
A shock detector, shock indicator, or impact monitor is a device which indicates whether a
physical shock or
impact
Impact may refer to:
* Impact (mechanics), a large force or mechanical shock over a short period of time
* Impact, Texas, a town in Taylor County, Texas, US
Science and technology
* Impact crater, a meteor crater caused by an impact event
* Imp ...
has occurred. These usually have a
binary output (
go/no-go
A go/no-go test is a two-step verification process that uses two boundary conditions, or a binary classification. The test is passed only when the ''go'' condition has been met and also the ''no-go'' condition has failed.
The test gives no inform ...
) and are sometimes called ''shock 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.
[Harris, C. M., and Peirsol, A. G. "Shock and Vibration Handbook", 2001, McGraw Hill, ISBN 0-07-137081-1]
By contrast, a
shock data logger is a
data acquisition
Data acquisition is the process of sampling signals that measure real-world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems, abbreviated by the ...
system for analysis and recording of shock pulses.
Overview
Shocks and impacts are often specified by the peak acceleration expressed in g-s (sometimes called
g-force
The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...
s). The form of the shock pulse and particularly the duration are equally important.
[ 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.][
A shock detector can be evaluated:
* Separately in a laboratory ]physical test A physical test is a qualitative or quantitative procedure that consists of determination of one or more characteristics of a given product, process or service according to a specified procedure.ASTM E 1301, Standard Guide for Proficiency Testing ...
, perhaps on an instrumented shock machine.
* 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 proper test method
A test method is a method for a test in science or engineering, such as a physical test, chemical test, or statistical test. It is a specified procedure that produces a test result. To ensure accurate and relevant results, a test method should b ...
s and verification and validation
Verification and validation (also abbreviated as V&V) are independent procedures that are used together for checking that a product, service, or system meets requirements and specification (technical standard), specifications and that it fulf ...
protocols are important for all phases of evaluation.
Technologies
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 in patent classification A patent classification is a system for patent examiner, examiners of patent offices or other people to categorize (code) documents, such as published patent applications, according to the technical features of their content. Patent classifications ...
01P15/00: "Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration"
Analogue constructions include:
* Spring-mass systems which can be triggered by a shock[
*Magnetic balls which can be dislodged from a holder][
*Disruption of the surface tension of a liquid
*Breakage of an inexpensive brittle component with a known fragility][
More sophisticated electronic systems use ]accelerometer
An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...
s and associated microelectromechanical systems
MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...
.[
]
Monitor shipments
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.[Yam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6]
Some shipments need more than one shock detector to better monitor all directions of impacts.[ 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:][
* 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 extra ]calibration
In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...
prior 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
Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...
, puncture, and compression can also cause damage yet would not trigger a shock detector.
Impacts to people
Personal protective equipment
Personal protective equipment (PPE) is protective clothing, helmets, goggles, or other garments or equipment designed to protect the wearer's body from injury or infection. The hazards addressed by protective equipment include physical, elect ...
such as helmet
A helmet is a form of protective gear worn to protect the head. More specifically, a helmet complements the skull in protecting the human brain. Ceremonial or symbolic helmets (e.g., a policeman's helmet in the United Kingdom) without protecti ...
s are sometimes equipped with impact monitors. 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.
Crash sensors on bicycle helmet
A bicycle helmet is a type of helmet designed to attenuate impacts to the head of a cycling, cyclist in collisions while minimizing side effects such as interference with peripheral vision.
History
History of designs
A cycle helme ...
s can detect a crash and call for assistance. Fall sensors are available to senior citizens to call for help when a fall is detected.
Other uses
A related use of an impact detector is as automobile air bag
An airbag is a vehicle occupant-restraint system using a bag designed to inflate in milliseconds during a collision and then deflate afterwards. It consists of an airbag cushion, a flexible fabric bag, an inflation module, and an impact sensor. ...
sensor. These sophisticated sensors are used to trigger the protective air bag system used on current vehicles.
Active hard-drive protection In computer hardware, active hard-drive protection refers to technology that attempts to avoid or reduce mechanical damage to hard disk drives by preparing the disk prior to impact. This approach is mainly used in laptop computers that are frequentl ...
systems sense impacts to laptop computer
A laptop computer or notebook computer, also known as a laptop or notebook, is a small, portable personal computer (PC). Laptops typically have a Clamshell design, clamshell form factor (design), form factor with a flat-panel computer scree ...
s to help minimize damage from drops.
Some emergency locator beacon
An emergency locator beacon is a radio beacon, a portable battery powered radio transmitter, used to geolocalization, locate airplanes, vessels, and persons in distress and in need of immediate rescue. Various types of emergency locator beacons ar ...
s, such as Emergency Locator Transmitter
An emergency position-indicating radiobeacon (EPIRB) is a type of emergency locator beacon for commercial and recreational boats; it is a portable, battery-powered radio transmitter used in emergencies to locate boaters in distress and in nee ...
s, are activated by a specified shock or impact.
Interpretation
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.
* 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,
* 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 have false positive
A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resu ...
signals where a shock detector is triggered but there is no damage to a product or no injury to a person. Likewise false negative
A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resu ...
s are also possible.
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 but would not trigger a shock detector.
See also
* Concussion grading systems
*Concussions in sport
Concussion, a type of mild traumatic brain injury that is caused by a direct or indirect hit to the head, body,neck, or face. Concussions can be caused by various mechanisms, is a common injury associated with sports and can affect people of al ...
*Football helmet
A football helmet is a type of protective headgear used mainly in gridiron football, although a structural variation has occasional use in Australian rules football. It consists of a hard plastic shell with thick padding on the inside, a Face ma ...
* Head impact telemetry system
*Head injury criterion
The head injury criterion (HIC) is a measure of the likelihood of head injury arising from an impact. The HIC can be used to assess safety related to vehicles, personal protective gear, and sport equipment.
Normally the variable is derived from t ...
*Package cushioning
Package cushioning is used to protect items during shipment. Vibration and Shock (mechanics), impact shock during shipment and loading/unloading are controlled by cushioning to reduce the chance of product damage.
Cushioning is usually inside a s ...
*Sudden Motion Sensor
The Sudden Motion Sensor (SMS) is Apple's motion-based data protection system used in their notebook computer systems. Apple introduced the system January 1, 2005 in its refreshed PowerBook line, and included it in the iBook line July 26, 2005. ...
*Confusion matrix
In the field of machine learning and specifically the problem of statistical classification, a confusion matrix, also known as error matrix, is a specific table layout that allows visualization of the performance of an algorithm, typically a super ...
* Evaluation of binary classifiers
*Type I and type II errors
Type I error, or a false positive, is the erroneous rejection of a true null hypothesis in statistical hypothesis testing. A type II error, or a false negative, is the erroneous failure in bringing about appropriate rejection of a false null hy ...
References
Bibliography
* DeSilva, C. W., "Vibration and Shock Handbook", CRC, 2005,
* Harris, C. M., and Peirsol, A. G. "Shock and Vibration Handbook", 2001, McGraw Hill,
* Yam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, {{ISBN, 978-0-470-08704-6
Helmets
Measuring instruments
Mechanics
Packaging
Safety engineering