PCB Piezotronics Larson Davis CAL250 User manual
Precision Acoustic Calibrator
Manual
CAL250
I250.01 Rev J
APPENDIX
Larson Davis
CAL250
Operators Manual
Copyright
Copyright 2018 PCB Piezotronics, Inc. This manual is copyrighted, with all rights reserved. The manual may not
be copied in whole or in part for any use without prior written consent of PCB Piezotronics, Inc.
Trademarks
PCB®is a registered trademark of PCB, Inc.
Disclaimer
The following paragraph does not apply in any state or country where such statements are not agreeable with local
law:
Although PCB Piezotronics, Inc. has reviewed this documentation, PCB Piezotronics Inc. makes no warranty or
representation, either expressed or implied, with respect to this instrument and documentation, its quality,
performance, merchantability, or fitness for a particular purpose. This documentation is subject to change without
notice, and should not be construed as a commitment or representation by PCB Piezotronics, Inc.
This publication may contain inaccuracies or typographical errors. PCB Piezotronics, Inc. will periodically update
the material for inclusion in new editions. Changes and improvements to the information described in this manual
may be made at any time.
Recycling
PCB Piezotronics, Inc. is an environmentally friendly organization and encourages our customers to be
environmentally conscious. When this product reaches its end of life, please recycle the product through a local
recycling center or return the product to:
PCB Piezotronics, Inc.
Attn: Recycling Coordinator
1681 West 820 North
Provo, Utah, USA 84601-1341
where it will be accepted for disposal
Product Warranty
For warranty information, refer to our Terms and Conditions of Sale on our website at
www.larsondavis.com/TermsConditions.aspx.
CAL250 Manual Using the CAL250 Calibrator 1-1
CHAPTER
1Using the CAL250
Calibrator
Features of the CAL250
The Larson Davis Model CAL250 is a battery-operated precision
microphone calibrator used for the calibration of sound level meters
and other sound measurement equipment. The CAL250 delivers a
full 114.0 dB level output signal @ 251.2 Hz. It has been designed
for field or laboratory use and its accuracy has been calibrated to a
reference traceable to the National Institute of Standards and
Technology (NIST).
• Automatic compensation sensors provide accurate
calibrations in extreme environments
• An effective volume of > 100 cm3 (6 in3) ensures an accurate
calibration, even if the microphone and microphone adapter
are not fully seated
• An accurate tone is measured even with a weakened battery
• Special adaptors make possible the use of 1/4”, 3/8”, 1/2”
microphones, as well as 1” microphones without an adaptor
CAL250 Accessories
The CAL250 includes the following accessories:
• ADP019: Adaptor for 1/2” microphone
• CCS003: Storage case
• 9 V alkaline battery
Optional Accessories
The following optional accessories are available:
• ADP020: 3/8” adaptor
• ADP021: 1/4” adapter
1-2 Installing the Battery CAL250 Manual
Installing the Battery
The CAL250 will run for
approximately 100 hours on
one nine-volt battery. This
will give you nearly 4200
calibrations.
The CAL250 uses a nine-volt battery and it is recommended that
you use an alkaline battery to extend the running time of your
calibrator.
Follow the steps below to install the battery:
Step 1 Locate the end cap at the bottom of the calibrator, as this
functions as the battery door.
Step 2 Unscrew the cap by hand, in a counterclockwise direction
until battery is exposed.
Step 3 Pull the battery out of the compartment and undo the
battery from the clip.
Step 4 Snap a new battery onto the clip, then place the battery
back into the compartment.
As the battery becomes
weaker, the calibration tone
will not deteriorate, but the
operating time will decrease
until the time is too short to
accomplish an adequate
calibration.
Step 5 Replace the battery cap and tighten using only finger/
hand strength.
FIGURE 1-1 Battery End Cap
Nine-volt
Battery
CAL250 Manual Microphone Calibration 1-3
Microphone Calibration
The CAL250 provides a nominal tone of 250 Hz at 114 dB. If the
device being calibrated has only A-weighting, it should be
calibrated to read 105.4 dB.
WARNING!
Do not remove the
microphone grid cap while
calibrating, as it may lead to
microphone damage.
To calibrate the microphone, follow the steps below:
Step 1 Place the instrument so that you can perform the
calibration. The preferred method for calibrating with the
CAL250 is to mount the preamplifier in a fixed, vertical
position.
Step 2 Insert the proper microphone adapter fully into the
calibrator. Make sure it fits snugly.
FIGURE 1-2 Cal250 with ADP019
If using a 1” microphone
remove the 1/2” adaptor in
order to place the calibrator
over the microphone.
Step 3 Insert the microphone fully into the adapter opening.
Make sure it fits snugly.
