testo 425 - Digital hot wire anemometer0560 0425
Instruction manualContents

Contents
1
2
2.1
2.2
3
4
5
5.1
6
6.1
6.2
6.2.1
6.2.2
6.2.3
6.3
6.3.1
7
7.1
7.1.1
7.1.2
7.1.3
7.1.4
7.1.5
7.1.6
7.1.7
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5
7.3
8
8.1
8.2
8.2.1
8.2.2

About this document ...........................................................................5
Safety and disposal..............................................................................5
Security ..................................................................................................5
Disposal .................................................................................................6
Product-specific information...............................................................7
Intended use .........................................................................................7
Product description .............................................................................8
Instrument overview ...............................................................................8First steps .............................................................................................9
Inserting / changing batteries .................................................................9
Getting to know the product .................................................................10
Connecting probes ...............................................................................10
Switching the instrument on and off .....................................................10
Switching the display illumination on and off ........................................10
Establishing a Bluetooth® connection ...................................................10
Establishing a Bluetooth® connection to the testo Smart App ..............11
Using the product...............................................................................13
Controls on the measuring instrument..................................................13
Implementing settings ..........................................................................14
Opening configuration mode ................................................................16
Setting the unit .....................................................................................16
Setting the area ....................................................................................16
Reading absolute pressure ..................................................................17
Carrying out a reset of the setting menus.............................................17
Carrying out a reset of the measuring instrument.................................17
Measuring ............................................................................................18
Changing the measurement channel display .......................................18
Freezing a reading, displaying the maximum/minimum value ..............18
Resetting maximum/minimum values ...................................................18
Carrying out multi-point mean calculation ............................................19
Carrying out continuous mean calculation............................................19
Printing data .........................................................................................20
Controls via testo Smart App ............................................................22
Overview of operating controls .............................................................22
App options ..........................................................................................23
Setting the language ............................................................................23
Displaying App Info ..............................................................................24

Contents
8.2.3
8.3
8.3.1
8.3.2
8.3.3
8.4
8.4.1
8.4.2
8.4.3
8.4.4
8.4.5
8.5
8.6
8.7
8.7.1
8.7.2
8.8
9
9.1
9.2
10
11
11.1
11.2

Displaying the tutorial .......................................................................... 24
Application menus ............................................................................... 24
Selecting an application menu ............................................................. 24
Setting favourites ................................................................................. 25
Displaying information about an application ........................................ 25
Making measuring instrument settings ................................................ 25
Configuring the measuring instrument menu ....................................... 27
Setting Auto Off ................................................................................... 29
Activating damping .............................................................................. 29
Setting the Correction Factor ............................................................... 29
Setting the area ................................................................................... 30
Display of the readings ........................................................................ 30
Adjusting the view ................................................................................ 31
Exporting readings ............................................................................... 31
Excel (CSV) Export .............................................................................. 32
PDF Export .......................................................................................... 32
Perform Firmware update .................................................................... 33
Maintaining the product .................................................................... 35
Inserting / changing batteries ............................................................... 35
Cleaning the instrument ....................................................................... 35
Technical data for testo 425.............................................................. 36
Tips and assistance........................................................................... 38
Questions and answers ....................................................................... 38
Accessories and spare parts................................................................ 39

1 About this document

1 About this document•

The instruction manual is an integral part of the instrument.

•

Keep this documentation to hand so that you can refer to it when necessary.

•

Always use the complete original instruction manual.

•

Please read this instruction manual through carefully and familiarize yourself
with the product before putting it to use.

•

Hand this instruction manual on to any subsequent users of the product.

•

Pay particular attention to the safety instructions and warning advice in orderto prevent injury and damage to the product.

2 Safety and disposal
2.1

Security

General safety instructions•

Only operate the product properly, for its intended purpose, and within theparameters specified in the technical data.

•

Do not apply any force.

•

Do not operate the instrument if there are signs of damage to the housing or
connected cables.

•

Dangers may also arise from objects to be measured or the measuring
environment. Always comply with the locally valid safety regulations whencarrying out measurements.

•

Do not store the product together with solvents.

•

Do not use any desiccants.

•

Only perform maintenance and repair work on this instrument that is
described in this documentation. Follow the prescribed steps exactly when
doing the work.

