This refers to a change in velocity over time. In dynamic measurements, acceleration is a fundamental quantity measured by accelerometers; it is typically expressed in units of *g* or m/s², where 1*g* ≈ 9.80665 m/s².
A specialized type of transducer designed to measure acceleration. These devices operate based on the inertial force generated when an internal mass (seismic mass)—connected to a piezoelectric element—is subjected to external acceleration. Types include:
This refers to a mechanical motion characterized by alternating periods of acceleration and deceleration around a reference point. Such motion is typically periodic or oscillatory and is often expressed in terms of displacement, velocity, or acceleration values. Vibration may occur along one or more axes (axial, radial, or along three orthogonal axes); multi-axis analysis is applied to machinery exhibiting complex motion.
This is the process of monitoring machine parameters—such as vibration, temperature, or oil quality—to detect significant deviations that indicate the onset or progression of faults within the equipment. Condition monitoring serves as the empirical foundation for implementing predictive maintenance strategies.
This involves the use of control systems, such as PLCs or DCSs, to manage and operate industrial equipment and processes with minimal human intervention. These systems typically utilize feedback from sensors to facilitate closed-loop control.
A characteristic that describes the variation in a sensor’s sensitivity (output value relative to the input) across its operational frequency range. An ideal sensor exhibits a perfectly flat frequency response within its specified bandwidth.
The natural frequency of the sensing element or its internal structure—the frequency at which the oscillation amplitude reaches its maximum. At this point, signal distortion is likely to occur, unless the mounting structure provides significant damping.
In charge amplifier circuits or sensor circuitry, this refers to the time required for a signal—generated by a step input (such as a constant acceleration)—to decay (returning toward its initial value). This parameter determines the system’s low-frequency cutoff.
Certain crystalline materials, such as quartz or PZT, possess the property of generating an electrical charge proportional to the mechanical stress or strain applied to them. This phenomenon forms the operating principle for most dynamic sensors.
This is the ratio of the sensor’s output signal to the magnitude of the physical quantity being measured. For accelerometers, it is typically expressed in units of mV/g or pC/g and is standardized at a reference frequency—usually 1 Hz (1 cycle per second).
This section addresses specific electrical and mechanical characteristics that are critical to the performance of high-efficiency dynamic sensors.
This refers to an unwanted output signal generated by mechanical stress or bending at the mounting surface—occurring even in the absence of actual acceleration. This parameter indicates the extent to which external mechanical forces affect the sensor’s accuracy. For industrial sensors, the typical value is less than…
This is an electronic circuit used in “charge-mode” (pC) sensors. It converts a high-impedance output (expressed in Coulombs or picocoulombs) into a low-impedance voltage signal (expressed in millivolts), making measurements easier and more resistant to noise. The input impedance ranges from $10^{13}$ to $10^{15} \Omega$, with a typical conversion ratio of 1 mV/pC.
This refers to the amount of electrical charge generated by the sensor per unit of applied acceleration. It is typically expressed in units of pC/g. This specification is essential for selecting the appropriate charge amplifier.
This is the DC voltage level present at the sensor’s output, even when the mechanical input is zero (i.e., no acceleration is applied). This parameter is particularly critical for ICP® or IEPE sensors, as it indicates the health status of the internal circuitry and the bias of the FET transistor.
Mathematical operations performed on a signal: First-stage integration converts acceleration into velocity, while second-stage integration converts acceleration into displacement. These transformations are typically carried out to analyze vibration behavior and calculate kinetic energy.
A physical phenomenon wherein the mass of a sensor—mounted on a structure under test—alters the structure’s dynamic response (including its effective stiffness and resonant frequency). This effect must be minimized in precision measurements, particularly when dealing with lightweight or thin-walled structures.
The frequency at which resonance occurs.
This represents the relative change in a sensor’s sensitivity or its bias voltage per degree of temperature change. It is typically expressed as a percentage per degree Celsius. This parameter characterizes the stability of the sensor’s performance in industrial environments subject to thermal fluctuations.
This is the process of comparing a sensor’s output against a known, traceable reference standard under controlled conditions, in order to determine the device’s accuracy and establish its actual sensitivity value. This process is typically performed using a shaker and a laser reference.
