Cirrus CR:270 Series User manual

CR:270 Series User Manual
Page 1
CR:270 Series
Sound Level Meters
User Manual
This manual, the software to which it relates, the
program code and drawings are all:
© Copyright Cirrus Research plc 1989-2015

CR:270 Series User Manual
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The content of this manual, any illustrations, technical information and descriptions within this document
were correct at the time of going to print. Cirrus Research plc reserves the right to make any changes
necessary, without notice, in line with the policy of continuing product development and improvement.
No part of this publication may be duplicated, reprinted, stored in a data processing system or transmitted
by electronic, mechanical, photographic or other means, or recorded, translated, edited, abridged or
expanded without the prior written consent of Cirrus Research plc.
No liability is accepted for any inaccuracies or omissions in this manual, although due care has been taken
to ensure that is it complete and accurate as possible.
Accessories supplied by Cirrus Research plc have been designed for use with the instrumentation
manufactured by Cirrus Research plc. No responsibility is accepted for damage caused by the use of any
other parts or accessories.
In order to take account of a policy of continual development, Cirrus Research plc reserves the right to
change any of the information contained in this publication without prior notice.
Produced by Cirrus Research plc, Acoustic House, Bridlington Road, Hunmanby, North Yorkshire, YO14
0PH, United Kingdom.
© Copyright Cirrus Research plc 2015
Reference Number 01/03/CR:270/01
Document Printing Date Tuesday, 23 June 2015

CR:270 Series User Manual
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Overview. ..................................................................................................................... 4
Recommended Accessories .............................................................................................4
Quick Start ................................................................................................................... 5
First time use. .............................................................................................................. 6
Fundamental Precautions. ..............................................................................................6
CR:270 Controls............................................................................................................ 7
Weighting.....................................................................................................................7
Range ..........................................................................................................................7
Response .....................................................................................................................8
Display.........................................................................................................................8
Max Hold......................................................................................................................8
Reset Display................................................................................................................8
Reset All.......................................................................................................................9
Calibration Adjustment...................................................................................................9
CR:273 & CR:274 Additional Functions ....................................................................... 10
General Overview ........................................................................................................10
Controls .....................................................................................................................10
Switching on the filters ............................................................................................................10
Selecting the Active filter .........................................................................................................10
Turning off Octave filters .........................................................................................................11
Filters and Weighting ...................................................................................................11
Display and Indicators................................................................................................ 11
Annunciators ..............................................................................................................11
Full (Centre colon) ..................................................................................................................11
Overload (+) ..........................................................................................................................11
Battery low ............................................................................................................................11
Summary...............................................................................................................................12
Calibration.................................................................................................................. 13
Recommended Calibrators ............................................................................................13
Procedure...................................................................................................................13
Replacing the batteries............................................................................................... 15
Types of batteries........................................................................................................15
Selection of Hearing Protection .................................................................................. 16
Example of the Octave Band Method..............................................................................17
Example of the HML Method .........................................................................................18
Rating Plate Information ............................................................................................ 19
Specification............................................................................................................... 24
CE Certificate of Conformity ....................................................................................... 25
Equipment Description ............................................................................................... 25
Warranty Information. ............................................................................................... 26
Cirrus Research Offices .............................................................................................. 27

CR:270 Series User Manual
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Overview.
The CR:270 series of instruments is a range of Digital Integrating Sound Level Meters.
The instruments in the range are:
CR:271 Type 1 Integrating Averaging Sound Level Meter
CR:272 Type 2 Integrating Averaging Sound Level Meter
CR:273 Type 1 Integrating Averaging Octave Band Sound Level Meter
CR:274 Type 2 Integrating Averaging Octave Band Sound Level Meter
This manual will refer to the CR:27x where the features are common to all the
instruments listed above. Where there are differences between both the specification
and operation of any of the instruments, these will be stated with reference to the
particular instrument.
The CR:270 series have all the features necessary to make a wide variety of Industrial
noise measurements, and they comply with the Standard IEC 804 (BS 60804) for Inte
grating Averaging Sound Level Meters, conventionally called 'Leq Meters' and IEC 651
(BS 60651) for Sound Level Meters, meeting both these specifications to Type 1 and
Type 2 accuracy where applicable. The CR:273 and CR:274 instruments also features
octave band filters that meet or exceed the requirements of IEC 1260.
The CR:270 series of instruments are ideally suited to the following uses:
Determination of Leq for assessment of hearing loss risk.
Measurement of machine noise.
Sound Power Level measurements by the survey method.
Specification of hearing defenders using the octave band method (CR:274 & CR:273
) or HML method (CR:272 & CR:271)
Measurement of the absolute peak of a signal.
Measurement of the 'Peak' action level under the EC directive.
Recommended Accessories
A full range of accessories are available for the CR:270 Series. These include the
following:
Item Description
CR:513A Acoustic Calibrator
UA:237 Windshield
CK:250 Attache Case
CP:22 Pouch
These accessories can be purchased at a later date. The attache case allows the sound
level meter, acoustic calibrator, windshield and miscellaneous accessoires to be
transported safety.
Please refer to the current Cirrus Research pricelist for full details of the accessories
available for the CR:270 series of instruments.

