/0/0/0/1/3/T ； 0~5m3/h ； Installed with DN25 flanges; the internal diameter of the flow meter is DN15. Pipe types: globe valve DN32, with a diameter reduction from 32 to 25 after the globe valve. The flow meter is mounted using DN25 flanges, and it itself has a diameter of DN15. Environment: The installation location is fine, and the U-bend is well constructed. The straight sections at the front and back are fine. Phenomenon: When the valve is opened, the flow rate shown is very low, around 0.5 m3/h; when the valve is closed to a small degree, the flow rate increases to around 3 m3/h. The greater the opening degree of the valve, the higher the actual flow rate, yet the value displayed by the flow meter first increases and then decreases (this issue was identified after multiple on-site observations). Inspection: 1. Suspicion of foreign objects in the pipeline; after removing the flow meter, the U-tube was inspected – its inner wall was smooth, but there was a foreign object the size of a pea near the lower elbow. 2. A foreign object was found on the vortex street generator of the flow meter; it was very small and removed using a screwdriver (this was not the root cause). 3. The manufacturer used a computer to examine the original waveform of the vortex flow meter and found abnormalities in the waveform; when the stop valve was fully opened, the waveform of the flow meter became chaotic and the Karman vortices disappeared. Solution: Unable to resolve. Reason: 1. The pipe has a DN32 diameter, which is too large; moreover, it is installed in front of the flow meter. A stop valve should not be placed in front of an ultrasonic flow meter – instead, a ball valve should be used. A ball valve serves two purposes: one is to shut off the flow for maintenance purposes, and the other is to allow full opening, thereby creating a straight pipe section that has little impact on the ultrasonic flow meter. 2. Party A uses a very low flow rate of around 2 m3/h; therefore, a DN25 stop valve should be installed downstream of the flow meter to regulate the flow. In reality, there is no stop valve downstream of the flow meter, which makes the design unreasonable. 3. The large diameter of the pipeline causes the flow rate to exceed 5 m3/h even when the globe valve is opened by about 5%, which is beyond the measurement capacity of the flow meter; as a result, the Karman vortex street in the pipeline disappears and measurement becomes impossible. Therefore, we need a smaller globe valve installed downstream of the flow meter to regulate the low flow rates. Compromise: After discussing this with Party A, it is recommended that the valve be opened to no more than 5%, meaning it should be used at a very low level, so as to ensure that the flow meter reading does not exceed 4.5 m3/h and normal measurement can be maintained. There is another issue: when the DN32 stop valve is opened to a very small degree, it emits a whistling sound and vibrations, which are extremely annoying. 1.4 Electromagnetic flowmeter 2018/12/17 Phenomenon: 【Reverse measurement】【Range change】For the split-type electromagnetic flowmeter produced by Jiangsu Hongguang Instrument Factory, flow is actually present, but the flow reading shows 0.00. Environment: The sensor is covered with insulation sheeting, making it impossible to see its installation direction ； I checked the instrument parameters and everything was fine; the small-signal cutoff was set to 0, yet the instantaneous flow rate still showed 0 ； This flow is installed at the pump outlet, in a vertical pipe, with the flow direction from bottom to top. Solution: Change the measurement direction to the opposite one. The accumulation direction has been changed to reverse. The measurements are normal; the small-signal cutoff value that was just changed is restored to 0.3% ； Checked the flow rate with the central control system, and it showed an incorrect value ； 【Signal Conversion】PLC, AI module range: 0-20mA; the control room range has been changed to -37.5-150 m³/h ； Instrument current: 4-20mA; instrument range 0-150 m³/h ； The central control display matches the on-site display ； 【By adjusting the slope and zero point of the control panel’s signal range, the control panel’s signal curve can be made to overlap partially with the on-site signal curve, thereby covering the entire range of the on-site signal; in this case, the values displayed on the control panel will match those shown on site.] If the AI module operates in a 0-10mA range, then using the same method to align the curves will result in normal readings for signals within 10mA; for values above 10mA, the computer is unable to display them accurately. