Topic
PID
14 guides across the knowledge base.
Tasks and Execution Priority
How a controller schedules its work: the continuous task, periodic tasks at a fixed rate, event tasks triggered by something happening, how priority preempts, and where each kind of logic belongs.
7 min readUpdated Sep 5, 2026
Control Strategies
Choosing how a loop is controlled before choosing how to program it: on-off with deadband, staging, PID, ratio and feedforward, cascade, split range, and override, with the water and wastewater applications each fits and the questions that pick between them.
11 min readUpdated Sep 5, 2026
Distribution Pressure Control
How a booster or high service pump station holds discharge pressure with variable speed pumps, how pumps are staged, and what stops the system hunting.
9 min readUpdated Sep 5, 2026
Wet Well Level PID Control
Holding a wet well level with a variable speed pump instead of bang-bang control: the loop structure, the minimum speed floor, the stop and restart logic at low inflow, tuning for a slow integrating process, and where level PID is the wrong idea.
11 min readUpdated Sep 5, 2026
Booster Pump Stations
Inline stations that raise pressure from one zone to another: suction pressure protection, discharge pressure control with drives, staging, the hydropneumatic tank alternative, surge and check valve behavior, and the interlocks that keep a booster from collapsing the zone it draws from.
9 min readUpdated Sep 5, 2026
Disinfection Control
Controlling chlorine and chloramine dosing at a water plant: the CT concept and how contact time is credited, flow-paced and residual-trimmed feed, gas, hypochlorite, and on-site generation systems, the point-of-entry residual as the compliance measurement, and the interlocks that stop a feed system from over- or under-dosing.
11 min readUpdated Sep 5, 2026
Aeration Control
Controlling the largest energy user at a wastewater plant: the DO cascade to airflow, blower staging and turndown, most-open-valve pressure control across basins, ammonia-based aeration control, the instruments each strategy depends on, and the interlocks that keep blowers out of surge.
11 min readUpdated Sep 5, 2026
Flow Control in Water Pumping
Controlling the flow a pumping system delivers: speed against valves, flow-paced pumping to a treatment rate, the flow loop with its ramp limits and its meter placement, and the loop tuning that keeps a flow controller steady.
8 min readUpdated Sep 5, 2026
Membrane Control
The control system of a membrane skid: the loops for permeate flow, recovery, and dosing, the permissives and trips, the start, run, flush, and shutdown sequences, and the data the operators and the membrane supplier need from the historian.
9 min readUpdated Sep 5, 2026
How to Create a PID Loop in a PLC
Set up a PID instruction from scratch: scale the PV and CV, pick the action, set the execution rate, configure limits and anti-windup, tune conservatively, and test the manual and auto transitions before it controls anything.
10 min readUpdated Sep 5, 2026
Valve Hunting
A modulating valve that never settles: a loop tuned too hard, a positioner gain too high, stiction producing a limit cycle, a noisy command or feedback, an oversized valve working near its seat, or two loops fighting. The manual test that separates them.
8 min readUpdated Sep 5, 2026
Valve Slow to Respond
A valve that takes far longer to move than it should: a pneumatic supply restricted or leaking; a positioner tuned slow; an electric actuator whose speed is fixed; a stem binding in cold or packing; or a rate-limited output. Measuring the stroke time.
8 min readUpdated Sep 5, 2026
The Chlorine Residual Loop Is Slower Than You Think
Residual control loops oscillate because the measurement arrives minutes after the dose changes, and the tuning was done as if it arrived at once. Where the delay comes from, and how to control a loop whose dead time is longer than its response.
10 min readUpdated Sep 5, 2026
PID Control for Pumps and Valves
What each term actually does, how to tune a loop on a real pump station, and the handful of mistakes that cause most of the oscillation people blame on tuning.
11 min readUpdated Aug 19, 2026
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