Standard Accelerometer Research Articles

A MEMS resonant accelerometer for low-frequency vibration detection

According to their inherent characteristics, MEMS resonant accelerometers are suitable for low-frequency, low-g acceleration measurement. In this paper, we report a MEMS accelerometer based on double-ended-tuning fork resonators. The scale factor of our sensor is 1153.3 Hz/g and the bias stability of the oscillator is 58 ppb (parts per billion) for an averaging time of 1 s. The static test showed that the resolution of our sensor was 13.8 μg. The dynamic performance was demonstrated by single-frequency and hybrid-frequency vibration tests, and the results showed that our device is suitable for detecting low-frequency vibration (0.5–5 Hz). The cross-axis sensitivity is 1.33%. Compared with a standard charge accelerometer, our device showed its superiority in mixed acceleration measurement, which makes it a potentially attractive option for geophone or seismometer applications.

A Wireless Sensor Telemeter for in situ Cage Vibration Measurement and Corroboration with Analytical Results

ABSTRACTThis article presents both experimental and analytical investigations on the dynamic behavior of the cage in a ball bearing. For the experimental investigation, a wireless sensor telemeter system was designed and developed to monitor the cage motions. The sensor, which was integrated on the bearing cage, is composed of a commercially available capacitor–inductor (LC) circuit. The LC circuit on the rotating cage was coupled to a transceiver that was stationary and positioned in close proximity to the cage. In order to achieve the objective of the analytical investigation, the explicit finite element method (EFEM) was used to simulate the bearing cage. The EFEM cage model was then combined with the dynamic bearing model to simulate the cage motion during operation. The results from the experimental measurement using the telemeter were then compared with the analytical modeling. The developed telemeter demonstrated the capability of the cage telemeter in detecting various bearing frequencies. These include the cage frequency, shaft frequency, and ball pass frequency on the outer race (BPFO), which was introduced by creating a spall on the bearing outer race. Compared to standard accelerometers that are commonly used to measure vibrations on the bearing housing, the cage telemeter has shown advantages in sensing cage motions and detecting bearing defects regardless of the location of the damage. Analytical simulation using the EFEM cage model correlated well with the experimental results and provided more insight into the bearing cage dynamics.

Wristband accelerometers to motivate arm exercise after stroke (WAVES): Activity data from a pilot randomised controlled trial

Encouraging impaired limb use during routine and rehabilitation activities after stroke is challenging. We evaluated changes in stroke arm activity related to vibration prompts delivered by a wrist-worn accelerometer (“CueS wristband”). A pilot randomised controlled trial was conducted with adults < 3 months after stroke causing any arm impairment. All received instruction for a self-directed four-week programme encouraging bimanual tasks, and wore a wristband on the impaired side 8am–8pm. Intervention wristbands were programmed to deliver vibration prompts if hourly activity targets were unmet. To allow for incremental recovery, patient preference and diurnal variability, the target was selected as 5%, 10% or 20% above median levels recorded hourly over the previous 3 days. Data were downloaded at twice weekly reviews. Activity counts per minute (CPM) were calculated from CueS mean signal vector magnitude (1 s epoch) at the first (baseline) and the last (endpoint) review. Standard accelerometers recorded natural arm activity over 72 h starting at 4 and 8 weeks post-baseline. Mann Whitney U test compared CPM between groups, and for 1 hour before/after prompts amongst intervention participants. Thirty-three participants (14 intervention; 19 control) enrolled over 16 months: mean age 71 years (SD11); 13 male; mean days post-stroke 30 (SD19); median baseline Action Research Arm Test 20/57 [IQR 3.5,41]. Median number of prompts delivered were 7 per participant/day [IQR: 6,8]. Median CPM during 1 hour before/after prompts was 651 versus 759 (+16.6%; P = 0.002). CPM increased immediately after prompting, suggesting a direct behavioural impact. Compared to control, the intervention group continued to increase CPM beyond wristband removal. Whilst these results are encouraging, this was a small study and data may not reflect only arm activity. Personalised prompts delivered by a wrist-worn accelerometer may enhance self-directed arm activity after stroke.