This refers to a change in velocity over time. In dynamic measurements, acceleration is a fundamental quantity measured by accelerometers; it is usually expressed in units of *g* or m/s², where 1*g* ≈ 9.80665 m/s².
This is a specialized type of transducer designed to measure acceleration. These devices operate based on the inertial force generated when an internal mass (seismic mass)—connected to a piezoelectric element—is subjected to external acceleration. Types include:
This refers to mechanical motion characterized by periodic changes in acceleration and deceleration around a reference point. Such motion is typically periodic or oscillatory and is often expressed in terms of displacement, velocity, or acceleration. Vibration can occur along one or more axes (axial, radial, or along three orthogonal axes); multi-axis analysis is used for systems exhibiting complex motion.
The process of monitoring machine parameters—such as vibration, temperature, or oil quality—is used to detect significant deviations that indicate the occurrence or development of faults in equipment. Condition monitoring serves as the empirical foundation for implementing predictive maintenance (PdM) strategies.
This involves the use of control systems, such as PLCs or DCSs, to manage and operate industrial equipment and processes with minimal human intervention. These systems typically utilize feedback from sensors to facilitate closed-loop control.
A characteristic that describes the variation in a sensor’s sensitivity (the ratio of output to input) across its operational frequency range. An ideal sensor exhibits a perfectly flat frequency response within its specified bandwidth.
This refers to the natural frequency of the sensor element or its internal structure—the frequency at which the oscillation amplitude reaches its maximum value. At this point, signal distortion is likely to occur, unless the mounting structure provides significant damping.
In charge amplifier circuits or sensor circuitry, this is the time required for a signal—resulting from a step input (such as a constant acceleration)—to decay back toward its initial value. This parameter determines the system’s low-frequency cutoff limit.
A property of certain crystalline materials, such as quartz or PZT, wherein they generate an electrical charge proportional to the mechanical stress or strain applied to them. This phenomenon forms the operating principle for most dynamic sensors.
This is the ratio of the sensor’s output signal to the magnitude of the physical quantity being measured. For accelerometers, it is typically expressed in units of mV/g or pC/g and is standardized at a reference frequency—commonly 1 Hz (1 cycle per second).
This section addresses specific electrical and mechanical characteristics that are critical for the performance of high-efficiency dynamic sensors.
This refers to an unwanted output signal generated by mechanical stress or bending on the mounting surface—occurring even in the absence of actual acceleration. This parameter indicates the extent to which external mechanical forces affect the sensor’s accuracy. For industrial sensors, the typical value is less than [value].
This is an electronic circuit used in “charge-mode” (pC) sensors. It converts a high-impedance output (measured in Coulombs or picocoulombs) into a low-impedance voltage signal (measured in millivolts), thereby facilitating measurement and enhancing noise immunity. The input impedance ranges from $10^{13}$ to $10^{15} \Omega$, with a typical conversion ratio of $1 \text{ mV/pC}$.
This refers to the amount of electrical charge generated by the sensor per unit of applied acceleration. It is typically expressed in units of pC/g. This specification is essential for selecting an appropriate charge amplifier.
This is the DC voltage level present at the sensor’s output, even when the mechanical input is zero (i.e., no acceleration is applied). This parameter is particularly critical for ICP® or IEPE sensors, as it indicates the health status of the internal circuitry and the bias of the FET transistor.
A mathematical operation performed on the signal: a first-stage integration converts acceleration into velocity, while a second-stage integration converts acceleration into displacement. These conversions are typically performed to analyze vibration behavior and calculate kinetic energy.
This is a physical effect wherein the mass of a sensor—mounted onto a structure under test—alters the structure’s dynamic response (including its effective stiffness and resonant frequency). This effect must be minimized in precision measurements, particularly when dealing with lightweight or thin-walled structures.
The frequency at which resonance occurs.
This represents the relative change in a sensor’s sensitivity or bias voltage per degree of temperature change. It is typically expressed as a percentage per degree Celsius. This parameter characterizes the stability of the sensor’s performance in industrial environments subject to thermal fluctuations.
