DCS control valve proportional-integral control

In DCS (Distributed Control Systems), for control valves using proportional-integral (PI) control, it is usually necessary to adjust the proportional band (PB, sometimes also referred to as proportional gain) and integral time (TI) in order to achieve optimal control performance. Here are the general steps: 1. **Define control objectives**: First, determine the performance goals you want the control loop to achieve, such as fast response, reduced overshoot, or lower steady-state error. 2. **Conduct manual tests**: Before starting adjustments, manually change the setpoints or outputs to observe the relationship between the process variable (PV) and the control valve output (MV), as well as the system’s dynamic response. 3. **Adjusting the Proportional Band (PB)**: The proportional band determines the intensity of the proportional action; the smaller the proportional band, the stronger the proportional effect. Typically, one can start with a larger proportional band and then gradually reduce it until oscillations begin to occur in the system; after that, the proportional band is increased slightly until the system stabilizes. If the proportional band is too small, the system may become overly sensitive and experience excessive oscillation. If it is too large, the response may be too sluggish. 4. **Adjust the integration time (TI)**: The integration time determines the speed of the integration process; the shorter the integration time, the faster the integration occurs. The integral action is intended to eliminate static errors. If the integration time is set too short, the system may oscillate ； If it is too long, the system’s speed of adjusting for deviations will slow down. A longer integration time can be set initially, and then gradually reduced until the system is able to eliminate the deviation within an acceptable time. 5. **Perform closed-loop testing**: After adjusting the parameters, conduct a closed-loop test on the system, observe the actual response, and make fine-tuning adjustments as needed. Check whether the system can quickly return to a steady state after being perturbed. 6. **Recording and Monitoring**: Once satisfactory adjustment parameters are found, it is necessary to record them, and continuously monitor the system’s performance to be ready to make any necessary adjustments at any time. Please note that when making adjustments, it is also necessary to take into account the characteristics of the process, such as dead zones, lag, non-linearity, and other factors; moreover, each process may require a different adjustment strategy. There are also some advanced methods, such as the Ziegler-Nichols closed-loop method, which can be used to determine the control parameters more scientifically. In actual operation, it is necessary to follow the DCS system guidelines or the specific operating procedures of your company. .

The configuration engineer didn’t do a good job. Usually, a parameter is set during configuration, and adjustments are made during actual operation based on the real conditions; I’ve never encountered such a problem with TI!

Please send over the SV, PV, and MV curves; this graph shows only PV, and it’s hard to tell apart MV from it.

This post was last edited by liu530014416 on 2023-12-3 at 22:12. This is the MV curve; it applies to PB 100 and TI 60 in most cases. There’s no setting of 2500 for TI. If the PV fluctuates too much or the control valve isn’t selected appropriately, then no adjustments will work.

Personally, I feel that the oscillations are too strong, and there are periodic intense disturbances. By identifying the source of these disturbances and eliminating them, it becomes possible to increase the impact of scaling and integration.