Improving Hip-Worn Accelerometer Estimates of Sitting Using Machine Learning Methods.

ABSTRACTPurposeThis study aimed to improve estimates of sitting time from hip-worn accelerometers used in large cohort studies by using machine learning methods developed on free-living activPAL data.MethodsThirty breast cancer survivors concurrently wore a hip-worn accelerometer and a thigh-worn activPAL for 7 d. A random forest classifier, trained on the activPAL data, was used to detect sitting, standing, and sit–stand transitions in 5-s windows in the hip-worn accelerometer. The classifier estimates were compared with the standard accelerometer cut point, and significant differences across different bout lengths were investigated using mixed-effect models.ResultsOverall, the algorithm predicted the postures with moderate accuracy (stepping, 77%; standing, 63%; sitting, 67%; sit-to-stand, 52%; and stand-to-sit, 51%). Daily level analyses indicated that errors in transition estimates were only occurring during sitting bouts of 2 min or less. The standard cut point was significantly different from the activPAL across all bout lengths, overestimating short bouts and underestimating long bouts.ConclusionsThis is among the first algorithms for sitting and standing for hip-worn accelerometer data to be trained from entirely free-living activPAL data. The new algorithm detected prolonged sitting, which has been shown to be the most detrimental to health. Further validation and training in larger cohorts is warranted.

Investigation and validation of consumer device accelerometers for the assessment of whole-body vibration

AbstractThere exist a discrepancy between the usage of the expensive standard accelerometer and the cheap and accessible consumer device accelerometer for the measurement of whole-body vibration (WBV). This study investigated the validity of accelerations (g-forces) obtained from a consumer device accelerometer by simultaneously using the consumer device accelerometer with a standard accelerometer during evaluation of WBV experienced by earthmoving equipment operators. The consumer device accelerometer is a software (WBV) compatible with iOS devices from operating system 5 and above (LIS331DLH, 3-axis, ±2 g acceleration range, MEMS type) while the standard accelerometer used during this study is a GCDC tri-axial accelerometer (GCDC X16-4 3-Axis, G-Force Data logger, ±18 g acceleration range, MEMS type). The two accelerometers were mounted following the basicentric axes of the seated operators and put on before earthmoving operation. Data from both the accelerometers were analysed using MATLAB. Results got...

Implementations and pilot comparison of primary low intensity shock calibration

&lt;p class="Abstract"&gt;This paper first presents two main technical concerns for a possible low intensity shock comparison: variety of primary shock calibration systems and feasibility of comparison artifact. For the primary calibration system, the mechanical excitation includes hammer-anvil collision, pneumatic driven projectile impact and Hopkinson bar. The shock pulses generated are smooth monopole shape by the first two types with air bearings, but dipole shape by the third type. For the comparison artifact, a standard accelerometer of single-ended type with a charge amplifier consists of an accelerometer measuring chain whose nonlinearity of amplitude and phase frequency responses is investigated. Based on the nonlinear fact of comparison artifact at frequency domain and the spectrum range difference of mechanical excitations of the calibration system, strict comparison conditions had to be laid down for measurement of shock sensitivity at specific acceleration levels and pulse durations.&lt;/p&gt;The pilot comparison, coded as APMP.AUV.V-P1, is successfully organized by Asia Pacific Metrology Programme. Some comparison results of both monopole excitation and dipole excitation are shown with the expanded uncertainty. The completion of this pilot comparison can serve as part of the basis for a planned key comparison targeted at a low intensity shock range at Consultative Committee level.