CR:270 Series User Manual
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Quick Start
Power On
Set Switches
for Calibration
Calibrate
Instrument
Check Battery
Select
Function
Check
Range
Reset
Sound Level
SPL
Average
Sound Level
Leq
Peak Level
LPeak(C)
Record
Measurement
Check
Calibration
Power Off
50-100
Range
'S'
Response
Display
SPL
Max Hold
Off
dB(A)

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First time use.
The instrument should be inspected for any signs of damage.
The two batteries type 6F22 (NEDA 1604 or PP3) should be fitted into the battery
compartment. See section 8 for details of changing the batteries.
Ensure that the MAX HOLD button is out. This is the lower of the three push buttons. If
this is not done, the display will be held. Push RESET ALL to ensure all functions are
reset to zero.
The lower of the four slide switches, WEIGHTING, should be pushed to the right hand
position marked dB(A).
The upper of the four slide switches, DISPLAY, should be pushed to the right hand
position marked SPL.
When using the CR:274 octave band instrument, the octave band filter may be enabled
when the instrument is switched on. Hold down the OCTAVE FILTER button for 5
seconds until none of the filter indicators are lit. See section 6. If so, the meter is ready
to calibrate and use.
Fundamental Precautions.
Always check the battery before and after each measurement. The CR:270 monitors the
battery continuously while operating.
Ensure that the black HOLD button is OUT. If this is not done, the display will not freeze
the last reading and the central colon will be displayed in the LCD.
Always check the instrument calibration before and after each measurement.
To obtain the most accurate readings, the microphone should be pointed at the source
of the noise and held away from the observer.
In wind over 5ms-1 a foam windshield should be used. The UA:237 windshield should be
used with the CR:270. Do not operate the meter continuously at temperatures greater
than 40 degrees celsius or you will get errors of reading and the instrument may suffer
deterioration.
Remember to switch off after use or the batteries may leak and rot the case.
Never operate the unit in rain or snow. While the CR:270 is not affected by damp,
actual water in the microphone will cause errors of reading and may permanently
damage the capsule.
Keep the instrument still while measurements are being taken.
If the meter is being used out of doors, care should be taken to keep the unit away
from large objects which will cause sound reflections and thus give incorrect readings.
When the CR:270 is used inside buildings, thought should be given to the best site. If
in doubt make several measurements in different positions.

CR:270 Series User Manual
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CR:270 Controls
Weighting
This is the lowest position slide switch, Marked OFF
dB(C) dB(A). The CR:274 and CR:273 instruments
feature dB(Lin) in the place of dB(C).
The left hand position OFF disconnects all power
from the instrument and empties the Leq store.
Thus if the unit is turned off, all the accumulated
Leq data is lost. Therefore, always read the meter's
Leq value before turning the CR:27x to 'OFF'.
Similarly the PEAK(C) data is also lost. Normally for
industrial measurements the switch should be in
the 'A' position where the CR:27x will measure in
dB(A).
Under NO CIRCUMSTANCES should this switch or
the range switch be moved during an
Leqmeasurement as the Leq will be reset by the
instrument to prevent nonsensical results due to
mixtures of levels or weightings.
The centre position, marked dB(C) permits use as a
normal sound level meter with the 'C' Weighting
filter in circuit.
The right hand position dB(A) permits use as a
normal sound level meter with the 'A' filter in
circuit.
Range
This is the three position slide switch which selects
the operating range of the meter.
In the left hand position, marked <75 the
instrument measures levels on average below 75dB
although it will function accurately up to 80dB. For
Leqmeasurements averaging over 75dB you are
recommended to switch to the centre or right slide
position.
In the centre position, marked 50 - 100 the instrument measures levels in the range 50
to 100dB although it will function accurately up to 110dB. For Leq measurements
averaging over 100dB you are recommended to switch to the right slide position.

