Casella USA CEL 240 Series Instruction Manual

CASELLA USA
CEL-240 DIGITAL SOUND LEVEL METER
FREQUENTLY ASKED QUESTIONS
Casella USA Page 1 of 6
[phone] 31 Jan 2008
[email protected]
CEL 240 Series
Digital Sound Level Meter
Frequently Asked Questions
Casella USA is proud to announce the CEL-240 sound level meter. These
FAQ’s help to give an overview of the current models, answer some of the
more typical questions that arise and describe how they fit into the overall CEL
product portfolio of noise measurement instruments.
INTRODUCTION
How does the instrument fit into the CEL range?
COMPARISON OF MODELS
What models are there in the range?
What are the main features & benefits of the CEL-240?
OPERATION
How long will standard alkaline batteries last in a CEL-240?
Can rechargeable batteries be used in a CEL-240?
How can the instrument be powered from an external source?
Can the microphone of a CEL-240 be removed?
Can the CEL-240 be used for outdoor measurements?
How quickly does the digital display update during measurements?
Is the time history trace stored in the CEL-240?
What outputs are available from the CEL-240?
What are the characteristics of the ac output?
What are the characteristics of the dc signal?
What are the characteristics of the digital output?
INSTRUMENT FUNCTIONS
What measurement ranges does the CEL-240 cover?
What results can be measured in a CEL-240?
What rms frequency weightings are available in the CEL-240?
What time weightings are available in the CEL-240?
What exchange rates or Q values are available in the CEL-240?
How do I calibrate the CEL-240?
ACCCURACY & RESULTS
What accuracy is the instrument designed to fulfil?
Are any results saved when using the SLM mode?
APPLICATIONS
What markets is the instrument designed for?
How are these markets catered for by the CEL-240?
CEL-240
“EZ does it”

CASELLA USA
CEL-240 DIGITAL SOUND LEVEL METER
FREQUENTLY ASKED QUESTIONS
Casella USA Page 2 of 6
[phone] 31 Jan 2008
[email protected]
Jenny Pearson,
FAQ’s: INTRODUCTION
How does the instrument fit into the CEL range?
CEL-200 Series
The simplest meters in the CEL range remain the CEL-200 series including the
existing CEL-231 and 254 models and now the new CEL-240. These 3 models are
ANSI type 2 accuracy sound level meters with Sound Pressure Level (SPL),
Maximum Noise Level (Max) and Impulse response (not CEL-231) measurement
capabilities.
CEL-300 Series
The intermediate range of convertible personal noise dosimeters or logging
sound level meters is in the form of the CEL-320 or CEL-360. Simply swap out
the microphone inputs to convert the dosimeter into the sound level meter or vice
versa. Both models feature ANSI type 2 accuracy for overall measurements. The
new CEL-350 dBadge dosimeter adds a small badge style dosimeter with cable-
less microphone to the range for added convenience.
CEL-400 Series
The mid range sound level meters are the CEL-430, 450 and 490 providing
recording of level against time or level against frequency. The 450 and 490
instruments are fitted with parallel (real time) frequency analysis capability in
either full octave or third octave bands. ANSI type 1 and type 2 / data logging or
non-data logging models are available for the CEL-400 sound level meter range.
CEL-500 Series
The top of the range meters are the CEL-553, 573 and 593 real time analyzers which
feature parallel capture of level against time and frequency. A range of versatile upgrade
options for such specific tasks as Rapid Data Storage, Building Acoustics, Sound
Quality and Long Term Logging measurements are also available. All models meet the
ANSI type 1 models are available.

