Calculation of Settings by Mental Arithmetic (PDF)

Calculation of the settings by mental arithmetic and rules of thumb ( “one minute settings calculation”) Parameters and abbreviations:  1" = approximately 25 mm (25.4 mm)  sound velocity steel = approximately 6 mm per µSec (5960 m/s)  sound velocity water = approximately 1.5 mm per µSec (1480 m/...

Calculation of the settings by mental arithmetic and rules of thumb ( “one minute settings calculation”) Parameters and abbreviations:  1" = approximately 25 mm (25.4 mm)  sound velocity steel = approximately 6 mm per µSec (5960 m/s)  sound velocity water = approximately 1.5 mm per µSec (1480 m/s)  Total Window Length (TWL) = 40 µSec  Backwall (BW) at 50% off Total Window Length  Start of 2nd window (2nd W) = 1.0 µSec  Backwall (BW) at 50% of 2nd Window  Offset Trigger Delay (OTD) for a standard UT head = 40 µSec  minimum time between end of total window (ETW) and next initial pulse (NIP) = 70 µSec  holdoff = rep-rate (in µSec ) - 70 µSec to avoid triggering on serial data  Inner Radius (IR)  Initial Pulse (IP) Example (for 6" pipe, WT 7.1 mm, OTD 40 µSec) : 6" = 150 mm ==> ((150 / 2) x 2) / 1.5= 100 µSec 7.1 mm ==> (7.1 x 2) / 6 = 2.4 µSec (2.366) delay: OTD + IR + WT -1/2 TWL 40+ 100 + 2.4 - 20 = 122 µSec (122.4) maximum rep-rate: Delay + TWL + min. time 122 + 40 + 70 = 232 µSec ==> 1 / 232 x 10-6 = 4310 meas/sec The actual rep-rate should be a little lower, so the holdoff will fit nicely between the end of the total window and the next initial pulse holdoff: time IP to NIP (= rep-rate) - 70 µSec 232 - 70 = 162 µSec 2nd window length: (WT-start 2nd W) x 2 (2.4 - 1.0) x 2 = 1.4 x 2 = 2.8 µSec These calculations will give us the approximate settings without the use of a calculator within minutes and, obviously, need finetuning for the real settings. Keep in mind that this calculation is merely meant to be a fast guide. Also keep in mind that the maximum rep-rate is not only limited by the time between the end of the total window and the next initial pulse, but also by the maximum speed of the motor (approximately 25x for DC, 13x for stepper) The meas/rev can be calculated by dividing the rep-rate by the motor speed.  1 half OTD transducer to mirror 3 4 2 Inner radius (IR) mirror to inner wall (1480 m/s) 3 Wall thickness (WT) Innerwall to Backwall (5960 m/s) 4 Wall thickness (WT) backwall to Innerwall (5960 m/s) 5 Inner radius (IR) Innerwall to mirror (1480 m/s) 2 5 6 half OTD mirror to transducer 1 Offset Trigger Delay (OTD) 6 2 Inner radius (IR) 1 3 Delay 4 Total window (TW) 5 1st window (L1st W) 6 Start 2nd window (S2nd W) 7 Length 2nd window (L2nd W) 8 Holdoff 4 Time between total window (TW) and next initial 9 5 pulse (NIP) 3 7 9 6 1 2 8