Comprehensive Guide to Troubleshooting Common Flow Meter Issues

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This post was last edited by yinkuilin6868 on 2016-6-4 09:47. Flowmeters are among the most commonly used instruments in industry; only by mastering the methods for troubleshooting common flowmeter issues can problems that arise during production be identified and resolved promptly. Classification of flowmeters ★ There are a wide variety of methods for measuring flow rate and different types of instruments, and there are also numerous classification methods. To date, there are as many as 60 types of flow meters available for industrial use. ★ Based on the objects of measurement, there are two main categories: closed pipes and open channels. ★ Based on the purpose of measurement, it can be divided into mass measurement and flow measurement, with the corresponding instruments being mass meters and flowmeters respectively. ★Based on the measurement principle, they can be classified into mechanical principles, thermal principles, acoustic principles, electrical principles, optical principles, atomic physics principles, etc. ★ According to the most popular and widely used classification system, they can be divided into: positive displacement flowmeters, differential pressure flowmeters, float flowmeters, turbine flowmeters, electromagnetic flowmeters, vortex flowmeters, mass flowmeters, and ultrasonic flowmeters, among others. Common faults of flow meters and their solutions 1. Positive displacement flow meters ◆ ◆ ◆ Gear flow meters Phenomena, causes, and corrective actions: The gear does not rotate. 1. Debris has blocked the pipeline. 2. The liquid being tested solidifies. 1. Clean the pipes, filters, and flow meters. 2. Dissolve the liquid. The bezel rotates while the pointer remains still or moves intermittently. 1. The fork connecting the dial is loose. Dirt gets into the header transmission. 2. The pointer or counter is stuck. 3. The transmission is disengaged. Remove the dial head, turn the pull fork by hand; if the gauge rotates smoothly, then the pin connecting the dial head to the shaft has come loose ； If not, check level by level. Oil leakage at the steering seal coupling shaft is caused by worn sealing packing; tighten the gland or replace the packing. Instrument error compensation and low-flow error cause the eccentric wheel to collide with the housing, due to bearing wear or displacement of the fixed drive gear assembly. Replace the bearings, check the drive gear to see if the wheel body rotates, and verify that the screws fixing the gear are not loose. The error variation is large; 1. The liquid pulsation is significant. 2. Contains gas. 1. Reduce pulsation. 2. Add a degasser. ◆ ◆ ◆Elliptical gear flow meter: Causes and corrective measures. The rotor does not rotate 1. The filter is clogged. 2. Impurities entering the flow meter cause the rotor to get stuck. 1. Clean the filter. 2. Check whether the filter screen is damaged and clean the inside of the flow meter. The rotor rotates normally but the counter does not count. 1. The transmission gears are not engaging properly. 2. The rivets at various connection points have come loose, or the pins have fallen off. 1. Remove the counter and inspect all stages of the transmission and the counter. 2. Do not subject the magnetic coupling to excessive torque, otherwise it will lose its magnetism due to pole misalignment. Oil leakage at the steering seal coupling shaft is caused by worn sealing packing; tighten the gland or replace the packing. Mechanical seal coupling leakage 1. The gland is too loose. 2. Packing wear. Replace the sealing packing and add sealing oil. The indicated value is less than the actual value. 1. Flow rate is outside the specified range. 2. The viscosity of the medium is relatively low. 3. Rotating parts such as the rotor are not flexible. 1. Keep the flow rate within the specified range or change the gauge specifications. 2. Recalibrate by replacing the adjustment gear to make corrections. 3. Inspect the rotor, bearings, drive gears, etc., and replace worn parts. The indicated value is 1 higher than the actual value; there are large fluctuations in flow rate. 2. Gas is mixed into the medium. 3. The viscosity of the medium is too high. 1. Reduce the pulsation of flow rate in the pipeline. 2. Install a degasser. 3. Recalibrate, replace the adjustment gear pair, and make corrections to it. 2 Differential pressure flow meter: Causes and corrective measures for an indication of zero or very slight movement. 1. The balance valve is not fully closed or is leaking. 2. The high and low pressure valves at the base of the throttling device are not open. 3. Blockage in the valves and pipelines between the throttling device and the differential pressure gauge. 