Scarlet Tech ST-25D User manual

ST-25D
User Guide
Sound Level Meter
ST-25D

Precaution
* Use the sound level meter gently, especially for microphone part, microphone is
delicate sensor that require careful handling, please avoid any crashing, knocking and
hitting, no water or oil entering.
* If choose to use alkaline batteries, please use high capacity of alkaline batteries. And
remember to remove the batteries when don’t use sound level meter for more than one
week.
* Do calibration before and after measurement if needed.
* Keep sound level meter powering on status at least 8 hours every month for charging
internal clock battery.

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Contents
1. General Introduction
2. Specification
3. Structure Features and Function
4. Preparation
4.1 Preparation before using
4.2 Use of windscreen
4.3 External power supply
4.4 Check and change battery
5. Calibration
5.1 Sound calibration Interface
5.2 Use ST-120 to calibrate
5.3 Directly input sensitivity level
5.4 Calibration record
6. Operation
6.1 Main menu
6.2 Measurement interface
7. Setup
7.1 RTC
7.2 Analyzer setup interface
7.3 Basic setup interface
8. Data Recall
8.1 Once measurement result
8.2 24H automatic monitoring result recallrecall
8.3 Integral measurement result recall
8.4 Delete data
8.5 Change to U-disk mode and recall
8.6 File Format Description
9. GPS Positioning Measurement
9.1 Distance measurement
9.2 Calibrate the RTC
9.3 GPS positioning measurement
10. Data Export
11. Overload Indication
12. Annex
12.1 Response characteristics
12.2 GPS overview
12.3 Filter attenuation characteristics
13. Safety, Handling, & Maintenance

General Introduction
Model ST-25D has advantages of low power dissipation, powerful function, friendly and
colorful display screen and abundant content. The instrument can measure A, C, Z
frequency weighting and F, S, I time weighting, and it can also measure multiple
assessment indexes at the same time. Its dynamic range is higher than 122dB.
The instrument enables statistics and integral analysis functions.
The design of low power dissipation and the automatic switchover of battery and the
external power can support the instrument to work for a long time. With embedded 32
MB flash memory turns ST-25D a reliable data logger. It also has a pre-installed 32GB
SD card for WAV recording function.
The instrument can be applied in environment protection, labor health, industrial
enterprise and research and teaching etc. It can also achieve measurement of environ-
mental noise, sound power level, machine equipment noise and building acoustics.
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Model ST-25D
Specification
2
Fulfils Standard
Normal Frequency
Measurement Range
Measurement Level
Resolution
Frequency Weighting
Time Weighting
Main Parameters of
Measurement
Datalogging
Audio recording
GPS
Bluetooth
Power Supply
Output Interface
Run Mode
Dimensions
Display
Graphic
Weight
Operation Environment
Package Contents
IEC 61672 Class 2 / IEC 61260 Class 2 / IEC61252:2002
20 Hz ~ 12.5kHz ± 1 dB (not including microphone)
28dB-133dB (145dB Peak)
Z(FLAT): 38 ~ 130dB / C peak: 145dB / Z(FLAT): peak: 145dB
0.1dB
A, C, Z parallel (synchronous)
F, S, I, parallel (synchronous), peak, Lin. Average
[Statistical] Lxyi, Lxyp, Lxeq, Lxymax, Lxymin, LxN, SD.
[Integral] Lxyi, Lxyp, Lxeq,t, Lxeq,T, Lxymax, Lxymin, Lxpeak, LAE, LC-A, SEL.
Note1: x is A, C, Z; y is F, S, I; LxN has five parameters, the user can define them and
N is chosen from 1 to 99.
Note2: 24H Measurement indexes：Ld, Ln, Ldn besides the indexes above
32MB Flash memory
48kHz, 32bit; 8kHz, 8bit
Location, Transport speed
Build-in; Support print measurement data
4 x AA Batteries or USB 5V external power supply
AC*, DC**, RS-232, USB
Key, Limit, Clock, Interval
260 x 80 x 30 mm
2.6-inch color display with 240*320 resolution
Statistic distribution graph, Accumulative distribution graph
0.35kg
Air temperature: - 15°C ~ + 55°C
Relative humidity: 20% ~ 90%
Sound Level Meter, Calibration Certificate, ½” Prepolarized Condenser
Microphone(Pre-installed), Windscreen, SD card(Pre-installed), RS-232 Cable, Mini
USB Cable, 5V Power Adapter, AA Batteries, User Manual, Waterproof Carry Case
*AC: Chosen between AC and 1 kHz. Its output can be connected to 8Ωearphone (output power: 150mW,
harmonic distortion: <0.1%).
**DC: Output the instantaneous sound pressure level of three frequency weighting (A, C, Z) and three
time weighting (F, S, I), output scale: 15mV/dB. For 100dB, its output voltage is 1.54V (sensitivity
level:-28dB)

