Let’s discuss the material addition plan with the forum members

Ideals are lofty, but reality is harsh! Consider the actual installation conditions of the equipment on site; if it’s ideal, either option will work. Consider the addition amount, pipe size, and weighing deviation rate. Depending on the size of the metering tank, if the amount added is small, it would be better to install a drip feeding tank (with weighing function) above the reactor. If the metering tank is on the same floor and the liquid is pumped into the reactor, consider the volume remaining in the pipes. Also take into account the weighing error of the metering tank, as well as whether flexible connections are used to completely eliminate the effects of stress. It is best to have a well-designed system with flow meters for measurement, and to ensure that the pipes connected to the flow meters are not empty (consider adding return pipes).

The first approach is simple and direct, requires minimal skills from the operator, and is easy to implement. However, this fixed dripping rate may not be quick enough to respond to the dynamic changes in the fluid in practical operations, posing a risk of over- or under-dosing. The second option is more flexible, as it allows the dripping rate to be adjusted based on real-time conditions, which better meets the needs of dynamic adjustment. Although the continuous variation in the SV value may pose control challenges, this method allows for more precise control over the addition of materials; it enables finer adjustments, especially when approaching the target amount, to prevent exceeding the required quantity. It is recommended to conduct preliminary tests, taking into account practical operational experience and specific process requirements, in order to evaluate which approach is more suitable for your system. If the system changes little and high precision is not required, the first option can be chosen ； If high requirements are placed on accuracy and adjustment flexibility, it is recommended to try the second approach and to refine the PID parameters further to ensure the stability of the control system. You can also consider setting a safety threshold to prevent excessive dripping. .

The first approach is simple and direct, suitable for situations where the drop volume and time are relatively fixed. The operation is intuitive and easy to implement and debug, but the drawback is a lack of flexibility, as it cannot automatically adjust the dripping rate according to the actual dripping process. The second option is more intelligent and flexible, capable of adjusting the dripping rate in real time based on the remaining time and amount, making it more suitable for applications that require high precision. However, the control algorithm for this approach is relatively complex, requiring more precise adjustment of PID parameters to ensure the stability and response speed of the control system. It is recommended to select an appropriate solution based on actual production needs and on-site conditions. If the process requires high precision in droplet addition and short completion times, the second approach can be considered, along with thorough simulation and testing prior to production to ensure the stable operation of the control system. If the process requirements are relatively relaxed, or if budget and technical support are limited, the first option may be more suitable. .

The SV of the PID controller has been calculated; what about the PV of the PID controller? ?

It is possible to determine the flow rate indirectly by weighing, but I recommend calculating the flow rate based on time once there is a change in weight. For example, if the weight is 100.1 and it drops to 100.0 after 20 seconds, the flow rate would be 0.3 kilograms per minute; of course, it can also be expressed in kilograms per hour, which would be 18 kilograms per hour. Procedurally, value fluctuations should be ignored; if the historical weight is greater than the current weight, it is ignored. Of course, it can also be handled in this way: when the value drops by 0.1 kilogram, record time A; then start timing with B, and after a delay of 5 seconds, if the value still hasn’t increased, use A as the denominator to calculate the flow rate, while assigning the value from B’s timing to A’s timing. Generally, it’s no problem to add it drop by drop within a few minutes. Calculate the dripping flow rate. At first, you don’t know the exact value of this flow rate. Your metering pump likely adjusts the flow rate by changing the frequency of the motor; initially, the frequency is set based on experience to start the pump in operation. When the electronic scale shows a change, the flow rate can be determined. A formula can be used to calculate the frequency required by the motor. Once the flow rate can be determined from these value changes, the adjusted frequency can be calculated. For example, if the current frequency is 30 Hz and the flow rate is 5 kilograms per minute, while the desired flow rate is 6 kilograms per minute, then the adjusted frequency would be 36 Hz. This does not require PID calculation to handle, nor does it need to be computed frequently.

Please have the external process control engineer handle it

If timer B does not reach 5 seconds before jumping again, add the time from B to A and reset timer B.

