wtw SenTix 950 User manual

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SenTix®950
SenTix®980
pH combination electrodes with refillable
liquid reference system
Operating manual

SenTix
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Note
The latest version of the present operating manual can be found on the
Internet under www.WTW.com.
Copyright ©Weilheim 2009, WTW GmbH
Reprinting - even as excerpts - is only allowed with the explicit written
authorization of WTW GmbH, Weilheim.
Printed in Germany.

SenTix General information
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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 communi-
cation 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 SenTix
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Technical data
General data
Measurement and application characteristics
Shaft dimensions, shaft material, electrical connection
Connection cable
Accuracy of the IDS measuring technique
WTW model Reference electrolyte Junction NTC Special features
SenTix®950 KCl 3 mol/L, Ag+free Ceramic Yes Plastic shaft
SenTix®980 KCl 3 mol/L, Ag+free Platinum Yes
WTW model pH measuring range Allowed temperature
range
SenTix®950 0.000 ... 14.000 0 ... 80 °C (32 ... 176 °F)
SenTix®980 0.000 ... 14.000 0 ... 100 °C
(32 ... 212 °F)
WTW model Membrane resistance
at 25 °C Typical application
SenTix®950 < 1 GOhm Field
SenTix®980 < 600 MOhm Laboratory
WTW model Shaft Electrical connection
Length
[mm] Ø[mm] Material Electrode
connection Meter con- nection Cable length
SenTix®950 120 12 Polyamide Fixed cable Digital plug 1.5 m
SenTix®980 120 12 Glass Fixed cable Digital plug 1.5 m
Diameter 4.3 mm
Smallest allowed bend radius Fixed installation: 20 mm
Flexible use: 60 mm
Plug type Socket, 4 pins
Measured parameter Accuracy (± 1 digit)
pH ± 0.004
U [mV] ± 0.2
T [°C] ± 0.1

SenTix Commissioning, measuring, calibration
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Commissioning, measuring, calibration
Commissioning The electrode is filled with reference electrolyte solution in the factory. Pre-
pare the electrode for measuring as follows:
zOpen the refilling opening for the reference electrolyte solution. Depend-
ing on the model, the stopper of the refilling opening is an elastomer stop-
per or a slider.
The refilling opening must always be open during calibration and
measurement!
zRemove 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.
zSenTix®950: Remove any gas bubbles behind the pH membrane by
shaking.
zConnect the electrode to the meter.
zCalibrate the electrode according to the operating manual of the meter
and observe the following rules while doing so:
Calibration
and measurement:
General rules
zMake sure the refilling opening for the reference electrolyte solution is
open.
zAvoid 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 wa-
ter and then carefully dab it dry.
zImmerse the electrode in the solution in a vertical or slightly tilted position.
Make sure the immersion depth is correct. The junction must be complete-
ly 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-
Refilling
opening
Refilling
opening

Storage SenTix
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trolyte in the electrode must be at least 2 cm above the level of the solu-
tion.
zProvide 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 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
During short
measuring breaks With the refilling opening open, 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
Prevent contact of the pH membrane to the beaker bottom to avoid scratches
on the pH membrane.
Overnight or
longer Put the clean electrode in the watering cap that is filled with reference electrolyte (KCl 3 mol/L, Ag+free) and close the refilling opening.
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.
Junction
Referenceelectrolyte
(Example)
Glass membrane
Shaft

SenTix Aging
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Note
During longer storing periods, salt sediments may develop on the watering
cap. They do not affect the measuring characteristics and can easily be re-
moved with deionized water when the electrode is put into operation again.
Aging
Every pH electrode undergoes a natural aging process. With aging, the re-
sponding behavior becomes slower and the electrode slope and asymmetry
change. Moreover, extreme operating conditions can considerably shorten
the lifetime of the electrode. These are:
zStrong acids or lyes, hydrofluoric acid, organic solvents, oils, fats, bro-
mides, sulfides, iodides, proteins
zHigh temperatures
zHigh changes in pH and temperature.
The warranty does not cover failure caused by measuring conditions and
mechanical damage.
Maintenance and cleaning
Refilling the
reference
electrolyte
During operation, a small amount of reference electrolyte leaks through the
junction from the electrode into the test sample. If the level of reference elec-
trolyte becomes too low with time, refill it through the refilling opening. Refill-
ing is very easy with the enclosed dropping bottle. Proceed as follows:
zCut off the tip of the dropping bottle at a right angle until the opening in the
tip can be seen
zOpen the refilling opening of the electrode
zPress the tip of the dropping bottle into the refilling opening while turning
it slightly
zPump the reference electrolyte in the shaft using the dropping bottle
zPull the dropping bottle out of the refilling opening while turning it slightly
as necessary.

Maintenance and cleaning SenTix
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Cleaning Remove water-soluble contamination by rinsing with deionized water. Re-
move other contamination as follows:
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.
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 solu-
tion.

SenTix Wear parts and accessories
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Wear parts and accessories
Note
Detailed information on our wide range of buffer solutions and more acces-
sories is given in the price list of the WTW catalog "Laboratory and field in-
strumentation".
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.
Description Model Order no.
Reference electrolyte solution 250 mL
(KCl 3 mol/L, Ag+free)
KCl-250 109 705
Pepsin cleaning solution 3 x 250 ml PEP/pH 109 648

Disposal SenTix
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