Instrumentation and SCADA · Understanding Plant Instruments
What Are Accuracy and Repeatability?
A useful instrument must give readings that are close enough and steady enough for the job.
Accuracy means how close a reading is to the real value. Repeatability means the instrument gives nearly the same result when the condition has not changed. A stable wrong reading is still wrong.
A pressure gauge returns to the same mark each day, but a checked reference shows it is several pounds off. It repeats well, yet it needs correction or replacement.
The amount of accuracy needed depends on the job. A rough tank indicator may be fine for a quick field check but not for a compliance total. A laboratory reference may need tighter control than a room thermometer. Operators should know which instruments guide reporting, chemical feed, alarms, or equipment protection. Those devices deserve prompt attention when checks fail. Never adjust a reading only because it differs from what you expected. First confirm the reference and the checking method.
Give compliance and protective instruments the fastest response after a failed check.
Key point: Accuracy is how close a reading is to the real value; repeatability is giving the same result when nothing changed. A stable wrong reading is still wrong.
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Wastewater Instrumentation, SCADA, and Process Control Fundamentals
This page comes from the course. It covers plant instruments, signals and control, flow, level, pressure and water-quality measurement, SCADA and alarms, and instrument maintenance, one step at a time, with short knowledge checks and a certificate of completion.
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