Cirrus Research CR308 User manual

Instrument
Handbook
CR:308 & CR:310
Entry-Level
Sound Level Meters

Page 2 CR:308 & CR:310 – User Manual
About this manual
The instructions in this user manual refer to the operation of Cirrus Research plc CR:308 and
CR:310 entry-level sound level meters.
The instruments described in this manual are the CR:308 and CR:310.
This manual describes the recommended usage of the CR:308 and CR:310. Any warnings will
be indicated by the following symbol:
The additional information required for testing in accordance with IEC 61672 is provided as a
supplementary document, ‘Optimus Sound Level Meters Technical Data Part B’, which is
available for download at: www.cirrusresearch.co.uk/library/user-manuals/
It is not possible to change the way that the instrument measures through software or firmware.
Any legal metrology aspects of the instrument cannot be affected by any changes made in the
instrument.

CR:308 & CR:310 – User Manual Page 3
Copyright
Copyright © Cirrus Research plc 2010-2021
All rights reserved.
You may re-use this document/publication (not including the Cirrus Research plc logo and other
product logos) free of charge in any format for research, private study or internal circulation
within an organisation. You must re-use it accurately and not use it in a misleading context.
You must not modify text, images or illustrations in any way. The material must be acknowledged
as Cirrus Research plc copyright, and you must give the title of the source document/publication.
Where any third-party copyright material is identified, you will need to obtain permission from
the copyright holders concerned.
Trademarks
Cirrus Research plc, the Cirrus Research plc Logo, doseBadge, DOSEBADGE, Optimus, the
NoiseTools Logo and the Noise-Hub Logo are either registered trademarks or trademarks of
Cirrus Research plc in the United Kingdom and/or other countries. Microsoft and Windows are
registered trademarks of Microsoft, Inc. All other trademarks acknowledged.
Updates
In the interests of continuous product improvement, Cirrus Research plc reserves the right to
make changes to product specifications without notice.
To understand the latest updates that have been implemented into this product and to download
the most current version of this user manual, visit our website at
www.cirrusresearch.com
Revision 2 | August 2021

Page 4 CR:308 & CR:310 – User Manual
Contents
1Introduction ......................................................................................................................................................... 5
2First use ................................................................................................................................................................6
3Instrument overview .......................................................................................................................................... 7
4Instrument displays.............................................................................................................................................9
4.1 CR:308 & CR:310 main display ................................................................................................................................. 9
4.2Calibration display........................................................................................................................................................ 9
4.3 CR:308 alarm set display ..........................................................................................................................................10
4.4 CR:310 measurement display ..................................................................................................................................10
5Instrument keypads ..........................................................................................................................................11
5.1 CR:308 keypad ...........................................................................................................................................................11
5.2 CR:310 keypad ...........................................................................................................................................................11
6Instrument operation .......................................................................................................................................12
6.1 Selecting the frequency and time weighting.........................................................................................................12
6.2 Maximum, minimum and LCpk values ....................................................................................................................12
6.3 Setting the level alarm (CR:308 only) .....................................................................................................................12
6.4 Performing and printing a measurement (CR:310 only)......................................................................................13
7Instrument calibration ......................................................................................................................................15
8Specifications and technical information......................................................................................................16
8.1 Instrument specifications..........................................................................................................................................16
8.2 Reference information for periodic testing ...........................................................................................................16
9Options and accessories..................................................................................................................................19
10 Serial connection..........................................................................................................................................20
11 Declaration of Conformity..........................................................................................................................21
12 Product guarantee and extended warranty.............................................................................................22
13 Cirrus Research contact details .................................................................................................................23

CR:308 & CR:310 – User Manual Page 5
1Introduction
Welcome to your new CR:308/CR:310 entry-level sound level meter.
The CR:308 and CR:310 are general-purpose digital sound level meters designed to IEC 61672
Class 2. The instrument has ‘F’ (fast) and ‘S’ (slow) time response and ‘A’ and ‘C’ frequency
weightings. Additional features include max and min hold for the measurement duration, LCpk,
and limit alarm, which you can configure to indicate if your set threshold has been exceeded.
Except for the alarm indication function, the CR:310 includes all the features of the CR:308. In
addition, it can display the Leq value and print results directly from the meter to a portable
printer.

Page 6 CR:308 & CR:310 – User Manual
2First use
Before using your meter for the first time, please check the contents of your instrument’s case,
which should include the following:
•Sound level meter and Class 2 microphone
•Windshield
•2 x AA batteries
Optional accessories
•Class 2 acoustic calibrator
You may have other accessories, depending on your package.
Before starting a measurement, remove the black microphone protective cap (if fitted) and where
necessary, place the windshield carefully over the end of the microphone capsule.