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image012.jpg【Inference: Simple formula for converting 4-20mA to 0-20mA】: Converting {4–20mA} {0–600 m³/h} to {0–20mA} {–150–600 m³/h} allows the PLC display to match the on-site display ； 0-（600-0）/4=-150 ； If the lower limit of the flow range is 0, then -600/4=-150 is calculated directly to obtain the lower limit of the PLC range. From the image, it can be seen that the Y-axis distance corresponding to the black line between 0 and 4 is 1/4 of the actual range. 20190501【Empty pipe condition not resolved】Model: OPTIFLUX4300C. Phenomenon: The flow meter does not show a value of 0 when there is an empty pipe condition. Solution: After consulting the manufacturer’s technical team, the setting ‘setup-selftest-empty pipe detect’ – which triggers an alarm for empty pipes – was changed to ‘cond. + empty pipe’. As a result, the flow rate gradually dropped to 0.00. This seems to be related to the conductivity level in the presence of an empty pipe. Instruction manual parameter function table: Not valid for CAP option (capacitive) and PF option (partially filled)! Switch for conductivity measurement: off and on (measurement of electrode resistance). Options: Off (no electrode resistance measurement, no conductivity measurement, and no indication of an empty pipe) / Conductivity (only conductivity measurement) / Conductivity + empty pipe (conductivity measurement and indication of an empty pipe; error category: application); Flow indication: “= 0” when the pipe is empty / Conductivity + empty pipe (conductivity measurement and indication of an empty pipe; error category: measurement outside specifications); Flow indication: “= 0” when the pipe is empty / Conductivity + empty pipe (conductivity measurement and indication of an empty pipe; error category: information); Flow indication: “= 0” when the pipe is empty. 【Not applicable to CAP option (capacitive) and PF option (partially filled)! Switch for conductivity measurement (electrode resistance measurement).】 Selection: (No electrode resistance measurement, conductivity measurement, or empty pipe indication) / Conductivity (only conductivity measurement) / Conductivity + Empty pipe (conductivity measurement and empty pipe indication; incorrect category for the application); Flow indication “= 0” when the pipe is empty / Conductivity + Empty pipe (conductivity measurement and empty pipe indication; incorrect category per the measurement standards), indicating flow. 【2020-04-16】The electromagnetic flowmeter displays 0; there is an empty pipe alarm, and the conductivity reading is 0.00000 μS/cm. Manufacturer: Yokogawa Electric; Model: Split-type electromagnetic flowmeter ； AXFG4A-G000122JA12/CH ； Bore diameter: DN25; Range: 0-8 m3/h. Phenomena: 1. Alarm for empty pipe ； 2. When the valve is opened and tap water flows through it – not soft water or deionized water – the flow rate shows 0.000 with no change, or it displays some random fixed value or a negative number; the current output is 4mA ； (Because we have set the air traffic control alarm to output 4mA forcibly) Analysis: Tap water necessarily has conductivity, and ordinary electromagnetic flowmeters can measure it properly ； Unless it is steam condensate, deionized water, or purified water, the electromagnetic flowmeter cannot measure properly, showing an empty tank and a low conductivity value. Check the [Diagnosis] menu to view the process conductivity; it is found to be 0.0000 ； (Cause: An incorrect wiring connection prevented the sensor from transmitting signals to the transmitter.) We did not check the wiring, as we were confident that it was correct. Check the [Fault] alarms: CPU fault, reverse calculation fault ； Motherboard failure ； Coil short circuit ； Coil open circuit ； EEP failure (memory card) ； Almost all those fault codes have triggered alarms ； There is suspicion that the transmitter and sensor are not compatible; although the high-frequency and low-frequency parameters of the sensor have been sent back to the transmitter, it is still suspected that Yokogawa’s new version of software may be able to recognize the sensor, and proper matching is required for installation. (Party A purchases 20 split-type electromagnetic flowmeters, which are installed randomly; the sensors and transmitters are also installed randomly. The high-frequency and low-frequency parameters of the sensors need to be reconfigured in order to enable proper measurement. ) The instructions for resolving these alerts simply state four words: Contact customer service. We are also very worried. Reset to factory settings 3 times, change range coefficients 2 times ； Remove