Shock detector
Ashock detector,shock indicator,orimpact monitoris a device which indicates whether aphysical shockorimpacthas occurred. These usually have abinary output(go/no-go) and are sometimes calledshock overload devices.Shock detectors can be used on shipments of fragile valuable items to indicate whether a potentially damaging drop or impact may have occurred. They are also used in sports helmets to help estimate if a dangerous impact may have occurred.[1]
By contrast, ashock data loggeris adata acquisitionsystem for analysis and recording of shock pulses.
Overview
[edit]Shocks and impacts are often specified by the peak acceleration expressed in g-s (sometimes calledg-forces). The form of the shock pulse and particularly the duration are equally important.[1]For example, a short 1 ms 300 g shock has little damage potential and is not usually of interest but a 20 ms 300 g shock might be critical. Depending on the use, the response to this time sensitivity of a shock detector needs to be matched to the sensitivity of the item it is intended to monitor.
The mounting location also affects the response of most shock detectors. A shock on a rigid item such as a sports helmet or a rigid package might respond to a field shock with a jagged shock pulse which, without proper filtering is difficult to characterize. A shock on a cushioned item usually has a smoother shock pulse., and thus more consistent responses from shock detector.
Shocks are vector quantities with the direction of the shock being important to the item of interest, Shock detectors also can be highly sensitive to the direction of the input shock.[1]
A shock detector can be evaluated:
- Separately in a laboratoryphysical test,perhaps on an instrumented shock machine.[2]
- Mounted to its intended item in a testing laboratory with controlled fixturing and controlled input shocks.
- In the field with uncontrolled and more highly variable input shocks.
Use of propertest methodsandVerification and validationprotocols are important for all phases of evaluation.
Technologies
[edit]A wide variety of technologies are available ranging from simple analog indicators to more sophisticated electronics. Usually a device provides an optical indication of a triggered event but sometimes electrical or RFID signals can be provided. Hundreds of shock detectors are described in patents listed inPatent classification01P15/00: "Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration"[3]
Analogue constructions include:
- Spring-mass systemswhich can be triggered by a shock[1]
- Magnetic balls which can be dislodged from a holder[1]
- Disruption of the surface tension of a liquid
- Breakage of an inexpensive brittle component with a known fragility[1]
More sophisticated electronic systems useaccelerometersand associatedmicroelectromechanical systems.[1]
Monitor shipments
[edit]
A shock detector can be mounted on a package (inside or outside) or directly on the product being shipped. Mounting on the package is usually done to detect excessive handling such as high drop heights while mounting on the product is done to more closely indicate product damage.[4]
Some shipments need more than one shock detector to better monitor all directions of impacts.[4]Large or long items sometimes have shock detectors at both ends of the shipping container.
The shock detector indicates whether the goods in transit were likely to have been subjected to potentially damaging conditions. Based on this data, the options may be:[4]
- If there have not been unusual shock, continue to use the shipment as is, without special inspection
- If potentially damaging hazards have occurred, thoroughly inspect the shipment for damage or conduct extracalibrationprior to use
- The consignee may choose to negotiate with the carrier, shipper, or supplier or even to reject a shipment where sensors indicate severe handling
Shock and impact are not the only hazards that can cause damage;vibration,puncture, and compression can also cause damage yet would not trigger a shock detector.
Impacts to people
[edit]
Personal protective equipmentsuch ashelmetsare sometimes equipped with impact monitors.[5][6]These are intended to help managers know if an excessive impact has occurred and help direct needed rest or medical attention. Research is continuing, including specialized mouthguards to help classify head impacts.[7]
Crash sensors onbicycle helmetscan detect a crash and call for assistance. Fall sensors are available to senior citizens to call for help when a fall is detected.[8]
Other uses
[edit]A related use of an impact detector is as automobileair bagsensor. These sophisticated sensors are used to trigger the protective air bag system used on current vehicles.[9]
Active hard-drive protectionsystems sense impacts tolaptop computersto help minimize damage from drops.
Someemergency locator beacons,such asEmergency Locator Transmitters,are activated by a specified shock or impact.
