MiPNet19.01
B: OroboPOS service
22
OROBOROS INSTRUMENTS
OROBOROS Oxygraph-2k
The response time of the sensor signal may remain high with a
biphasic pattern (exponential phase followed by a slow drift) even after
polishing and cleaning with ammonia. Repeat the cathode/anode cleaning
cycle several times.
2.3. Cleaning of the electrical connection
Unscrew the POS head and inspect both sides of the electrical connection
(gold pin and threads). Remove any contamination such as grease and
moisture with a fine paper cloth. If necessary, wash with distilled water and
then with pure alcohol, and apply contact oil from the OroboPOS-Service kit
to the connections. Before screwing the POS head onto the POS connector
used for membrane application, clean the POS connector of moisture and
any other contamination (particularly any salt crystals from the electrolyte).
Similarly, clean the electrical cable connection to the O2k-Main Unit.
3.
Membrane mounting
For mounting a new membrane, the POS head is screwed on the sensor
connector. Check the O-ring on the POS head to ensure that it fits properly
and its surface is smooth and intact. You may apply a tiny amount of
grease to the O-ring of the sensor head (Fig. 2). Rinse the mounting tool
(OroboPOS service kit) with distilled water to wash off any electrolyte
crystals (Fig. 4).
As electrolyte, use KCl solution (1 mol∙dm
-3
; 74.56 g potassium
chloride per litre, in distilled water). Add distilled water to the electrolyte
powder (Fig. 1) up to the 10 ml mark. Alternatively, dissolve 1.49 g KCl in
distilled water with a total volume of 20 ml. Store at room temperature or
4 °C in a closed bottle. To prevent the formation of gas bubbles in the
electrolyte, heat the electrolyte solution by shaking the sealed electrolyte
container in hot water (40-70 °C) before filling the electrolyte reservoir of
the POS.
POS membranes are contained in a small box (Fig. 1, item 6). They
are fully transparent. Each membrane is separated by a non-transparent
white paper sheet. Do not add the paper to the oxygen sensor. Separate
the membrane from the paper sheets, carefully avoiding any mechanical
damage of the transparent membrane. Do not touch the central area of the
membrane with your fingers. The pair of forceps is used for separating the
membrane and positioning a new membrane into the membrane guide of
the POS mounting tool (Fig. 4 [1]).
Fix the PEEK membrane ring (which seales the membrane against the
sensor body) to the membrane ring holder (Fig. 4 [2]). With the POS head
filled with electrolyte, slide the membrane guide down the POS connector,
and move the lower ring on the POS connector down to bring the
membrane guide into a fixed position (Fig. 4 [3]). Then slide the membrane
ring holder into the membrane guide and press firmly down to slide the
PEEK membrane ring over the POS head (Fig. 4 [4]).