CASELLA USA
CEL-240 DIGITAL SOUND LEVEL METER
FREQUENTLY ASKED QUESTIONS
Casella USA Page 3 of 6
[phone] 31 Jan 2008
[email protected]
FAQ’s: COMPARISON OF MODELS
What models are there in the range?
A single model variant is available – the CEL-240. It is a completely new design compared to the
earlier CEL-231 & 254 models in the original 200 series.
What are the main features & benefits of the CEL-240?
The main differences between the CEL-240 and the earlier 231/254 instruments are the use of digital
signal processing (DSP) technology and a low power consumption microprocessor that is unique in
such a low cost instrument. The meter features the instantaneous sound level plus the maximum
hold feature on all screens plus a real time bar graph display. This makes the CEL-240 model
extremely useful in circumstances where the noise levels are fluctuating and where the time history
trending graph will be useful for seeing changing noise levels of short events. A simple digital output
is also available to link to a personal computer for basic data logging applications.
FAQ’s: OPERATION
How long will standard alkaline batteries last in a CEL-240?
A set of 3 x AA alkaline cells can power a CEL-240 for more than 35 hour’s continuous operation at
normal room temperature. Lower temperatures will reduce useful battery life. Good quality alkaline
batteries are recommended for longest running time.
Can rechargeable batteries be used in a CEL-240?
A set of 3 x AA NiMH rechargeable batteries can be used instead of alkaline batteries and battery life
will be around the same time at normal room temperature. The rechargeable batteries will operate
successfully down to lower temperatures than an alkaline battery set. NiMH batteries must be
recharged outside the CEL-240 and can be used repeatedly in these instruments. When NiMH
batteries are run down they can be recharged in a few hours and used again up to the number of
recharge cycles recommended by the battery manufacturer. Typically this will be around 300 – 500
charge cycles.
How can the instrument be powered from an external source?
The CEL-240 is designed to be powered from an external supply via the USB connector that is
available on the bottom of the meter. This takes the usual 5Vdc supply from the USB port of a laptop
or desktop computer via a suitable cable.
Can the microphone of a CEL-240 be removed?
The microphone unit of a CEL-240 is not removable therefore remote operation is not normally
possible. In special circumstances it may be possible to fit a length of plastic tubing of ¼” internal
diameter over the end of the microphone in order to place the open end near to a machine noise
source that would be dangerous to approach so closely.
Can the CEL-240 be used for outdoor measurements?
The CEL-240 is not designed for extended use outdoors since it is not completely sealed against the
likely wind and rain that would spoil such measurements.

CASELLA USA
CEL-240 DIGITAL SOUND LEVEL METER
FREQUENTLY ASKED QUESTIONS
Casella USA Page 4 of 6
[phone] 31 Jan 2008
[email protected]
How quickly does the digital display update during measurements?
The digital display shows samples of the continuous rms sound pressure level updated twice every
second. This is a compromise between updating the display too quickly making it too difficult to see
the readings and being too slow for the update routine in which case the display would appear very
sluggish. In a non-integrating instrument tests have shown about 2 or 3 times a second to be about
the optimum rate that the brain can interpret without missing valuable information.
Is the time history trace stored in the CEL-240?
The CEL-240 has a display mode that allows the user to see the last 1 minute or 5 minute trend of
the changing instantaneous noise levels as they vary. These samples are not stored in the
instrument but are available at the mini USB connector at the bottom of the meter for output to a
suitable data logging device such as a computer.
What outputs are available from the CEL-240?
The 2.5 mm three-pole jack socket on the bottom of the case of the CEL-240 provides both the ac
and log dc signals to external equipment. The ac output signal is used for connection to an audio
tape recorder or spectrum analyser. The dc output is used to provide a signal to a data logger or
paper chart recorder.
What are the characteristics of the ac output?
The ac output is a conditioned signal that has been passed through the selected frequency
weighting. This means that it will give either an ‘A’ or ‘C’ response signal that represents the pressure
waveform at the microphone. The ‘C’ setting is recommended for making audio recordings since it
has a better (wider and flatter) frequency response than the ‘A’ weighting. The ac signal is available
on the 2.5 mm jack socket at a level of up to 0.85 V rms for full scale deflection. This means that for a
sound level of 100 dB measured on the Lo range of the meter the output would be 0.85 V rms. A
signal at half the range FSD would output a voltage of 0.425 V rms and so on. A signal may still be
present below the minimum scale deflection but may not still be linear at such low levels.
What are the characteristics of the dc signal?
The dc signal is a more slowly varying voltage after the time weighting network in the meter.
Therefore, it will represent the same signal as seen on the display. It will have the selected ‘A’ or ‘C’
frequency and either the Slow, Fast or Impulse time weighting. The signal is optionally available on
the 2.5 mm stereo jack socket at a level of up to 1.3 V rms at full scale deflection on each range. It
increases at a rate of nominally 18.6 mV/dB for each range. A noise level of 100 dB on the Lo range
would produce an output of 1.3 V rms while the same noise level but measured on the Lo range
would produce an output of 0.742 V rms.
What are the characteristics of the digital output?
The digital output is produced every 1 second and provides both the A and the C frequency weighted
sound level with the selected time response (S, F or I). The CEL-240 has been designed to appear
as an industry standard memory card format when connected to a personal computer. The optionally
available program for the CEL-240 called dB24 produces a standard text file format data file in the
form of a list of date, time and the 1 second A and C sound levels with a carriage return. This can be
imported into many standard office programs such as word processors or spreadsheets for further
manipulation and graphing.