The process of comparing a sensor’s output against a known, traceable reference standard under controlled conditions, in order to determine the device’s accuracy and establish its actual sensitivity value. This process is generally carried out using a shaker and a laser reference.
This is a comparative calibration method in which the sensor under test and a standard reference sensor are mounted side-by-side on a shaker, ensuring that both experience virtually the same vibration input; their outputs are then compared.
A measure of how closely a sensor’s input-output relationship conforms to an ideal straight line across its defined dynamic range. Deviation from this straight line is typically expressed as a percentage of the “Full Scale Range” (%FSR).
The ability of a sensor to provide consistent and reproducible output results when inputs and environmental conditions are repeated identically multiple times. High repeatability indicates the electronic and mechanical stability of the sensor. Repeatability is also influenced by factors such as temperature, humidity, and the mounting method.
The smallest change in a measured physical quantity (such as acceleration or force) that a measurement system can reliably detect. This value is primarily limited by the system’s “noise floor.”
A measure of how closely a sensor’s input–output relationship conforms to an ideal straight line across its entire defined dynamic range. Deviation from this straight line is typically expressed as a percentage of the “full-scale range” (%FSR).
The ability of a sensor to provide consistent and reproducible output results when inputs and environmental conditions are repeated identically multiple times. High repeatability indicates the electronic and mechanical stability of the sensor. Repeatability is also influenced by factors such as temperature, humidity, and the method of installation.
The smallest change in a measured physical quantity (such as acceleration or force) that a measurement system can reliably detect. This value is primarily limited by the system’s noise floor.
Amplitude is a measure of the variation in a signal’s value over time. “Peak-to-peak amplitude” refers to the variation between the minimum and maximum values of a signal. “RMS amplitude” refers to the Root Mean Square amplitude, which is the square root of the mean of the squares of the signal values.
The difference between the indicated value and the actual value of the measured variable. It is typically expressed as a relative error, representing a percentage of the sensor’s output reading.
Machinery that constitutes a critical part of a plant. If such machinery fails, the entire plant cannot operate at full capacity. These machines may or may not have backups and are generally subject to continuous monitoring.
A circuit that performs mathematical integration. It converts a velocity signal into displacement, or an acceleration signal into velocity. A double integrator converts an acceleration signal into displacement.
A term generally used for instrumentation equipment. In the context of machinery, a “protection monitor” may receive inputs from various sensors—such as those measuring temperature, vibration, or rotational speed (RPM)—as well as 4–20 mA signals. At a minimum, the monitor compares actual measured values against alarm setpoints, checks the integrity of the sensors and wiring, and provides relay outputs for “ALERT” and/or “DANGER” warnings. When a monitor accepts inputs from traditional vibration sensors—which produce dynamic signals requiring internal signal conditioning—it is referred to as a “vibration input monitor.” Conversely, when a monitor accepts only 4–20 mA inputs (such as those from vibration transmitters, PLCs, or DCS systems), it is often called a “4–20 mA input monitor.”
An oscillatory motion in which the amplitude pattern repeats over time.
Measuring the temporal relationship between two signals, or between a specific vibration signal and a “once-per-shaft-revolution” event, is referred to as phase angle measurement.
One or more monitoring channels, each consisting of: 1) a proximity sensor system; 2) a signal conditioner; and 3) a monitor.
A non-contact device that measures the displacement and position of an observed surface relative to the probe’s mounting location. Proximity probes used for monitoring rotating machinery typically operate on the eddy-current principle, measuring the displacement and position of a shaft relative to its bearing(s) or the machine casing.
A transducer whose output (typically an electrical signal) is proportional to the input acceleration.
A transducer whose output (typically an electrical signal) is proportional to the input acceleration.
The degree to which a displayed value corresponds to an approved standard value or a desired value.
Note: The term “limit of error” is used here solely as a qualitative concept.
A range of a quantity that can be modified by means of an adjuster.
Examples: Zero adjustment, span adjustment, or bias adjustment.
Clean air introduced into equipment from an external source to serve the following purposes: 1. Preventing the ingress of corrosive gases; 2. Preventing temperature increases within the equipment; 3. Preventing the entry of explosive gases (e.g., in explosion-proof installations).
