EUTECH INSTRUMENTS TURBIDIMETER TN-100 WATERPROOF PORTABLE... User manual

Instruction Manual
TN-100/ T-100
Portable Turbidimeter
Technolo
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68X357701
Rev. 1 10/03

Preface
This manual functions in two ways: first as a step by step guide to help
you operate the waterproof TN-100/ T-100 turbidimeter; second, it serves
as a handy reference guide.
It contains basic instructions that you must follow during the operation,
care and maintenance of the instrument. The safety protection provided by
this equipment may be impaired if it is used in a manner not described in
this manual. It is recommended that all operators should read this manual
prior to working with this instrument.
Eutech Instruments/ Oakton Instruments cannot accept any responsibility
for damage or malfunction to the meter caused by improper use of the
instrument.
The information presented in this manual is subject to change without
notice as improvements are made, and does not represent a commitment
on the part of Eutech Instruments Pte Ltd/ Oakton Instruments.
Note: Eutech Instruments Pte Ltd/ Oakton Instruments reserves the
right to make improvements in design, construction, and appearance
of our products without notice.
Copyright © 2003 All rights reserved.
Eutech Instruments Pte Ltd
Oakton Instruments
Rev. 1 10/03

TABLE OF CONTENTS
1OVERVIEW .......................................................................................1
1.1 Unpacking TN-100/ T-100 Meter and Accessories 1
1.2 Display 2
1.3 Keys and Functions 3
1.4 Battery Installation 4
2TURBIDITY CALIBRATION..............................................................5
2.1 Calibration Standards 5
2.2 Indexing 5
2.3 Calibration Procedure 6
2.4 Restoring Factory Calibration 8
3TURBIDITY MEASUREMENT.........................................................10
3.1 General Information 10
3.2 Turbidity Measurement Procedure 10
3.2.1Preparation of Sample Vial 11
3.2.2Measurement Procedure 12
3.3 Single-Shot or Continuous Measurement 13
4TROUBLESHOOTING GUIDE........................................................15
5ROUTINE MAINTENANCE.............................................................16
5.1 Vials – Handling, Cleaning and Care 16
6ACCESSORIES...............................................................................17
7SPECIFICATIONS...........................................................................18
8ADDENDUM 1: TURBIDITY ...........................................................19
8.1 Definition 19
8.2 Why Is It Important? 19
8.3 Measurement Principle 19
8.4 Nephelometric Turbidity Units (NTU) 20
8.5 Indexing a Vial 20
9ADDENDUM 2: GUIDE TO GOOD MEASUREMENT TECHNIQUE
21
9.1 Maintain sample vials in good condition 21
9.2 Match Sample Vials 21
9.3 Degassing 21
9.4 Timeliness of Sample 22
9.5 Other Important Sampling Techniques 22
9.6 Calibration 23
9.7 Dilution 23
10 WARRANTY....................................................................................24
11 RETURN OF ITEMS........................................................................24

Instruction Manual TN-100/ T-100
1
1 OVERVIEW
Thank you for selecting the waterproof portable TN-100/ T-100
turbidimeter. The TN-100/ T-100 allows you to measure turbidity of an
aqueous sample in the field. This instrument operates on the
nephelometric principle of turbidity measurement and is designed to meet
the criteria specified in ISO 7027 and DIN 27027 standards (see
Measurement Principle on page 19).
1.1 Unpacking TN-100/ T-100 Meter and Accessories
The table below indicates the items that you should find in your
turbidimeter shipment.
Item Quantity
1. Field Portable TN-100/ T-100 Turbidimeter with 4 “AAA”
batteries
1
2. Instruction Manual 1
3. Instrument Carrying Case 1
4. Light Shield Cap 1
5. Calibration Set (0.02, 20.0,100, 800 NTU Standards) 1
6. Empty Vials 3
7. Plastic bottle (empty – for collecting sample) 1
8. Silicone Oil 1
9. Lint free cloth 1
Remove TN-100/ T-100 turbidimeter from the packing carton. Carefully
inspect all items to ensure that no visible damage has occurred during
shipment. If the items you received do not match your order, please
contact your nearest distributor immediately.
WARNING: Extra care should be taken when
unpacking, opening, and handling the calibration
standards and sample vials. Surface scratches or
finger smudges on the vial surface may cause
measurement errors. Handle these items by their
caps only.
Batteries provided with the meter package are to be installed prior to use.
See Section 1.4 - Battery Installation on page 4.
Figure 1 depicts the meter. The three main components of the instrument
are the sample well, the display, and the keypad. The following sections
will describe the functionality of the display and the keypad. The proper
use of the instrument and the sample well will be discussed in later
sections.