1-4 Microphone Calibration CAL250 Manual
Step 4 With the microphone connected to the instrument being
calibrated, press the CAL250 ON button. With a fresh
battery, the calibrator will issue a tone for more than 60
seconds before automatically shutting off (see note
below).
Step 5 Make a reading. If the reading is not within tolerance,
refer to the instrument’s manual for instructions on how
to adjust the instrument.
When making a sequence of measurements, a calibration check and
an adjustment (if necessary) of the instrument should be made at
the beginning. At the end of the measurement sequence, the
calibration should be checked again. The inaccuracy of the
measurements will be at least as large as the difference between the
level measured for the initial calibration (or calibration check) and
the level measured for the final calibration check.
Turn Calibrator OFF
The button on the CAL250 calibrator is not an ON/OFF button.
Each time the ON button is pressed, the tone sound approximately
60 seconds on a fresh battery. In order for the calibrator to turn off,
wait 60 seconds, do not press the ON button again. Wait until the
calibrator times out.
Calibration History
Larson Davis strongly recommends that a history of each
calibration adjustment be kept for each piece of equipment.
Normally, most modern equipment requires little or no adjustment
once the initial calibration is performed. Systematic drifts are
possible, and these should be recorded for corrective action.
The Larson Davis Models 706, 720, 812, 814, 820, 824, 831, 870
and LxT sound level meters keep a history of each calibration
change that can be printed before an overall reset.
Environmental Precautions
While the CAL250 will perform normally under a wide variety of
gradually changing environmental conditions, some precautions
should be taken when sudden changes occur:
•The temperature of the CAL250 should be stable. If the
temperature changes suddenly, provide a stabilization time of 15
minutes. This will ensure that the temperature compensation
sensors are at the same temperature as the rest of the unit.
CAL250 Manual Microphone Calibration 1-5
• While humidity will not affect the CAL250, avoid condensing
moisture. Also, avoid environments over 90% relative humidity
because condensation can easily take place.
• The CAL250 is insensitive to magnetic fields; however, the
instrument being tested may not be. Therefore, calibration
should not be done near motors, dynamos, high voltage wires,
or other sources of electromagnetic fields.
Calibrator Calibration
The American National Standards Institute says, “An acoustical
calibrator should be recalibrated at least annually by the instrument
manufacturer or an acoustical test laboratory qualified to perform
calibration.” (American National Standards Institute. Specifications
for Acoustical Calibrators. ANSI S1.40, 1984, par. 5.2)
Larson Davis believes the frequency of recalibration depends on
the number of calibrators being used and the number of instruments
being calibrated. With this in mind, the following guidelines are
presented for your consideration:
• For one calibrator and one measurement instrument, the
CAL250 should be certified at least yearly.
NOTE: If a systematic drift of
several dB occurs, there is no
reliable way to verify which
instrument is at fault, even
though it is more likely to be
the measurement instrument.
• For one calibrator and several measurement instruments,
one calibration a year is recommended. but if no systematic
drift occurs, every two years might be satisfactory.
NOTE: If the CAL250 is
being used to calibrate
several instruments, then the
history of calibration
adjustments can usually
pinpoint which instrument is
drifting. If all the
measurement instruments are
drifting in the same direction
by an amount you consider
significant, the CAL250
should be re-certified.
• For several calibrators and several instruments, one
calibration a year is recommended.
NOTE: If several instruments and several calibrators are in use,
then the history of calibration adjustments would precisely pinpoint
any problem pieces of equipment. Furthermore, it is probably
satisfactory to recalibrate only one of the calibrators each year.
1-6 Microphone Calibration CAL250 Manual
CAL250 Manual A-1
APPENDIX
ACAL250 Specifications
The specifications contained in this chapter are subject to change without notice. Please refer to cali-
bration and test results for data on a specific unit.
Standards Met
• ANSI S1.40-2006, Specifications and Verification Procedures for Sound Calibrators, Class 1
• IEC 60942-2017, Class 1, Electroacoustics: Sound calibrators
• IEC 61010-1: 2001, Safety requirements for electrical equipment for measurement, control, and
laboratory use--Part 1, General requirements
• IEC 61326-1: 2012 Electrical equipment for measurement control and laboratory use--EMC
Requirements, Part 1, General requirements
Microphone Compatibility
The CAL250 is for use with the following microphone types:
• 1” WS1P, WS1F and WS1D without any adaptor
• 1/2” WS2P, WS2F and WS2D with ADP019 adaptor (supplied)
• 1/4” WS3P, WS3F and WS3D with ADP021 adaptor (optional)
Size according to IEC 61094-1:2000
• 1” LS1P without any adaptor
• 1/2” LS2P with ADP019 adaptor (supplied)
• 1/8” with ADP023 adaptor (optional)
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