4. The vapor pressure tube has not been completely condensed. 5. The gasket between the throttling device and the process pipeline is not tight enough. 6. Internal failure of the differential pressure gauge. 1. Close the balance valve and repair or replace it. 2. Open the high and low pressure valves. 3. Flush the pipeline, repair or replace the valve. 4. Start the timer after complete condensation. 5. Tighten the bolts or replace the gasket. 6. Inspect and repair. Indicates that the high and low pressure pipelines are reversed at minus 1 degree. 2. Reverse connection of the signal line. 3. Severe leakage or rupture in the high-pressure side piping. 1-2. Check and connect properly. 3. Replace the part or the pipe. The indication is 1 unit low. The high-pressure side pipeline is not airtight. 2. The balance valve is not tight or not properly closed. 3. The air in the high-pressure side pipeline has not been completely removed. 4. The zero point of the differential pressure gauge or secondary instrument is out of adjustment or displaced. 5. The throttle device and differential pressure gauge are not matched, violating the design specifications. 1. Check for and eliminate leaks. 2. Inspect, shut down, or repair. 3. Drain the air. 4. Check and adjust. 5. Replace the accompanying differential pressure gauge. The indication is high by 1. The low-pressure side pipeline is not airtight. 2. Air is accumulated in the pipeline on the low-pressure side. 3. The pressure of the steam is below the design value. 4. Zero drift of the differential pressure gauge. 5. The throttle device and differential pressure gauge are not matched. 1. Check for and eliminate leaks. 2. Drain the air. 3. Adjust according to the actual density. 4. Check and adjust. 5. Replace the accompanying differential pressure gauge. The indicated fluctuations are large: 1. The flow rate parameters themselves exhibit excessive fluctuations. 2. The pressure sensing element is sensitive to parameter fluctuations. 1. Adjust the high and low pressure valves to a lower setting. 2. Appropriately adjust the damping effect. Instruction inactive. 1. Anti-freeze measures failed; the differential pressure gauge and the pressure guiding pipes are frozen due to hydraulic fluid freezing. 2. The high- and low-pressure valves are not open. 1. Enhance the effectiveness of anti-freezing facilities. 2. Open the high and low pressure valves. 3 Metal float flow meters: Causes and corrective measures. Oscillation of the pointer in a float flow meter 1. Medium pulsation. 2. Unstable air pressure. 1. Increase damping. 2. Use voltage or current stabilization devices. The pointer stops in one position and remains there. 1. The valve was opened too quickly, causing the float to get stuck. 2. The float guide rod is not concentric with the stop ring. 1. Slow down the valve opening speed. 2. Remove the gauge for adjustment. Large measurement errors. 1. Installation does not meet requirements. 2. The density of liquid media varies significantly. 3. Temperature and pressure have a significant impact. 4. Pipeline vibration. 1. The installation angle, whether vertical or horizontal, shall not exceed 20 degrees. 2. Calculate the error correction coefficient, multiply it by the reading to obtain the true flow rate. 3. Use temperature and pressure compensation. 4. Hire a professional to adjust the component positions. 4 Turbine flowmeters: Causes of phenomena and corrective measures. No display when the fluid is flowing normally. 1. There is an open circuit or poor contact in the power cable, fuse, etc. 2. Poor internal contact in the display unit. 3. The coil has a broken wire. 4. There is a fault inside the sensor flow channel. 1. Use an ohmmeter to check. 2. Use the replacement “backup version” method for inspection. 3. Check the coil for any broken wires or loose solder joints. 4. Remove foreign objects from the sensor, and clean or replace damaged parts. The flow rate is gradually decreasing. 1. The filter is clogged. 2. The valve core in the sensor section is loose, resulting in a reduced valve opening. 3. The sensor impeller encounters obstructions or foreign objects enter the bearing clearance, resulting in increased resistance. 1. Clean the filter. 2. Determine whether the valve core is loose by checking if adjustment via the valve handwheel is effective. 3. Remove the sensor to clear debris, and recalibrate it if necessary. The fluid is not flowing, yet the flow rate display shows a value other than zero. 1. The shielding of the transmission line is not properly grounded. 2. Pipeline vibration causes the impeller to vibrate as well. 3. The stop valve does not close properly. 4. Degradation or damage to the electronic components between the circuit boards inside the display unit. 1. Check whether it is properly grounded. 