In the actual industrial production process, people, to save energy and reduce consumption, improve production efficiency and product quality, we need to pay attention to the measurement of object flow through the pipeline is how much mass flow. Today, we discuss the common failures of coriolis mass flow meter together.
1. Fault problem: Zero point drift
1.1 Analysis of the cause
The U-tube sensor is not complete. There is a mixture of liquid and gas situation
First, complete the preparatory work, then follow the inspection procedure for the site. If no problems are found, the operator can start the pump to flush the pipeline and flowmeter if the process conditions allow. After stopping the pump and waiting for a minute, then closing the shut-off valve downstream of the sensor, we need to observe whether the zero point is still drifting.
If it is also zero drift on the zero adjustment operation, if the standard zero is still often zero drift (less than 3% of the range), we then check the amount of small flow excision. We can appropriately modify the excision amount at this point, but not more than 3% of the range.
1.3 Zeroing operation steps
- Close the shut-off valve downstream of the sensor.
- Ensure that the sensor is a full tube.
- Ensure that the fluid being measured has completely stopped flowing
- Then operate the transmitter panel function keys to enter the zeroing menu
- The default password to enter the offline menu of the transmitter is 1234, as shown in the diagram on the right.
- When zeroing is in progress, the top line of the display will be covered with dots, and the status LED will flash yellow.
1.4 Modifying the minor flow excision procedure (performed by HART275)
- Connect 250Ω resistors to transmitter outputs 1 and 2.
- Connect the HART signal line to outputs 1 and 2 of the transmitter (Figure 1 below).
- After power on communication is normal, find the mass or volume flow rate cut-out value according to the following tree (Figure 2).
2. Fault problem: U-tube noise, high vibration
2.1 Cause Analysis
U-tube is not full of the tube, or there is a foreign body inside the box, the drive gain becomes more significant than 20% or more.
2.2.1 Inspection and preparation
First, complete the preparatory work, then carry out the site inspection according to the inspection steps. If no problems are found, check whether the K1, K2, K3, and FD coefficients of the sensor core processor are consistent with the nameplate parameters.
2.2.2 Checking the parameters
If there are no problems with the parameters, then, if the process conditions allow, we can let the operator start the pump on the pipeline and flowmeter U-tube flushing, the last flush once to flush foreign bodies away. Then let the U-tube be full of media, and then zeroing (refer to fault problem one zeroing steps).
2.2.3 Check the amplitude of the vibration
If the flowmeter vibrates, we must remove the U-tube for cleaning and inspection. When dismantling it, we should close the upstream and downstream valves and then slowly open the drain valve. At this point, we then drain with the oil catcher. It is to prevent contamination of the ground or the meter box.
When opening the drain valve, please do not open it too far at a time to prevent a sudden spurt of the medium in the pilot line. However, we should not face the drain valve head-on. We should look sideways.
We should also take the necessary sheltering measures. The operator should stand upwind. It is to prevent static electricity from the combustible medium. It also prevents chemical damage from dangerous chemicals. It also prevents burns from hot media and frostbite from liquid hydrocarbons.
2.2.4 Installation of fittings
When cleaning and checking the filter, we clean up and finish back to install. The gasket should choose a suitable metal winding gasket. The gasket should be installed right in the middle, and the bolts should be installed with standard force and evenly.
2.2.5 Instrument operation check
18.104.22.168 Instrument commissioning.
We should carefully check whether the meter body’s valves, pressure lines, and sealing points are connected reliably. As well as each emptying point, drainage points are closed. The power supply and signal lines are connected reliably.
22.214.171.124 After commissioning the instrument
We do not leave the site immediately when the meter is in operation. We need to observe the process to prevent the medium from leaking and clean up the construction site after confirming it is correct. Then, inform the staff that the instrument is put into operation usually, close the various operation tickets issued before construction and file the operation tickets for inspection.
2.3 Checking the K-factor procedure (performed by HART 275)
- Connect 250Ω resistors in parallel to outputs 1 and 2 of the transmitter.
- Connect the HART signal line to outputs 1 and 2 of the transmitter (refer to Figure 1 for wiring). Check the relevant parameters according to the following tree diagram after regular communication has been switched on.
3. Fault problem: Density and temperature parameters or large fluctuations
3.1 Analysis of the cause
U-tube sensor coefficients are not set correctly, or the sensor is not full of tubes
3.2.1 Checking the sensor
We have to check whether the sensor K1, K2, K3, and FD coefficients are consistent with the nameplate parameters (refer to fault 2 for viewing steps). If we find that the coefficients are not constant, it could be that the core processor has been changed. Then we need to find the original processor and install it.
3.2.2 Removing the processor
When we replace the processor, the transmitter is to be done with the power off. Then, we have to loosen the fixing screw in the center of the core module, gently pull the core processor out of the housing and grasp and carefully remove the core processor from the sensor vertically upwards.
We try not to rotate or turn the core processor to avoid bending or damaging the pins.
3.2.4 Density parameters
If the density parameter fluctuates, consider whether the drive gain exceeds 20% and whether there is a mixture of gas and liquid phases in the sensor, the fluctuations can then be resolved by leaving the sensor with a full tube.
4. Fault problem: The transmitter head is zeroed for no apparent reason
4.1 Analysis of the cause.
Automatic zeroing of the totalized quantity at the full range or by human error
The zeroing function of the transmitter panel is disabled, operating as shown in the Figure.
5. Fault problem: The transmitter accumulation volume does not accumulate for no reason
5.1 Cause Analysis
Accumulation has been stopped by human error.
Disable the accumulation function of the transmitter panel, and proceed as shown in Figure.
6. Fault Problem: No density, temperature, or volume instantaneous flow variables are displayed on the transmitter display panel
6.1 Analysis of the cause
The transmitter display configuration menu is not set to display the appropriate variables.
Use the HART 275 to enter the “Online Menu – Display Setup Options” (see problem 1 for HART communication).
Then configure the variables to be displayed as follows.
7. Fault problem: The transmitter does not communicate with the DCS
7.1 Cause Analysis
- The transmitter power supply tripped the power off does not work.
- Communication line disconnection 485 conversion module failure.
- Transmitter communication protocol is incorrect address code is wrong.
7.2 Solution: Check the power supply line.
- Check that the power supply line is OK after re-opening the air to play on.
- Re-connect the communication line terminals, and replace the 485 conversion module.
- The ADDRESS MODBUS option is only displayed when the PROTOCOL item is set to RTU or ASCII.
- When the HART address is 0, the LOOP CUR HART item can still be used to turn off the loop current mode, and the transmitter will then prompt the A101 alarm message.
- To confirm the option type setting item, press SCROLL to select it, then press SELECT to like it when the screen alternately displays ST or E/SAVE? Then, press SELECT again to confirm. The offline menu is automatically exited if no key is pressed within 2 minutes.