Machine Learned Classification Of Physical Activity In Multiple Free Living Days In Adults

Accelerometer cut points misclassify important behaviors. In addition, the intensity paradigm is not helpful for promotion of specific behaviors for public health. Advances in computational techniques to classify accelerometer data into behaviors have been limited by training and testing within controlled observational settings. Previous studies have shown that accelerometers may not work well in older or obese populations, but these studies were limited to a single accelerometer feature, counts per minute. PURPOSE: To compare machine learned algorithms from accelerometer features developed across multiple days of data to estimate minutes of sitting, standing, walking, and biking. METHODS: We collected 268,325 minutes (523 days) of hip worn accelerometer and GPS data in a sample of scripted activities and in two free living adult cohorts with annotated person worn image data as the ground truth. One cohort was cyclists (N=40, 70% male, mean age 36, mean BMI 23.4). The other cohort was overweight and obese women (N=36, mean age 55, mean BMI 32.0). A Random Forest technique and Hidden Markov Model smoothing were employed to predict minute level behaviors from over 40 accelerometer features. Leave one out cross validation was applied. RESULTS: The algorithm, trained and tested on the scripted activities, performed with a mean accuracy of 92.7%. When applied to the cyclists, it performed with 70.9% accuracy. The algorithm, trained and tested on the cyclists, performed with a mean accuracy of 91.3%. The algorithm, trained on the cyclists and applied to the overweight and obese women, performed with 73.4% accuracy. The algorithm, trained and tested on the women, performed with a mean accuracy of 87.2%. The standard intensity cut points performed with 36.5% accuracy for walking, 8.7% accuracy for bicycling, and 77.2% for sedentary behaviors. The accelerometer features varied by age and obesity status. CONCLUSION: Standard accelerometer cut points greatly misclassify key behaviors such as walking and bicycling. Algorithms developed in a controlled observational setting do not accurately predict free living behavior over multiple days. Algorithms developed on one population may not apply to another group with different demographic and health characteristics. Supported by grant # U54 CA155435

Final report on pilot comparison of low intensity shock APMP.AUV.V-P1

This is the final report for pilot comparison APMP.AUV.V-P1 in the area of low-intensity 'shock', which in this case means monopole and dipole shock acceleration. The aim of this comparison was to measure the shock voltage sensitivity of one Accelerometer Chain with primary means under monopole shock excitation in the acceleration range from 500 m/s2 to 5 000 m/s2, and under dipole shock excitation with the reference acceleration of 1000 m/s2 and pulse duration from 0.03 ms to 2.0 ms. Four laboratories with primary shock calibration capability have participated in the comparison with National Institute of Metrology, P R China as pilot lab. One standard accelerometer of back-to-back type with a charge amplifier (Accelerometer Chain) was circulated among the participants. The pilot comparison reference values have been calculated using the weighted mean value of the results. The degrees of equivalence calculated from the data submitted by the four laboratories, support the uncertainty of measurement reported by them for the calibration of the shock sensitivities of accelerometer. At the reference acceleration of 1 000 m/s2 and pulse duration of 2 ms (specified in ISO 16063-13:2001), the participating laboratories calibrated the Accelerometer Chain with their claimed relative expanded uncertainty (k = 2), the smallest of which equal to 0.5%, i.e. smaller than the limit specified by the ISO standard. The completion of APMP.AUV.V-P1 can serve as part of the basis for a planned key comparison targeted at low intensity shock range at CC level.Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCAUV.

Applications of Laser Interferometry in Providing Traceable Vibration Measurements in India

The paper discusses the advantages of laser interferometry in providing traceable vibration measurements with lowest levels of uncertainty of measurement due to which it has been established as National primary standard. The potential high precision measurements can be achieved with air bearing exciters of beryllium armature having lowest transverse motion, by special vibration isolation and by data acquisition at a high sampling rate. The national standards briefly described are mainly used for the primary calibration of reference standard accelerometers which are used in accredited calibration laboratories. Strengths, weaknesses, opportunities and threats (SWOT) analysis of laser interferometer approach is discussed. The expanded measurement uncertainty (k = 2) of 0.3 to 1.8 % in range 5 Hz to 20 kHz was re-affirmed by absolute calibration of standard reference accelerometers by laser interferometery technique using multi-point laser positions.

