Product category:
Tooling and tools
News Release from: Norbar Torque Tools | Subject: USM-II
Edited by the Engineeringtalk Editorial
Team on 27 October 2000
Ultrasonic stress measurement goes
mobile
Precise measurement of the clamp load produced by a bolt or other threaded fastener is now possible in the field with the introduction of the USM-II by Norbar Torque Tools.
Precise measurement of the clamp load produced by a bolt or other threaded fastener is now possible in the field with the introduction of the USM-II by Norbar Torque Tools The USM-II has all the features of the ground-breaking USM-I launched last year but in a portable, battery-powered unit which can go out on site and into production areas inaccessible to the mains-powered unit
Weighing just 1.7kg the USM-II is housed in an aluminium case with stainless steel end plates and powered by four internal size "C" batteries that can be easily replaced by the operator.
It features an alphanumeric membrane keypad that enables bolts to be labelled by name rather than by code number.
The USM-ll provides accurate measurement of the clamping force produced when initially tightening a fastener in a safety-critical application.
It provides more precise control of this force than can be achieved by measuring the torque or torque and angle applied by the tightening tool.
The USM-II is also ideal where the clamping force produced by a threaded fastener must be monitored over its service life without disturbing it.
Provided the untensioned length of the fastener was either measured with the USM-II before it was tightened, or the fastener can be loosened and measured in situ, the clamping force it produces can then be re-measured at any time without disturbing it again.
Although ultrasonic devices for measuring bolt length have been available for some years they have until now been costly and difficult to use.
Norbar has used advanced digital signal processing techniques in the USM-II to make it significantly easier to use than the previous generation of ultrasonic bolt meters, and make the price far more accessible.
The USM-II has now put precision ultrasonic measurement within reach of production, maintenance and quality control engineers who in the past have relied on torque measurement alone.
Even accurate measurement of the torque applied to a fastener can only provide an approximation of the clamping force produced, as the actual force generated by a given torque depends on factors such as the friction generated between the thread and the nut.
While torque control is perfectly satisfactory for most fasteners there is a range of applications in industries such as aerospace, marine engineering, petrochemical, nuclear power, offshore and injection moulding that benefit from the far greater accuracy of control over clamping force provided by the USM-II.
The USM works by introducing a sonic pulse at one end of the fastener and measuring the time taken for the echo to return.
As the fastener is tightened, two things happen that can be measured.
The change in bolt length as it stretches increases the echo time, and the increasing stress level in the bolt reduces the sound velocity, which further increases the echo time.
The change in ultrasonic length is displayed as elongation or tension and this data can be used to calculate the induced stress.
Up to 5000 readings from 1000 bolts can be stored in the USM-II's 2 MB memory and recorded data can be downloaded via an RS232 output to a PC, and uploaded again at a later date for future monitoring work.
A 0-10V analogue output can be used to precisely control the torque applied to fasteners by torque tools such as Norbar's Pneutorque during initial installation.
Low noise and automatic gain features allow signal detection and measurement in the most difficult applications.
Automatic digital signal analysis optimises the measurement process and warns of potential problems.
This key feature differentiates the Norbar USM instruments from competitive products, making lengthy set up and extensive operator training a thing of the past.
With the introduction of the USM-II Norbar now has the most complete range of instruments for the precise measurement, recording and control of fastener tension, on the factory floor or on site. Request a free brochure from Norbar Torque Tools ...
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