Errors of measurement for the UDM-3 ultrasonic flaw detector

Conclusions

• 1. The method of [1] for adjusting the instrument to a material can give a relative error of measurement more than ±2% if there is an additional signal delay.

• 2. The referred and relative errors may be reduced by using a standard specimen as close as possible in size to the workpiece, which serves to eliminate most of the error arising from this source in multiple measurements.

• 3. If limits have been specified for the refered or relative errors and values are known for δt, r_i, and the speed of ultrasound, we can define limits to r_meas within which the errors in measuring the distance due to signal delay are not more than the specified values.

• 4. The error of measurement due to signal delay may be eliminated if not less than two echo signals are displayed on the oscilloscope during the adjustment and during direct measurement; the instrument should thus be set up from the difference of the readings corresponding to the first and n-th echo signals.

  These conclusions apply also to instruments of DUK-66 type, which use the same method of adjustment as the UDM-3.