Instruction Manual TN-100/ T-100
2
Sample Vial
Sample Well
Index Mark
Liquid Crystal Display
Keypad
Figure 1: Parts of TN-100/ T-100 Turbidimeter
1.2 Display
All the LCD segments and annunciators that can appear on the display are
shown in Figure 2. The display is used for reporting the turbidity reading
and to provide guidance for the operation of the instrument. In addition,
the display has several other annunciators that are used to communicate
error messages and provide user guidance.
CAL 13 CAL 24
mg/l
NTU
ppm
%pH
TAvg
14-segment Liquid Crystal Display
Battery Indicator
Calibration
Standards
Units of
Measurement
Figure 2: Customized LCD when switched on

Instruction Manual TN-100/ T-100
3
1.3 Keys and Functions
The keypad has five keys: ON/OFF, CAL, ▲, ▼, and READ/ENTER.
Keys Functions
ON/OFF -Powers on and shuts off the meter. With the auto switch-off feature
the meter automatically shuts off 20 minutes after last key press.
CAL -Initiates the calibration mode of the meter. When pressed, the meter
is set to accept the first calibration standard.
-It is also used to exit the calibration mode if the user does not want
to follow the complete calibration procedure.
READ /
ENTER -When in measurement mode, the READ/ENTER key is used to perform a measurement.
-Single-shot measurements: When the key is pressed and released
immediately (a quick key stroke of less than 0.3 seconds), the
display will blink [-Rd-] for 10 times and then display the measured
value.
-Continuous measurements: If the READ/ENTER key is pressed and
held, the instrument will perform a continuous measurement during
which the display is updated every 2 seconds. This can be used for
indexing vials. (This function is not available in calibration mode).
After the READ/ENTER key is released, the instrument will
automatically perform a single-shot measurement.
-When in calibration mode, the READ/ENTER key is used to confirm
the measurement for the calibration standards.
▲and▼-Active only during calibration mode. These keys are used to select
the calibration point in an incremental/ decremental manner.
NOTE: This meter is also fitted with an auto incrementing feature, i.e.
after the successful calibration of one point it auto selects the next
calibration point, or automatically exits the calibration mode after the
fourth calibration point.
READ
ENTER
CAL
OFF
ON
WATERPROOF

Instruction Manual TN-100/ T-100
4
1.4 Battery Installation
Four AAA-sized batteries are included in your meter’s packaging:
1. Use a Philips screwdriver to remove the two screws holding the
battery cover. See Figure 3.
2. Remove the battery cover.
3. Insert the batteries. Follow the diagram inside the cover for correct
polarity.
4. Replace the battery cover onto its original position using the two
screws removed earlier.
5. The meter is now ready to operate.
Philips Screws
Battery cover
Four 'AAA'-sized batteries
Figure 3: Battery Installation
NOTE:
Dispose used batteries in accordance with your local
regulations.

Instruction Manual TN-100/ T-100
5
2 TURBIDITY CALIBRATION
The TN-100/ T-100 turbidimeter was calibrated and tested prior to leaving
the factory. Therefore, it is possible to use the instrument directly out of
the box. However, re-calibration of the instrument is recommended to help
you become familiar with the operation of the instrument and the
calibration procedures. In addition, re-calibration is recommended at least
once every month for optimum accuracy.
It is recommended that you perform a full calibration using all 4 standards
provided to ensure full-range accuracy. However, the TN-100/ T-100
turbidimeter provides flexibility for you to calibrate at selected ranges
suitable for your application.
In addition, the instrument comes with a light shield cap to shield off stray
light during calibration and measurements.
2.1 Calibration Standards
We recommend that you use the following materials during calibration to
achieve the accuracy stated in this manual:
CAL 1: 800 NTU Calibration Standard
CAL 2: 100 NTU Calibration Standard
CAL 3: 20.0 NTU Calibration Standard
CAL 4: 0.02 NTU Calibration Standard
It is well known that diluted Formazin is unstable. If you choose to use
Formazin to calibrate the instrument, ensure that you are using a fresh
stock suspension of Formazin to achieve the accuracy quoted for the
instrument. Calibration standards offered are more stable than Formazin
and have a limited shelf life of 12 months. If you use the supplied
calibration standards to calibrate the instrument, review the expiration date
(indicated on cap label) to ensure that the standards have not expired.
It is important that the calibration standards are not
violently shaken or agitated because air entrapment
in the fluid introduces an error factor during
calibration which subsequently will lead to an
inaccurate measurement.
2.2 Indexing
Due to the high quality of the glass vials provided, indexing is not required.
You only need to align the mark on the vial with the mark on the meter.
However, in order to achieve a better accuracy of the measurement, you
can proceed with indexing of the vials. See Section 8.5 - Indexing a Vial
on page 20 for more information.

