An encoded scan stores one data set every time the encoder advances by the scan resolution. If the probe moves faster than the instrument can produce complete frames, the missing positions are either left empty or filled by repeating the last frame. The limit is simply v = frame rate × scan resolution.

At 20 frames per second and a 1 mm resolution that is 20 mm/s, about 1.2 m per minute – slow enough that a hand scan will overrun it on a good day. Halving the resolution to 0.5 mm halves the allowable speed again. This is why law count discipline matters: it buys scan speed directly.

Run below the theoretical limit, not at it. Hand scanning is not uniform, encoders slip and instruments occasionally miss a trigger, so a margin of 20 to 30 percent is normal practice. Where a procedure demands full data, switch on the instrument’s data completeness or skipped line indicator and rescan any pass that reports missing positions.

Worked example

Acquisition (frame) rate	19.8 Hz
Scan axis resolution	1 mm
Working margin (0 to 1)	0.8
Theoretical maximum scan speed (mm/s)	19.8
Recommended working scan speed (mm/s)	15.84
Recommended working scan speed (m/min)	0.95
Time to scan one metre at the working speed (s)	63.1

At 19.8 frames per second and 1 mm between stored positions the probe may advance 19.80 mm/s. Applying a 0.8 working margin gives 15.84 mm/s, which is 15.84 × 0.06 = 0.95 m/min, so one metre of weld takes 1000/15.84 = 63.1 s.

Use at your own risk — verify before you act

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