the sensor, submerge it in water for 2 tests, and calibrate the zero point once ； It has no effect at all. I called Yokogawa customer service, but they didn’t respond. Recollection: The Krohne split-flow meter also experienced a situation where the conductivity was zero, with no measurement values available ； At that time, a wiring error was discovered: one wire was connected to an open terminal. It turned out that the terminal was damaged, so another terminal was used in its place; as a result, there was a mismatch, and an extra open terminal remained. Just right one signal wire was connected to this open terminal, which prevented the signal from being received. As a consequence, the flow measurement value remained at 0, and the conductivity value was also 0 ； Solution: Suspecting a problem with the wiring, I checked the sensor connections and found an error on the transmitter side – the SA/A wires and the shield/signal wires were connected incorrectly; both had the letter A on them, which must have been due to carelessness. The wiring measurement returned to normal immediately; although the parameters were still at their factory settings, measurements could now be taken. All parameters have been updated, and the measurements are normal. Summary: Incorrect methods for solving problems lead to inefficiency ； Too confident. The process of resolving instrument issues requires a certain set of procedures; one cannot act arbitrarily or rely on personal intuition ； There’s a problem with the instrument: check the wiring first, and examine it carefully ； Then use a multimeter to check whether the circuit is functioning properly ； Then use a multimeter to check whether the output signal is normal ； If everything is normal, rule out wiring issues and check problems with the instrument itself, analyzing it from a theoretical perspective. For example: CPU failure, motherboard failure, inversion function failure, conductivity of 0, coil open circuit ； A conductivity of 0 and an open circuit in the coil both indicate that there may be a disconnected, incorrectly connected, or loose wiring in the electromagnetic flowmeter; the wiring should be checked. On the afternoon of April 16, 2020, an integrated vortex flow meter from Croni produced a reading at full scale. Model: VFM1091GA13A0100100013 ； Range: 0-900 m3/h ； Medium: Compressed air. Phenomenon: The computer shows that the instrument is outputting at full scale. Solution process: My first thought at that time was that there was an issue with the parameters; I planned to climb up using a safety belt to check the settings of the instrument parameters, suspecting that the range was too small ； Then the colleague asked the person on duty in the workshop if there was a ladder, in order to prepare for climbing up. At that moment, I remembered the process of dealing with the vortex flowmeter issue at Yokogawa today, and told myself that I couldn’t rely on intuition; instead, I had to solve the problems in order, starting with the simpler ones first. (Aside: There’s another piece of experience here: A recent batch of Crony instruments purchased has been experiencing frequent malfunctions – they freeze, the measurements fluctuate, the display goes black with no data shown. Turning off the power and then turning it back on often resolves the issue.) ； ) Drawing on the experience of restoring power after a outage, as well as the lessons learned from the difficulties encountered when dealing with the Yokogawa flowmeter, we need to conduct careful measurements and inspections this time, avoiding hasty actions to prevent repeating those mistakes. Solution: Remove the flow signal wire from the PLC cabinet (it’s a 2-wire system, with the signal wire serving as the power supply for the instrument). Set the multimeter to the mA range and insert it into the circuit to measure the current; the measured value was 3.98 mA. The measurement was taken over 20 seconds. It takes about 10 seconds for the flow meter to start working properly ； The current remained stable at 3.98 mA for 20 seconds, and the wiring issue was resolved. The current flow is normal after power is cut off and restored. However, the cause of the problem with the flow meter is unknown. Analysis: It only takes a few minutes to solve this problem. If one acts on intuition by looking for a belt or a ladder and climbing up to fix the issue, it will result in time wastage, pose safety risks, and it may even be impossible to identify the cause of the problem ； Carrying out signal measurements step by step can actually help resolve problems quickly; of course, some prior experience and lessons are also required. 