GE Ultrasonic USM Go, Operator'S Manual

Page: 124 / 190

Chapter 3. Making Measurements
106 USM Go Operator’s Manual
3.16 JISDAC Evaluation Mode
Note:
Evaluation modes, such as JISDAC , are selected in the EVAL MODE function in the EVAL menu. The selected evaluation mode
menu then appears in the ACQUIRE menu bar. While operating in JISDAC mode, the Gate A TOF MODE must be set to PEAK or
JFLANK .
Conventional measurements can be made using the JIS Distance Amplitude Correction ( JISDAC ) mode. This mode operates based on a set
of user-recorded data points. These points are recorded from the JIS/DAC menu, as described below.
The JISDAC mode displays all echoes at their true amplitude. However, when operating in JISDAC mode, a Distance Amplitude
Correction curve is superimposed on the A-Scan display. The curve represents constant reflector size at varying material depth.
When displayed, the JISDAC curve visually represents a line of constant reflector peaks over a range of material depths. Remember that in
JISDAC mode, the only deviation from traditional display and operation is the appearance of the JISDAC curve and a series of OFFSET
curves. All A-Scan echoes are displayed at their non-compensated height. A JISDAC curve can be based on up to 15 data points
(i.e. material depths). A JISDAC curve is programmed using a series of same-reflector echoes at various depths, covering the range of
depths to be inspected in the test material. Because near field and beam spread vary according to transducer size and frequency, and
materials vary in attenuation and velocity,
JISDAC must be programmed differently for different applications.
The dynamic range of the JISDAC function is 60 dB, and the maximum curve slope is 12 dB per microsecond. Successive data points do
not have to progressively decrease in amplitude. That is, the JISDAC curve does not have to have a constantly descending slope.