Sep
26
The process gain may be negative or positive depending on the process design. To provide the correct response a feedback control block must take into account the process gain direction—whether to increase or decrease the manipulated input to correct for a control error. For example, the inlet flow to a tank may be manipulated to …
Aug
25
The extreme capability of the pH measurement and the broad spectrum of applications and process conditions create exceptional requirements for electrode design, mixing uniformity, control valve precision, deadtime minimization, nonlinearity compensation, and control strategies. pH loops are often the most challenging loops in the plant. Slight deficiencies in the mechanical, piping, process, measurement, and control …
Aug
22
In many processes, it is desirable to have an overdamped response. To achieve that response, the proportional gain used in the PID is typically much less than that required for an underdamped or unstable response. When selecting the PID gain, it is important to consider that the process gain may change with the operating conditions. …
Aug
08
From a control perspective, it is highly desirable that the process gain be constant. If the process gain is constant, then the same proportional gain may be used over the entire operating range of the control loop. However, if for example the valve characteristic has not been selected based on the process requirements, then the …
Aug
04
The increasing emphasis on saving energy and capital costs can lead to pump and piping designs that inadvertently cause a severe loss of turndown in flow loops and a significant increase in noise , delay, and lag in temperature and pH loops. The deterioration in loop performance can create an insidious reduction in process efficiency …
Aug
01
As addressed in my July 18th and July 25th blogs, to achieve best control performance, it is important that the final control element moves to a position that matches that requested by the control system. The minimum size of change in the PID output that the control element can respond to can be quickly confirmed …
Jul
28
Mixing changes the game. Mixing has a broad impact on disturbances, interactions, and noise. Mixing breaks paradigms on tuning, control, and performance. Mixing is at play in key unit operations offering incredible tightness of control and forgiveness of mistakes enabling exceptional product quality. I became sensitized to the role of mixing early in my career …
Jul
25
As addressed in my July 18th blog, when a valve positioner is installed on a valve actuator, as long as it is functioning properly it will automatically increase the actuator pressure until the valve moves to a position that matches that requested by the control system. Feedback of the stem position is used by the …
Jul
18
When commissioning a control system, it is important to be aware of whether a regulating valve is equipped with a positioner. If a valve does not have a positioner, then as part of loop commissioning it may be necessary to install a positioner on the valve to achieve the desired control performance. For various reasons, …
Jul
15
A loop is only as good as its setpoint. Most loops are not operating at the best setpoint for 9 major reasons. For sustainable manufacturing we need to understand and address these reasons to achieve better setpoints to reduce the energy, raw material, recycle, and waste and provide more flexible production while maintaining product quality. Reducing …
