ASTM E317:2006 pdf free download – Standard Practice for Evaluating Performance Characteristics of Ultrasonic Pulse- Echo Testing Instruments and Systems without the Use of Electronic Measurement Instruments.
If so specified, both total noise and electrical noise should he reported.
6.6 Accuracy of €‘alibra ted Ga in Controls:
6.6.1 Significance—When quantitative measurement of signal amplitudes are to he made by comparison against a reference indication, the use of accurately calibrated gain controls may be desirable or necessary, particularly when the amplitude ratio differs significantly from unity. For this procedure, it is assumed that the controls are calibrated in conventional decibel units. Refer to 6.1.2 regarding gain control nonienc lat ure.
6.6.2 Apparatus—A precision external attenuator, terminating resistor, and test set-up similar to that described in 6.3.3.1 are required. The attenuator must have a range at least equal to that being checked plus the additional needed to bring the test signal on scale at highest instrument sensitivity specified.
NOTF I 2—The maximum range for any single panel control function is usually 60 dB or less. This method is not recommended for checking larger ranges. obtained for example. by sequential use of more than one control, since cross-talk may become a problelTi.
N0TF 13—A test precision of 1 .0 dB is assumed to be adequate and obtainable, Greater precision requires either smaller attenuator steps or use of colTecflon factors for the display screen readings. Refer also to Note
6.6.3 Procedure—Select a test system configuration that will produce a stable, on-screen, mid-scale indication when the instrument controls are set for the minimum desired sensitivity and the external attenuator has sufficient available attenuation to equal the desired test range. Use the fine-gain control when available, or pulse-length adjustment to set the reference indication precisely at the 60 % fs graticulc line. Record the settings of the external attenuator and the calibrated controls, noting whether they represent decibel gain or decibel attenuation. Increase the instrument gain in the smallest available calibrated increment, and add sufficient external attenuation to return the test indication as closely as possible to the 60 % fs reference line. With 1 .0 dB or smaller attenuator increments available, the adjusted amplitude should always lie between 56 % Is and 60 % fs when the correct step is used. Record the new gain control and external attenuator settings. Repeat the procedure until the full range of the relevant instrument control has been checked.
6.6.4 Interpretation of Data—Unless otherwise instructed by the requesting document, use the results as follows: For each control range tested, tabulate the readings of the control against the incremental attenuation added externally.