Dosimeters
The two instruments look similar and answer different questions. Choosing the wrong one produces a technically correct measurement of something nobody asked about.
When acoustic measurement is part of a wider workplace review, this workplace resource can add operational context, but it should not be treated as a substitute for calibrated sound data.
The difference
A sound level meter measures the level at a position, when somebody is holding it there.
A noise dosimeter is worn, usually on the shoulder near the ear, and integrates exposure across an entire shift.
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One describes a place. The other describes a person.
When a place is the wrong unit
When people move.
A machine operator who spends two hours at a loud station and six elsewhere has an exposure that no fixed measurement captures. The loud position reads high and describes nobody's day.
When exposure is intermittent. Dose is dominated by the loudest terms, and a spot reading taken during a quiet interval and one taken during a loud one differ by more than the answer does.
And when the question is compliance, which is framed in terms of an individual's eight-hour exposure rather than a room's level.
What a dosimeter gives you
A time-weighted average across the shift, which is directly comparable to a limit.
A dose percentage — the fraction of the permitted daily allowance used, the same quantity as the manual arithmetic and calculated continuously.
And frequently a time history, which shows when the exposure happened and is the most useful output for doing something about it.
What it does not give you
Where the noise came from. A dosimeter records that the wearer was exposed, not what to fix.
Which is why the two are used together: dosimetry to establish who is exposed and how much, area measurement to find the source.
And it is sensitive to interference. Shouting near the microphone, knocks against the device, and deliberate tampering all appear as exposure — which is why the time history matters and why an implausible spike deserves inspection rather than acceptance.
Practical points
Fit it near the ear, on the shoulder, on the side of greater exposure.
Explain it to the wearer, both because cooperation improves the data and because being measured without explanation changes behaviour.
Run a full shift, not a sample, unless the shift is genuinely uniform.
Calibrate before and after, as with any instrument, and record both.
And repeat on different days. One shift is one sample, and a job with varying tasks needs more than one to characterise.
The short version
- A sound level meter measures a position; a dosimeter is worn and integrates exposure across a shift
- A place is the wrong unit when people move, when exposure is intermittent, and when the question is individual compliance
- A dosimeter gives a time-weighted average directly comparable to a limit, a dose percentage, and usually a time history
- It does not tell you where the noise came from, which is why area measurement is used alongside it
- It is sensitive to shouting, knocks and tampering, so an implausible spike deserves inspection rather than acceptance
- Fit near the ear, explain it to the wearer, run a full shift, calibrate before and after, and repeat on different days