SenTix® 950
SenTix® 980
pH combination electrodes with refillable
liquid reference system
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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.
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Copyright © Weilheim 2009, 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.
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Technical data SenTix
Technical data
General data
WTW model Reference electrolyte Junction NTC Special features
SenTix
SenTix
WTW model pH measuring range Allowed temperature
SenTix
SenTix
®
950 KCl 3 mol/L, Ag+ free Ceramic Yes Plastic shaft
®
980 KCl 3 mol/L, Ag+ free Platinum Yes
Measurement and application characteristics
range
®
950 0.000 ... 14.000 0 ... 80 °C (32 ... 176 °F)
®
980 0.000 ... 14.000 0 ... 100 °C
(32 ... 212 °F)
WTW model Membrane resistance
Typical application
at 25 °C
SenTix
SenTix
®
950 < 1 GOhm Field
®
980 < 600 MOhm Laboratory
Shaft dimensions, shaft material, electrical connection
WTW model Shaft Electrical connection
SenTix
SenTix
Length
[mm]
®
950 120 12 Polyamide Fixed cable Digital plug 1.5 m
®
980 120 12 Glass Fixed cable Digital plug 1.5 m
Ø [mm] Material Electrode
connection
Meter connection
Connection cable
Diameter 4.3 mm
Smallest allowed bend radius Fixed installation: 20 mm
Flexible use: 60 mm
Plug type Socket, 4 pins
Cable
length
Accuracy of the IDS measuring technique
Measured parameter Accuracy (± 1 digit)
pH ± 0.004
U [mV] ± 0.2
T [°C] ± 0.1
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SenTix Commissioning, measuring, calibration
Refilling
opening
Refilling
opening
Commissioning, measuring, calibration
Commissioning The electrode is filled with reference electrolyte solution in the factory. Pre-
pare the electrode for measuring as follows:
z Open the refilling opening for the reference electrolyte solution. Depend-
ing on the model, the stopper of the refilling opening is an elastomer stopper or a slider.
The refilling opening must always be open during calibration and
measurement!
Calibration
and measurement:
General rules
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 SenTix
®
950: Remove any gas bubbles behind the pH membrane by
shaking.
z Connect the electrode to the meter.
z Calibrate the electrode according to the operating manual of the meter
and observe the following rules while doing so:
z Make sure the refilling opening for the reference electrolyte solution is
open.
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.
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– 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 Immerse the electrode in the solution in a vertical or slightly tilted position.
Make sure the immersion depth is correct. The junction must be completely submersed in the solution. The junction is in the area of the bottom end
of the shaft (see figure). At the same time, the level of the reference elec-
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Storage SenTix
Junction
Referenceelectrolyte
(Example)
Glass membrane
Shaft
trolyte in the electrode must be at least 2 cm above the level of the solution.
z Provide approximately the same stirring conditions for measuring as for
calibrating.
Note
Prevent contact of the pH membrane to the beaker bottom to avoid scratches
on the pH membrane.
Subsequent
calibrations
During short
measuring breaks
Overnight or
longer
The frequency of subsequent calibrations depends on the application. The
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
With the refilling opening open, immerse the electrode in reference
electrolyte (KCl 3 mol/L, Ag
rinse the electrode with the test sample or deionized water.
Note
Prevent contact of the pH membrane to the beaker bottom to avoid scratches
on the pH membrane.
Put the clean electrode in the watering cap that is filled with reference
electrolyte (KCl 3 mol/L, Ag
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,
+
free) for at least 24 hours.
Ag+
+
free). Prior to the next measurement, shortly
+
free) and close the refilling opening.
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SenTix Aging
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, 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.
Refilling the
reference
electrolyte
Maintenance and cleaning
During operation, a small amount of reference electrolyte leaks through the
junction from the electrode into the test sample. If the level of reference electrolyte becomes too low with time, refill it through the refilling opening. Refilling is very easy with the enclosed dropping bottle. Proceed as follows:
z Cut off the tip of the dropping bottle at a right angle until the opening in the
tip can be seen
z Open the refilling opening of the electrode
z Press the tip of the dropping bottle into the refilling opening while turning
it slightly
z Pump the reference electrolyte in the shaft using the dropping bottle
z Pull the dropping bottle out of the refilling opening while turning it slightly
as necessary.
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Maintenance and cleaning SenTix
Cleaning Remove water-soluble contamination by rinsing with deionized water. Re-
move other contamination as follows:
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)
Proteins Immerse in pepsin cleaning solution PEP/pH
for approx. 1 hour.
Note:
Make sure the level of the reference
electrolyte is above that of the cleaning solution.
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.
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SenTix Wear parts and accessories
Wear parts and accessories
Description Model Order no.
Reference electrolyte solution 250 mL
(KCl 3 mol/L, Ag
Pepsin cleaning solution 3 x 250 ml PEP/pH 109 648
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
Disposal
When the electrode is at the end of its operational lifetime, please dispose of
it as electronic waste and not with unsorted municipal waste. It is illegal to
dispose of it with the household refuse.
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Disposal SenTix
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