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Hand-held Analyzer Type 2250 –
Instruction Manual
10
• τ is the exponential time constant in seconds for time weighting F or S
• ξ is a dummy variable of time integration from some time in the past, as indicated by –∞ for the lower
limit of the integral, to the time of observation t
• p
x
(ξ) is the x frequency-weighted instantaneous sound pressure
• p
0
is the reference sound pressure, equal to 20 µPa
The exponential time constants are stated in Table 2.2.
Time-weighted Sound Level, I Time-weighted
The I (Impulse) time-weighted sound level, L
xI
(t), is defined as ten times the logarithm to base ten of
the ratio of a given mean-square sound pressure to the square of the reference sound pressure, p
0
,
followed by a peak detector with a decay time constant of 1500 ms. The mean-square sound pressure
being obtained with a frequency weighting, x, and time weighting with a 35 ms time constant, where:
• x is A for A-weighted, C for C-weighted or Z for Z-weighted
• p
0
is the reference sound pressure, equal to 20 µPa
The I time-weighted sound level is a continuous function of time and is expressed in decibels (dB).
L
xI
(t) is not displayed but is the base for L
xI
(T
n
), L
xI
(SPL)(T
n
), L
xImax
(T), L
xImin
(T) and L
xIm
(T).
Instantaneous Time-weighted Sound Level
The instantaneous time-weighted sound level, L
xy
(T
n
), is defined as the time-weighted sound level,
L
xy
(t), sampled at t = T
n
where:
• x is A for A-weighted, C for C-weighted or Z for Z-weighted
• y is F for Fast-weighted, S for Slow-weighted or I for Impulse-weighted
• T
n
= t
0
+n·∆t
• t
0
is some starting time
• n is an incrementing integer
•
∆t is the display update interval
The instantaneous time-weighted sound level is, in other words, updated every
∆t second and is ex-
pressed in decibels (dB).
The symbols used on the screen of Type 2250 for instantaneous time-weighted sound levels are (for A,
C and Z frequency-weighting and F, S and I time-weighting): L
AF
, L
AS
, L
AI
, L
CF
, L
CS
, L
CI
, L
ZF
, L
ZS
,
L
ZI
.
Sound Pressure Level (SPL)
The sound pressure level, L
xy
(SPL)(T
n
), is defined as the greatest time-weighted sound level, L
xy
(t),
within a time interval starting at t = T
n
and ending at t = T
n
+ ∆t where:
• x is A for A-weighted, C for C-weighted or Z for Z-weighted
• y is F for Fast-weighted, S for Slow-weighted or I for Impulse-weighted
• T
n
= t
0
+ n·∆t
• t
0
is some starting time
• n is an incrementing integer
Table 2.2
Exponential time
constants and cor-
responding aver-
aging times
Time Weighting
Time Constant
(seconds)
Averaging Time
(seconds)
Fast 0.125 0.25
Slow 1 2
BE171211.book Page 10 Thursday, May 27, 2004 1:01 PM
- Technical 1
- Documentation 1
- Hand-held Analyzer Type 2250 2
- Safety Considerations 3
- Table of Contents 4
- Chapter 1 6
- 1.2 System Overview 7
- 1.3 Hardware Setup 8
- CHAPTER 1 10
- Chapter 2 12
- 2.4 Frequency Weightings 13
- 2.5 Measured Quantities 13
- Table 2.1 14
- Frequency weight 14
- IEC 61672 – 1, Ta 14
- Table 2.2 15
- Exponential time 15
- CHAPTER 2 16
- ∆t where: 17
- 2.5.4 Spectrum Measurements 18
- Chapter 3 20
- 3.6 EMC test procedures 21
- 3.6.4 Accessories 22
- Chapter 4 24
- 4.5 Microphone 25
- 4.6 Frequency Response 25
- CHAPTER 4 26
- 4.6.3 Low-frequency Responses 27
- 4.7 Directional Response 31
- Table A.25 35
- Table A.32 37
- Table A.34 to Table A.36 39
- Table A.44 to Table A.46 42
- 4.8 Self-generated Noise 44
- 4.9 Measuring Range 46
- 4.9.4 Indicator Range 47
- 4.9.5 Linearity Range 47
- 4.9.6 Pulse Range 47
- 4.9.7 Linear Operating Range 47
- 4.10 Detectors 48
- 4.10.2 Linear Averaging 49
- 4.10.3 Peak 49
- 4.11 Spectrum Analysis 50
- 4.11.3 Linear Operating Range 51
- 4.11.4 Measurement Range 52
- Fig.4.31 53
- The most sensitive 53
- Table 4.13 53
- Magnetic Fields 53
- 4.13.2 Trigger Socket 54
- 4.14.1 Output Socket 54
- 4.14.2 Headphones Socket 54
- 4.15 Power Supply 55
- 4.16 Warm-up Time 55
- 4.17 Real-time Clock 55
- Appendix A 58
- angle of incidence to 65
- ‘UA 1404’ 69
- A.4 Directional Responses 71
- APPENDIX A 100
- Instruction Manual 101
- 500 Hz – 3550 Hz 105
- 4000 Hz – 10600 Hz 106
- 11200 Hz – 20000 Hz 107
- Appendix B 110
- APPENDIX B 112
- B.3 Irrelevant Topics 116
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