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Structure Features and Function
The outline of the Sound Level Meter is shown in Figure 1. It consists of microphone,
preamplifier and the main unit. During normal operation, the measuring microphone
and the preamplifier are installed on the head of the main unit, connected with the
main unit through knurled nut. Extension cable can also be used between the main unit
and the preamplifier. The function of the connector’s pin between preamplifier and the
sound level meter is shown in Figure 2.
The outline of the sound level meter is sharp to reduce the reflection of the sound wave.
The nominal influence caused by the reflection on the shell and the indication features
under different incidence direction can be found in annexes. The shell is mold with ABS
plastic. The batteries are put in battery box, which is very convenient for users to
replace the batteries just by taking off the battery cover plate. All buttons are located
at the central of the obverse side. Measuring results are shown on the 240×320 OLED
display.
The GPS antenna slot, SD card slot and SD card indicator are located on the side, AC
output (3.5mm phone jack), GPS and Status indicator, RS-232 and mini USB port are on
the bottom of the device, the detail definition and function of pins is shown in the
following figures.

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Fig 1 Main structure
Microphone
Windscreen
GPS antenna port
Windscreen anti-drop hook
Preamplifier
Knurled nut
Display
Security slot
SD card indicator
SD card slot
(pre-installed a 32GB SD card)
Keypad
Mini USB port
Battery indicator
Status indicator
AC output
GPS indicator
RS 232
ST-25D

Fig 2 Preamplifier-Main device connector (X9 socket)
Fig 3 AC output (3.5mm phone jack/stereo socket)
Fig 4 Mini USB port
AC output signal’s amplitude won't exceed 1V. Its relationship with input signal is shown
in the table below:
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Pin
1
2
3
4
5
6
Definition
Power supply
Not connected
Signal input
Not connected
Signal ground
Not connected
AC output
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2
AC
input signal minus 10dB
input signal plus 10dB
AC
0.44V, 1kHz sine wave
0.7V, 1kHz sine wave
1. +5V
2. UD-
3. UD+
4. NC
5. GND

Fig 5 RS232 port
Fig 6 LED indicators
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Pin
1
2
3
4
5
6
7
8
9
Definition
Power
RXD
TXD
Online
Ground
DC Output
Not connected
Not connected
Not connected
Working status
indicator
Working status indicator
LED behavior
Flashes
Static On
Off
Status
Measurement starts
Measurement paused
Measurement Stopped
GPS status indicator
LED behavior
Flashes in every 1 second
Off
Status
Positioning information is available
GPS module is not installed or in sleep mode
GPS status
indicator

ST-25D
Fig 7 Keypad
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Name
On/Reset
Cancel
Left
Right
Up
Down
Set
Enter
Delete
Off
Output
Backlight
On/pause
Function
Power on; Restart the instrument
Move the cursor to left
Move the cursor to right
The value is added by 1; Page up; Change option
The value is deceased by 1; Page down; Change option
Enter the settings interface
Enter the current operation
Delete the current data or cancel the current operation
Power off the instrument
Finish the measurement ahead of time and save the measurement data
Turn on/off the backlight
Start or pause the measurement
Return to previous menu from the current menu
; Load the default parameters in the main menu interface
EnterCancel
Delete
On / Reset
Left Right
UpDown
Setup
Backlight
Start / Pause
OutputOff
Icon