•

Use only original spare parts from Testo.

Batteries•

Improper use of batteries may cause the batteries to be destroyed, or lead to
injury due to current surges, fire or escaping chemicals.

•

Only use the batteries supplied in accordance with the instructions in the
instruction manual.

•

Do not short-circuit the batteries.

•

Do not take the batteries apart and do not modify them.

52 Safety and disposal•

Do not expose the batteries to heavy impacts, water, fire or temperatures inexcess of 60 °C.

•

Do not store the batteries in the proximity of metal objects.

•

In the event of contact with battery acid: rinse affected areas thoroughly withwater, and if necessary consult a doctor.

•

Do not use any leaky or damaged batteries.

Warnings
Always pay attention to any information denoted by the following warnings.
Implement the precautionary measures specified!
DANGER
Risk of death!
WARNING
Indicates possible serious injury.
CAUTION
Indicates possible minor injury.
CAUTION
Indicates possible damage to equipment.

2.2

Disposal•

Dispose of faulty rechargeable batteries and spent batteries in accordancewith the valid legal specifications.

•

At the end of its useful life, deliver the product to the separate collection
point for electric and electronic devices (observe local regulations) or return
the product to Testo for disposal.

•

6

WEEE Reg. No. DE 75334352

3 Product-specific information

3 Product-specific information•

Do not carry out measurements on live components.

•

Do not expose handles and feed lines to temperatures in excess of 70°C
unless they are expressly approved for higher temperatures. Temperature
specifications on probes/sensors refer only to the measuring range of thesensor system.

•

Only open the measuring instrument if this is expressly described in the
documentation for the purposes of maintenance or servicing.

4 Intended use

The testo 425 is a compact instrument for measuring flow velocities andtemperatures by means of a permanently connected flow/temperature probe(hot wire probe). It is intended for indoor use only.
The product is designed for the following tasks/areas:•

Volume flow measurements in ducts•

Measuring flow velocities in rooms• Temperature measurement of flows
The product should not be used in the following areas:•

In potentially explosive atmospheres.

•

For diagnostic measurements in the medical field.

75 Product description

5 Product description
5.1

Instrument overview

1 Control keys

2 Display

3 Probe4 Battery compartment

Explanation of icons
Refer to instruction manual
CAUTION
Damage to sensor possible!
- Do not touch sensor!
- Close the protective sleeve after the measurement.

8

6 First steps

6 First stepsc

6.1

Inserting / changing batteries

WARNUNG
Serious risk of injury to the user and/or destruction of the instrument.
There is a risk of explosion if the batteries are replaced with ones thatare the wrong type.
- Only use non-rechargeable alkaline batteries.



The instrument is switched off.

1

Open the battery compartment (on the back of the instrument) via thesnap lock.

2

Insert or replace batteries (3 x AA
alkaline batteries).
Observe the polarity!

3

+ - +

Close the battery compartment.
When not in use for a long period: Take out the batteries.

Symbol explanation
Do not allow children under 6 years of age to play with batteries.
Do not throw batteries in the trash.
Do not charge batteries.
Do not place batteries near fire.
Batteries are recyclable.
96 First steps

6.2

Getting to know the product

6.2.1

Connecting probes

6.2.2

Switching the instrument on and off

The required probes are permanently connected or integrated. It is not possible
to connect any additional sensors.

Switching on

1 Press the On/Off key (0.5 sec).

 Measurement view is opened:
The current reading is displayed or ----- lights up if no reading isavailable.
Switching off
1 Press and hold down (2 sec) the On/Off key.

 The display turns off.
6.2.3

Switching the display illumination on andoff

The measuring instrument is switched on.

1

Press and hold down (2 sec) the MENU/ENTER key.

 The display illumination is switched on or off.
6.3

Establishing a Bluetooth® connection
The instrument can be connected to the testo Smart App via
Bluetooth® connection

10

The measuring instrument is switched on.

6 First steps



To enable the Bluetooth® connection
for the first time, press and hold(approx. 2 sec) the ◄ key.
While the instrument is trying toestablish a Bluetooth® connection,
the icon flashes on the display.
Bluetooth® remains enabled until it isdisabled manually by pressing andholding (approx. 2 sec) the ◄ key.
The measuring instrument saves theBluetooth® setting and, dependingon the configuration, starts up with
Bluetooth® enabled or disabled.

