INSTRUMENTATION FOR
SOUND AND VIBRATION MEASUREMENTS
SV 33A
Acoustic calibrator
User’s manual
Warsaw, March 2017
SVANTEK Sp. z o.o. www.svantek.com e-mail: office @ svantek.com.pl
02-872 Warszawa, ul. Strzygłowska 81 tel./faks: +48 22 51 88 300
VAT EU PL5270105272 REGON 002175672 KRS 000192065
Registered in the Warsaw District Court, XII Economic Department Initial Capital 100 000 PLN
SV 33A USER MANUAL.
Contents
1. Introduction ........................................................................................................... 2
1.1. Calibration .................................................................................................... 2
1.2. Accuracy of calibration ................................................................................. 2
1.3. Classification of sound level meters and acoustic calibrators ....................... 2
2. Acoustic calibrator SV 33A ................................................................................... 3
2.1. General description ...................................................................................... 3
2.2. Usage of the calibrator ................................................................................. 4
2.2.1. Button functions .................................................................................... 4
2.2.2. Indicators .............................................................................................. 5
2.3. Replacing the battery ................................................................................... 6
3. SV 33A Datasheet ................................................................................................ 8
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1. Introduction
1.1. Calibration
One of the fundamental questions that are most frequently asked while taking
a measurement is whether its result is accurate. Proceeding with a measurement
without having a positive answer to this question may result in obtaining data of
no practical use and wasting our time. However, we may easily obtain the answer
by performing a calibration of the sound level meter together with the microphone
and its preamplifier. Calibration of the measurement device may be done in two
ways: by comparing the calibrated device with a reference device of known
parameters; or using a template of the measured quantity to perform a reference
measurement. Acoustic devices are usually calibrated in the latter fashion with
so-called, acoustic calibrators. Acoustic calibrator is a device, which produces
acoustic pressure of defined level and frequency. In other words, such calibrator is a
template of acoustic pressure. With help of such a template we can check the
accuracy of the measurements performed with the sound level meter and/or calibrate
it if the error occurs.
1.2. Accuracy of calibration
Each measurement performed with any measurement device is burdened with
an error. Result obtained from such measurement is only an estimate of the real
value of the measured quantity. It is impossible to remove the error completely,
as the values given by the meter are discrete whereas the measured quantity is
of continuous nature. Hence, the purpose of calibration is to limit this inevitable error
to a certain acceptable level. Maximum absolute value of the error of measurement
(or of the generated signal in the case of the calibrator) is called the tolerance and is
strictly defined by the standards for the given type of device.
A sound level meter is calibrated correctly if and only if the measurement error
is within the range of tolerance defined by the standards for the meter of a given
class.
1.3. Classification of sound level meters and acoustic calibrators
The acoustic calibrators (see IEC 60942: 2003) and the sound level meters
(see IEC 61672: 2002) are divided into classes and types respectively, according to
their accuracy. Type 0 imposes the strictest requirements on the device. Devices of
this class are ranked as the most precise. Each of the following types (1, 2 and 3)
allows for the wider range of tolerance (see Table 1).
Table 1. Tolerance values for the given types of acoustic devices excluding maximum expanded
uncertainty of measurement (f = 1 kHz)
Class / Type
Sound level meter, [dB]
Acoustic calibrator, [dB]
2
LS 1 2
- 0.7 1.0
0.10 0.25 0.40
SV 33A USER MANUAL.
As indicated in Table 1, an acoustic calibrator has significantly lower tolerance
than a sound level meter of the same class. Intuitively, we understand, that
the calibrator, as a reference for acoustic pressure must be more precise than
a measurement device.
Taking acoustic measurements according to norms and standards imposes
the requirement of calibrating the measurement channel before each measurement
or measurement session and very often as well after the measurement for result
verification purposes.
2. Acoustic calibrator SV 33A
2.1. General description
The SV 33A acoustic calibrator is a small, portable one-range Class 1 device
(sound source), see Picture 1. Powered by two LR03/AAA batteries, it contains
a loudspeaker producing acoustic pressure, reference microphone for monitoring
generated level, pressure and temperature sensors for measurements
of atmospheric conditions and a microprocessor system controlling the operation
of the calibrator. Sinusoidal waveform of 1 kHz frequency is digitally generated
and feeds the loudspeaker. Sampled signal from the reference microphone indicates
the level of currently generated signal in a feedback loop. On the basis
of information about the level of the signal, actual values of pressure and
temperature, microprocessor adjusts amplification of the loudspeaker signal in order
to produce appropriate sound pressure level in the calibrator’s chamber.
Due to the feedback regulation loop the SV 33A calibrator does not require
adjusting and operates in a wide range of temperature, pressure and humidity (see
SV 33A Datasheet).
Picture 1. Acoustic calibrator SV 33A
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The SV 33A is designed for calibration of sound level meters with ½”
microphones. Picture 2 shows the way of insertion of a ½” microphone into calibrator.
