The Uses of Ultrasonic Bolt Tension Meter


Ultrasonic Bolt Tension Meter (UBTM) measure the elongation produced by tightening a threaded fastener. Our line of monitors can measure the elongation very accurately in fasteners of virtually any material from 1/2 inch to 100 feet in length. The operator uses the to instrument measure the length of a bolt or fastener before it is tightened and again after it is tightened to calculate the delta or change in length. The on-board microcomputer automatically interprets this measurement to display the time (nanoseconds), elongation, load, stress, or %strain from stretching a fastener.

Why UBTM is used?
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 Bolt Tension Meter 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 utilize material constants to eliminate the effects of stress and temperature variations on sound velocity, providing an accurate elongation or load measurement.

Different UBTM Tools
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.

With accuracy rivaling that of strain-gauges, the USM-3, Ultrasonic Bolt Tension 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. While, 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.

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