6.3.1

Establishing a Bluetooth® connection to thetesto Smart App
To establish a connection via Bluetooth®, you need atablet or smartphone with the Testo Smart App alreadyinstalled on it.
You can get the App for iOS instruments in the App Storeor for Android instruments in the Play Store.
Compatibility:
Requires iOS 13.0 or later/Android 8.0 or later,
requires Bluetooth® 4.2.

Bluetooth® is enabled in the measuring instrument.

1

Open the testo Smart App.

The app automatically searches for Bluetooth® devices in the vicinity.

2

In the Sensors menu, check whether the required instrument isconnected.

11

6 First steps

If necessary, switch the instrument to be connected off and on again
to restart the connection module.

When the testo Smart App is connected to the measuring instrument,
the icon appears on the measuring instrument display.
The measuring instrument automatically synchronizes its date andtime settings with the testo Smart App.
Once connected successfully, the current measured value from themeasuring instrument appears on the app screen in the Live view.

12

7 Using the product7 Using the productFor technical reasons, the accuracy of the sensor improves with longer
operating time of the sensor.
For accurate measurements in ppm or calibrations, the device must be
switched on for at least 10 minutes (after the warm-up phase).
Please note that the instrument switches itself off by default after 10
min of inactivity. You can avoid this by disabling the Auto-off function(see chapter 6.2.1).
Lighters are only suitable to a limited extent for a function test due tothe different liquid gas mixtures used in commercial lighters and theselectivity of the sensor based on the gas set (GAS button).

7.1

Controls on the measuring instrument



The instrument is switched on.

The testo Smart App is installed on the smartphone and connectedto the instrument via Bluetooth®.



Settings and controls are implemented either on the instrument or via
the app.
If the measuring instrument is connected to the testo Smart App,settings can only be made via the app. The measuring instrument thenremains in the measurement view and other menus, e.g. Settings,
cannot be opened.

13

7 Using the product1
2

On/Off / MODE/END key
Bluetooth® / ◄ key

3

Battery indicator

4

Parameter 1 unit

5

Parameter 1 measured value display

6

Parameter 2 measured value display

7

Parameter 2 selected unit

8

Print / ► key

9

Illumination / MENU/ENTER key

7.1.1

Implementing settings

Selecting, opening and setting functions

1 Press the relevant key to select the functions
Secondary assignment (long press)
All keys with a grey corner have a secondary assignment, which can beselected by pressing and holding the key for a longer time (2 sec).

14

7 Using the product
Adjustable functions
Ensure correct settings: all settings are transferred immediately. Thereis no Cancel function.
Function

Setting options/comments

Bluetooth® (long press)

Switch the Bluetooth® connection onor offArrow left

Freeze reading (HOLD function),
display maximum/minimum value.

On/Off (long press)

In configuration mode:
Decrease value, select option
Switches the instrument on or off

MODE/END

Select or end multi-point or continuous
mean calculation.

Display illumination (long press)

OFF (display illumination not active) orON (display illumination active)

MENU/ENTER

Open configuration mode
Start continuous measurement /record multi-point readings(Operation also possible directly on
measuring instrument if it is connectedto the app)
In configuration mode:
Confirm input

15

7 Using the product

Function

Setting options/comments

Print (long press)

Output readings via external printerArrow right

Change second measurement
parameter (bottom line)
In configuration mode:
Increase value, select option

7.1.2

Opening configuration modeThe instrument is switched on and is in the measurement view.

1

Press MENU/ENTER until the display changes.

 The instrument is now in configuration mode.
MENU/ENTER to switch to the next function. You can leave Press
configuration mode at any time. To do this, press MODE/END until the
instrument has changed to the measurement view. Any changes thathave already been made in configuration mode will be saved.

7.1.3


Configuration mode is open, “UNITS” is displayed.

1

Press ◄ / ► to choose between metric (“METR”) and imperial(“IMPER”) units of measurement and confirm with MENU/ENTER.

2

Press ◄ / ► to set the required unit for the top line (m/s, fpm) andconfirm with MENU/ENTER.

3

Press ◄ / ► to set the required unit for the bottom line (m3/h, l/s, cfm)
and confirm with MENU/ENTER.