2. Reinforce the pipeline, or install brackets before and after the sensor to prevent vibration. 3. Inspect or replace the valve. 4. Use the “short-circuit method” or check item by item to identify the source of interference and locate the fault point. There is a significant difference between the value displayed on the instrument and the value obtained from empirical assessment: 1. Fault inside the sensor’s flow channel. 2. Insufficient back pressure at the sensor causes cavitation, affecting the rotation of the impeller. 3. Reasons related to pipe flow. 4. Internal failure of the display unit. 5. Aging-induced demagnetization of permanent magnetic material components in the detector. 6. The actual flow rate through the sensor has exceeded the specified range. 1-4. Identify the cause of the fault and find solutions tailored to that specific cause. 5. Replace the demagnetized component. 6. Replace with a suitable sensor. 5 Electromagnetic flowmeter: Causes of phenomena and corrective measures. No flow signal output from the instrument: 1. Abnormal power supply to the instrument. 2. The cable connection is abnormal. 3. The liquid flow condition does not meet the requirements. 4. The sensor components are damaged or there is an adhering layer on the inner wall being measured. 5. The converter components are damaged. 1. Check whether the voltages output by the power supply circuit board are normal. 2. Connect the cables correctly. 3. Check the liquid flow direction and whether the tube is fully filled with liquid. 4. Regularly clean the scum layer formed on the surface liquid. 5. Replace the damaged components. The output value fluctuates by 1. Electromagnetic interference caused by external stray currents and the like. 2. The pipe is not filled with liquid or the liquid contains bubbles. 3. The power board of the flow meter is loose. 1. Check whether there are any large electrical appliances or welders in operation in the environment where the instrument is located. 2. Fill the tube with liquid or calm the bubbles. 3. Disassemble the flow meter and reattach the circuit board. The flow measurement value does not match the actual value. 1. Fault in the transmitter circuit board. 2. The liquid flow rate is too low, and it contains tiny bubbles. 3. The signal cable is not properly connected. 4. The parameter settings of the converter are inaccurate. 1. Check whether the transmitter circuit board is intact. 2. Ensure that the flow rate of the liquid being measured in the pipeline is above the minimum flow limit value. 3. Check whether the signal cable connections and the cable’s insulation are in good condition. 4. Reset the converter settings, and verify the converter’s zero and full-scale values. The output signal is out of range 1. There is an error in the wiring of the signal cable. 2. The parameter settings of the converter are incorrect. 3. The converter and sensor models are not compatible. 1. Check the connection of the signal circuit. 2. Check whether the various parameter settings of the converter, as well as its zero and full-scale values, meet the requirements. 3. Swap the models of the converter and sensor. 6 Vortex flow meter: Causes of phenomena and corrective measures. There is flow in the pipeline, but the instrument gives no output; the instrument has no display and provides no output. 1. There is a fault with the power supply. 2. The power supply is not connected. 3. The connection cable is broken or the wiring is incorrect. 1. Reconnect power or replace the power supply. 2. Turn on the power. 3. Reconnect the wires and check the cables. The instrument indicates no output: 1. The flow rate is too low and is not within the measurement range. 2. There is a fault in a certain stage of the amplification board. 3. The probe body is damaged. 4. The pipeline is blocked or the sensor is stuck. 1. Increase the flow rate or select a different flow meter. 2. Replace the motherboard. 3. Replace the probe. 4. Reinstall the instrument. Cause of phenomenon and corrective measures: No flow but output is present after power is applied, and the output signal remains stable. 1. The output frequency is 50 Hz, indicating power-line interference. 2. The amplification board is damaged, resulting in self-oscillation. 1. Use shielded cables and reconnect the wires in accordance with the specifications. 2. Replace the amplifier. The output signal has changed. 1. There are strong electrical devices or high-frequency interference near the flow meter. 2. The pipeline experiences severe vibrations. 3. The magnification factor or trigger sensitivity of the amplification board is too high. 4. The pipeline valves are not fully closed, resulting in leakage. 1. Re-select the installation location. 2. Reinforce the pipes at the meter installation location. 