SenTix® 940
SenTix® 940-3
SenTix® F900
SenTix® F 900-3
pH electrode with gel electrolyte
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Operating manual
SenTix
Note
The latest version of the present operating manual can be found on the
Internet under www.WTW.com.
10
Copyright © Weilheim 2010, WTW GmbH
Reprinting - even as excerpts - is only allowed with the explicit written
authorization of WTW GmbH, Weilheim.
Printed in Germany.
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SenTix General information
General information
Automatic sensor
recognition
The sensor electronics with the stored sensor data is in the connecting head
of the electrode. The data include, among other things, the sensor type and
series number. With each calibration, the calibration data is written in the
sensor and the calibration history is recorded. The data is recalled by the
meter when the sensor is connected and is used for measurement and for
measured value documentation. Storing the calibration data in the sensor
ensures that the correct slope and asymmetry are automatically used if the
sensor is operated with several meters.
The digital transmission technique guarantees the failure-free communication with the meter even with long connection cables. If the sensor firmware
is enhanced by WTW, it can be updated via the meter.
Technical Data
General data
WTW Model Reference
elektrolyte
SenTix
SenTix
SenTix
SenTix
®
940 Gel Fiber Yes Plastic shaft
®
940-3 Gel Fiber Yes Plastic shaft
®
F 900 Gel Fiber Yes geringe Temperaturempfindlichkeit,
®
F 900-3 Gel Fiber Yes geringe Temperaturempfindlichkeit,
Junction NTC Special fatures
Iod/Iodid-Referenzsystem
Iod/Iodid-Referenzsystem
Measurement and application characteristics
WTW model pH measuring range Allowed
temperature
range
SenTix
SenTix
SenTix
SenTix
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®
940 0.000 ... 14.000 0 ... 80 °C < 1 GOhm Field
®
940-3 0.000 ... 14.000 0 ... 80 °C < 1 GOhm Field
®
F 900 0.000 ... 14.000 0 ... 80 °C < 1 GOhm Field
®
F 900-3 0.000 ... 14.000 0 ... 80 °C < 1 GOhm Field
Membrane
resistance at
25 °C
Typical application
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Commissioning, measuring, calibration SenTix
Shaft dimensions, material, electrical connection
WTW model Shaft Electrical connection
Length
[mm]
Ø [mm] Material Combination
electrode
Meter connection
Cable
length
connection
SenTix
SenTix
SenTix
SenTix
®
940 120 12 PPE/PS Fixed cable Digital plug 1.5 m
®
940-3 120 12 PPE/PS Fixed cable Digital plug 3 m
®
F 900 120 12 COC Fixed cable Digital plug 1.5 m
®
F 900-3 120 12 COC Fixed cable Digital plug 3 m
Connection cable
Diameter 4.3 mm
Smallest allowed
bend radius
Plug type Socket, 4 pins
Fixed installation: 20 mm
Flexible use: 60 mm
Accuracy of the IDS measuring technique
Measured parameter Accuracy (± 1 digit)
pH ± 0,004
U [mV] ± 0,2
T [°C] ± 0,1
Commissioning, measuring, calibration
Commissioning Prepare the electrode for measuring as follows:
z Remove the watering cap from the electrode tip. Possible salt deposits in
the area of the watering cap do not affect the measuring characteristics
and can easily be removed with deionized water.
Note
Please keep the watering cap. It is required for the electrode to be stored.
Always keep the watering cap clean.
z Remove any gas bubbles behind the pH membrane by shaking.
z Connect the electrode to the meter.
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z Calibrate the electrode according to the operating manual of the meter
and observe the following rules while doing so:
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SenTix Storage
Calibration
and measurement:
General rules
z Avoid the carryover of any solution (sample or buffer solution) from one
measurement to the next by taking the following measures:
– Shortly rinse the calibration and sample beakers with the solution the
beakers are to be filled with next.
– Between measurements, rinse the electrode with the solution that fol-
lows. Alternatively, you can also rinse the electrode with deionized water and then carefully dab it dry.
z To measure in aqueous solutions, it is recommended to immerse the elec-
trode in a vertical or slightly tilted position.
z Observe the correct depth of immersion and make sure the contact be-
tween the junction and test sample is thorough. The junction is in the area
of the bottom end of the shaft (see arrow).
Subsequent
calibrations
During short
measuring breaks
SenTix
SenTix
®
940
®
F900
Caution: Only the shaft part of the combination electrode may be immersed!
z For measurements in aqueous solutions, provide approximately the same
stirring conditions for measuring as for calibrating.
The frequency of subsequent calibrations depends on the application. Many
meters provide an option where you can enter a calibration interval. After the
calibration interval has expired, the meter will automatically remind you of the
due calibration.
Storage
Immerse the electrode in reference electrolyte (KCl 3 mol/L, Ag+ free). Prior
to the next measurement, shortly rinse the electrode with the test sample or
deionized water.
Note
Do not scratch the pH membrane.
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Aging SenTix
Overnight or
longer
Put the clean electrode in the watering cap that is filled with reference
+
electrolyte (KCl 3 mol/L, Ag
free).
Note
pH electrodes must not be stored dry or in deionized water. The electrode
could be permanently damaged by this. If the liquid in the watering cap has
dried up, condition the electrode in reference electrolyte (KCl 3 mol/L, Ag+
free) for at least 24 hours.
Note
During longer storing periods, salt sediments may develop on the watering
cap. They do not affect the measuring characteristics and can easily be removed with deionized water when the electrode is put into operation again.
Aging
Every pH electrode undergoes a natural aging process. With aging, the responding behavior becomes slower and the electrode slope and asymmetry
change. Moreover, extreme operating conditions can considerably shorten
the lifetime of the electrode. These are:
z Strong acids or lyes, hydrofluoric acid, organic solvents, oils, fats, bro-
mides, sulfides (except for SenTix
®
F 900), iodides, proteins
+
z High temperatures
z High changes in pH and temperature.
The warranty does not cover failure caused by measuring conditions and
mechanical damage.
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SenTix Maintenance and cleaning
Maintenance and cleaning
Cleaning Remove water-soluble contamination by rinsing with deionized water. Other
types of contamination have to be removed as follows while the contact time
with the detergents should be kept as short as possible:
Contamination Cleaning procedure
Fat and oil Rinse with water containing household wash-
ing-up liquid
Lime and hydroxide deposits Rinse with citric acid (10 % by weight)
Note
Hydrofluoric acid, hot phosphoric acid and strong alkaline solutions destroy
the glass membrane.
After cleaning Rinse the electrode with deionized water and condition it in reference
electrolyte solution for at least 1 hour. Then recalibrate the electrode.
Wear parts and accessories
Description Model Order no.
Reference electrolyte solution 250 ml
to fill the watering cap
(KCl 3 mol/l, Ag
Note
Detailed information on our wide range of buffer solutions and more accessories is given in the price list of the WTW catalog "Laboratory and field instrumentation".
+
-free)
KCl-250 109 705
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Wear parts and accessories SenTix
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