Instruction Manual TN-100/ T-100
6
2.3 Calibration Procedure
1. Place TN-100/ T-100 turbidimeter on a flat and level surface.
2. Select the calibration function of the instrument by pressing the CAL
button once. The [CAL] annunciator will blink momentarily and the
meter will prompt for the first calibration standard CAL 1 standard (800
NTU).
3. Insert the CAL 1 standard (800 NTU) into the sample well, aligning the
mark on the vial with the mark on the meter. See Figure 10 on page
12.
4. Press down until the vial snaps fully into the instrument.
5. Cover the vial using the light shield cap.
6. Press READ/ENTER key.
7. The [CAL 1 800 NTU] annunciator will blink for about 12 seconds.
When the instrument has completed calibration for this point, it prompts
you to insert the next calibration standard into the sample well [CAL 2
(100 NTU).
8. Repeat the calibration sequence for each calibration standard.
9. After you successfully calibrate the CAL 4 standard (0.02 NTU), the
display will show [STbY].
10.The meter is now ready to perform next measurement.
Figure 4 shows the complete calibration sequence.
NOTES:
1. If you wish to exit the calibration mode you may
do so at the end of any step by pressing the CAL
key. The meter will accept only the values
calibrated prior to exiting.
2. You can skip a calibration point by pressing ▲or
▼keys and move on to the next calibration point.
3. After a successful calibration of one point, it will
auto select the next calibration point. It will
automatically exit calibration mode after the fourth
calibration point.
4. If an error occurs during calibration, the display
will present an error message. The meter will
abort calibration and return to the measurement
mode without saving the last calibration value.
5. For a list of error messages, refer to Section 4:
Troubleshooting Guide on page 15.

Instruction Manual TN-100/ T-100
7
CAL 1
800 NTU
NTU
CAL 1
NTU
NTU
CAL 3
CAL 3
NTU
CAL 2
NTU
CAL 2
READ
ENTER
NTU
CAL 1
CAL
Place the CAL 1
standard into the
sample well
Place the next CAL
3 standard into the
sample well
Flashes about
5 times
Flashes about 10
times or more
Flashes about 10
times or more
Flashes about 10
times or more
Flashes about 10
times or more
CAL 3
CAL 4
20.0 NTU
0.02 NTU
NTU
NTU
CAL 4
CAL 4
READ
ENTER
READ
ENTER
Place the next CAL
2 standard into the
sample well
Place the next CAL
4 standard into the
sample well
The TN-100/ T-100 meter is now ready
for measurement
CAL 2
100 NTU
READ
ENTER
Figure 4: Calibration Sequence

Instruction Manual TN-100/ T-100
8
2.4 Restoring Factory Calibration
The TN-100/ T-100 turbidimeter allows you to reset the meter back to the
factory default calibration values. This feature is extremely useful when
there are errors in calibration or when you have new calibration standards.
1. With the meter switched off, press ▲and ON/OFF keys simultaneously
for about 2 seconds.
2. The display will flash [URST] (User-Reset) for 2 seconds and show
[No], which is the default value.
3. Use ▲or ▼key to select between [YES] or [No].
[YES] = To restore meter back to factory calibration values
[No] = To retain last calibrated values
4. After selecting [YES] or [No], press READ/ENTER key.
5. The display will flash [--Rd--] 10 times.
6. Once it stops flashing, it will show [--Rd--]. It is now ready to take
turbidity measurements.
Figure 5 shows the sequence for restoring factory calibration values.