Displayed content
Statistics
Integral
GPS (Optional)
Overload
Calendar Clock
List
All
Fig.
Big
Huge
Sim.
Once
24H
LAFp, LASp, LAIp,
LZFp, LZSp, LZIp,
LCFp, LCSp, LCIp
Wei: A, Wei: C, Wei: Z,
one of them
Ts
Tm
Tl
Ready
R: -(number)
W: (number)
Run
End
Pause
ATE
(Optional)
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Fig 8 Status bar & icon definition
Remark
The bars from the left: Statistics, Integral
Color: white means open, red means startup
status
There is overload indicator when exceeds the
measurement upper limit.
Power supply switchover: When the battery
and external power supply power the
instrument meanwhile, battery power is
cut-off completely, the analyzer first uses
external power source. When external power
is low and cutoff, the instrument switches
back to battery power and the instrument
won't close down.
Statistics, integral
The measuring interface of 24H in statistics
Statistics, integral
Integral
Integral
Integral
Statistics
Statistics
Integral
Integral
Pressing key in the measuring interface
can choose the measuring time by grade
Mini-printer is optional
Meaning
Analysis mode
Analysis mode
GPS positioning measurement
The number of working analyzers
Statistics & Integral are
measuring.
Overload
The upper line shows hour, minute
and second, the bottom line shows
year, month and day.
Status of power supply, means the
instrument is powered by external
power supply.
Status of power supply, means the
instrument is powered by battery.
Status of power supply, means the
voltage of external power supply
and the battery is low.
Display interface
Display interface
Display interface
Display interface
Display interface
Display interface
Measuring mode
Measuring mode
Measuring index
Frequency weighting
The setting measuring time
The start-up measuring time
The remaining time
The measurement is not started.
The remaining time of voice note
The remaining time of run mode of
key and delay
The measurement is going on.
The measurement is finished.
The measurement pauses.
Sending data to mini-printer
SD card
48k 32bit record
8k 8bit record
Slave mode of Bluetooth
Master mode of Bluetooth
A SD card installed
No
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Preparation
4.1 Preparation before using
①Check whether the microphone has been installed correctly.
②Check whether battery has been put in.
③ If necessary, calibrate it with a sound calibrator. Regular method is in chapter 5.
④ The meter should be tested by relevant department regularly (such as one year), so
as to ensure its accuracy.
4.2 Use of windscreen
If windy, you may use a windscreen to reduce the influence of wind noise. There are
different models for you to choose. Windscreen can reduce noise about 10-15 dB．See
Appendix D the influence of free-field responses for a meter with a windscreen when
there are no wind.
4.3 External power supply
The Sound Level Meter can be connected with external power through the USB socket
at the lower right of the instrument. At this time, the inner battery will be cut-off
automatically. The voltage range of the external power supply is 4.3 V~6.5 V. The shell of
plug is the cathode and the core of plug is the anode. When the Sound Level Meter is
used for long time continuously, it is recommended to use external power supply.
4.4 Check and change battery
While operating, the meter will check battery power automatically, if it is low, the
under-voltage indicator on will be lighted, which reminds to change battery. After you
change the battery, the meter will operate normal again.