7.1.4

16

Setting the unit

Setting the areaConfiguration mode is open, “AREA” is displayed.

1

Press ◄ / ► to select whether the cross-sectional area is to beentered in m² or in mm² and confirm with MENU/ENTER.

7 Using the product2

Press ◄ / ► to set the cross-sectional area and confirm with
MENU/ENTER.
The measuring instrument can show a maximum of 5 digits in thedisplay (99999 mm²). Conversions from m² to mm² with a value greaterthan 0.09 m² are therefore not possible!

7.1.5

Reading absolute pressureThanks to a built-in absolute pressure sensor (measurements are taken on themeasuring instrument, not on the probe head), no additional input of the air
density is required.

Configuration mode is open.

1

Press ◄ / ► to scroll through the configuration menus until “P_ABS”(absolute pressure) is displayed.

 The current ambient air pressure is displayed.
7.1.6

Carrying out a reset of the setting menusConfiguration mode is open, “M. RES” (menu reset) is displayed.

1

Press ◄ / ► to select the required option and confirm with
MENU/ENTER:o
NO: Do not carry out reset.
o
YES: Carry out reset. All concealed menus that were hidden
via the testo Smart App are displayed again.

 The instrument returns to measurement view.
7.1.7

Carrying out a reset of the measuring
instrument

Configuration mode is open, “RESET” is displayed.

1

Press ◄ / ► to select the required option and confirm with
MENU/ENTER:o
NO: Do not carry out reset.
o
YES: Carry out reset. The instrument is reset to the factory
settings.

 The instrument returns to measurement view.
17

7 Using the product7.2

Measuring The instrument is switched on and is in the measurement view.
1

Position the probe.
The arrow mark on the probe headmust point in the direction of flow.
The correct measurement value isdetermined by rotating the probeslightly in both directions until the
maximum value is displayed.

2

7.2.1

Read the measured values on the display.

Changing the measurement channel
display

1 - Switch between the display of temperature (°C, °F) and calculated
volume flow (m3/h, l/s, cfm):
Press ► .

7.2.2

Freezing a reading, displaying the
maximum/minimum value

The current reading can be frozen. The maximum and minimum values since
the last time the instrument was switched on in the standard view or during a
multi-point or continuous measurement can be displayed.
1

Press ◄ several times until the desired value is displayed.

The following are displayed in turn:o
Hold: frozen measured valueoMax: Maximum valueo
Min: Minimum valueoCurrent measuring value

7.2.3

Resetting maximum/minimum values

The maximum/minimum values of all channels can be reset to the current
reading.
1
18

Press ◄ several times until Max or Min is shown.

7 Using the product2

Hold down ◄ (approx. 2 s).

All maximum and minimum values are reset to the current reading.

7.2.4

Carrying out multi-point mean calculation

1

Press MODE/END.

The number of readings recorded is displayed in the upper line, while
the current reading is displayed in the lower line.

2

To record readings (in the desired quantity):

flashes.

Press MENU/ENTER (several times).
3

To end measurement and calculate the mean value:
Press MODE/END.

andflash.

The number of measured values and the calculated multi-point meanvalue are displayed.
4

To switch back to the measuring view:
Press MODE/END.

7.2.5
1

Carrying out continuous mean calculation
Press MODE/END twice.

The elapsed measuring time (mm:ss) is displayed in the upper line,
while the current reading is displayed in the lower line.

2

Start measurement:

flashes.

Press MENU/ENTER.

197 Using the product3

To interrupt/continue measurement:
Press MENU/ENTER each time.

4

To end measurement and calculate the mean value:
Press MODE/END.

andflash.

The measurement period and the calculated continuous mean value
are displayed.
5

To switch back to the measuring view:
Press MODE/END.

7.3

Printing dataA testo Bluetooth®/IRDA printer (order no. 0554 0621) is connected
via Bluetooth and switched on.
When first setting up a connection between the testo measuring
instrument and the testo Bluetooth®/IRDA printer, the initialization
phase can last up to 30 seconds.

1

Press and hold ► to transfer the data to the printer.

 Data is printed out (LED on the printer lights up green).