2020-05-14 SE electromagnetic flowmeter: The value displayed on-site did not match the value shown on the computer; it read 0.0 m3/h on-site, while the computer displayed 3 m3/h ； Process: Use a multimeter to measure the circuit current ； The signal wire must be removed from the terminal before measuring the current to achieve high accuracy; otherwise, there will be an error of 8 mA. Practical tests have shown that in a poor electrical environment with significant interference, this issue occurs. Remove the signal wire and measure the current at 4.8mA ； Connect the signal wire to the terminal; at this point the WP9035 is connected in series. Then use a multimeter to measure the current, which is 4.2mA. The output current of the WP9035 is also 4.2mA, indicating that there is no problem with the isolation distributor 9035. When the wiring was removed on-site, the current measured was 3.99 mA; after connecting a signal wire and inserting it into the multimeter, the current was 4.8 mA, which indicates that the problem lies not in the flow meter ； The problem is not the flow meter nor the components in the PLC cabinet; it must be a cable issue, presumably related to the shielding layer and grounding. The signal cable shield was removed from the ground bar, and the current value is normal. It indicates that there is a problem with the grounding. Comprehensive analysis: In this workshop, electrical cables and instrument cables are stored together in large numbers. Variable-frequency cables have a significant impact on instrument signals; either the signals become abnormal when grounded, or they become abnormal when not grounded. 2020-10-21|16:19:01 Question: [The electromagnetic flowmeter is installed in a vertical pipe, with the fluid flowing vertically downward.] The conditions were available to modify the pipe into a U-shaped bend, but this was not done; instead, the flowmeter was installed directly in the vertical pipe, with the fluid flowing from top to bottom. The installation of the electromagnetic flowmeter violates the relevant specifications, namely the \"GB50093 Code for Construction and Quality Inspection of Automated Instrumentation Projects\"; relevant provisions regarding the installation of electromagnetic flowmeters are listed in 6.5.7.2: file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image014.jpg. The feed pipeline in the workshop has a diameter of DN32; the flow meter is installed in a vertical pipe, with the fluid flowing from top to bottom, entering the tank from its roof. A diaphragm valve is installed downstream of the flow meter. The client requires that it be installed vertically, as this ensures that the vertical section containing the flow meter remains filled with fluid by controlling the opening degree of the diaphragm valve. No obvious issues have been found with flow measurement at present; further checks are pending. 1.4.1 No reading on the electromagnetic flowmeter – Low conductivity of steam condensate; Model: CP60-F0040CM1S1ZA0M0d–Electromagnetic flowmeter–Password: 20000 ； 56360: Manufacturer: Control system: SUPCON Company; Zhejiang SUPCON Automation Instruments Co., Ltd. Medium: Steam condensate from a power plant. Phenomenon: When the valve is opened, the flow meter shows no reading, and water flow can be clearly heard coming from the valve. Display: Air traffic control alarm ； Airway ratio: around 1145, estimated to be the ratio of water conductivity to the airway threshold (400) ； Analysis: The conductivity of condensed steam is low, below the empty-tube threshold of the electromagnetic flowmeter (400); the unit is unknown, possibly μS or mS ； I thought that lowering the conductivity threshold for air traffic control would suffice, so I set it to 100, 50, 1, and 0.01, but it didn’t work; none of these values resulted in a measurement, all showed 0.000, with an air traffic control alarm being triggered in each case. Solution: Turn off the air traffic control alarm, and the measurement is normal. Summary: For pipes where steam condensate may flow, the empty pipe alarm should be turned off when installing a flow meter; otherwise, measurement is not possible. This situation generally occurs with domestically produced flow meters. For the Cologne flowmeter, simply change the empty value from the default of 60 to around 10. In this way, normal measurement is possible when steam condensate or pure water flows through the pipe. 1.5 Mass flow meter: file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image016.jpg file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image018.png. The installation direction of the mass flow meter can be reversed through settings; however, it