1. A reduction in the magnitude (amplitude) of a signal. 2. A decrease in the amplitude of vibration over time (related to balancing).
Maintaining vibration or synchronous force—associated with the rotational speed—within a specified range; this is achieved by analyzing the mass distribution of the rotor and, if necessary, adjusting that distribution.
Contact capacity is defined based on the maximum allowable voltage that can be applied to the contact section, as well as the maximum allowable current at which the contact can be opened or closed.
An input signal that indicates the open or closed state of an electrical contact.
An output signal generated as a result of an electrical contact opening or closing.
The classification of a contact, determined by variations in the circuit configuration of switches and similar components.
Examples:
Single-Pole, Normally Closed (SPNC).
Single-Pole, Double-Throw (SPDT).
Double-Pole, Double-Throw (DPDT).
🔹Crest Factor
The ratio of the peak value to the effective (RMS) value.
The rotational speed at which a rotating system undergoes resonance.
The complete set of states or values that a periodic phenomenon or function passes through over its entire interval before returning to its initial state.
The natural frequency of vibration in a linear system that possesses damping.
A device designed to absorb energy in order to reduce shock or the amplitude of vibration.
The ratio of the actual damping coefficient to the critical damping coefficient in a system characterized by linear viscous damping.
Note: The damping ratio is also commonly expressed as a percentage of critical damping.
A measure representing the lag or slowness in a system’s response. It is generally defined as the time interval between the application of a step input signal and the point where the tangent line intersects the time axis.
Note: This is also referred to as “effective dead time.”
The measurement of dimensional changes in the gap (clearance) between the rotor and the casing, occurring due to differences in their respective rates of thermal expansion.
A signal characterized by a parameter that represents a set of discrete (digitized) values in numerical form.
A transducer whose output (typically an electrical signal) is proportional to the input displacement.
An electrical contact output in which no electrical power (voltage/current) is supplied to the contact mechanism from the actuation side.
The response characteristics of equipment when subjected to time-varying inputs.
The degree of deflection (sag) of a rotor shaft in rotating machinery—occurring when the rotor is stationary or rotating at a very low speed—due to its own weight or asymmetrical cooling.
An adverse effect exerted on circuits and components by an external magnetic field.
Note: Radio Frequency Interference (RFI) is a well-known example of this.
Vibration in which the points undergoing vibration trace an elliptical geometric locus (path).
The algebraic difference between the measured value and the ideal value of the variable being measured.
An external force applied to a system or an input.
A classification based on the explosive nature or ignition temperature of explosive gases present (or assumed to be present) in a hazardous environment where explosion-proof equipment is installed.
Protection against explosion or fire originating from the equipment itself, when installed in a hazardous environment containing explosive gases (combustible gases or vapors from flammable liquids).
Equipment designed with an explosion-proof construction.
Note: The following types of construction are commonly used for industrial electrical control equipment: 1. Flameproof construction; 2. Intrinsically safe construction; 3. A combination of 1 and 2.
The intensity of the magnetic field present at the equipment’s installation site (a field not generated by the device itself).
The frequency at which failures occur in equipment or a system—which has already operated for a specific duration—during a subsequent unit of time.
A balancing procedure performed using the machine’s own bearings and support structure, without the use of a separate, dedicated balancing machine.
A type of explosion-proof construction in which, should explosive gases ignite within a fully enclosed housing, the enclosure is capable of withstanding the explosion pressure and preventing the escape of flames that could otherwise ignite explosive gases in the surrounding environment. This construction must be tested and certified by regulatory authorities.
A rotor that does not meet the defined criteria for a “rigid rotor.”
The rotational speed at which one of the primary flexural modes of a flexible rotor reaches its maximum amplitude. In this state, the deflection of the rotor is more significant than the displacement at the bearings.
The shape (mode) that a rotor assumes while passing through a flexural critical speed.
Vibration that manifests as a change in the curvature of an elastic body.
The ratio of the root-mean-square (RMS) value to the mean value over a half-cycle that crosses the zero line at two points.
A structure that supports a mechanical system.
Note: A foundation may be stationary in space, or its own motion may induce excitation in the mechanical system it supports.
The spectral analysis (spectrum analysis) of a vibration phenomenon.
