IVIE IE-10A, Руководство владельца и оператора

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BODY EFFECTS
ON MEASUREMENTS
Something which must be considered when making sound measurements w i t h a
hand-held analyzer, i s t h e e f f e c t o f t h e o p e r a t o r ' s body on t h e readings.
The o p e r a t o r ' s body may d e t r a c t s u b s t a n t i a l l y from the accuracy of t h e
measurements.
A t
frequencies around 400 Hz, sound r e f l e c t i n g from t h e
body could cause up t o 6dB o f e r r o r , i f measurements are made w i t h i n
t h r e e f e e t of the o p e r a t o r . To minimize t h i s e f f e c t , t h e should
be h e l d as f a r away from t h e body as p o s s i b l e .
FOR BACKGROUND N O I S E
Often t h e need a r i s e s t o make SPL measurements i n the presence of background
noise.
This can be e a s i l y done as l o n g as t h e SPL o f the primary source
i s a t l e a s t 3dB g r e a t e r than the background noise.
Following are t h e
steps f o r making such a measurement.
1.
Measure the t o t a l noise. (background primary source)
2. Turn o f f the p r i m a r y noise source and measure the background n o i s e
only. Both t e s t s should be made w i t h t h e i n t h e same l o c a t i o n .
3.
Calculate t h e d i f f e r e n c e between t h e two readings measured on t h e
I f t h e d i f f e r e n c e i s l e s s than accurate
cannot be made. If t h e d i f f e r e n c e i s between 3dB and 10 dB, t h e
f o l l o w i n g c h a r t can be used t o make t h e needed c o r r e c t i o n .
N O I S E
dB
Figure 22
To use t h e chart, t h e d i f f e r e n c e
o f t h e two measurements on t h e h o r i z o n t a l
a x i s .
From t h a t p o i n t , go up t o
i n t e r s e c t t h e curve, and then l e f t t o
t h e v e r t i c a l axis. Then s u b t r a c t t h e
v a l u e on t h e v e r t i c a l a x i s from t h e
t o t a l n o i s e l e v e l f i r s t measured.
Example: T o t a l noise
=
75 dB
Background n o i s e
=
72 dB
D i f f e r e n c e
=
3 dB
Chart c o r r e c t i o n
=
3 dB
Primary source n o i s e
=
75dB
-
3dB 72 dB.
If t h e noise d i f f e r e n c e between t h e background noise and t h e primary
noise i s g r e a t e r than 10 dB, no c o r r e c t i o n i s necessary.
ADDING SOUND LEVELS
If two primary sources a r e measured independently,
i t
i s p o s s i b l e t o
what the sound l e v e l would be i f b o t h sources were o p e r a t i n g
together. The f o l lo w i n g c h a r t can be used t o t h i s , when b o t h
t e s t s a r e made w i t h t h e i n the same l o c a t i o n .
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