Specifications

USN52 L Operating Manual Page 77
13.1 Preparing to Calibrate
Before calibrating for digital thickness or flaw distance measure-
ments, the A-scan display must be calibrated. Follow the proce-
dures in Chapter 9 to prepare initial instrument settings and cali-
brate the A-scan display for the type of probe to be used.
To obtain correct digital thickness or distance measurements the
USN52 L must be calibrated for the specific material to be mea-
sured.
NOTE: All calibration procedures require a calibration stan-
dard (test block) of the same material, velocity of sound,
and temperature as the material to be tested, and whose
precise thickness is known. Some additional test block re-
quirements are included with the procedures in this chap-
ter.
GATE LOGIC must be set to POSITIVE or NEGATIVE (ref. Sec-
tion 10.2) and TOF and MEASURE modes selected that are ap-
propriate for the type of probe and measurements to be taken.
Section 13.9 provides information on FLANK and PEAK TOF
modes.
If MEASURE is set to 0 TO 1st (zero to first echo), the USN52 L
measures thickness or flaw distance by measuring the distance
(time) from the acoustic zero point to the first echo whose ampli-
tude exceeds threshold (a-THRESH) in the gate. Position of the
zero point is set using the ZERO function.
If MEASURE is set to MULTECHO (multiple echo), the unit mea-
sures the distance (time) between the first two echoes that exceed
threshold level in gate a.
Refer to Chapter 10 for detailed instructions on gate operation.
Calibration procedures in this chapter cover the following MEA-
SURE mode and probe combinations:
• 0 TO 1st - Single Element Contact Probe
• 0 TO 1st - Single Element Delay Line Probe
• 0 TO 1st - Dual Element Probe
• MULTECHO - Single Element Contact Probe
• MULTECHO - Single Element Delay Line Probe
13. Calibrating for Digital Measurement