The vibration mode associated with the lowest natural frequency.
A balancing operation performed at a rotational speed where the rotor can no longer be considered a rigid body.
A load that possesses a reactance component.
A value added to an input signal.
The impedance observed within a device’s circuit when viewed from its input terminal.
The absence of a common line between the input and output signals of a piece of equipment.
The measurement range within which a transducer’s specifications (such as sensitivity, scale factor, linearity, etc.) are met.
A transducer whose output is proportional to its input within a specified frequency range.
The interval between the maximum and minimum values of the variables being measured.
The difference between the upper and lower limits of the measurement range (the variation in output from the beginning to the end of the range).
The time required from the start of the measurement process until the final result is obtained.
The average time between successive failures occurring within a specific period and under defined conditions during the useful life of the equipment.
The average time required to perform repair operations.
A value added to the output signal.
The impedance present within the internal circuitry of the equipment, as viewed from the output terminal.
The maximum algebraic difference between the extreme values (maximum and minimum) of a vibratory quantity over a specified interval.
The maximum value within a specified interval.
The difference between the phase angles of two periodic quantities having the same frequency. For a sinusoidal quantity, this is equal to the difference between the phase angles measured from a common reference.
The ability of equipment to deliver the required performance over a specified period and under defined conditions.
The smallest interval between two adjacent values that can be distinguished from one another.
The frequency at which the phenomenon of resonance occurs.
The ratio of the change in the displayed value to the change in the measured quantity within the equipment.
The difference between the upper and lower limits of a range.
A condition of a rotor where, due to centrifugal force, a force or vibratory motion is exerted on the shaft.
The amount of unbalance in a rigid rotor shaft, defined as the maximum permissible value within a plane perpendicular to the shaft.
Measures velocity in millimeters per second (mm/s). It is typically of the IEPE (piezoelectric with an internal amplifier) type or the moving-coil type.
A measuring instrument capable of displaying the level of vibration (in terms of peak value, RMS, etc.) on a scale.
The process of setting the equipment’s zero point to a specific value or position through electrical or mechanical adjustment.
This involves the direct measurement and display of a sensor’s instantaneous output amplitude as a function of time. This representation is particularly important for analyzing transient events, impacts, and instantaneous waveforms (such as in a shock test).
The overall vibration magnitude measured across a wide range of frequencies, rather than at a single specific frequency.
In more technical terms, when a vibration sensor (such as an IEPE sensor) records a vibration signal, that signal consists of a combination of waves with various frequencies. If these are considered collectively—for instance, across a range from 10 Hz to 10 kHz—and the power average or RMS (Root Mean Square) value is calculated, the resulting figure is referred to as the broadband vibration level.
A pair of plots showing the amplitude ratio and phase shift as a function of frequency for a frequency response.
The load resistance that can be connected while ensuring the device operates within its guaranteed performance specifications.
A quantitative measure of unbalance (at a specific plane) in a rotor, independent of its angular position. This value is equal to the product of the “unbalance mass” and the “mass eccentricity.”
Note: The unit for unbalance is, for example, g-mm (gram-millimeter).
The angular position of the unbalance mass, measured relative to a reference line within a polar coordinate system established on a plane perpendicular to the shaft’s centerline.
A process that involves the collection, processing, display, and—specifically—interpretation of vibration waveforms from the machine casing or shaft, in relation to the machine’s condition.
The use of vibration sensors to assess the integrity of large structures—such as bridges, high-rise buildings, and tanks—under operational or environmental conditions (e.g., earthquakes or wind).
The use of vibration data to forecast the potential failure of machinery components (such as bearings, gearboxes, and rotors) before a complete breakdown occurs, employing trend analysis methods.
Measuring the vibration of new machinery at the installation site to ensure that its vibration parameters fall within the limits specified in the contract (e.g., in accordance with standards such as ISO 10816).
The consistency and uniformity of a sensor’s output in relation to a gradual increase in its input; for the definition of the actual value, refer to the term “Linearity.”
Directly proportional to the frequency *f*, defined by the relationship ω = 2πf.
A frequency at which the dynamic stiffness of a system reaches its minimum, resulting in a reduction in the vibration response.