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Calibration
There are two interfaces: calibrate and record. The instrument can save sound calibra-
tion record of 256 groups.
: Press key to calibrate.
: Press key to save the new sensitivity level.
: Press key to enter the modified parameters.
Function of main keys is shown below:
"Condition": the temperature of the environment.
"Mic. Model", "Mic. Series" and "Class 2" are preset when the meter leaves the factory, which
can’t be changed by the user.
"Up" is the upper limit of measurement when the instrument is equipped with the current
sensitivity of microphone. The upper limit is defined according to the maximum RMS value of
1kHz sine wave.
"Low" is the lower limit of the instrument under the current sensitivity of microphone which is
7dB more than self-generated noise.
"Free field" is set according to the microphone that the instrument is equipped. The amendment
value of free field is 0.2dB which also can be changed by the user.
"Mic. Sensiti." is the sensitivity level of the microphone after last calibration. This sensitivity level
includes the preamplifier’s attenuation.
"Calibrator SPL" is the actual level after calibration by the sound level calibrator.
"New Sensiti" is the sensitivity level of the microphone after new calibration or the modification
by hand.
"Current SPL": is changing with the environment which is shown as dBA or dBC. When the
instrument is calibrated by 1kHz calibrator, the unit of Current SPL is recommended to use dBA.
And when calibrated by 250Hz pistonphone, the unit is recommended to use dBC.
When the user enters the "Calibrate" submenu from main menu, shown below:
5.1 Sound calibration Interface

5.2 Use ST-120 to calibrate
At the first time of sound calibration, set the "calibrator’s sound pressure level" accord-
ing to the certificate of inspection of the corresponding sound level calibrator. General-
ly, the sound level calibrator’s sound pressure level is 94.0dB. If the sound pressure
level is not 94.0dB, set it according to the actually inspected result.
Take 94.2dB for example, press key, and press or key to move the cursor to
"Calibrator", and then adjust the value to 94.2 by or key. At last, press to
save the Calibrator SPL.
Every time the user presses or key, the value increases or decreases by 0.1dB.
When the user presses and holds or key, the value increase or decreases by 1dB.
The adjustment continues till the key is released. The above steps can be performed
only when the displayed sound pressure level differs from the used sound pressure
level.
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In the current mode, the cursor can only be moved on "dBA" at the right side of "Current
SPL" and "Calib.". If the user wants to modify the parameters, they should press Key,
shown below:
The status changing from "Ready" to "Modify" allows the user to modify "Free field",
"Calibrator SPL", and "New Sensiti." by pressing or key. When key is pressed,
the modified content will be saved.
When the new sensitivity level that is calibrated differs from the last one by more than
4dB, then the new sensitivity level can’t be saved. And the instrument should be
recalibrated according to the prompt, if the microphone is verified with no problem
(such as change the microphone), the user can set the new sensitivity level manually
and calibrate it again.

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Insert the ½ inch microphone to the hole of ST-120 sound calibrator, turn on the power
supply. Press key. The meter automatically starts calibration. The sound pressure
level is displayed after "Current SPL". This sound pressure level is approximately equal
to the calibrator’s sound pressure level minus free field correction. The sensitivity level
is displayed after "New Sensiti.".
During calibration, a number is displayed on the bottom
right corner of the screen, which changes from 0 to 21 and
then stops. Then the user presses key, the new micro-
phone sensitivity level will be saved.
If the newly calibrated sensitivity level differs from the last
saved sensitivity level by over 4dB, the meter will prompt
"As the sensitivity level difference exceeds 4dB, it can’t be
saved. Please check whether the calibration is correct.".
The user should check whether the microphone is
damaged. If the user doesn’t press key, the meter will
still use the original microphone sensitivity level.
5.3 Directly input sensitivity level
If no calibrator is available, the user can also directly input the microphone’s sensitivity
level. Press key, and press or key to move the cursor to "New Sensiti.", and
then adjust the value by or key until it arrives the expected value. At last, press
to save the Calibrator SPL.
ST-25D

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The interface displays the calibration message of current serial number, move the
cursor to the "No", and press or key to view the calibration message of the other
serial number. The message includes: calibration date, environment condition, type and
serial number of microphone, correction value in free field, sensitivity level of micro-
phone, measurement range and so on.
5.4 Calibration record
When the cursor is moved to the "Calibrate" and press the or key to enter the
Calibration record interface, shown below:

