Operating And Measurements; Operation; Meter/Microphone Placement; Background Noise - 3M 1100 SLM User Manual

8

Operating and Measurements

Operation

Operating and Measurements
Operation
Before taking measurements with the model 1100, there is a
series of quick checks and considerations that should be
performed or noted. After switching the unit ON, check for a
LOBAT indication on the display, replace battery if necessary.
(See "Battery check", page 6).
Although the model 1100 will maintain accurate calibration
over a long period of time, the calibration should be checked
and the meter re-calibrated, if necessary, before each use. The
calibration should also be checked after each use. (See
"Calibration check", page 7). Set the RESPONSE,
WEIGHTING, and RANGE (dB) switches as needed. Hold,
set, or tripod mount the meter in the desired location. If a MAX
measurement is needed, be sure to reset the meter before
taking the measurements. It is always a good idea to
document all measurement conditions and meter settings for
possible future reference.

Meter/Microphone Placement

Whenever possible, the meter should be tripod-mounted in a
relatively open area to minimize reflections from the body or
other large reflective structures. Avoid placement against a
wall or in a corner. A threaded bushing on the back will accept
a standard 1/4-20 tripod fitting.
The microphone cartridges used on the models 1100 and 2100
are free-field microphones. Point the meter directly at the noise
source (0 degrees).
Random incidence measurements may be taken with the 1100
if the plastic random incidence corrector supplied with the
BK4936 microphone is used. The random incidence corrector
is a black plastic lipped sleeve packed in the BK4936 packing
container. To attach the corrector, position the end of the
sleeve without the lip over the grid of the microphone and
gently press down until a snap fit is achieved. Point the
microphone approximately 70° to the direction of the sound.

Background Noise

Background noise can cause considerable error in
measurement when its intensity is close to that of a particular
sound source of interest. When it is not possible to eliminate or
reduce the background noise, use the curve shown in Figure 4
to correct for the effect of the background noise on the
measurement.
056-652, Rev.D
Operating &
Measurements
1100/2100 SLM models