Erratum to: Guidelines for tilt measurements realized by MEMS accelerometers

The paper discusses thoroughly a problem of determining tilt over various measurement ranges by measuring Cartesian components of the gravity acceleration with application of accelerometers that are Microelectromechanical Systems (MEMS). The presented standard and original methods are based on various mathematical relationships between the components and the pitch and the roll. Their application results in the fact that the realized measurements are characterized by different sensitivity and accuracy (experimentally evaluated to be of 0.18°–2° for a tilt sensor built of standard MEMS accelerometers). Each method is discussed in detail with regard to the respective sensitivity and accuracy of the measurement, and its application scope is determined. Essential part of the paper are guidelines for an optimal selection of the number and type of MEMS accelerometers, as well as appropriate mathematical formula, to be used in a specific case of tilt measurement.

Physical activity levels and patterns in older adults: the influence of a DVD-based exercise program.

The use of multimedia to influence health behaviors offers unique advantages over more traditional center-based programs, however, little is known about the effectiveness of such approaches in improving physical activity levels over time. The purpose of this study was to examine the efficacy of a progressive and age-appropriate, DVD-delivered exercise program in promoting physical activity levels among older adult cohorts. Community dwelling older adults (N = 307, Mean age = 71 years) were randomized to one of two groups: a 6-month home-based DVD-delivered exercise (i.e., FlexToBa™) intervention group or a healthy aging DVD control group. Physical activity was assessed objectively using a standard 7-day accelerometer wear period and subjectively using the Godin Leisure Time Exercise Questionnaire, at baseline and follow-up. Analysis of covariances indicated a statistically significant treatment effect for subjectively [F(1,250) = 8.42, P = .004, η(2) = .03] and objectively [F(1,240) = 3.77, P = .05, η(2) = .02] measured physical activity. The older cohort (>70) in the FlexToBa condition further had significantly larger improvements in physical activity levels compared to their younger counterparts. From a public health perspective, media-delivered interventions such as the FlexToBa program might prove to be cost-effective, have a broader reach and at the same time be effective in improving physical activity levels in older adults.

Guidelines for tilt measurements realized by MEMS accelerometers

The paper discusses thoroughly a problem of determining tilt over various measurement ranges by measuring Cartesian components of the gravity acceleration with application of accelerometers that are Microelectromechanical Systems (MEMS). The presented standard and original methods are based on various mathematical relationships between the components and the pitch and the roll. Their application results in the fact that the realized measurements are characterized by different sensitivity and accuracy (experimentally evaluated to be of 0.18°–2° for a tilt sensor built of standard MEMS accelerometers). Each method is discussed in detail with regard to the respective sensitivity and accuracy of the measurement, and its application scope is determined. Essential part of the paper are guidelines for an optimal selection of the number and type of MEMS accelerometers, as well as appropriate mathematical formula, to be used in a specific case of tilt measurement.

Invited Article: Expanded and improved traceability of vibration measurements by laser interferometry

Traceability to the International System of Units has been established for vibration and shock measurements as specified in international document standards, recommendations, and regulations to ensure product quality, health, and safety. New and upgraded laser methods and techniques developed by national metrology institutes and by leading manufacturers in the past two decades have been swiftly specified as standard methods in the ISO 16063 series of international document standards. In ISO 16063-11:1999, three interferometric methods are specified for the primary calibration of vibration transducers (reference standard accelerometers) in a frequency range from 1 Hz to 10 kHz. In order to specify the same (modified) methods for the calibration of laser vibrometers (ISO 16063-41:2011), their applicability in an expanded frequency range was investigated. Steady-state sinusoidal vibrations were generated by piezoelectric actuators at specific frequencies up to 347 kHz (acceleration amplitudes up to 376 km/s(2)). The displacement amplitude, adjusted by the special interferometric method of coincidence to 158.2 nm (quarter the wavelength of the He-Ne laser light), was measured by the standardized interferometric methods of fringe counting and sine-approximation. The deviations between the measurement results of the three interferometric methods applied simultaneously were smaller than 1%. The limits of measurement uncertainty specified in ISO 16063-11 between 1 Hz to 10 kHz were kept up to frequencies, which are orders of magnitude greater; the uncertainty limit 0.5% specified at the reference frequency 160 Hz was not exceeded at 160 kHz. The reported results were considered during the development of ISO 16063-41 by specifying the instrumentation and procedures for performing calibrations of rectilinear laser vibrometers in the frequency range typically between 0.4 Hz and 50 kHz--the interferometric methods may be applied within expanded frequency ranges using refined techniques and procedures. It is concluded that calibration frequencies up to 0.5 MHz are attainable in compliance with the first international document standard for the calibration of laser vibrometers.