3. Decrease the magnification (GB) or sensitivity (SB) counterclockwise. 4. Check the valve. Phenomenon, Cause, and Countermeasures: Unstable flow output. Reasons include improper selection and installation, as well as issues with the pipelines. 1. Strong electrical interference signals are present; the instrument is not grounded, resulting in the flow rate being affected by these interference signals. 2. The straight pipe section is insufficient, or the inner diameter of the pipeline does not match that of the instrument. 3. The impact of pipeline vibration. 4. The flow meter is not installed concentrically. 5. The fluid fills the pipe completely. 6. The traffic is below the lower limit or above the upper limit. 7. Cavitation occurs in the fluid. 1. Reconnect the shield ground. 2. Replace and reinstall in a different location. 3. Reinforce the pipes to reduce vibrations. 4. Reinstall the instrument. 5. Check the fluid flow conditions and the installation location of the instruments. 6. Increase or decrease the flow rate, or adjust the filtering parameters of the amplification board. 7. Install valves downstream of the instrument to increase back pressure. Instrument-related reasons: 1. Incorrect settings in the instrument menu. 2. The motherboard is damaged. 1. Reset the menu according to the requirements. 2. Replace the motherboard. 7 Mass flow meter: Causes of phenomena and corrective measures. The instantaneous flow rate always shows the maximum value. 1. The cable is disconnected or the sensor is damaged. 2. The fuse inside the transmitter is burned out. 3. Clogging of the sensor measurement tube: 1. Replace the cable or replace the sensor. 2. Replace the fuse. 3. After clearing the blockage, gently tap the sensor housing, then measure the AC and DC voltages; if this still doesn’t work, the installation stress is too high – reinstall it. When the flow rate increases, the flow meter indicates a negative increase; the sensor’s flow direction is opposite to that indicated by the housing, indicating that the signal wires are connected reversely. Change the installation direction and adjust the wiring of the signal lines. When the fluid is flowing, the flow rate shows positive and negative fluctuations; these fluctuations are significant, and at times it remains at a negative maximum value. 1. The grounding resistance of the power supply’s AC/DC shielding wires is greater than 4Ω. 2. Pipeline vibration. 3. The fluid consists of gas and liquid phases. 4. There is a strong magnetic field or radio frequency interference around the transmitter. 1. Re-ground. 2. Replace the connection pipeline to the flow meter with a flexible metal hose. 3. Make an opening in the pipe above the flow meter and install a valve to discharge the gaseous components. 4. Change the environment around the transmitter. 8 Ultrasonic flowmeters: Causes of phenomena and corrective measures. The velocity display values change drastically when the sensor is installed in areas where there is significant pipe vibration, or downstream of control valves, pumps, or throttle orifices. Install the sensor in a location far from vibrations or move it upstream of the device that alters the flow pattern. The sensors are fine, but the flow rate is low or non-existent. 1. The paint and rust in the pipes have not been removed completely. 2. The pipe surface is uneven or installed at a weld seam. 3. The sensor is not properly coupled to the pipeline; there are gaps or bubbles at the coupling surface. 4. Installing the sensor on the sleeve weakens the ultrasonic signal. 1. Clean the pipeline again and install the sensor. 2. Smooth the pipe or install the sensor away from the weld. 3. Reinstall the coupling agent. 4. Move the sensor to the section of the pipe without a sleeve. Incorrect readings: 1. The sensors are installed at the top and bottom of horizontal pipes, and sediment interferes with the ultrasonic signals. 2. The sensor is installed on a pipe with fluid flowing downward, and the pipe is not fully filled with fluid. 1. Install the sensors on both sides of the pipeline. 2. Install the sensor on the pipe section filled with fluid. The flow meter was working normally, but suddenly it stopped measuring the flow rate. 1. The medium being measured changed. 2. The medium under test vaporizes due to excessive temperature. 3. The temperature of the medium being measured exceeds the sensor’s maximum allowable temperature. 4. The coupling agent under the sensor has aged or been depleted. 5. The instrument exceeds its own filtering value due to high-frequency interference. 6. Data loss in the computer. 7. The computer freezes. 1. Change the measurement method. 2. Cool down. 3. Cool down. 4. Reapply the coupling agent. 5. Stay away from sources of interference. 6. Re-enter the value. 7. Restart the computer.