Wtw SenTix 950 Manual de usuario

ba75843e01 08/2009

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.

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

16 ba75843e01 08/2009

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

20 ba75843e01 08/2009

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