Calibrating an Ultrasonic Testing Machine.
In the NDT profession you utilize many different tools and instruments to aid you in the search for discontinuities (discontinuities are any break in the material i.e.: crack cold shuts etc). There are quite a few testing methods that use different means of searching parts internally as well as externally for cracks or any other flaw in the material being tested. Ultrasonic testing utilizes ultrasonic sound waves to inspect parts for deep seeded discontinuities. .
Here is how to calibrate the UT instrument to use a pulse echo (sends and receives a single pulse of sound) unit transducer for a longitudinal wave (l-waves are caused by sending the ultrasonic waves into the specimen at an angle of 0 degrees) scan. The equipment required for UT is the instrument that contains the Cathode Ray Tube (CRT). You"ll also need coaxial cable, a transducer (5 or 2.5mHz), couplant (a gel or liquid), and a calibration block (Standard IIW calibration block). The assembly of all of the equipment is quite simple. You insert the coax cable into the UT instrument. Then you connect the coaxial cable to the transducer. Turn the instrument on, and make sure you have a baseline across the bottom of your CRT screen. There should also be a high signal or pip on the screen to the absolute left (the pip on the absolute left of the screen is the initial pulse). .
The first step in getting your UT machine calibrated is setting the screen size. The screen on the UT instrument has a 10x10 grid screen. The baseline represents the speed of which the pulse-echo unit transducer receives the pulse after it is sent into the specimen. The goal of this procedure is to make this line represent a measurement in this case we want each graticule to represent one inch. Apply couplant to eliminate the interface between the transducer and the block. Place the transducer on the IIW block so the sound will be sent through the 4-inch section that doesn't have any holes or anything that will reflect sound.