is best to install it according to the directions specified in the manual. Negative in, positive out. 1.6 Differential Pressure Flow 1.6.1 Ebara Flow Rate [Other Gases] 2019/1/15 Three-valve assembly: Differential pressure flow is unavailable without a three-valve assembly ； The three-valve assembly was not purchased along with the source component, which forced us to borrow one from elsewhere; even after borrowing it, the threaded holes did not match, and the on-site workers had to bend the source pipe in order to install it somehow. Process conditions on 5/4/2019: Air volume in the 3.1-meter pipeline is around 470,000 cubic meters; the pressure relative to the external atmospheric pressure is -0.02 KPa. There are 2 exhaust fans with a capacity of 250,000 cubic meters each, and 6 blowers with a capacity of 100,000 cubic meters each. 】Observation: 【The computer in the 2.4-meter flow control room displayed 0.0㎥/h】【Air was being drawn inward on the positive pressure side of the flow meter’s pressure tapping hole, while air was being drawn in on the negative pressure side without any exhaust】, and after removing the flow meter, high-speed gas flow was present inside the pipeline; a large amount of external air was drawn in, to the point where it almost pulled a safety helmet into the pipeline as well. 【The flow rate reading at 3.1 meters is on the low side, and an alarm is triggered almost every 2 hours; the alarm values correspond to a flow rate of 990,000 to 1.5 million cubic meters】【To view the error records of the differential pressure transmitter: all errors are of the type “over range” or “over limit”, which indicates that the negative pressure side is blocked, resulting in too low negative pressure; as a result, the difference between positive and negative pressure becomes too large, causing an overflow.】 ； It was caused by that. 】 Reason: 【The negative pressure sides of both flow rates are blocked by dirt】 Method: 【Clear the blockage using a high-pressure water gun】 Model parameters: 【Testing coefficient: K=1.45; Throttling element model: BXY-FG-CB2400C; Insertion-type Ebara flow meter, special pressure tapping】 ； Diameter: 2420×10mm ； Operating condition density: 1.118 kg/㎥ ； Working pressure: 5 kPa, gauge pressure ； Operating temperature 60℃ ； Range: 0–250,000 N㎥/h ； Recommended range for the differential pressure transmitter: 0–2612 Pa (4–20 mA). Model of the throttling element: BXY-FG-CB3100C; it is an insertion-type Ebara flow meter with a special pressure tapping mechanism ； Diameter: 3120×10mm ； Operating condition density: 1.118 kg/㎥ ； Working pressure: 5 kPa, gauge pressure ； Operating temperature 60℃ ； Range: 0–500,000 N㎥/h ； Recommended range for the differential pressure transmitter: 0–3757 Pa (4–20 mA). File:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image020.png. P: Local atmospheric pressure = 101325 Pa. P: Pressure of the process gas, in Pa. ΔP: Differential pressure value measured by the transmitter (4–20 mA). t: Process temperature; a temperature transmitter should have been installed, but it isn’t available on site. Given that the temperature at the site remains stable between 58–60°C over long periods (more than 20 days), t is set to 60°C by default. Therefore, although a range of 0–250,000 m³/h or 0–500,000 m³/h is specified, this range does not correspond to 4–20 mA. The flow rate is calculated using a formula based on the differential pressure; it is the differential pressure values (0–3757 or 0–2616) that correspond to 4–20 mA. Thus, it is [K and the range of differential pressure] that determine the maximum flow rate, rather than 4–20 mA. Analysis: In a 3.1-meter pipeline, the negative pressure port of the gauge is prone to being blocked by condensation or dirt, resulting in unstable differential pressure, fluctuations in this value, and regular alarms (in this case, an alarm occurs approximately every 2 hours) ； Furthermore, through analysis of the historical data, it was found that traffic alarms have no significant relationship with the process gas pressure, nor with the frequency changes of the inverter. After ruling out process-related issues, an inspection of the site showed that the pressure tapping holes were properly sealed; however, the suction force on the negative pressure side was low, and it was not possible to move anything by blowing through it, which indicated a blockage. Upon disassembly, dirt was indeed found to be causing the blockage. High-pressure water guns were used to clean each pressure tapping hole, thereby clearing them. After reinstallation, measurements showed normal values, with the differential pressure increasing significantly from 