Posted to News on 9th Jul 2008, 13:19
Ultrasonic bolt tension meter is easy to use
Measurement of the torque applied to a bolt or other threaded fastener during tightening usually provides sufficient feedback, but there are more specialised tasks where measurement of the fastener tension is essential to ensure the integrity of the mechanical joint. To address this requirement, Norbar is introducing the USM-3 ultrasonic bolt meter - a compact, lightweight, portable unit that gives precise measurement of elongation and load in threaded fasteners.
Traditionally, ultrasonic measurement has been a highly skilled task, requiring extensive knowledge of material properties to determine the correct transducer diameter, the correct transducer frequency and to interpret the results. The USM-3 overcomes all of these challenges and gives the operator a highly accurate and easy-to-use tool for determining the tension in a fastener. Real-time, precise bolt measurement can be accomplished in fasteners of any metal from 25mm (1inch) to over 15m (50feet) long.
How it works
Ultrasonic measurement is based on the time-of-flight principle. In use, a small transducer placed against the head or stud end of the fastener sends an ultrasonic sound wave through the length of the bolt. When the echo signal returns, the microprocessor in the USM-3 converts the transit time to a precise length, using constants based on the bolt material and digital signal.
Processors derive a precise elongation or load measurement, taking into account the effects of stress and temperature variations on the sound velocity to give an accuracy that exceeds that of strain gauges. The USM-3's 1/4 VGA back-lit LCD display provides easy-to-interpret results of load, elongation data and waveform. Norbar's five-point DSP algorithm also provides an evaluation of signal quality.
The USM-3 can provide a 0-10V analogue output to shut off torque tools when a predetermined bolt stretch or load has been attained. In addition, the onboard flash memory can store measurements on up to 80 bolts, with up to five measurements of load and elongation for each bolt. An RS232 interface enables these results to be uploaded to a PC, on which Norbar's Windows-based Sonic Bolt software can perform a theoretical load-to-stretch calculation for long-term mechanical joint integrity analysis. The software can also provide Excel-formatted reports.
Norbar's USM-3 is an evolution of its popular USM-2, with significant improvements in both utility and performance. The new model offers eight times more memory and twice the processor speed, together with increased capacity and faster response. In addition, the 1/4 VGA display is significantly larger than that of the USM-2, enabling more data to be presented in a more user-friendly fashion.