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Operation
There are four display interfaces in the main menu interface: measurement interface,
setup interface, recall interface and calibration interface.
In the main menu, there are four submenus: Measurement, Setup, Recall, and Calibrate.
The bottom shows status bar of storage space, the blue indicates the used space. When
the user presses key, the system parameters are restored to the default values. The
and keys allow the user to move the cursor leftwards/rightwards. When
pressing key, the user can go to the corresponding submenu. There are two
submenus in setup interface: analyzer setup and basic setup.
6.1 Main menu
When the user presses key for above 2s and then releases it, the meter goes to the
main menu:
6.2 Measurement interface
When the cursor is on the "Measure", if the user presses key, the meter goes to the
measurement interface which consists of statistical analysis interface, integral
measurement interface and GPS positioning interface.
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

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6.2.1 Statistic Analyzer
At Main menu, pressing the key when the cursor is at "Measure" will enter the
measuring interface. In the Statistic analyzer, there are two mode: Once and 24H.
The setup parameters can’t be changed in measurement interface but they can be
displayed by turn. The parameters of “Sta.1” and “Sta.2” only can be changed in “Setup”
->“Analyzer” -> “Statistic”.
Note: The green options mean the menu status can be changed by , and ,
keys.
The blue background frame at the first line respectively displays from left to right:
current analyzer mode, work status, calendar clock and power indication. When the
cursor is moved to the option of "Statistics", the user can use or key to change
the menu options. Power indication displays socket icon which means the instrument is
powered by external power supply, and battery icon means the instrument is powered
by batteries. The power voltage symbol can accommodate up to 16 lines. When these 16
lines are filled, the power voltage is about 5.6V. When the power voltage is lower than
3.6V, the indication is changed to " ", which means the meter is in under-voltage
status.
The black background frame in the middle shows measurement content. The blue
background frame at the bottom line respectively displays from left to right: display
mode, measurement mode, measurement time and measurement status. The measure-
ment status includes: Ready, Start, Pause, Wait, Print and Over. The cursor can stay on
"LIST1", "ONCE" and "Ts", the user can use or key to change the menu options.

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6.2.1.1 Once measurement interface
In the noise measurement interface, when the menu in the measurement mode
displays “Once”, the meter goes to “Once” measurement mode. In the “Once” measure-
ment interface, there are two display modes: List and Fig. interface.
6.2.1.1.1 List measurement interface
The list interface has two pages: List1 and List2. In this interface, the meter synchro-
nously displays six measurement indexes on one screen. The display content includes
Instantaneous value and Statistic value, shown below:
“Sta.1: A F:” means the current weighting is A frequency weighting and F time weight-
ing. When the cursor is on “Sta.1: A F”, the user can press or keys to enter “Sta.2:
Z F” measurement interface which means the current weighting is Z frequency weight-
ing and F time weighting. “Sta.1” and “Sta.2” open at the same time in the measurement
interface which can be displayed switchover, and the operation won’t affect the
measurement result.
The black background frame in the middle shows six measurement indexes of the
current frequency weighting and time weighting in the “List1”: Linst, Leq,T, Lmax, Lmin,
L10, L50 and L90. The indexes shown in “List2” include: Linst, Lmin, L5, L95, SEL and SD.
6.2.1.1.2 Fig. measurement interface
When the cursor is on “List2”, the user can enter Fig. display interface by pressing or
keys. The statistic distribution graph and accumulative distribution graph is displayed
in the interface. When the measurement is started, the statistic distribution graph and
accumulative distribution graph are calculated at the same time and refreshed every
0.5 second.

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1) Statistic distribution graph
In the middle is “Sta. Figure”, the y-ordinate is percentage, and the x-ordinate has 140
points, every point represents 1dB. When the cursor is moved to “94dB”, the user can
view the percentage that every sound pressure level takes up by pressing the or
key.
2) Accumulative distribution graph
In the middle is “Acc. Figure”. The y-ordinate of the graph is percentage, and the
x-ordinate is the sound pressure level which has 140 points, every point represents 1dB.
When the cursor is moved to “94dB”, the user can view the accumulative percentage
that every sound pressure level takes up by pressing the or key. We can figure
out any statistical sound pressure level with this method.
Note: The green options mean the menu status can be changed through cursor and
parameters key.