20

7 Using the product1 Instrument name3 Date and time of printout
5 Measurment values

2 Firmware version and serial
number
4 Measuring type and measured
duration
6 Measurement parameters21

8 Controls via testo Smart App

8 Controls via testo Smart App

If the measuring instrument is connected to the testo Smart App, it is primarily
operated via the app. The measuring instrument remains in the measurement
view and settings menus cannot be opened on the measuring instrument.

8.1

Overview of operating controls

1 Choice of applications

2

Switch between the views (live,
graphic, table)

3

Display of connected measuring
instruments including readings

4 Start/stop

5

Measurement configuration (themenu changes depending on themeasuring instrument connected
and the application selected)

6

Configuration of the measuring
instrument

Additional symbols on the user interface of the app (not numbered)
One level backExit view
Share measurement data/report
Searching22

8 Controls via testo Smart App
Favourite
Deleting
Further information
Display report
Multiple selection
The Main menu can be accessed via theicon at top left. To exit the main
menu, select a menu or right-click on the guided menus. The last screen
displayed is shown.
MeasureCustomer
MemorySensors
Settings
Help and Information
Other applications

8.2

App options

8.2.1

Setting the language

1

Click on2

Select Settings.

3

Select Language.

.

 A selection list is displayed.
23

8 Controls via testo Smart App

4

Select the required language.

 The language is changed.
8.2.2

Displaying App InfoIn App Info you can find the version number of the installed App.

1

Click on2

Select Help and Information.

3

Select Instrument information.



The version number of the app and the ID are displayed.

8.2.3

.

Displaying the tutorial
The tutorial guides you through the first steps in operating the testo
Smart App.

1

Click on2

Select Help and Information.

.

 The tutorial is displayed. In the tutorial, swipe to display the next page.
3

Click X to quit the tutorial.

8.3

Application menus

8.3.1

Selecting an application menu

1

Click on

A selection of menus for various applications is displayed.

2

Select the required application.

.

 Your selected application is displayed.
24

8 Controls via testo Smart App

8.3.2

Setting favourites

1

Click on

A selection of menus for various applications is displayed.

2

Select the application you want to set as a favourite.

3

Click on

The star is displayed in orange:

8.3.3
1

.

.
.

Displaying information about an application
Click on.

 A selection of applications is displayed.
2

Click on.

 The information about an application is displayed.
8.4

Making measuring instrument settings

 The measuring instrument is connected to the testo Smart App.
1

Click on.

 The main menu opens.
2

Click on Sensors.

 The Sensors menu opens.
3

Click on the required measuring instrument.



Information about the model, order number, serial number andfirmware version is displayed.

4

Click on the Settings tab.

25

8 Controls via testo Smart App
window with settings for the respective measuring instrument
 - Aopens.
In addition to the settings that can be performed on the measuring
instrument, additional settings can also be made.
5

Click on the blue text under a setting
heading to activate or disablesettings or to open an input window
to enter a specific value or select aunit.
For details on the settings options,see the following sub-sections.

26

8 Controls via testo Smart App



8.4.1

Changes to the measuring
instrument settings in the app aretransferred directly to the measuring
instrument. Synchronization with theapp is confirmed on the measuring
instrument via “SYNC DONE”.

Configuring the measuring instrument
menu

The testo Smart App can be used to set which settings menus should beavailable or hidden on the measuring instrument itself.
The Settings tab in the Sensors menu is open.



27

8 Controls via testo Smart App
1

Activate Customization instrument
menu and click on the blue text
Change instrument menu list
under the settings heading.



The Customization instrument
menu dialogue opens.
On the measuring instrument, thefollowing menus can be displayed or
hidden:oSetting the unitoAreaoFunnel factor(testo 417 only)2Deactivate the checkboxes for themeasuring instrument menus thatare no longer to be displayed on themeasuring instrument itself.

The menus belonging to thedeactivated entries will no longer be
displayed in the measuring
instrument menu after the next
synchronization.
These settings can be reset
via the menu reset “M.RES”
and then all settings menus
will be displayed on themeasuring instrument again.

28

8 Controls via testo Smart App

8.4.2

Setting Auto Off

 The Settings tab is open.
1

Enable Activate Auto-off using the slider.



The measuring instrument switches off automatically if no key ispressed for 10 min.
Exception: a frozen reading is shown on the display (“Hold” isdisplayed).