Instruction Manual TN-100/ T-100
9
READ
ENTER
READ
ENTER
Press and
keys simultaneously and
hold for 2 seconds before
releasing
UP ON/OFF
[-Rd-] will flash 10 times
The meter is now ready for measurement
Press or key to
select or
UP DOWN
YES No
To restore factory
calibration
To retain last
calibration values
without retrieving
factory calibration.
METER OFF
OFF
ON
Figure 5: Restoring Factory Calibration

Instruction Manual TN-100/ T-100
10
3 TURBIDITY MEASUREMENT
3.1 General Information
The waterproof TN-100/ T-100 turbidimeter allows you to measure the
turbidity of a grab sample. The turbidity is reported in Nephelometric
Turbidity Units (NTU). Readings above 1000 NTU are outside the range of
this instrument.
NOTE:
Before switching on the TN-100/ T-100 turbidimeter,
a sample vial MUST be placed in the sample well.
You can use any of the calibration standards for this
purpose.
The light shield cap provided could be used to cover
the vial during measurements.
The meter will go through a power sequence as shown in Figure 6.
CAL 13CAL 24
mg/l
NTU
ppm
%pH
TAvg
NTU
OFF
ON
"Rd" will flash 10 times
before a reading appears
(assuming you have
placed a vial into the
sample well of the meter
A reading will only appear
if you have placed a vial
or any of the calibration
standards provided into
the sample well.
Otherwise an error
message "Err 8" will
appear.
Figure 6: Power-up sequence
3.2 Turbidity Measurement Procedure
An accurate turbidity measurement depends on good measurement
techniques. Factors such as clean sample vials, positioning of vial in the
sample well, covering the vial with the light shield cap, meter calibration,
handling of meter, and others, have to be taken into consideration. Please
see Section 5.1: Vials – Handling, Cleaning and Care on page 16 and
Section 9: ADDENDUM 2: Guide to Good Measurement Technique on
page 21 for more information.

Instruction Manual TN-100/ T-100
11
3.2.1 Preparation of Sample Vial
1. Grab liquid with the plastic bottle provided.
2. Obtain a clean and dry sample vial (Figure 7).
3. Take care to handle the sample vial by the top.
4. Rinse the vial with approximately 10 ml of the sample
water, capping the vial with the black screw cap and
gently inverting it several times. Discard the used sample
and repeat the rinsing procedure two more times.
5. Fill the rinsed vial with the remaining portion
(approximately 10 ml) of the grab sample up to the
mark indicated in the vial. Cap the vial with the
supplied black screw cap.
6. Wipe the vial with the soft, lint-free cloth supplied. Ensure that the
outside of the vial is dry, clean and free from smudges.
7. Apply a thin film of silicone oil (supplied) on the sample vial (see Figure
9). Wipe with a soft cloth to obtain an even distribution over the entire
vial’s surface.
NOTES:
1. The purpose of oiling the vial is to fill small
scratches and to mask the imperfection in the
glass.
2. Do not apply large quantity of oil as this may
collect dirt and dust.
8. You are now ready to place the vial into the meter for measurement.
Figure 9: Apply a thin film of silicone oil
Figure 7:
Sam
p
le Vial

Instruction Manual TN-100/ T-100
12
3.2.2 Measurement Procedure
1. Place TN-100/ T-100 turbidimeter on a flat and level surface.
2. Place the sample vial inside the sample well and align the vial’s mark
with the meter’s index mark. See below.
A
lign index mark on
the sample vial with
the index mark on
the TN-100/ T-100
turbidimeter and
push till it is fully
snapped in
IMPORTANT :
Place meter on a flat
and level surface.
DO NOT hold it on
hands while operating
the meter. It may lead to
inaccurate readings
Light shield cap for
covering the vial during
measurements
Figure 10: Align sample vial's mark with meter's index mark
3. Push the vial until it is fully snapped in.
4. Cover the vial with the light shield cap.
5. Turn on the meter by pressing the
ON/OFF key.
6. After the power-sup sequence, the
display blinks [--Rd--] for about 12
seconds. See Figure 11.
7. A value will appear. Note the reading.
8. If necessary, please the second sample
vial into the sample well. Remember to
align the vial’s mark with the meter’s
index mark.
9. Press READ/ENTER key. The display
blinks [-- Rd --] and a value will appear.
Note the reading.
10.Repeat steps 2 through 9 for all of your
samples.
Flashes about 10
times
SAMPLE
Unknown
NTU
Place vial
into the
sample well
NTU
READ
ENTER
Measurement mode can start from
either situation:
1. [STbY] after calibration;
2. After powering up the meter
Figure 11: Reading turbidity
value

