Signals and functions
Quantity or condition in a process which is intended to be measured and controlled.
Quantity or condition which the automatic controller applies to a controlled system.
Signal established as a standard to be followed by a controlled variable in a control system.
Constant reference signal which fixes an operating point or a point of initial response.
Input which is established or varied by some means external to an automatic control system.
Signal where information is contained in its deviation from a centre frequency.
Signal that is a direct measure of the output of a system and is compared directly with its input.
ERROR [ACTUATING] SIGNAL
Difference between the reference input and the primary feedback signal.
FREQUENCY RESPONSE FUNCTION
Variation with frequency of the gain and the phase shift of the output in response of a system to a sinusoidal input.
ERROR [ACTUATING] SIGNAL RATIO
Frequency response of error to input signal.
CLOSED-LOOP HARMONIC RESPONSE [CONTROL RATIO]
Frequency response of output to input signal.
OPEN-LOOP HARMONIC RESPONSE [LOOP RATIO]
Frequency response of the output to error signal.
Magnitude of the output from a linear system in response to a sinusoidal input of unit amplitude.
Phase angle of the open-loop harmonic response.
Magnitude of the open-loop harmonic response.
1. Factor by which the loop gain must be multiplied to cause instability of closed-loop control system. 2. Loop gain at phase crossover.
Point in the plot of loop gain at which the magnitude of loop gain is unity.
Point in the plot of loop gain at which the phase angle is 180¢.
Additional phase lag that, when introduced into the open-loop frequency response at gain crossover, causes instability of a closed-loop system.
Output of a system as a function of time, following the application of a standard input.
Time for the output of a system first to reach a specified value in response to a step input.
Time for the output of a system to increase from one specified percentage of the final value to another, in response to a step input.
Time for the absolute value of the difference between the output of a system and its steady-state value to become and remain less than specified amount, in response to a step input.
Function which is zero for all values of time prior to a certain instant and constant thereafter.
Reduction in the amplitude of a signal whilst the waveform is maintained.
Attenuation increasing with time.
Interval of time by which a particular phase of one waveform follows the corresponding phase of another.
Control without the use of feed back.
Control by a system in which the input signal to its actuator is a function of the error signal.
Control by a system in which the input signal to its actuator is proportional to the error signal.
Control by a system in which the input signal to its actuator is proportional to the derivative of its error signal.
Control scheme whereby the signal that drives the actuator equals the time integral of the error signal.
Accuracy and Errors
Capability of an instrument to follow the true value of a given phenomenon.
Degree of reproducibility among several independent measurements of the same true value under specified conditions.
Property of an instrument that determines its scale factor.
Extent to which the sensitivity of an instrument remains constant with time.
Gradual change with time in the properties of a system or in its response to a constant input.
Absence of drift when an indicating instrument is at zero.
Smallest change in input that produces a detectable change in the output of an instrument.
Resolution capable of stepless adjustment.
Range of values through which the input of a system can be varied without initiating output response.
Difference between desired and actual value of the controlled variable.
Difference, due to approximations in design, between the function actually generated by a mechanism and the one that it was required to generate.
Maximum (minimum) of the transient response of a system caused by varying the input from one steady value to another.
Difference between instantaneous system error and steady-state error for a specified stimulus.
Error that remains after the transient response has expired.
Constant error as a result of which the output of a device is not zero when the input is zero.
STATIC ERROR BAND
Spread of error due to the failure of a readout device to return to zero when the input is zero.
DYNAMIC ERROR BAND
Spread or band of output-amplitude deviation when the frequency of a constant-amplitude sine wave is varied over a specified part of the frequency spectrum.
Total interval over which an instrument operates.
Range of frequencies over which a given device operates to a required standard.
Ratio of real to analogue values.
Devices and Components
Component required to produce the manipulated variable or the actuating signal in a control system.
Device that measures the error in a feedback control system and regulates the power needed to reduce or eliminate the error.
Component that produces the primary feedback from a controlled variable.
AUTOMATIC [FEEDBACK, CLOSED-LOOP] CONTROL SYSTEM
Any operable arrangement of one or more automatic controllers connected with one or more processes.
Feedback control system in which the reference input is a function of time.
Servosystem in which the controlled variables is a mechanical quantity.
Feedback control system the primary concern of which is to keep the value of the controlled variable constant.
Regulator used to keep the speed of an engine constant.
Device used to reduce the magnitude of a shock or vibration.
Absorber which operates by the dissipation of energy.
Device to modify the natural frequencies of a vibrating system.
Device used to increase the stiffness of an elastic system (usually by a large factor) whenever the displacement becomes larger than a specified amount.
Device used to interpolate between the graduations of a measuring scale.
Device for translating the changing magnitude of one kind of quantity into corresponding changes of another kind of quantity.
Transducer , the output of which is proportional to its displacement input.
Transducer, the output of which is proportional to its velocity input.
Transducer , the output of which is proportional to its acceleration input.
Light source that can be adjusted to flash at a desired rate.
Optical device in which a beam of light is divided into two parts which travel different paths and recombine to form interference fringes.
Point in a circuit used as a common reference or datum point for measuring voltages.
Device for sensing, selecting and transmitting of signals for control purposes.