8.4.3

Activating damping
If the readings fluctuate wildly, it is advisable to damp the readings.

 The Settings tab is open.
1

Enable Activate damping using the slider.

2

Click on Average of the measured values.

 The window for Average of the measured values opens.
3Enter a value between 2 and 20 measured values.



Changes to the measuring instrument settings in the app aretransferred directly to the measuring instrument. Synchronization withthe app is confirmed on the measuring instrument via “SYNC DONE”.

8.4.4

Setting the Correction Factor
If parts of the cross-sectional area are covered (e.g. by lattice bars), thiscan be corrected via the correction factor.
The correction factor indicates the proportion of free space in the crosssectional area.
For example: If 20% of the area is covered, the correction factor must
be set to 0.8 (80% free space).
The correction factor can only be set via the testo Smart App and not
directly on the measuring instrument.

 The Settings tab is open.
29

8 Controls via testo Smart App
1

Select Correction factor.

2Enter the value for the correction factor and save.

changes are transferred to the measuring instrument and Thesynchronization with the app is confirmed on the measuring instrument
via “SYNC DONE”.

8.4.5

Setting the area
The cross-sectional area of the measuring point can be set both via the
testo Smart App and directly on the measuring instrument.
The display of this setting on the measuring instrument cannot be
hidden.

 The Settings tab is open.
1

Select Area.

2Enter the value for the cross-sectional area and save.

changes are transferred to the measuring instrument and Thesynchronization with the app is confirmed on the measuring instrument
via “SYNC DONE”.

8.5

Display of the readings
The available readings can be displayed in different views.

•

Live view:
The readings transmitted by the measuring probes can be displayed in a live
view. Readings from all connected measuring probes are displayed.

•

Graphic view:
Up to four different readings can be displayed in graph format. Readings to
be displayed can be selected by tapping on a reading above the diagram.

•

Table view:
In the table view, all readings are displayed in sequence according to date
and time. Different readings from the individual measuring probes can bedisplayed by pressing ◄ ►.

30

8 Controls via testo Smart App

8.6

Adjusting the view
1
2

Click on.

Select Edit view.

overview of all measurement channels and their measurement
 Anparameters is displayed.

8.7

3

Deselect the “check mark” to hide a measuring instrument’s
measurement channel.

4

Click ▼ to select the unit of a measurement channel.

5

Click OK to confirm the settings.

Exporting readings

ExportReportDelete31

8 Controls via testo Smart App
1

Click on2

Select Memory.

3

Click on Select measurement.

8.7.1

Excel (CSV) Export

1.

Click on.

 A selection of export options is displayed.
2

Click on Start export.

 A selection of sending/export options is displayed.
3

Select the required sending/export options.

8.7.2

PDF Export

1

Click on Report.

 A selection window is displayed.
2

If required, activate the Create PDF with all readings button.

3

Click on Create.
For measurements, please be aware that the option Create PDF withall readings is only possible up to 30 pages, due to the resulting filesize and number of pages. In the testo DataControl software, however,
PDF reports can be created for all measurements without any
restrictions.

 A report containing all the information is created.
selection window is displayed. The report can be sent via e-mail or ABluetooth.
®

4

Click on E-mail or Bluetooth®.

 The report will be sent.
32

8 Controls via testo Smart Appc

8.8

Perform Firmware update
Ensure that the option for Enable update for connected instruments
in Instrument Information is always enabled.



If a new firmware is available for yourmeasurement instrument, an update
notification is shown after connecting
the instrument with the testo SmartApp.

1

Click Start Update to perform the
update.
If you click Later, the Update
notification is shown again during thenext connection.

During the instrument update theBluetooth connection must not be
disconnected.
The update needs to be performed
completely and takes approx. 5-10
minutes depending on the used
smartphone.

33

8 Controls via testo Smart App
After the update the measuring instrument is restarting.
The firmware can be checked in the instrument menu or via the app.
A restart of the testo Smart App is recommended after the instrument
update.

34

9 Maintaining the product9 Maintaining the productc

9.1

Inserting / changing batteries

WARNUNG
Serious risk of injury to the user and/or destruction of the instrument.
There is a risk of explosion if the batteries are replaced with ones thatare the wrong type.
- Only use non-rechargeable alkaline batteries.



The instrument is switched off.