150 Pa to 870 Pa. 2.4-meter pipeline, equipped with a Ba flow meter; the pipeline pressure is -0.2 KPa relative to atmospheric pressure ； Inhaling is stronger on the positive-pressure side compared to the negative-pressure side; it’s not possible to blow air into the negative-pressure side through the mouth, while on the positive-pressure side, the air is sucked back into the mouth before it can even be blown out ； Remove the flow meter, use a high-pressure water gun to clean each hole; once they are cleared, reinstall it in the pipeline and measure a normal flow rate of around 120,000 cubic meters. However, if the alarm is triggered again after 4 hours or if the pressure difference drops to zero, blowing with compressed air for 10 seconds is sufficient; this suggests that condensation water may be blocking the air path. If the pressure difference returns to zero after a day, blowing with compressed air at 0.15 MPa yields little effect, with the flow rate reaching only around 70,000 cubic meters. This measurement is 50,000 cubic meters lower than what should be expected according to the process parameters, and it does not correspond to the flow rate expected based on the fan frequency; moreover, the flow rate is gradually decreasing, indicating that the air path is still getting blocked. In this case, blowing with compressed air at 0.3 MPa for 2 minutes results in a flow rate of 120,000 cubic meters, showing that using compressed air at 0.3 MPa has a significant cleaning effect. The measurement results now match the process parameters fairly well. This indicates that the process gas is relatively dirty; we have contacted the automation team to set up interlocks, so that if the flow rate drops to 0, an automatic purge will take place for 1 minute. Summary: The flow meter in Ba relies on unstable and inaccurate measurements, resulting in low differential pressure values. Generally, this is either due to air leakage at the pressure sampling hole or the hole being blocked by the process medium; removing the differential pressure transmitter and blowing into it with your mouth can help determine whether there is a blockage (do not use your mouth to blow if the medium is toxic). Using a high-pressure water gun to clean the area can resolve the issue. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image021.pngfile:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image023.jpgAfter cleaning with a high-pressure water gun. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image025.jpg Green represents the flow meter used for the 3.1-meter pipeline: it triggers an alarm every 2 hours, with a flow rate of 990,000 to 1.5 million cubic meters. Brown represents the Ebara flow meter for 2.4-meter pipes: there is a trend of a gradually decreasing differential pressure value. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image027.jpg Green: the alarm curve for a flow rate of 3.1 meters; the red and yellow lines represent the fan frequency curves. There is no clear relationship between frequency and flow rate alarms, and changes in frequency are not the cause of these alarms – alarms can occur even when the frequency remains constant. Brownish-red curve: Pressure curve after flow through a 3.1-meter pipeline; the large pressure fluctuations are also not significantly related to the flow alarm. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image029.jpg On 2019/5/14, two differential pressure transmitters equipped with Etoeba flow meters were replaced. The replacement was completed at 18:00 in the afternoon, and by 08:00 on 2019/5/16, the readings were normal with no alarms. Recollection: In January 2019, I remember that Yulong called me once. After the 2.4-meter pipeline was equipped with flow meters, Yulong said that the differential pressure transmitters of the two flow meters were installed in the wrong direction, resulting in incorrect measurement ranges. However, after checking and reviewing the range parameters, it was found that the meters weren’t installed incorrectly; the differential pressure corresponding to flow in a 2.4-meter pipeline is 0–2612 Pa ； The flow rate for a 3.1-meter pipeline corresponds to a differential pressure of 0~3757 Pa ； Since the differential pressure transmitter of the 3.1-meter flow meter was installed, it has been giving intermittent alarm signals. At first, this did not draw the attention of either the client or us; it wasn’t until April that the client pointed out that the readings from the 3.1-meter flow meter were inaccurate, with the measured values being too low, and that alarms were triggered at full scale from time to time. Thinking about it now, and