Comparison of steps and energy expenditure assessment in adults of Fitbit Tracker and Ultra to the Actical and indirect calorimetry

Epidemic levels of inactivity are associated with chronic diseases and rising healthcare costs. To address this, accelerometers have been used to track levels of activity. The Fitbit and Fitbit Ultra are some of the newest commercially available accelerometers. The purpose of this study was to determine the reliability and validity of the Fitbit and Fitbit Ultra. Twenty-three subjects were fitted with two Fitbit and Fitbit Ultra accelerometers, two industry-standard accelerometers and an indirect calorimetry device. Subjects participated in 6-min bouts of treadmill walking, jogging and stair stepping. Results indicate the Fitbit and Fitbit Ultra are reliable and valid for activity monitoring (step counts) and determining energy expenditure while walking and jogging without an incline. The Fitbit and standard accelerometers under-estimated energy expenditure compared to indirect calorimetry for inclined activities. These data suggest the Fitbit and Fitbit Ultra are reliable and valid for monitoring over-ground energy expenditure.

Vibration‐ and acoustic‐emissions based novelty detection of fretted bearings

PurposeThe purpose of this paper is to examine the use of a new feature reduction technique with novelty detection on vibration and acoustic‐emission sensors monitoring bearings mounted in the test benches of automotive manufacturers.Design/methodology/approachSignals from standard accelerometers and acoustic‐emission sensors were gathered from bearings operating under steady conditions on an accessory‐drive test bench. The bearings under test were subject to a variety of faults including fretting. These signals were processed and reduced to standard feature vectors, the dimensionality of which was reduced using a new principal‐component‐like technique optimized for novelty detection. The reduced data were analyzed with a novelty detection technique called the Support Vector Data Descriptor.FindingsThe classification results from these sensors, after being reduced with the proposed feature reduction technique, are substantially improved over those achievable with only standard novelty detection; nearly zero‐percent classification error was achieved.Research limitations/implicationsThe feature reduction technique depends, in part, on the availability of the fault type in question – potentially violating the normal novelty detection assumption of limited abnormal data. This may require the manufacturer to gather real or simulated fault data prior to running tests.Practical implicationsIncipient faults may be detectable at a much earlier stage in a manufacturer's component failure analysis. Test engineers may use this technique to reliably automate the fault detection process and enable improved root‐cause analysis through the earlier identification of faults.Originality/valueThe application of the feature reduction technique will provide manufacturers and researchers with a new means of improving fault detection in machinery components.

Capturing the pattern of activity: Exposure variation analysis of accelerometer data

Purpose: Physical activity, in particular moderate to vigorous physical activity (MVPA), sedentary behaviour (SB) are known to impact on health. Less well established is how patterning of activity affects health. Capturing the complex time pattern of activity using accelerometry remains a challenge. Occupational health research suggests Exposure Variation Analysis (EVA) could provide a useful tool. The purpose of this paper is to 1) explain the application of EVA to accelerometer data, 2) demonstrate how EVA thresholds, derivatives could be chosen, used to examine adherence to MVPA, SB guidelines, 3) explore the validity of EVA outputs.Methods: EVA reduces a complex time-line of exposure into a two-dimensional matrix showing combinations of exposure level (in categories) and duration of uninterrupted sequences (in categories). Data from 4 individuals with different daily activity patterns were collected to demonstrate the applicability of EVA. EVA outputs were also compared for accelerometer data collected from 3 occupational groups with known different activity patterns: seated workstation office workers, standing workstation office workers and teachers. Standard accelerometer data collection procedures were used. Data processing by a custom LabVIEW program calculated EVA matrices and derivatives aligned to common guidelines.Results: Data from one individual is presented in a time-based line graph form in conjunction with the resultant EVA matrix and EVA graph. Line graphs and related EVA graphs for 3 further individuals highlight the use of EVA derivatives for examining compliance with MVPA and SB guidelines. For the seated office workers, standing office workers and teachers, analyses confirm no difference in bouts of MVPA but very clear differences as expected in extended bouts of SB and brief bursts of activity, thus providing evidence of construct validity of the EVA approach.Conclusion: The major advantage of EVA is its ability in a single analysis to simultaneously capture the time pattern of activity at various levels of intensity according to the choice of the researcher. Whilst presented here with four levels of intensity, sedentary, light, moderate and vigorous, EVA could be utilised with dichotomous data such as sitting vs standing, or adjusted to match future refinements of activity guidelines. EVA offers a unique and comprehensive generic method that is ideal for processing large quantities of accelerometer data. EVA is able, for the first time, to concisely capture the time pattern (both frequency and intensity) of activity, and can be tailored for both occupational and public health research.