1

Open the battery compartment (on the back of the instrument) via thesnap lock.

2

Insert or replace batteries (3 x AA
alkaline batteries).
Observe the polarity!

3

+ - +

Close the battery compartment.
When not in use for a long period: Take out the batteries.

9.2

Cleaning the instrument
1 If the housing of the instrument is dirty, clean it with a damp cloth.
Do not use any aggressive cleaning agents or solvents! Mild householdcleaning agents and soap suds may be used.

35

10 Technical data for testo 425

10 Technical data for testo 425•

Adjustment conditions for flow probes:
Adjustment in free jet Ø 350 mm, reference pressure 1013 hPa,based on testo reference Laser Doppler Anemometer (LDA).

•

Due to the thermal measuring principle, higher measurement
uncertainties can occur in temperature measurement at low flow
velocities (< 1 m/s). The probe should be switched on outside a duct
under the following conditions: Ambient temperature: 20°C
Flow: approx. 0 m/s.

Collapse the telescope after use and do not constrict with the cable.
Start with the telescopic links closest to the handle.
FeatureValue

Measurement parameters

Storage temperaturem/s, fpm°C, °Fm³/h, cfm, l/s±(0.03 m/s + 4% of measuring value) (0.01 to
20 m/s)±(0.5 m/s + 5% of measuring value) (20.01 to
30 m/s)±0.5 °C (1 … 30 m/s)
0.01 m/s
0.1 °C
0.01 to 30 m/s-20 to +70 °C-20 to +50 °C (instrument)-20 to +70 °C (probe)-20 to +50 °C

Operating humidity

0 to 80 %RH / For indoor use only

IP class

IP20

Level of contamination

PD2

Max. operating altitude≤ 2000 m above sea level

Nominal output

2 W @ 4,5 V DC

Battery type3 x 1.5 V AA battery(included in the scope of delivery)>35 hAccuracy

Resolution
Measuring range
Operating temperature

Battery life36

10 Technical data for testo 425

FeatureValue

Dimensions

Instrument: 171 x 60 x 28 mm
Probe: 180 x Ø12 mm
Cable: 1.5 m
268 g

Weight37

11 Tips and assistance

11 Tips and assistance
11.1 Questions and answers
Question

Possible cause

Possible solution

is displayed(top right on thedisplay)
Instrument
switches itself off

Instrument battery isalmost spent

Replace instrument battery

Display responds
sluggishlyDisplay: ----Display: OOOOO
Display: UUUUUDisplay: BT Fail

Display: Print Fail•

Auto Off function isswitched on•

Switch off Auto Off
function•

Remaining battery
capacity is insufficient•

Change the battery.

Ambient temperature isvery lowSensor error

Increase ambient
temperature
Please contact your dealeror Testo Customer Service.
Permissible measuring
Keep within the permissible
range has been exceeded measuring range
Permissible measuring
Keep within the permissible
range has been undershot measuring range• Check Bluetooth®
Bluetooth connection
connections.
could not be established

Printout could not be
performed successfully

Display: Probe Fail

Probe damage

Display: OTA FailThe update process "overthe air" of the measuring
instrument could not becompleted successfully.
Connection to the testo
Smart App wasinterrupted. Keys arelocked for 3 s.

Display: APP Lost

38•

Restart measuring
instrument, restart testo
Smart App.

•

Check Bluetooth®
connections, switch off
and then on again if
necessary.

•

Switch printer off and thenon again.

Please contact your dealeror Testo Customer Service.
Restart the measuring
instrument and testo Smart
App and check theBluetooth® connection.
Restart the measuring
instrument and testo Smart
App and check theBluetooth® connection.

11 Tips and assistance
If we have not been able to answer your question: please contact your local
dealer or Testo Customer Service. See the back of this document or the
www.testo.com/service-contact web page for contact details.

11.2 Accessories and spare parts
Description

Order no.

Bluetooth®/IRDA printer0554 0621

For a complete list of all accessories and spare parts, please refer to the productcatalogues and brochures or visit our website www.testo.com

39Testo SE & Co. KGaA
Celsiusstr. 2
79822 Titisee-Neustadt
Germany
Phone: +49 (0)7653 681-0
E-mail: info@testo.de
www.testo.com

0970 9425 en 02 - 08.2023