CASELLA USA
CEL-240 DIGITAL SOUND LEVEL METER
FREQUENTLY ASKED QUESTIONS
Casella USA Page 5 of 6
[phone] 31 Jan 2008
[email protected]
FAQ’s: INSTRUMENT FUNCTION
What measurement ranges does the CEL-240 cover?
The CEL-240 is equipped with two measurement ranges each covering a 70 dB dynamic span.
These ranges cover the overall levels from 30 to 100 dB on the low (Lo) range setting, and levels
from 60 to 130 on the high (Hi) range setting.
What results can be measured in a CEL-240?
The CEL-240 will measure the following parameters during the measurement run:
The instantaneous sound pressure level during the run,
The maximum RMS level or Lmax,
The last 1 minute or 5 minutes displayed as a trend graph over the full 70 dB
range selected
What rms frequency weightings are available in the CEL-240?
Two broadband frequency weightings are provided in the CEL-240 for the collection of the rms noise
levels – the ‘A’ and ‘C’ weightings according to the international standards defined in IEC-651 and
ANSI S1.4. Tolerances for these weightings are as specified in the type 2 classifications of these
documents. This allows the CEL-240 to be used for measuring the NRR rating method for choosing
hearing protectors against excessively high workplace noise exposure.
What time weightings are available in the CEL-240?
The CEL-240 is equipped with the Slow and Fast and Impulse time weightings to suit all
requirements for general-purpose noise measurements. Use the Slow time response to “dampen” the
readings to make it easier to see what is happening. Use the Fast response to more accurately follow
the changing noise levels as they rise and fall. Use the Impulse response only when the regulations
require it.
What exchange rates or Q values are available in the CEL-240?
There is no specific exchange rate available in the meters since this function is only associated with
instruments that can measure the time average noise levels. Noise levels must be visually averaged
by watching the digital display for the collection of noise dose results to satisfy the US Noise at Work
regulations as specified in the OSHA, MSHA or DoD relevant documents. For most Noise at Work
measurements for OSHA the meter should be set to the A frequency weighting and the Slow time
response on the 60 to 130 dB Hi range.
How do I calibrate the CEL-240?
The CEL-240 has a unique easy calibration routine that simply involves fitting the acoustic calibrator
over the microphone and switching it on. The CEL-240 will automatically detect the 1 kHz fixed level
tone and will offer the user the choice to perform the calibration or to leave it as it was and abort the
process. One push of the button on the front panel of the instrument will set the gain circuits in the
meter to match to expected level of the calibrator and the process takes about 5 seconds to
complete. No adjustments with screwdrivers or other keypad controls are required. The auto-
calibration function can be used with 114.0 and 94.0 dB acoustic calibrators that operate at the
industry standard frequency of 1 kHz. This is pre-programmed into the CEL-240 in the configuration
menu prior to the calibration process being initiated. It remains in the meter’s memory until changed
by the user.

CASELLA USA
CEL-240 DIGITAL SOUND LEVEL METER
FREQUENTLY ASKED QUESTIONS
Casella USA Page 6 of 6
[phone] 31 Jan 2008
[email protected]
FAQ’s: ACCURACY & RESULTS
What accuracy is the instrument designed to fulfil?
The CEL-240 instrument complies with the international standards in the type 2 classifications that
classify the sound level meter as general-purpose instruments. This specifies an overall expected
accuracy of +/- 2 dB under normal measurement conditions. Use of the instruments as dosimeters by
visually averaging fluctuating noise levels may produce wider tolerances than this depending on how
well the “on time” of a notional average level is measured.
Are any results saved when using the SLM mode?
Results are not saved in the instrument when any of the available display modes are used. The CEL-
240 is intended to allow the instruments to be used as a simple sound level meter for quick hand held
surveys or as a simple front end to a data logging system in conjunction with a personal computer
running the optional dB24 software.
FAQ’s: APPLICATIONS
What markets is the instrument designed for?
There are three main markets for the CEL-240.
- a simple meter for monitoring noise exposure in the workplace
- a general purpose sound level meter for many environmental nuisance sources
- a short term noise meter for quick measurements on specific noise sources
How are these markets catered for by the CEL-240?
For many basic noise measurements the A weighted Slow response sound level will be all that is
required. For more specific noise measurements of sounds with a transient nature the C weighting
and the maximum hold feature will be of help. The meter can also be used as a simple teaching aid
in many noise or general sound studies especially with the optional digital output to a computer. The
tripod mount allows the meter to be fixed at a chosen location for longer term measurements that are
not likely to be adversely affected by the weather conditions.
For more details on the CEL-240 series, or any of the other Casella USA products, please contact
us:
Casella USA
17 Old Nashua Road, #15
Amherst, NH 03031
[phone]
[e-mail]
www.CasellaUSA.com