The difference in the logarithms of the amplitude ratios at the frequency where the combined phase angle is 180 degrees lag is the gain margin.
The signal change before the output unit (valve or similar) moves.
Electronic hardware where the field devices are wired.
The integral part of the PID controller. With integral action, the controller output is proportional to the amount and duration of the error signal. If there is more integral action, the controller output will change more when error is present.
An upset to the process not from changing the set-point.
Lag time is the amount of time after the dead time that the process variable takes to move 63.3% of its final value after a step change in valve position.
Measurement is the same as the process value.
In manual mode the output is set manual.
The controller can be set in auto, manual, or remote mode.
Refers to the software that the process operator operates the process with.
Output of the controller.
The amount a process exceed the set point during a change in the system load or change in the set point.
Controller including Proportional, Integrating and Derivative controller functions. Cfr. ANSI/IEE Standard 100-1977.
The actual value in the control loop, temperature, pressure, flow, composition, pH, etc
Controllers replacing relay logic, usually with PID controllers.
The actual value in the control loop, temperature, pressure, flow, composition, pH, etc. See Process Value.
With proportional band the controller output is proportional to the error or a change in process variable. Proportional Band = 100/Gain
Same as the derivative or "D" part of PID controllers.
A data storage location in a PLC.
A controller changing the a output variable to move the process variable back to the set point
The variation in outputs for the same change of input.
Same as the integral or "I" part of PID controllers.
Integral action continuing to change the controller output value after the actual output reaches a physical limit.
The rate of interrogating a transmitter.
The rate at which a controller samples the process variable and calculates a new output.
The set point is the desired value of the process variable.
Same as lag time.
A transmitter sense the actual value of a system and transforms the value to a standardized signal - 4-20 mA is common for analog signals - as input for the control system.
Instrumentation and process control systems - design and documentation.
Devices - sensors - communicating physical properties to observers.
Proportional, integrating and derivative process controllers.
Standard signals used for transmission from sensor to controller.
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