Instruction Manual TN-100/ T-100
13
NOTE:
1. NEVER pour liquid directly into the sample well of
the instrument. Always use a vial. The instrument
will only accurately measure the turbidity of a
sample when vials sealed with the black caps are
used. The black cap serves as both seal and a
light shield.
2. NEVER attempt to clean the sample well. The
optics may be damaged.
3. The instrument will automatically power off 20
minutes after the last key press for battery
conservation.
3.3 Single-Shot or Continuous Measurement
You can use TN-100/ T-100 turbidimeter to take a single reading or
perform continuous measurement. The latter is only used for indexing the
vials. See Section 8.5 - Indexing a Vial on page 20 for more information.
For single-shot measurement:
1. Make sure the meter is sitting on a flat
and level surface and is in measurement
mode. The display shows the last
measured value or [STbY] after exiting
calibration mode.
2. Place sample vial in the sample well.
3. Cover the vial with the light shield cap.
4. Press READ/ENTER key and release
immediately (<0.3 seconds). See Figure
12.
5. The display will blink [--Rd--] for 10 times
or more and then display the measured
value.
Press key and release
immediately
SAMPLE
Unknown
NTU
Place vial
into the
sample well
NTU
READ
ENTER
Flashes about 10
times
Figure 12: Single-shot measurement

Instruction Manual TN-100/ T-100
14
For continuous measurement:
1. Make sure the meter is sitting on a flat and level surface and is in
measurement mode. The display shows the last measured value or
[STbY].
2. Place the sample vial in the sample well.
3. Press READ/ENTER key and hold. See Figure 13.
4. Wait for the reading to stabilize before rotating the sample vial.
NOTE:
During continuous measurement, the display is
updated every 2 seconds. The displayed reading
may not be the actual turbidity value. For accurate
measurement, use single-shot measurement.
5. You can rotate the sample vial for
indexing purpose. See Section 8.5 -
Indexing a Vial on page 20 for more
information.
6. Once you release the READ/ENTER
key, the meter will automatically
perform a single-shot measurement.
NOTES:
1. After a measurement is completed and the
display is updated, a 4-second recovery time
occurs before the meter can perform another
function. If any key is pressed during the recovery
time, the meter will perform the corresponding
action at the end of the recovery period.
2. When performing a measurement, if the meter
detects stray light exceeding the amount
equivalent to 0.02 NTU in the low range, the
measurement is immediately aborted and an
error message [ERR 8] is displayed. Ensure the
vial sits properly into the sample well. Press the
ENTER/READ key to re-do the measurement.
SAMPLE
Unknown
NTU
Place vial
into the
sample well
Press and hold
NTU
READ
ENTER You can turn
the vial for
indexing
Figure 13: Continuous
measurement

Instruction Manual TN-100/ T-100
15
4 TROUBLESHOOTING GUIDE
The TN-100/ T-100 turbidimeter routinely performs self-diagnostics, and
will automatically generate messages to provide you with specific
diagnostic information. These messages are for your use and do not
indicate a reduction in the performance of the instrument or a failure of any
component in the instrument, unless otherwise stated in this list.
LCD
Message Description Corrective Actions
ERR 1
Calibration Error. The meter is
unable to recognize the 800 NTU
Calibration Standard.
Ensure to use the correct 800
NTU calibration standard. *
ERR 2
Calibration Error. The meter is
unable to recognize the 100 NTU
Calibration Standard.
Ensure to use the correct 100
NTU calibration standard. *
ERR 3
Calibration Error. The meter is
unable to recognize the 20.0 NTU
Calibration Standard.
Ensure to use the correct 20.0
NTU calibration standard. *
ERR 4
Calibration Error. The meter is
unable to recognize the 0.02 NTU
Calibration Standard.
Ensure to use the correct 0.02
NTU calibration standard. *
ERR 5
Calibration Error. There is not
sufficient signal to achieve the
appropriate resolution in the 0-
1000NTU range.
Re-do calibration with all 4
standards provided. *
ERR 6
General Calibration Failure. There
is not sufficient signal to achieve
the appropriate resolution in the 0-
100NTU range.
Re-do calibration with all 4
standards provided. *
ERR 7
General Calibration Failure. There
is not sufficient signal to achieve
the appropriate resolution in the 0-
20 NTU range.
Re-do calibration with all 4
standards provided. *
Excessive stray light detected. Ensure the vial is fully snapped
in the sample well.
ERR 8 Attempting a measurement when
low battery indicator is on.
Replace batteries.
ERR 9 Lamp Failure. Return unit.
Or When Turbidity value is above the
measurement range(>1000NTU)
Dilute sample. See Section 9.7
on page 23.
Low battery indication. The
batteries need to be replaced.
Replace batteries.
* If an error message appears, take the
appropriate corrective action and re-do the
desired procedure. If the problem persists,
contact Eutech Instruments or your dealer.
See Sections on Warranty and Return of Items on page 24.