Testing of MEMS capacitive accelerometer structure through electro-static actuation

The present paper discusses a method for testing a MEMS capacitive accelerometer structure through electrical actuation. The response of a standard MEMS capacitive accelerometer structure for different electrical actuation voltages has been analyzed. The accelerometer structure along with a capacitance sensing integrated circuit (IC) MS3110 is modeled and simulated. A set of proto-type accelerometer structures is fabricated and packaged in PGA packages. The packaged MEMS structures and MS3110 IC are integrated on a printed circuit board. The MEMS structure is actuated by applying the electrical signal through the actuation fingers and the change in capacitance is measured by the MS3110 IC. The simulated and measured results show some interesting phenomenon like dipping and frequency doubling which are useful for initial testing and characterization of a MEMS accelerometer structure.

A novel approach for realization of primary vibration calibration standard by homodyne laser interferometer in frequency range of 0.1 Hz to 20 kHz

The paper discusses the primary vibration calibration standard of NPL, India capable of calibrating the reference accelerometers in frequency range from 0.1Hz to 20kHz as per ISO 16063-11. The excitation subsystem produces constant vibration at a specified amplitude and frequency, while the measurement system uses NI interface for measuring the quadrature output. The acceleration level and voltage level at the calibration frequency f is determined by applying a Discrete Fourier Transform to the voltage and displacement signals, and then examining the spectral component at frequency f. A PC-based data acquisition system acquires the accelerometer voltage signal and analog quadrature interferometer photodetector signal pair as well as a digital quadrature pair whereby the software processes the demodulated photodetector signals to reconstruct the armature displacement. The validation of the calibration results for standard reference accelerometers with manufacturer results and uncertainty in calibration in entire frequency range 0.1Hz to 20kHz is reported in the present work.

Final report on bilateral comparison EURAMET.AUV.V-K1.2: Vibration acceleration

This report describes the results obtained in a bilateral comparison of primary vibration calibration facilities. Two piezoelectric standard accelerometers (one single-ended as well one back-to-back type) were calibrated first at METAS, then at the PTB and again at METAS after their return.The METAS and the PTB calibrations were found to be in excellent agreement, with a mean difference smaller than the expanded uncertainty (k = 2) of the comparison.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Advanced Vibration Sensing with Radar - ADVISER

&#x0D; &#x0D; &#x0D; A new low-cost stand-off vibration sensor based on the Doppler radar principle is presented. The baseline performance of this sensor was compared with a high-quality accelerometer in a well-controlled laboratory environment. This advanced vibration imaging sensor (ADVISER) was also validated for its prognostic health monitoring ability with a fault emulator. The ADVISER was able to detect machine misbalance and bearing damage at a distance of 4 feet without making any contact. This exceeded the performance of a high-quality screw accelerometer mounted directly on the bearing enclosure. In this paper, we present the sensor’s principle of operation, summarize results of comparing it with standard accelerometers, and conclude with its potential use in industrial and aerospace applications.&#x0D; &#x0D; &#x0D;