Picture 2. Calibration of the personal exposure meter with a ½” measurement microphone
2.2. Usage of the calibrator
2.2.1. Button functions
The SV 33A calibrator is equipped with a button for controlling operation of the
device. The button is used to turn ON and OFF the device. In this case the button
pushing has immediate effect.
Either when the SV 33A is ON or OFF pressing the button over 10 seconds and
releasing it will cause full reset of the system. Normally this function is not necessary.
It has been implemented in the case of inappropriate operation of the calibrator
caused by external (EM radiation, subnormal atmospheric conditions, etc) or internal
(inappropriate system reset as a result of battery replacement, etc) factors.
The operation time of the calibrator with a microphone put inside its chamber
is limited to 3-5 minutes. This functionality was added in order to save the battery,
e.g. when the calibrator is accidentally left with the microphone inside.
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Table 2. Functional description of the calibrator’s button
Button press Function description
Short, less than 10 sec. Turn on/off the device
Over 10 sec. Full reset of the system
2.2.2. Indicators
There are two LED to indicate the state of the SV 33A calibrator. One of them is
titled “114 dB” and shows the state of the generated level.
After the calibrator is put on the microphone and switched on, acoustic pressure
inside the calibrator’s chamber is adjusted to the desired level. During that process
“114 dB” diode blinks with a frequency of approx. 2 Hz.
Device is ready when this diode is on with a continuous light.
Notice: Calibration should not be performed until the “114 dB” diode light
is continuous.
Warning: In the case of water condensation inside calibrator SV 33A
can generate significantly lower acoustic pressure then specified.
Condensation can appear when cold device is moved to the warmer
environment. In such a case certain acclimatization time is required.
For the room temperature environment (ca. 20 deg C) the recommended
acclimatization time is approximately as follows:
30 minutes for the initial calibrator temperature -10 deg C
15 minutes for the initial calibrator temperature 0 deg C
2 minutes for the initial calibrator temperature +10 deg C
Before reaching acclimatization time SV33A cannot be used as a
reference sound source!
The diode called “LOW. BAT.” presents the batteries status. The batteries
voltages under 2.1 V cause “LOW. BAT.” blinking with approximately 2 Hz frequency.
It is recommended to not use the SV 33A calibrator in this state as the generated
level may differ from the declared values.
Notice: Replace the batteries, when diode “LOW. BAT.” blinks.
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Picture 4. The top view of the SV 33A calibrator with one diode on
2.3. Replacing the battery
The battery should be replaced as follows:
a) remove the rubber cover on the button and diodes’
b) holding the cover unscrew four fixing screws with
side
your fingers
c) take off the cover and remove discharged batteries
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d) put new batteries in place of the discharged ones
with polarization as indicated on the printed board and
calibrator’s case
e) put on the cover so that the diodes fit the
corresponding holes in it
f) holding the cover with one hand fasten the fixing
screws
g) put on the rubber cover
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3. SV 33A Datasheet
Output signal
Sound Pressure Level (SPL): 114 dB, with respect to 20 Pa in reference
conditions
Accuracy: IEC 60942: 2003 standard, Class 1
SPL Accuracy: 0.3 dB
Frequency accuracy: 0.02 %
Total Harmonic Distortions (THD): < 0.75 %
Reference conditions
Temperature: 23 C
Atmospheric pressure: 101.3 kPa
Humidity: 30-80 % RH
Effective microphone load
volume: 250 mm3, microphone type: 4134,
General data
Effective load volume sensitivity: 0.00025 dB / mm3
Level stabilization time: typical 7 sec., max. 10 sec.
Microphone dimensions: ½” and ¼” with reduction adapter SA30
Storage temperature range: -25 C do + 70 C
CE classification: EMC: EN 50081-1, EN 50082-1
Safety: EN 61010-1: 2001
Working conditions
Temperature range: from -10 C to +50 C
Atmospheric pressure range: from 65 kPa to 108 kPa
Humidity range: from 25 % to 90 % RH no condensation (*)
Environmental conditions influence (typical)
Temperature coefficient: 5·10-3 dB/C
Pressure coefficient: 1·10-4 dB/hPa
Humidity coefficient: 1.25·10-3 dB/%
Power supply
Battery type: two LR03 (IEC)/AAA (ANSI) alkaline batteries
Continuous operation time: 30 hours
Standby mode: approx. 2 years
Minimal working voltage: 2.1 V
Dimensions and weight
Weight: 280 g with batteries
Dimensions: 65 x 65 x 70 mm
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(*}
Warning: In the case of water condensation inside calibrator SV 33A
can generate significantly lower acoustic pressure then specified.
Condensation can appear when cold device is moved to the warmer
environment. In such a case certain acclimatization time is required.
For the room temperature environment (ca. 20 deg C) the recommended
acclimatization time is approximately as follows:
30 minutes for the initial calibrator temperature -10 deg C
15 minutes for the initial calibrator temperature 0 deg C
2 minutes for the initial calibrator temperature +10 deg C
Before reaching acclimatization time SV33A cannot be used as a
reference sound source!
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