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Natural Science Forum / Physics / Acoustics / September 2005Lep,d is it the same as TWA?
Anyone, Is Lep,d the same as TWA? or is it different. (Assuming the d is 8 hours?) Knowing my sample time, Leq and d how can I calculate Lep,d Thanks in advance Tom Retzlaff > Is Lep,d the same as TWA? or is it different. > (Assuming the d is 8 hours?) > > Knowing my sample time, Leq and d how can I > calculate Lep,d From the information I have, TWA and LEP,d appear to be the same. I don't know what you mean by "knowing d". d must stand for day or daily in LEP,d. Anyway, if you know the duration t, then the daily exposure can be calculated by adding the following to the Leq: 10*log10(t/tref) dB where tref is 8 hours. Obviously t and tref have to be in the same units. You will find a calculator button on my web site, on the page http://www.tonywoolf.co.uk/noiseregs.htm. This allows you to calculate the daily exposure for up to 3 different sessions in a day, each with a different duration and Leq.  SignatureTony Woolf My e-mail address has no hyphen - but please don't use it, reply to the group. I assume d is the workday (8 hours typical) but you know what they say about assuming ;-) TeeRetz >I assume d is the workday (8 hours typical) but you know > what they say about assuming ;-) You know what they say about newsgroups ;-) You may be told various things, it is up to you to sort the wheat from the chaff! It is assumed in the instructions for calculating LEP,d that it is possible to divide peoples' work up into days, however long or short. You then calculate the exposure for each day essentially as I wrote in my last post. I don't think that means that d represents a particular duration. But it doesn't really matter what each letter means, it is just a short way to write "personal daily exposure level". SignatureTony Woolf My e-mail address has no hyphen - but please don't use it, reply to the group. OK so from http://www.measure.demon.co.uk/docs/Council_Directive_86_188_EEC.html I see the Lep,d = Leq + 10log(Te/To) Where To is 28800 seconds. Te is the amount of time the worker is in the environment? So if I take a sample for 20min, and the noise is consistant over the workers day (his day is 2hours). I would calculate Lep,d by subtracting 10log(7200/28800) from Leq? would this be valid Lep,d or an estimate? True would require me to sample for 2 hours? and also would mathematically be eqiv. to TWA. Thanks TeeRetz > OK so from > http://www.measure.demon.co.uk/docs/Council_Directive_86_188_EEC.html [quoted text clipped - 8 lines] > the workers day (his day is 2hours). > I would calculate Lep,d by subtracting 10log(7200/28800) from Leq? NO!!! I wrote "adding" and there is a + in the equation. And why not do it in hours and add 10*log10(2/8)? You will be less likely to make a mistake. > True would require me to sample for 2 hours? and also would > mathematically be eqiv. to TWA. I don't use TWA. But from what I have read it is exactly the same as LEP,d. Knowing how long to sample is a different topic. You have to make some estimate of how much the noise is likely to vary, and measure for long enough to get a reliable answer. It is not always necessary to sample for a full day. I think I've said plenty here, I will leave this thread to see if anyone else wants to put a word in. SignatureTony Woolf My e-mail address has no hyphen - but please don't use it, reply to the group. >>True would require me to sample for 2 hours? and also would >>mathematically be eqiv. to TWA. TWA represents the noise dose in terms of a day of 8 hours at 90 dBA. If a steady noise level were less than 90, or the workday time duration less that 8.0 hours, TWA would be less than 90.0 dBA and vice versa, It might well be that Lep,d intends to make the same representation. HOWEVER, recall the the USA doubling exchange rate is 5 dB per dose doubled, while ISO and the rest of the world uses a 3 dB exchange rate. A small difference will always exist when the instantaneous noise level differs from 90 dBA. For the same true workday noise exposure, noise dose contributions for noise whose instantaneous level is more than 90 dBA, the TWA(5/dd) increment will be less that that accrued to Lap,d(3/dd). For noise dose contributions whose instantaneous noise level is less than 90 dBA, the TWA(5/dd) increment will be greater than that accrued to Lap,d(3/dd). The difference becomes quite striking for noises beyond 110 dBA. The US OSHA rules make up for this shortfall to some extent by prohibiting employee exposure to any instantaneous noise level greater than 115 dBA(slow). Angelo Campanella Oops..my mistake I meant to say adding( And that is what I'm doing) The backgroung on this is we are looking at a new soundlevel meter that displays both TWA and Lep,d and the values differ. I'm trying to figure out why before I contact the manufacturer and ask. BTW yes the weighting, exchange rate, etc. are the same. > > OK so from > > http://www.measure.demon.co.uk/docs/Council_Directive_86_188_EEC.html [quoted text clipped - 29 lines] > My e-mail address has no hyphen > - but please don't use it, reply to the group. I suspect that the TWA refers to the actual measurement period and the meter is not set to display an 8 hour TWA. It wouldn't be a CEL310 or similar would it? With these dose meters the Lep,d and TWA are displayed but you must calculate the 8 hour TWA. If you ran the meter for 8 hours, the two values should coincide. GB > Oops..my mistake I meant to say adding( And that is what I'm doing) > [quoted text clipped - 43 lines] >> My e-mail address has no hyphen >> - but please don't use it, reply to the group. |
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