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INDEX

H

Harmonic
Sinusoidal quantity with a frequency equal to an integer times the fundamental frequency.
Note: A sinusoidal quantity with a frequency equal to an integer of 2 or more times the fundamental frequency is called a higher harmonic.
High-Speed Balancing
Balancing performed at a rotating speed under which the rotor cannot be assumed to be a rigid body.
Hysteresis
Dependency of output value occurring from the past record and direction of changes with respect to changes of a given input.
Note:
(1) Generally, hysteresis is obtained by subtracting the dead band value from the
      maximum measurement interval occurring between the forward and backward
      travels of the measured-quantity indication (or output) after the transient state
      ahs settled.(unless otherwise noted, the indication or output is changed over
      the entire range.)
(2) If an extremely small input is reversed a few times, output is also expected to
      be reversed a few times. According to this method, the dead band is distinguished
      from the hysteresis.

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I

Inductive Load
Load containing a reactance component.
Input Bias
Bias added to the input signal.
Input Impedance
Impedance included in a circuit of a device when its inside is looked from the input terminal.
Input/Output Isolation
Synonym for isolation.
Input Resistance
Resistance component in a circuit when the equipment is viewed from the input terminal side of the equipment.
Insulation Resistance
Electric resistance between two conductors insulated by an insulator.
Example: More than 20 MΩ at 500 VDC (between each power terminal and the grounding terminal)
Interchangeability
Capable of being mutually interchanged.
For products, there is dimensional or characteristic interchangeability.
Internal Resistance
Resistance component in a circuit when the equipment is viewed from the input or output terminal side of the equipment.
Intrinsically Safe Construction
Explosion proof construction that the electric spark during normal operation or in a failure state, or heated part will not ignite the surrounding explosive gas, which has been proven by an official body’s evaluation or equivalent.
Isolation
No common line should exist between input and output signals of equipment.
Isolation between input and output signals of equipment.

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J

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K

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L

Linearity
Linearity obtained when the maximum deviation between a calibration curve and the specified straight line is approximated to become a minimum.
Linear Range
Measurement range that satisfies the specifications of a transducer, such as sensitivity, scale factor, linearity, etc.
Linear System
System whose response is proportional to the size of excitation.
Note: According to this definition, the dynamic characteristic of each element in the system is expressed by a series of linear differential equations and the principle of superposition can be applied to this system.
Linear Transducer
Transducer whose output is proportional to input within the specified frequency range.
Linear Viscous Damping Coefficient / Viscous Damping Coefficient
Ratio of damping force to speed.
Linear Viscous Damping / Viscous Damping
Energy consumed when an element or a part of an element in a vibration system receives a resistance for proportional to the element speed in the opposite direction.
Lissajous Figure
Steady diagram draw when two simple harmonic motions whose frequency rates are expressed by a simple integer ratio are initiated in mutual directions at right angles.
Note: The Lissajous figure varies with the difference of phase angles of simple harmonic motions.
Load
Part connected to the output side of equipment and consuming or absorbing output energy.
Low-speed Balancing
Balancing performed at a rotating speed at which the rotor is assumed to be a rigid body (generally, the speed slower than the operating speed).

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M

Mass Eccentricity
Distance from the shaft center line to the rotor center of gravity.
Maximum Load
Maximum load which can be connected to the output side of the equipment.
Measuring Period
Time interval between the present and nest measurements when measuring at fixed intervals.
Measuring Range
Range of the maximum and minimum measured variables.
Measuring Span
Difference between measurement result is obtained from the start of measurement.
Measuring Time
Time required from measurement start to acquirement of measurement result.
Modal Analysis
(1) To conduct response analysis in each mode and to obtain the response waveform
      of the entire system by adding response waveform.
(2) To obtain the maximum response value in each mode and to obtain the estimated
      maximum response value of the entire system by an appropriate method of addition.
Modal Balancing
Balancing operation to correct the flexible-rotor vibration amplitude to within the specified limit for each mode.
MTBF (Mean Time Between Failures)
Mean time between consecutive failures occurring in the specified period, and condition within the service life of each equipment.
MTTR (Mean Time to Repair)
Mean time required for repair work.

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N

Natural Mode of Vibration
vibration mode in a freely vibrating system.
Notes:
(1) If there is no attenuation in the system, the natural mode is the same as the normal mode.
(2) The natural mode of vibration exists corresponding to each degree of freedom in the system.
NC (Normally Closed)
Contact which opens when the contact is activated or at power-ON.
Note: Also called "b" contact.
NO (Normally Open)
Contact which closes when the contact is activated or at power-ON.
Note: Also called "a" contact.
Nyquist Diagram
Technique of evaluating the safety in a control system conceived by H. Nyquist.
Diagram which shows the shaft vibration vector of rotating machinery on polar coordinates with the number of revolutions as a parameter.

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Reference
Terms for measurement:
JIS Z8103
Terms for performance of industrial instruments:
Japan Electrical Measuring Instrument
Industry Association
Vibration Engineering Handbook:
Yoken-Do
Terms for electronic measuring instrument:
Japan Electrical Measuring Instrument
Industry Association

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