ProMinent DULCOMETER FLEP 010 SE Mode D'emploi page 5

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 may only be used to determine the fluoride ion activity in drinking water and other clear waters
which conform to the specifications in "Technical data".
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.
Assembly
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 Dosiertechnik GmbH! 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 FP V1 or FP 100 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!
• Observe 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.
300
250
200
150
100
50
0
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
FP 100 V1
4-20 mA FP V1
. The
s
is called
s