PV is also calculated; it’s simply the amount added drop by drop divided by time

This requires a high level of operational experience, and many trials are needed. But thanks to the forum member – it was very helpful; indeed, some processing and filtering of the data is necessary

GPT: Advantages and disadvantages of the two approaches. Approach 1: Fixed setpoint control. The first approach you mentioned involves dividing the total amount to be added, as set by the operator, in KG, by the time required, in MINs, to obtain a fixed dripping rate (SV setpoint). The actual dripping rate (PV) is then calculated based on the weight changes detected by the weighing system, and this value is fed back to the PID controller for adjustment. Advantages: Easy to implement: Once the target dosing amount and time are set, the control logic of the system is relatively simple; the operator only needs to enter the parameters once, and the PID control will carry out dosing at a constant rate. The system is relatively stable: Since SV is fixed, the entire control process remains unchanged, with no need for frequent adjustments, which makes it easy to maintain system stability. Disadvantages: Poor robustness: If there are uneven drops during the process (such as fluctuations in flow rate or changes in pump performance), this approach cannot handle such situations effectively; as a result, cumulative errors occur toward the end, preventing achievement of the precision required by the process. Lack of feedback adjustment mechanism: After the dripping process has proceeded for some time, if there is a deviation in speed, the system is unable to make timely dynamic adjustments. In particular, it is unable to self-correct for system disturbances or changes that may occur during the dropwise addition process. Application scenarios: This solution can be considered when the system has high stability, the pump flow rate remains consistent, and there is little environmental interference, as it is simple and does not require frequent adjustments. Option 2: Dynamic setpoint control. The idea behind the second option is to dynamically adjust the SV setpoint based on the remaining amount to be added and the remaining time. The required dripping acceleration rate is dynamically set by continuously recalculating the ratio of the remaining amount to the remaining time. Advantages: Dynamic adaptive adjustment: The advantage of this approach is its ability to make adjustments in real time based on the actual dripping progress. Especially when errors occur during the process, SV can be adjusted dynamically to ensure that the remaining amount can be delivered within the time left, thus avoiding significant errors in the final stages. Higher precision: Even if there is some uneven dripping in the initial stage, the system can make self-corrections through dynamic calculation of the remaining amount, ensuring accurate completion within the specified time. Disadvantages: High control complexity: The dynamic changes in SV introduce a certain level of control complexity. PID controllers may become unstable when the setpoint changes frequently, especially in systems with slow response, which can lead to over-shoot or oscillation in the system. Difficult to debug and optimize: As SV changes over time, adjusting PID parameters can become more challenging, especially in determining the appropriate PID values to balance the relationship between the dynamically changing SV and the actual control speed. Application scenarios: If the system experiences significant traffic fluctuations, many environmental disturbances, and high precision is required, this solution may be more suitable, as it has adaptive capabilities that allow for real-time adjustments. Optimization suggestions for the plan: Based on the improvements to Plan 2, you could consider adding a constraint condition on top of dynamically setting the SV. For example, the rate of change or range of SV can be set to prevent overly frequent and drastic adjustments to SV, thereby reducing the risk of system oscillation. This allows for improved system stability while maintaining the adaptive advantages of Option 2. You can introduce a feedforward control mechanism. Based on the actual amount of addition, predicting possible future changes in advance and making preliminary adjustments to the set values of the PID controller can reduce the lag and adjustment fluctuations of the controller. Real-time error correction: In Option 1, a mechanism for periodically checking errors can be introduced. For example, check the error between the actual amount of addition and the expected amount of addition at regular intervals (such as every 5 minutes). If the error exceeds a certain range, a minor adjustment is made to SV so that subsequent additions can better compensate for the error. This approach can enhance the robustness of Option 1. Hybrid control scheme: A combination of the two can be considered. In the initial phase (for example, the first 20 minutes), fixed SV control according to Scheme 1 is employed to ensure the system’s stability at the beginning. In the later stage (the last 10 minutes), if a large discrepancy is detected between the actual amount added and the set value, dynamic adjustment according to Plan B is activated, with the set value being corrected in real time to complete the remaining amount of addition. Summary: Option 1 is suitable for scenarios where the system is relatively stable and there is little environmental interference; it is simple to operate, but lacks the ability for dynamic adjustment. Option 2 is more suitable for scenarios with high precision requirements and significant system variations; it allows for dynamic adjustments, but it also involves greater complexity in control and higher difficulties in debugging. If the system permits, adopting a progressive control strategy that combines the advantages of these two approaches could be a more balanced option.