Question regarding instrument parameters

P: Proportional gain; I: Integration time; D: Derivation time. The larger P and I are, the weaker the control effect； The larger D is, the stronger the regulatory effect. D is generally used in situations where the parameter being regulated changes slowly, such as in temperature control. For general purposes, P=100, I=1 min, and D=0 are sufficient. Of course, the PID needs to be adjusted based on actual conditions. This is an unfinished topic; if I have time, I will post a more in-depth explanation on the following link. Stay tuned. http://bbs.hcbbs.com/thread-692942-1-1.html List some of the instrument-related concepts that you find most difficult to understand

This post was last edited by denghl on 2010-7-15 at 11:05; it was duplicated, so this is to make the correction. Please understand.

In practical applications, this issue is mainly addressed by adjusting the PI parameters; this helps to eliminate deviations and reduces the time required for adjustment. However, there is a phase deviation, and D serves as a complement to the previous two parameters, enabling the adjustment process to meet the requirements better in complex systems

Reply 4# azter: PI is used in simple control systems or single-loop systems. For more complex control loops, differential regulation is required in order to achieve lead control and eliminate disturbances, thereby improving the quality of control. The larger D is, the stronger the regulating effect, as the differential time appears in the simulation equation in a direct proportional manner; however, an excessively large value can also cause instability in the system. P refers to the proportionality, which is the reciprocal of the amplification factor K; thus, the higher its value, the weaker the regulating effect. I represents integration, and it appears in the analog equation in an inverse proportional manner, meaning that a higher value results in a weaker effect. In the PID control process, it’s not true that the larger the parameters, the better, nor that the smaller they are, the better. It is only through the establishment of mathematical models, the application of empirical formulas, simulation experiments, and practical experience that appropriate parameters can be determined in order to achieve good control quality.

What the people above have said is not repetitive; generally, the D parameter is used in systems with large time lags, such as temperature PID control. In some systems, such as those for pressure and flow regulation, the D parameter is not typically used. In addition to setting the PID parameters, it is important not to forget the sampling period parameter, which is also crucial for PID control and directly affects its performance.

Reply to 5# mainsj: In practical applications, it’s usually not very complex; most cases involve simple control, with only a few cases requiring complex control systems such as cascade control. She is right – for simple circuits, PI control is sufficient; PID is not used very often. Anyway, thank you

Adjust the parameters to find the optimal setting; check in ascending order. Start with the proportional term, then the integral term, and finally add the derivative term. If the curve oscillates frequently, increase the value of the proportional gain. If the curve wanders around in large loops, reduce the value of the proportional gain. If the curve takes a long time to return to its normal position, decrease the integral time. If the curve has long fluctuation cycles, extend the integral time further. If the oscillation frequency of the curve is high, first reduce the value of the derivative term. Large errors lead to slow fluctuations. The differential time should be increased. For the ideal curve, there are two waves – higher at the beginning and lower at the end, in a 4-to-1 ratio. Observe carefully, make adjustments as needed, and conduct thorough analysis; this way, the quality of the adjustments will remain high

It’s really difficult to get a system tuned properly, especially when it comes to distillation processes

The analysis of instrument issues is quite complex; for an instrument control system that has been in operation for a long time, there are various problems and causes to consider, as well as many hardware-related issues, making it difficult to determine the root causes