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In the right position, marked >80 the instrument measures levels in the range 80 to
140dB.
Thus, the total measuring range is about 32 to 140dB(A) for an instrument fitted with
the MK:202 Microphone Capsule, and 27 to 140dB(A) for an instrument fitted with the
MK:224 Microphone Capsule. Please note that the lower figure will depend on the
microphone capsule in use. See section 10 for the instrument specifications.
Response
This switch defines the three response speeds "Slow", "Fast" and "Impulse". The IEC
651 standard now calls these 'S', 'F' and 'I' respectively, so that they are the same in
any language.
On the "I" response it should be noted that the rise time constant is 35mS but the
descent time constant is 1.5 seconds, thus it should only be used for single impulses.
When in the "Impulse Max" position there is no decay time ie when the instrument is
set to Impulse Time Weighting, and the Max Hold button is pressed.
Display
This is a three position switch. In the centre position, coded PEAK(C) the CR:27x will
measure C weighted peak Pressure, in the right hand position 'SPL' and in the left hand
position it will measure Leq.
The position of the switch does NOT affect the acquisition of data by the Leq circuitry,
the switch simply determines what is displayed on the meter. Thus the switch can be
moved between the three positions while a measurement is being made. Indeed, it is
quite normal to leave the switch in the SPL position to see how the noise is varying and
then switch to Leq at the end to see what the average level was or to PEAK for the peak
value since last reset.
Max Hold
When this switch is pushed in, the maximum SPL level as selected by the response
switch is held and automatically updated by a further incoming signal. This is
conventionally called 'Max Hold'. The hold functions has a decay time of better than 1
dB per minute.
The Max Hold function can be reset whilst viewing by pressing the RESET DISPLAY
button.
The Max Hold function is automatically reset when the Display switch is moved from
PEAK to Max Hold. Therefore if the user wishes to make simultaneous measurements
of Max Hold with Leq or Peak then the Max Hold reading should be recorded before the
display switch is moved to Peak or Leq.
Reset Display
This button, when pressed, resets the function that has been selected for display.

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If Leq display mode is selected the Leq measurement is reset.
If PEAK(C) display mode is selected the peak level is reset.
If SPL display mode is selected the Max Hold is reset.
Reset All
This button, when pressed, simultaneously resets the Leq measurement, the PEAK(C) &
the SPL MAX HOLD reading.
As this button returns the Leq and Peak circuitry to zero it starts a new reading and
destroys the data currently in the instrument. It should be used with caution because
several hours work can be destroyed by pressing 'RESET ALL' accidently. In the Leq
mode the button does NOT cause the reading to go to zero. While 'RESET ALL' is
pressed the reading will be in an undefined random position as the meter is trying to
divide two very small numbers. 'RESET ALL' has no effect on SPL but does reset MAX
HOLD SPL. Do not hit the button hard or the CR:27x will integrate the resulting
acoustic noise of your finger on the button. This is particularly obvious on the 70 Peak
range where it almost impossible to use the button quietly enough NOT to generate a
noise.
Calibration Adjustment.
This is fitted above the LCD display and provides an adjustment to the amplifier gain of
the CR:27x. This is normally used for calibrating the CR:27x with the appropriate
microphone and calibrator.

CR:270 Series User Manual
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CR:273 & CR:274 Additional Functions
General Overview
The CR:273 & CR:274 sound level meters makes
use of virtually the same functions and controls as
the CR:271 & CR:272. The only functional
difference is that the CR:273 & CR:274 has an
octave filter set fitted which meets IEC 1260 to
type 1, with centre frequencies at 31Hz, 63Hz,
125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz &
16kHz. There is also a FLAT or linear filter instead
of dB(C).
Warning : The power consumption of the
instrument will increase slightly whilst the octave
filters are switched on.
Controls
One extra control is added, a tri-function push
button, labeled OCTAVE FILTER. While the octave
filters are not in use the red filter LED's situated in
the upper most label will all be extinguished.
Switching on the filters
One quick push (duration less than 1 second) of the
OCTAVE FILTER button will switch in the octave
filters, ie make them active. Once the octave filters
are switched in a red LED will be lit in the upper
most label. The lit LED will signify which octave
band filter is currently being utilised.
Selecting the Active filter
To make the next higher octave band filter active
press the OCTAVE FILTER button quickly while the
filters are switched in. This will cause the
instrument to step up to the next octave filter
band, ie if the 1kHz filter LED is lit and the OCTAVE
FILTER button is quickly depressed again then the 2kHz filter LED will light and the
1kHz filter LED will extinguish.
To make a lower octave band filter active depress the OCTAVE BAND button for slightly
longer, for approximately 1 second. This will step down to the adjacent lower octave
filter band.