analyzing based on the actual conditions on site, it seems that the two differential pressure transmitters were not installed in the correct positions. However, the root cause of the problem remains unclear. It is speculated that the differential pressure transmitter with a range of 3757 Pa was experiencing abnormal feedback output at some point, and since the abnormal value range did not include the calibration points during the instrument calibration, the problem was not detected during calibration. Let’s settle the issue with the Ba flow meter for now. 2019/10/30 1.6.2 Anti-clogging composite anemometry device (used in conjunction with a differential pressure transmitter) 【Liaoning Focus Technology】 Medium: High-temperature flue gas from boiler combustion ； Pipe diameter: 1200 millimeters. Flow type: designed specifically for power plants; equipped with anti-clogging flow measurement device ； Installation location: The flow detection element is installed on the main pipeline, while the differential pressure transducer is located at a distance from the detection element ； Positive and negative pressures are led to the differential pressure variator through a pressure guide tube of about 10 meters in length. Precautions for debugging: 3. Take photos and make markings after installation to indicate the positive/negative pressure and flow direction, to prevent it from being covered by insulation material. Flow meters are considered part of concealed works; in the future, the pipes will need to be insulated, and after insulation is applied, nothing can be seen of the flow meter except for the pressure tapping ports ； The brand names are not visible, nor is the direction of traffic. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image031.jpg 4. During the installation of the pressure transfer pipes, proper markings should be made to prevent the positive and negative pressure pipes from being connected incorrectly. The positive and negative pressure conduits can be laid simultaneously, and markings must be made at each turning point for these conduits, as their positions may swap at such turns. 5. The differential pressure transmitter has high precision; after it is properly installed, open the balance valve of the three-valve assembly ； Adjust the tilt angle of the transmitter so that 4.00mA is displayed. 1.7 Ultrasonic flow meters 1.7.1 Poor signal quality of ultrasonic flow meters: SSDO 47.5, SSUP 47.4. Apply a coupling agent in a thickness of about 8 mm, tighten the probe, and squeeze out 90% of the coupling agent until it is felt that the probe is in close contact with the metal wall of the pipe and can no longer be moved. At this point, the signal strength is 55; the E2 alarm on the ultrasonic flow meter disappears, as does the E0 alarm – all alarms are gone, and measurement proceeds normally. 1.7.2 The integrated ultrasonic flow meter Diyuan YYC-M1C-80L(10)RAT displays a negative flow value; it is a single-channel, split-type ultrasonic flow meter (with the transmitter installed separately from the main unit), designed for measuring condensate flow. The ultrasonic sensors are connected in a Z-shaped configuration, and the meter is installed in pipeline format, with the probe and the main unit combined into one unit. Check the wiring to ensure that the upstream and downstream connections are not reversed; also check the wiring of the manufacturer’s internal probes to confirm that the upstream and downstream connections there are not reversed as well. All lines are normal. The condensate flow in the pipeline is in the forward direction, and the flow meter is installed in the same direction as this flow. The flow value displayed by the transmitter is negative; solution: password 0000 ； Enter the system menu and set the traffic direction to reverse. file:///C:/Users/HASEE/AppData/Local/Temp/msohtmlclip1/01/clip_image033.jpg1.8 Float flow meter 2020-08-22 Generally, for 2-wire instruments, it is necessary to distinguish between the positive and negative terminals; if these are connected in reverse, the instrument will not turn on, nor will a proper 4-20mA feedback signal be generated. Sometimes, only a small current of around 2mA may be present. But today, this rule was broken. Discovery of unusual variants, Changzhou Shuanghuan Thermal Instrument Co., Ltd. – Metal tube float flow meter – LZD-40/1/RL/M6/D ； 2-wire system ； The 4-20mA signal doesn’t have a positive or negative distinction; the terminal blocks of the instrument don’t indicate positive or negative polarity. No matter how the wires are connected, the signal can still be transmitted properly. How is that possible? Automatic control instruments