# Machine controls and measurement

English

## Signals and functions

4.1.1 CONTROLLED VARIABLE
Quantity or condition in a process which is intended to be measured and controlled.
4.1.2 MANIPULATED VARIABLE
Quantity or condition which the automatic controller applies to a controlled system.
4.1.3 REFERENCE INPUT
Signal established as a standard to be followed by a controlled variable in a control system.
4.1.4 BIAS
Constant reference signal which fixes an operating point or a point of initial response.
4.1.5 COMMAND [INPUT]
Input which is established or varied by some means external to an automatic control system.
4.1.6 FREQUENCY-MODULATED SIGNAL
Signal where information is contained in its deviation from a centre frequency.
4.1.7 PRIMARY FEEDBACK
Signal that is a direct measure of the output of a system and is compared directly with its input.
4.1.8 ERROR [ACTUATING] SIGNAL
Difference between the reference input and the primary feedback signal.
4.1.9 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.
4.1.10 ERROR [ACTUATING] SIGNAL RATIO
Frequency response of error to input signal.
4.1.11 CLOSED-LOOP HARMONIC RESPONSE [CONTROL RATIO]
Frequency response of output to input signal.
4.1.12 OPEN-LOOP HARMONIC RESPONSE [LOOP RATIO]
Frequency response of the output to error signal.
4.1.13 GAIN
Magnitude of the output from a linear system in response to a sinusoidal input of unit amplitude.
4.1.14 LOOP PHASE
Phase angle of the open-loop harmonic response.
4.1.15 LOOP GAIN
Magnitude of the open-loop harmonic response.
4.1.16 GAIN MARGIN
1. Factor by which the loop gain must be multiplied to cause instability of closed-loop control system. 2. Loop gain at phase crossover.
4.1.17 GAIN CROSSOVER
Point in the plot of loop gain at which the magnitude of loop gain is unity.
4.1.18 PHASE CROSSOVER
Point in the plot of loop gain at which the phase angle is 180ยข.
4.1.19 PHASE MARGIN
Additional phase lag that, when introduced into the open-loop frequency response at gain crossover, causes instability of a closed-loop system.
4.1.20 TIME RESPONSE
Output of a system as a function of time, following the application of a standard input.
4.1.21 RESPONSE TIME
Time for the output of a system first to reach a specified value in response to a step input.
4.1.22 RISE TIME
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.
4.1.23 SETTLING TIME
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.
4.1.24 STEP FUNCTION
Function which is zero for all values of time prior to a certain instant and constant thereafter.
4.1.25 ATTENUATION
Reduction in the amplitude of a signal whilst the waveform is maintained.
4.1.26 DECAY
Attenuation increasing with time.
4.1.27 LAG [DELAY]
Interval of time by which a particular phase of one waveform follows the corresponding phase of another.
4.1.28 OPEN-LOOP CONTROL
Control without the use of feed back.
4.1.29 CLOSED-LOOP CONTROL
Control by a system in which the input signal to its actuator is a function of the error signal.
4.1.30 PROPORTIONAL CONTROL
Control by a system in which the input signal to its actuator is proportional to the error signal.
4.1.31 DERIVATIVE CONTROL
Control by a system in which the input signal to its actuator is proportional to the derivative of its error signal.
4.1.32 INTEGRAL CONTROL
Control scheme whereby the signal that drives the actuator equals the time integral of the error signal.

## Accuracy and Errors

4.2.1 ACCURACY
Capability of an instrument to follow the true value of a given phenomenon.
4.2.2 PRECISION
Degree of reproducibility among several independent measurements of the same true value under specified conditions.
4.2.3 SENSITIVITY
Property of an instrument that determines its scale factor.
4.2.4 GAIN STABILITY
Extent to which the sensitivity of an instrument remains constant with time.
4.2.5 DRIFT
Gradual change with time in the properties of a system or in its response to a constant input.
4.2.6 ZERO-LINE STABILITY
Absence of drift when an indicating instrument is at zero.
4.2.7 RESOLUTION
Smallest change in input that produces a detectable change in the output of an instrument.
4.2.8 INFINITE RESOLUTION
Range of values through which the input of a system can be varied without initiating output response.
4.2.10 SYSTEM ERROR
Difference between desired and actual value of the controlled variable.
4.2.11 STRUCTURAL ERROR
Difference, due to approximations in design, between the function actually generated by a mechanism and the one that it was required to generate.
4.2.12 OVERSHOOT (UNDERSHOOT)
Maximum (minimum) of the transient response of a system caused by varying the input from one steady value to another.
4.2.13 TRANSIENT ERROR
Difference between instantaneous system error and steady-state error for a specified stimulus.
Error that remains after the transient response has expired.
4.2.15 OFFSET ERROR
Constant error as a result of which the output of a device is not zero when the input is zero.
4.2.16 STATIC ERROR BAND
4.2.17 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.
4.2.18 FULL SCALE
Total interval over which an instrument operates.
4.2.19 BANDWIDTH
Range of frequencies over which a given device operates to a required standard.
4.2.20 SCALE FACTOR
Ratio of real to analogue values.

## Devices and Components

4.3.1 CONTROL ELEMENT
Component required to produce the manipulated variable or the actuating signal in a control system.
4.3.2 AUTOMATIC CONTROLLER
Device that measures the error in a feedback control system and regulates the power needed to reduce or eliminate the error.
4.3.3 FEEDBACK ELEMENT
Component that produces the primary feedback from a controlled variable.
4.3.4 AUTOMATIC [FEEDBACK, CLOSED-LOOP] CONTROL SYSTEM
Any operable arrangement of one or more automatic controllers connected with one or more processes.
4.3.5 SERVOSYSTEM
Feedback control system in which the reference input is a function of time.
4.3.6 SERVOMECHANISM
Servosystem in which the controlled variables is a mechanical quantity.
4.3.7 REGULATOR
Feedback control system the primary concern of which is to keep the value of the controlled variable constant.
4.3.8 GOVERNOR
Regulator used to keep the speed of an engine constant.
4.3.9 ABSORBER
Device used to reduce the magnitude of a shock or vibration.
4.3.10 DAMPER
Absorber which operates by the dissipation of energy.
4.3.11 DETUNER
Device to modify the natural frequencies of a vibrating system.
4.3.12 SNUBBER
Device used to increase the stiffness of an elastic system (usually by a large factor) whenever the displacement becomes larger than a specified amount.
4.3.13 VERNIER
Device used to interpolate between the graduations of a measuring scale.
4.3.14 TRANSDUCER
Device for translating the changing magnitude of one kind of quantity into corresponding changes of another kind of quantity.
4.3.15 DISPLACEMENT TRANSDUCER
Transducer , the output of which is proportional to its displacement input.
4.3.16 VELOCITY TRANSDUCER
Transducer, the output of which is proportional to its velocity input.
4.3.17 ACCELEROMETER
Transducer , the output of which is proportional to its acceleration input.
4.3.18 STROBOSCOPE
Light source that can be adjusted to flash at a desired rate.
4.3.19 INTERFEROMETER
Optical device in which a beam of light is divided into two parts which travel different paths and recombine to form interference fringes.
4.3.20 GROUND
Point in a circuit used as a common reference or datum point for measuring voltages.
4.3.21 SENSOR
Device for sensing, selecting and transmitting of signals for control purposes.