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Forum index » Science and Technology » Physics » Acoustics
Lep,d is it the same as TWA?
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teeretz
science forum beginner


Joined: 28 Sep 2005
Posts: 4

PostPosted: Wed Sep 28, 2005 12:10 pm    Post subject: Lep,d is it the same as TWA? Reply with quote
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
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Tony
science forum Guru Wannabe


Joined: 07 Sep 2005
Posts: 111

PostPosted: Wed Sep 28, 2005 3:06 pm    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
"teeretz" <teeretz@yahoo.com> wrote in message
news:1127916658.783458.73890@g47g2000cwa.googlegroups.com...
Quote:
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.

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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teeretz
science forum beginner


Joined: 28 Sep 2005
Posts: 4

PostPosted: Wed Sep 28, 2005 4:23 pm    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
I assume d is the workday (8 hours typical) but you know
what they say about assuming Wink
TeeRetz
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Tony
science forum Guru Wannabe


Joined: 07 Sep 2005
Posts: 111

PostPosted: Wed Sep 28, 2005 5:12 pm    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
"teeretz" <teeretz@yahoo.com> wrote in message
news:1127931831.626069.198200@g49g2000cwa.googlegroups.com...
Quote:
I assume d is the workday (8 hours typical) but you know
what they say about assuming Wink

You know what they say about newsgroups Wink 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".

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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teeretz
science forum beginner


Joined: 28 Sep 2005
Posts: 4

PostPosted: Wed Sep 28, 2005 5:50 pm    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
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
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Tony
science forum Guru Wannabe


Joined: 07 Sep 2005
Posts: 111

PostPosted: Wed Sep 28, 2005 7:52 pm    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
"teeretz" <teeretz@yahoo.com> wrote in message
news:1127937046.829601.9820@g14g2000cwa.googlegroups.com...
Quote:
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?

NO!!! I wrote "adding" and there is a + in the equation. And why not do it
in hours and add 10*log10(2/Cool? You will be less likely to make a mistake.

Quote:
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.

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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Angelo Campanella
science forum Guru Wannabe


Joined: 08 May 2005
Posts: 226

PostPosted: Wed Sep 28, 2005 8:10 pm    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
Tony wrote:
Quote:
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
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teeretz
science forum beginner


Joined: 28 Sep 2005
Posts: 4

PostPosted: Thu Sep 29, 2005 10:27 am    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
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.


Tony wrote:
Quote:
"teeretz" <teeretz@yahoo.com> wrote in message
news:1127937046.829601.9820@g14g2000cwa.googlegroups.com...
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?

NO!!! I wrote "adding" and there is a + in the equation. And why not do it
in hours and add 10*log10(2/Cool? 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.

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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GB
science forum beginner


Joined: 13 Jun 2005
Posts: 3

PostPosted: Fri Sep 30, 2005 8:45 am    Post subject: Re: Lep,d is it the same as TWA? Reply with quote
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

"teeretz" <teeretz@yahoo.com> wrote in message
news:1127996831.709848.245400@g44g2000cwa.googlegroups.com...
Quote:
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.


Tony wrote:
"teeretz" <teeretz@yahoo.com> wrote in message
news:1127937046.829601.9820@g14g2000cwa.googlegroups.com...
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?

NO!!! I wrote "adding" and there is a + in the equation. And why not do
it
in hours and add 10*log10(2/Cool? 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.

--
Tony Woolf
My e-mail address has no hyphen
- but please don't use it, reply to the group.
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