Interpretation
[edit]Shock detectors are used to indicate if a significant impact has occurred: This helps determine the need for follow-up actions. Variability is always present and must be accounted for in the analysis:
- Shock detectors have some variation of response to shocks under controlled laboratory conditions.[10][11]
- People respond as individuals to impacts. What might cause injury to one person might not be as severe to another.
- Fragile items and packaged goods respond with variation to uniform laboratory shocks,[12]
- Field shocks are highly variable
Of course, it is best when the shock detector properly signals when damage or injury is likely and when it is not. It is very possible to havefalse positivesignals where a shock detector is triggered but there is no damage to a product or no injury to a person. Likewisefalse negativesare also possible.[13]
| Damage or Injury |
No Damage or Injury | |
|---|---|---|
| Shock Detector Activated | Correct Signal | False Positive |
| Shock Detector Not Activated | False Negative | Correct Signal |
Shock detectors are intended to indicate a single severe shock or impact. In some instances a series of lesser shocks might cause damage or injury[14]but would not trigger a shock detector.
See also
[edit]- Type I and type II errors
- Concussions in sport
- Cushioning
- Concussion grading systems
- Head injury criterion
- Football helmet
- Sudden Motion Sensor
- Head impact telemetry system
- Evaluation of binary classifiers
- Confusion matrix
References
[edit]- ^abcdefgHarris, C. M., and Peirsol, A. G. "Shock and Vibration Handbook", 2001, McGraw Hill, ISBN 0-07-137081-1
- ^Vincent, R (2017)."On The Performance of Mechanical Shock Indicators"(PDF).Packaging Technology and Science.30.Retrieved12 September2021.
- ^G01P15/00 Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- ^abcYam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
- ^S, Foreman (13 November 2013)."A Comparative Analysis for the Measurement of Head Accelerations in Ice Hockey Helmets using Non-Accelerometer Based Systems"(PDF).ASTM Concussion Mechanisms Symposium (Nov 13, 2013).ASTM international.
- ^Moore, N C (29 January 2014)."Understanding concussions: Testing head-impact sensors".Michigan News:10–12.Retrieved3 Nov2014.
- ^Wu LC; Zarnescu L; Nangia V; Cam B; Camarillo DB. (November 2014). "A Head Impact Detection System Using SVM Classification and Proximity Sensing in an Instrumented Mouthguard".IEEE Trans Biomed Eng.61(11): 2659–68.doi:10.1109/tbme.2014.2320153.PMID24800918.S2CID22619767.
- ^Noury, N.; Herve, T.; Rialle, V.; Virone, G.; Mercier, E.; Morey, G.; Moro, A.; Porcheron, T. (2000).1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.00EX451).pp. 607–610.doi:10.1109/MMB.2000.893857.ISBN978-0-7803-6603-9.S2CID60860923.
- ^"What You Need to Know About Air Bags, DOT HS 809 575".Nhtsa.gov. Archived fromthe originalon 28 May 2010.Retrieved17 October2010.
- ^Singh, S P; Burgess, Stapleton (1994). "Reliability and Error Estimations of Mechanical Shock Recorders and Impact Indicators".Packaging Technology and Science.7(4): 187–194.doi:10.1002/pts.2770070405.
- ^Graesser, L; Singh, Burgess (1992). "A Performance Study for Two Portable Data Recorders Used to Measure Package Drop Heights".Packaging Technology and Science.5(1): 57–61.doi:10.1002/pts.2770050111.
- ^ASTM Research Report D10-1004,ASTM International
- ^Sheehan, R (January 1983). "Characterizing Shock Detector Performance".Packaging Technology.12(6): 26–30.
- ^Rivara, G R (2014).Sports-Related Concussions in Youth: Improving the Science, Changing the Culture.Institute of Medicine; National Research Council.Retrieved12 November2014.
Bibliography
[edit]- DeSilva, C. W., "Vibration and Shock Handbook", CRC, 2005,ISBN0-8493-1580-8
- Harris, C. M., and Peirsol, A. G. "Shock and Vibration Handbook", 2001, McGraw Hill,ISBN0-07-137081-1
- Yam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009,ISBN978-0-470-08704-6