CR:308 & CR:310 – User Manual Page 7
3Instrument overview
Microphone windshield
(microphone capsule underneath)
Backlit LCD display
Model number
Control keypad
Power button

Page 8 CR:308 & CR:310 – User Manual
Serial number label
Tripod mount
Battery compartment
USB power input
Serial connection for printer
(CR:310 only)
AC/DC out

CR:308 & CR:310 – User Manual Page 9
4Instrument displays
4.1 CR:308 & CR:310 main display
4.2 Calibration display
Press the CAL button.
Under-range indicator
Measurement indicator
Overload indicator
Noise level
Alarm indicator
(CR:308 only)
Battery level
Measurement type
Calibrator level
Correction to be
applied
Current
measurement level

Page 10 CR:308 & CR:310 – User Manual
4.3 CR:308 alarm set display
Press .
4.4 CR:310 measurement display
Threshold level
Alarm
enabled/disabled
indicator
Under-range/
overload indicator
Measurement duration
Overall
measurement
value

CR:308 & CR:310 – User Manual Page 11
5Instrument keypads
5.1 CR:308 keypad
5.2 CR:310 keypad
Set alarm
Power on/off
Softkey: Exit
Select measurement
view
A/C weighting toggle
Reset max/min
Fast/Slow toggle
Perform calibration
Softkey: CAL/OK
Start/stop measurement
Power on/off
Softkey: Exit
Select measurement
view
A/C weighting toggle
Reset max/min
Fast/Slow toggle
Perform calibration
Softkey: CAL/Print

Page 12 CR:308 & CR:310 – User Manual
6Instrument operation
Fit new batteries by sliding the battery cover open and inserting two AA batteries in the correct
orientation.
Switch on and allow the instrument to settle for 60 seconds before calibrating.
Before starting a measurement, calibrate the instrument as per the guidance in Section 7 of this
user manual.
6.1 Selecting the frequency and time weighting
Select the measurement frequency and time weighting required:
To toggle between A and C weighting, press
To toggle between fast and slow weighting, press
The measurement type is displayed in the main window:
LAF – A frequency weighting | fast time weighting
LCF – C frequency weighting | fast time weighting
LAS – A frequency weighting | slow time weighting
LCS – C frequency weighting | slow time weighting
To toggle the measurement values, press . This will toggle through the following
measurement values if the meter is set to LAF:
LAF > LAFMax > LAFMin > LCpk > LAF
Integrating averaging measurements Lxeq1s and Lxeq8h are available on the CR:310
instrument.
6.2 Maximum, minimum and LCpk values
Maximum, minimum and LCpk values are shown for the duration of time since the meter was
switched on or since the reset button was last pressed.
These values can be reset by pressing
6.3 Setting the level alarm (CR:308 only)
The level alarm function can be used to trigger an alert if the noise level exceeds a predetermined
value, which is set by you.

CR:308 & CR:310 – User Manual Page 13
To set the alarm level, press to enter the alarm setup display.
Set the desired level and enabled the alarm by using the arrow buttons. A tick denotes that the
alarm is active; a cross denotes that the alarm is disabled. When set, press to confirm.
NB: the alarm level should not be set to less than 129dB.
With the alarm enabled, the main display will indicate that the level has been exceeded by
showing an asterisk (*) next to the sound level reading. The triggered threshold value can be
reset by pressing
NV: this will also reset the maximum, minimum and LCpk measurement values.
6.4 Performing and printing a measurement (CR:310 only)
Press to start or stop a measurement.
While a measurement is running, the latest values will be displayed on the screen, with the
measurement duration shown at the bottom. Alternative measurement parameters can be
viewed by pressing the up/down arrow buttons.
Overload and under-range are denoted by the ^ and Vindicators in the top right corner of the
screen.
After stopping a measurement, the overall measurement values are displayed. Press the
up/down arrows to scroll through the overall measurement values.

Page 14 CR:308 & CR:310 – User Manual
If a printer is attached, the results can be printed by pressing (Print).
The measurement view can be cancelled by pressing (Exit).

CR:308 & CR:310 – User Manual Page 15
7Instrument calibration
Before each measurement, it is important to calibrate your instrument with an acoustic calibrator,
such as the Cirrus Research CR:514 1kHz 94dB calibrator.
To start the process of calibration, ensure the microphone is fitted correctly and place the
acoustic calibrator over the microphone.
Press to enter the calibration menu.
Use the arrow keys to set the CAL LEVEL to the acoustic calibration level (94.0dB for the CR:514
calibrator).
Use the arrow keys to set the CORRECT value to 0.2dB, which will make the adjustment for the
gap between the calibrator and the microphone (pressure field of the acoustic calibration and
the free field of the instrument and microphone (HY:205 microphone).
This will result in the meter reading 93.8dB when a 94dB calibrator is used.
Switch on the acoustic calibrator and insert the microphone capsule into the cavity on the
calibrator. Take care to not force the microphone, as this could cause damage to either the
instrument or the calibrator.
Press to automatically calibrate the meter.
Press to exit from the calibration display and return to the main display.