A circuit that allows only signals within a specific frequency range to pass through, while attenuating or removing all other components.
A mechanical mechanism used to decouple a sensor or piece of equipment from vibrations originating in the ground or the supporting base, thereby reducing environmental noise.
The DC reference voltage present at the output of a sensor.
Random noise with a broad frequency spectrum, distributed across the entire bandwidth of the system.
A property of electrical systems (such as a charge sensor and an amplifier input) that allows for the storage of electric charge; it is a factor in estimating the dynamic behavior of a sensor circuit.
Ensuring that the sensor housing has no electrical connection to the mounting surface, in order to prevent ground loops.
A device used to convert or process output signals based on electric charge.
A design configuration in which the input force is applied parallel to the axis of the piezoelectric crystal.
The process of observing machine parameters to identify and predict failures.
The physical phenomenon of vibrational energy dissipation—typically expressed as a percentage of critical damping—which plays a significant role in controlling dynamic response.
A logarithmic unit used to express the ratio of amplitude or power between two signals.
The number of independent paths of motion for a system; for example, the motion of a three-dimensional rigid body involves six degrees of freedom (3 linear + 3 rotational).
A method in electrical measurement where two signals sharing a common reference are compared in order to eliminate common-mode noise.
The distance traveled from an origin to a new position; typically obtained by double-integrating an acceleration signal.
A characteristic of a sensor wherein the output sensitivity remains approximately constant across its entire operating range.
A type of vibration mode characterized by the bending of a structure or sensing element.
The mathematical foundation for frequency analysis and the FFT algorithm, which converts a signal from the time domain to the frequency domain.
The oscillation of a system in the absence of an external driving force, governed solely by its initial conditions.
A plot of amplitude versus frequency, providing a graphical representation of a signal’s frequency content.
The amplification factor, or the ratio of the output magnitude to the input magnitude, within a measurement system.
An unintended current path in systems with multiple ground connections, which results in noise interference.
A signal component that is an integer multiple of the fundamental frequency. The presence of harmonics in a frequency spectrum indicates non-linear phenomena or mechanical defects within a machine.
A type of electronic filter that allows only signals with frequencies above a specified threshold to pass through.
The difference in a sensor’s output value at a specific point—depending on whether the input is approached from an increasing or decreasing direction—reflecting mechanical effects or fatigue within the sensing element.
A type of piezoelectric sensor featuring an internal semiconductor circuit (FET) that provides a low-impedance voltage output.
A general term for ICP® sensors; both types function essentially the same way, with the only difference being the brand name.
A specialized transducer that simultaneously measures force and motion; it is typically used in vibration testing to determine force and stiffness. It is employed to measure both the input force and the resulting vibration response during force transmission testing.
A mathematical process used to convert acceleration into velocity or vibration displacement.
A piezoelectric ceramic commonly used in the manufacturing of sensors due to its high sensitivity and stable electrical properties.
Refers to how closely a sensor’s response aligns with an ideal straight line across its entire operating range.
A type of sensor that draws its required power directly from the measurement current loop (e.g., 4–20 mA).
The ratio of applied force to vibrational velocity; it serves as an indicator of a system’s dynamic resistance to motion.
The rotational force (torque) required to secure a mounted sensor, which has a direct impact on its frequency response.
The inertial quantity within the design of a sensor’s seismic mass, which influences both sensitivity and resonant frequency.
The actual physical parameter that a sensor is intended to measure (e.g., acceleration, force, or pressure).
Unwanted electrical signals that reduce the clarity or resolution of a measurement.
Scaling data relative to a standard reference to allow for more accurate comparison of results.
The maximum instantaneous value of a signal within a specified time interval.
The standard type of sensor used for measuring vibration acceleration.
The degree to which successive measurements are close to one another under similar conditions.
The generation of an unwanted electrical charge due to temperature changes within a piezoelectric material; typically a source of noise in sensors.
A signal processing technique used to reduce common-mode noise and enhance differential accuracy.
A sensor design in which the force is applied perpendicular to the polarization axis of the piezoelectric crystal; it offers greater resistance to base strain.
The maximum impact intensity or instantaneous acceleration that a sensor can withstand without sustaining damage.
