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Ultrasonic Bolt Measurement

In certain critical bolting applications, factors such as friction or bolt/joint geometry are such that the measurement of applied torque alone will not provide the degree of accuracy necessary to control the preload to be monitored over the service life of the fastener. In these applications, ultrasonic measurement of fastener elongation and/or load has frequently proven to be the most accurate, reliable and cost effective solution.

Ultrasonic measurement of bolt preload is made possible by introducing a sonic pulse at one end of the fastener and accurately measuring the time of flight (TOF) required for the echo to return from the opposite end. Using material constants, the USM-3 converts this TOF into an "ultrasonic length" of the fastener, providing a baseline from which future measurements will be made. When the fastener is tightened, the TOF increases and the USM-3 will again utilise material constants to eliminate the effects of stress and temperature variations on sound velocity, providing an accurate elongation or load measurement.

The USM-3 uses state of the art hardware and software to achieve these measurements with maximum automation, and minimizes the need for operator interpretation. Offering digital recording and transmission of data, in addition to analog signal output the USM-3 provides a complete system for measurement, recording, and control of fastener tension in the most demanding applications.

Ultrasonic Stress Meter - USM

Ultrasonic Stress Meter - USM

With accuracy rivaling that of strain-gauges, the USM-3, Ultrasonic Bolt Meter, defines the state of the art in the measurement of the actual clamp load produced by tightening a threaded fastener. The USM-3 can measure fastener elongation or the resulting load, very accurately in fasteners of virtually any material from 1/2 inch to over 50 feet in length.

The USM-3 allows up to 30 hours field operation from 4 'C' cell alkaline batteries.

The measurement is achieved by determining the change in the transit time, of an ultrasonic shock wave along the length of the fastener as the fastener is tightened by any method.  The on-board microcomputer automatically interprets this time measurement to display the elongation or load in the fastener. Through the use of high speed digital signal processing and automated diagnostics, the USM-3 minimizes the requirements for extensive operator training.

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USM Transducers

USM Transducers

Magnetic Transducers are used with magnetic alloys, and consist of a rare earth magnet surrounding a piezo electric crystal which is protected by a wear plate. The diameter used in the description of transducers refers to the nominal diameter of the piezo electric crystal; therefore, the O.D. of a transducer is larger than the crystal diameter due to the annular magnet and transducer housing. Standard transducers can be used on application with contact temperatures of  up to 54°C (130°F). Hi-Temp transducers are available for applications with contact temperatures of up to 175°C (350°F). Special transducers are available for non-magnetic applications.

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USM Cables

USM Cables

Transducer cables are available in a variety of lengths from 10' to 50' long. Like transducers, transducer cables come in both standard and Hi-Temp versions.

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USM Ancillaries

USM Ancillaries

Spares and accessories for Norbar Ultrasonic Stress Meter (USM).

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