Instruction Manual TN-100/ T-100
16
5 ROUTINE MAINTENANCE
The supplied carrying case is optimal for protecting the instrument. If you
do not plan on leaving the instrument in the supplied carrying case, when
not in use, ensure that the instrument has been turned off and that a clean
sample vial fitted with a black cap has been placed in the sample well.
This will ensure that a minimal amount of dust and/or debris will be able to
settle on the optics of the instrument.
5.1 Vials – Handling, Cleaning and Care
Proper measurement of the turbidity of a sample requires the use of a vial
that is free of marks, smudges, scratches and any bacterial growth.
Therefore, sample vials must be handled with absolute care to avoid
contamination or damage, which might change the optical characteristics
of the glass. Scratches, fingerprints, and water droplets on the sample vial
or inside the sample well can cause stray light interference leading to
inaccurate readings.
Cleaning the vial is accomplished by washing the interior and exterior of
the vial in a detergent solution. Once cleaned, the vial should be rinsed
thoroughly 8 to 10 times with clean distilled water to eliminate the
possibility of detergent buildup and streaking.
Vials can also be acid washed periodically and coated with a special
silicone oil to fill small scratches and mask the imperfections in the glass.
Since the silicone oil required for this application should have the same
refractive characteristics as glass, it is recommended that the oil be
obtained from us. Care should be taken not to apply excessive oil that
could attract dirt or contaminate the sample well of the meter. Once the oil
has been applied to the vial, the excess oil should be removed with a lint-
free cloth. The result should be a sample vial surface with a dry
appearance, but with all imperfections filled with oil.
Sample vials should always be handled from the top or by the cap to avoid
fingerprints or smudges. After a vial has been filled with a sample and
capped, the outside surface should be wiped with a clean, lint-free
absorbent cloth until it is dry. Cleaned and dried vials should be stored
with the black caps on. The vials can be stored in the carrying case.
During normal operation you may use any typical glass cleaner along with
a lint free cloth or tissue (Kimwipes®), to clean the outside of the vials.
Condensation may appear on the vial when your sample is very cold and
the relative air humidity is high. When this happens, the turbidity that you
read may be higher than the actual turbidity due to the light scattered by
the condensate on the vial. If you find yourself in this circumstance, you
can alleviate the problem by either coating the vial with an anti-fogging
agent, or by running warm water over the vial for a short period of time to
warm the sample prior to measurement.

Instruction Manual TN-100/ T-100
17
6 ACCESSORIES
The items shown below are recommended accessories and replacement
parts for the instrument.
Item Description Eutech
Instruments
Order Code.
Oakton
Instruments
Order Code.
Waterproof TN-100/ T-100 portable
turbidimeter with set of 4 calibration
standards (800, 100, 20.0 & 0.02 NTU),
set of 3 sample vials, lint-free cloth,
silicone oil, batteries – all in a rugged
carrying case.
EC-TN100 35635-00
Calibration Set for normal operation
(includes 800, 100, 20.0 & 0.02 NTU
Standards)
ECTN100CALKT 35635-50
Sample Vials – pack of 3 vials ECTN100CUVKT 35653-55
Silicone Oil – 10ml ECSILICONEOIL ~
To order any accessory or replacement part, please contact your nearest
distributor or Eutech Instruments/ Oakton Instruments.