Four Channel Trigger Box

For Fiber Fracture Detection

Purpose

The fracture of high strength silica optical fiber, as well as weaker materials, may be conveniently detected in static or dynamic fatigue experiments by the associated acoustic emission [ref 1]. Each of the four channels of the Trigger Box accepts the signal from an acoustic transducer and produces a TTL pulse for  each fracture detected. The Trigger Box is a purpose designed component that provides a simpler and less expensive alternative to general purpose acoustic signal processing equipment. This equipment is suitable for use with EIA/TIA and IEC standard test procedures.

Description

The Trigger Box contains four independent channels. Each channel consists of an amplifier incorporating a high-pass filter to eliminate background noise and a variable sensitivity comparator feeding a pulse generator. The output pulse is made available for monitoring by, for example, a computer or chart recorder. A latched output is also provided to give a visual indication that a break has occurred since the last reset.

Features

Inputs

The acoustic signal input is via a front panel BNC designed for connection to a high sensitivity acoustic transducer with a resonance in the 100-200 kHz region (although any mV signal source may be used). A front panel potentiometer is provided for adjusting the sensitivity.
 

Outputs

A 5 V TTL pulse of duration adjustable from 10 to 200 ms is supplied for each break detected via a front panel BNC. The output state is monitored by a front panel LED. The output is also latched to a second front panel LED which indicates when a break has occurred since the last reset. This LED is reset by a front panel button.
 

Multiplexed Outputs

The four channel outputs, A, B, C and D, are multiplexed by simple addition and subtraction. The outputs are then suitable for connection to a chart recorder set to approximately 1V full scale sensitivity. Use of the multiplexed output means a one pen chart recorder can monitor two or four channels simultaneously and continuously. Since the chart recorder response is slow it operates in a ballistic mode producing a "blip" for each fracture. Three outputs are available via front panel BNC sockets:

Digital Interface

Buffered pulsed and latched TTL outputs, suitable for connection to a computer, are made available via a rear panel Canon D25 connector. TTL inputs permit remote resetting of the individual latches.
 

Audible Telltale

A circuit gives an audible "beep" when a trigger event is detected. May be configured to give beeps for any combination of channels including none or all four.

Options

Acoustic Transducers

Transducers (AE-R15) are available that are suitable for monitoring fibers for fracture. They feature high sensitivity above 20 kHz but reduced sensitivity in the audible range - this ensures excellent immunity to extraneous sounds. The sensor includes a 6 foot cable but replacement cables are available (AE-CBL).
 

Precision Bore Tubes

One of the most convenient methods for applying a static stress to optical fibers is to insert short lengths, bent double, into precision bore glass tubes. Typically 30 or more specimens can be inserted into a 6" long tube. The tube inside diameters are accurate to within a few m so that all specimens are under essentially the same stress. Therefore, it is not necessary to know which specimen fails, only when the failures occur. Precision bore glass tubes are available in a broad range of sizes and in either Pyrex (PB­P­x) or fused quartz (PB­Q­x). The Pyrex tubes are adequate for most test environments but the fused quartz tubes are more durable in caustic environments. Please call to discuss tube sizes and prices.

Computerized Monitoring System

A PC based computer system for monitoring up to 8 or 16 trigger boxes (32 or 64) is available. This system logs breaks and performs statistical data analysis on the fly (including censored data, i.e. including specimens yet to break). See the information on the Trigger Box Monitor System.

Ordering Information

^† contact us to discuss your specific requirements - replace x by the tuber inside diameter in µm.

References

1. M. J. Matthewson & C. R. Kurkjian, "Static fatigue of optical fibers in bending", J. Am. Ceram. Soc. 70 [9] 662-668 (1987).

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