SoundAdvisor Model 831C
Understanding Calibration Values
49
can be accurately measured without being influenced by the operational noise from the
meter (Noise Floor).
Noise Floor Level
The noise floor is calculated as the energy sum of the noise generated by the microphone,
preamplifier, and instrument circuitry. The appropriate noise floor, and nominal sensitivity
compute automatically in the 831C with the following preamplifiers and their commonly
paired microphones:
•
PRM831
•
PRM2103
•
ICP with ADP074
Overload Level
When using a microphone having a sensitivity of 50 mV/Pa, the input overload may occur
approximately as shown in Table 5.1.
Under Range Level
The Under Range level is the higher of the following levels:
•
Noise Floor + 9.14 dB (the under range value shown when self noise contributes ≥
0.5 dB to the readings).
•
Actual point where the log-linearity exceeds maximum permitted value.
Except for very low-noise-level microphones, the under range level is usually determined
by the noise floor + 9.14 dB.
LEARN MORE
For more information about measurement range, noise floor, linearity
range, and max peak levels as they relate to different microphones and gain
settings, see “SLM Performance (Nominal Values)” on page A-3.
5.1.3 Understanding Calibration Stability
The 831C maintains a stable value of sensitivity over long periods of time. Significant
changes in sensitivity, or a pattern of small but regular sensitivity changes, are indicative of
problems with the measurement system. To assist you in identifying these situations, the
831C provides 2 notifications:
• Calibration History Table
This table includes data and date/time for the 10 most recent calibrations. It’s a good idea
to periodically review the instrument’s Calibration History, which is found on the meter
under
Tools
3
Calibration
Cal Hist (
//*
)
• Large Change Notifications
During calibration, the meter makes an automatic comparison between the sensitivity
determined by the calibration and the previous value. A pop-up warning displays when the
difference between these two values exceeds 3 dB.
Table 5.1 Input Overload Levels
Input Gain, dB
Overload Level, dB Peak
0
143
20
123
Summary of Contents for 831C-FFT
Page 1: ...Larson Davis SoundAdvisor Model 831C Sound Level Meter Reference Manual...
Page 214: ...SoundAdvisor Model 831C A 50 FIGURE A 47 Model 831C with 377C20 Microphone...
Page 215: ...SoundAdvisor Model 831C A 51 FIGURE A 48 Model 831C with 377C20 Microphone...
Page 216: ...SoundAdvisor Model 831C A 52 FIGURE A 49 Model 831C with 377C20 Microphone...
Page 223: ...SoundAdvisor Model 831C A 59 A 10 Declaration of Conformity...
