Good Vibrations

摘要

It is said that in the 1960s quarry managers who received complaints about vibration from blasting would visit the complainant immediately before a blast, place a threepenny bit on the window sill and if it did not fall over during the blast the event would be considered to have been acceptable. Of course, this was at a time before vibration monitors were commonplace. The first mechanical instruments were very expensive and, therefore, rare and tricky to set up and use. The output acetate ribbon had to be blackened with carbon, placed on a light box and the maximum amplitude of the trace had to be physically measured with a ruler. A look-up table was then used to convert the readings into peak particle velocity (PPV).