Page 16 CR:308 & CR:310 – User Manual
8Specifications and technical information
8.1 Instrument specifications
Applicable standards
IEC 61672-1: 2013 Class 2
Measurement range
30dB(A) – 130dB(A)
40dB(C) – 130dB(C)
Frequency weighting
A and C
Time weighting
Fast (F) and Slow (S)
Display functions
Normal, Maximum, Minimum, CPeak
Measurement functions
LAF, LAS, LCF, LCS, LCPeak
Noise floor
<25dB(A) and 35dB(C)
Display flags
Alarm limit, overload and under-range
Auto calibration range
±4.5dB
Reference point
94dB (1kHz), 92.9dB (8kHz)
Settling time
60s
Display
Backlit 128x64 LCD
Resolution
0.1dB
Electrical input
5V power-in via mini-USB
Power
2 x AA/LR6 1.5V batteries or 5V DC via mini-USB input
Battery life
24 hours with alkaline batteries
Microphone
½” pre-polarised electret condenser type HY:205
Operating temperature
0°C to +40°C
Operating humidity
25% – 90%
Atmospheric pressure
65kPa – 108kPa
Storage temperature
-20°C to +60°C
Dimensions
215mm x 68mm x 32mm
Weight (including batteries)
220g
Electrical outputs
AC (tip 3.5mm jack) and DC (middle 3.5mm jack)
DC output
Voltage 15mV/dB, range 450mV – 1950mV
AC output
RMS 2V
8.2 Reference information for periodic testing
Reference level (1kHz)
94dB
Reference level (8kHz)
92.9dB(A)
Linear range 8kHz
30 – 130dB
Linear range 4kHz
30 – 130dB
Linear range 1kHz
30 – 130dB
LCPeak maximum (500Hz,
1kHz, 8kHz)
133dB
Self-generated noise floor
A-weighting = 25dB
C-weighting = 35dB
Self-generated noise floor
(with mic fitted)
A-weighting = 25dB
C-weighting = 35dB
Dummy microphone
capacitance
18pf
Recommended dummy
microphone
KP:66

CR:308 & CR:310 – User Manual Page 17
8.2.1 Multifrequency acoustic calibrator correction data (set to pressure and test on A-
weighting)
Frequency
Correction
125Hz
0.0
1kHz
0.2
8kHz
2.6
8.2.2 Free field correction for HY205 microphone
Frequency (kHz)
Free field correction (dB)
Frequency (kHz)
Free field correction (dB)
1
0.1
6.3
1.7
1.25
0.1
8
2.6
1.6
0.2
10
4.4
2
0.3
12.5
5.3
2.5
0.5
16
6.5
3.15
0.7
18
7.1
4
1.0
20
7.8
5
1.4
---
---
8.2.3 Case reflection and windshield attenuation data
Frequency (kHz)
Case correction
Windshield
correction
Uncertainty
63
0
0
0.27
125
0
0
0.27
250
0.13
0.05
0.27
500
0.18
0.08
0.27
1000
0.09
0.1
0.27
2000
-0.16
0.26
0.27
4000
0.01
0.53
0.32
8000
-0.10
0.26
0.30
16000
-0.17
-0.58
0.29
Add the above data to your measurement to correct.

Page 18 CR:308 & CR:310 – User Manual
8.2.4 Directionality plots and case reflection points

CR:308 & CR:310 – User Manual Page 19
9Options and accessories
The following table contains information about the model options and accessories available with
this sound level meter.
Cirrus Research part number
Descriptions
CR:308
Basic sound level meter with threshold
CR:310
Basic sound level meter with measurement
PR:310
Thermal printer (for use with CR:310 only)
CR:514
Acoustic calibrator
CK:380
Kit case (empty)
CK:381
CR:308 kit including case, meter and calibrator
CK:382
CR:310 kit including case, meter and calibrator
UA:30X
Spare windshield
CP:65
Carrying pouch for sound level meter and calibrator

Page 20 CR:308 & CR:310 – User Manual
10 Serial connection
DB9, RS232 communications rate at 9600 Baud.
1 bit start, 8 bits data, 1 bit stop, no parity