An instrument used for frequency analysis, capable of performing an FFT (Fast Fourier Transform) and displaying the vibration spectrum.
The measure of a structure’s resistance to mechanical deformation.
The electrical power required for the operation of the internal circuitry in IEPE/ICP® sensors.
A transducer converts mechanical energy into electrical energy.
The ratio of the acceleration transmitted to the sensor base compared to the acceleration of the sensor’s internal structure.
The speed of vibration; it is the integral of vibration acceleration.
The study of the dynamic behavior of structures based on vibration data.
An adjustment made to eliminate unwanted initial voltage or current at the sensor output.
The time required for the sensor output to return to a quiescent (resting) state following a transient excitation.
The conditioning unit, or power supply, provides the necessary constant current to the sensor and converts the sensor’s output characteristics for subsequent analysis. Charge-mode sensors require an external conversion unit to transform charge into voltage, whereas ICP® or IEPE sensors require only a constant current source.
Refers to the DC power required for the operation of the sensor’s internal semiconductor circuitry (such as a FET amplifier).
The constant current supplied to IEPE/ICP® sensors to power the transducer and control its voltage output.
Most standard ICP®-type accelerometers specify a useful frequency range of 10 Hz to 10,000 Hz (10 kHz) in their calibration certificates. In practice, however, the usable range may be slightly broader, depending on the specific sensor model and the permissible noise level within the system. This range ensures that the sensor’s response remains approximately linear within the industrial operating region, maintaining measurement accuracy across the actual vibration spectrum.
Piezoelectric sensors are inherently designed to measure dynamic quantities—that is, parameters that vary over time, such as vibrations, transient waves, or alternating forces. Their primary application is in the measurement of acceleration; however, depending on the design and calibration, this same technology can also be used to measure force, strain, and dynamic (transient) pressure. Since the piezoelectric effect relies on the generation of an electric charge in response to instantaneous mechanical displacement, these sensors are generally unsuitable for static or DC measurements; in the absence of input changes, the generated charge gradually leaks away, causing the output signal to decay. Only through specialized designs incorporating compensation circuitry is it possible to record low-frequency or quasi-static phenomena.
Depending on the application and operating conditions, piezoelectric sensors are designed using three primary mechanical configurations. In **compression mode**, force is applied axially to the piezoelectric crystal; this is the simplest and most common design, frequently used in industrial accelerometers. In **shear mode**, force is applied laterally—tangentially to the crystal’s surface; this configuration offers greater resistance to temperature fluctuations and base-induced stresses, resulting in an output signal with lower noise. Finally, **bending (or cantilever) mode** involves subjecting the crystal to a bending force; this is typically employed in educational sensors, low-sensitivity devices, or specialized applications. All three structures rely on the piezoelectric effect, wherein mechanical stress applied to the crystal generates an electrical charge proportional to the magnitude of the force.
The primary materials for piezoelectric sensors are selected based on factors such as sensitivity, stability, and operating temperature.
Natural material, characterized by thermal stability and low noise; suitable for high-temperature environments and precision measurement.
An engineered ceramic with a high piezoelectric coefficient; the most widely used material in industrial sensors.
Ceramics designed for specific conditions—such as extreme temperatures or ultra-high sensitivity requirements—for example, Barium-Strontium-Titanate.
The mounting method plays a critical role in measurement accuracy, particularly at high frequencies:
Provides the best mechanical contact and high-frequency response.
Suitable for surfaces where drilling is not permitted; offers moderate accuracy.
Fast and temporary, though it results in a loss of response at higher frequencies.
Used to reduce noise and low-frequency vibrations in large structures.
Poor mechanical contact or the use of a soft adhesive can lead to a loss of sensitivity and the introduction of unwanted resonance.
IEPE sensors produce a low-impedance (voltage) output signal that is resistant to environmental noise and the effects of cable length. These sensors require a constant-current power supply.
This source delivers a stable current to the sensor via a coaxial cable. This current provides the power necessary for the operation of the internal preamplifier circuit (typically a Field-Effect Transistor, or FET) while simultaneously transmitting an output voltage—proportional to the acceleration—to the measurement system.
