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ProMinent FLE 010 SE Notice D'utilisation page 5

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About this sensor
The sensor (potentiometric ion-selective electrode, ISE) consists of a shaft with SN6 thread, a Ag/AgCl
lead passed through a silicon seal, an internal electrolyte and a lanthanum fluoride crystal pasted into the
lower shaft end serving as ion-selective solid-state membrane. The sensor has no integrated reference
system.
The sensor shall be used only for the determination of the fluoride-ion activity in potable water which meets
the specifications in the "Technical data" section given below.
Transport and storage
ATTENTION
• The sensor must not be stored in distilled/de-ionized water!
• The sensor must be transported only in its own container!
Storage temperature: 1...50 °C
Humidity: max. 90 % relative humidity, no condensation
Storage time: max. 6 months
When stored more than a week: store sensor dry in its own container.
When stored less than a week: store the sensor in a fluoride solution with F - ≥ 1 ppm at a pH value
between 5 and 9.
Assembling
ATTENTION
• The LaF
crystal must not be soiled! For cleaning cf. "Cleaning".
3
• The LaF
crystal must not be scratched or touched by hand!
3
• When screwing-on the measuring transducer, always hold the sensor by its head - never on
the shaft!
• When dipping the sensor into the measuring water take care that no gas bubbles adhere to
the LaF
crystal!
3
Unscrew the blanking cap on the measuring vessel DLG IV, screw down the sensor and fasten it using a
17 mm spanner.
Screw down the reference electrode REFP-SE (part no.1018458) into the adjacent opening of the
DLG IV.
For measurements with automatic temperature correction, screw down a Pt 100 into one of the remaining
openings.
Installation
ATTENTION
Before using a potential compensation pin, contact ProMinent! Otherwise the sensor can be
damaged irreversibly.
Make sure that the SN6-contacts on the sensor and the transducer resp. are clean and dry.
Screw down the transducer 4 ... 20 mA F V1 onto the sensor by hand.
Screw down the SN6 plug of the transducer measuring cable onto the reference electrode.
Run-in time of the sensor
Allow the sensor to run in for 1 h at minimum 0.4 ppm F - .
Calibration
ATTENTION
• The sensor must be checked regularly and if necessary calibrated!
• Oserve legal requirements in force!
• Before the first calibration the sensor must be run in!
• Obey the instruction manual of the measuring instrument!
• Carry out a two-point calibration at first start-up!
For calibration the sensor, the reference electrode and - if present – the Pt 100 must be immersed in the
calibration solution. During calibration the solution must be uniformly stirred by a magnetic stirrer. For faster
potential equilibration the solution must have a conductivity > 1000 µS/cm (e.g. by using a corresponding
Na
SO
solution, e.g., 1 g/L).
2
4
For the determination of the slope (two-point calibration) the two calibration solutions must differ in their
fluoride content by at least 0.5 ppm.
The two-point calibration has to be performed less often than the one-point calibration.
NERNST's law E = E
s
fluoride-ion activity a(F - ) (cf. figure). At low concentrations holds: activity = concentration. The semi-
logarithmic plot results in a straight line with the angular coefficient S and the y axis intercept E
angular coefficient S is called the slope. Ideally at 25 °C the slope S = -59.16 mV/dec (a decade of
concentration corresponds to a concentration change by a factor of 10). The y axis intercept E
the standard potential of the couple sensor – reference electrode. The measuring instrument needs both
values for the calculation of the fluoride concentration from the measured potential. The one-point
calibration gives the y axis intercept while the two-point calibration yields both values.
250
200
150
100
50
0
- 50
0,01
Fluoride concentration c (ppm)
+ S lg a(F - ) shows a logarithmic relation between the measured potential E and the
S
E
s
0,1
1
10
100
1000
Measuring range
®
DULCOTEST
measuring transducer
4-20 mA F V1
. The
s
is called
s

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