WPI APOLLO 4000, Instruction Manual

Page: 44 / 74

APOLLO 4000
NITRIC OXIDE DETECTION
WORLD PRECISION INSTRUMENTS C-20
Maintenance of NO Sensors
The various NO sensors, if well cared for, will require very little maintenance.
Maintenance of the ISO-NOP
When the ISO-NOP sensor is not being used it should be left connected to the
APOLLO 4000 in ON position (or to Pre-Polarizer NSA-1 , NSA-2 or NSA-3 ) with the
tip suspended in distilled water. The basic structure of the ISO-NOP sensor is quite
simple (see
Fig. C6
). It consists of an internal NO-sensing working/counter
electrode combination. This electrode fits inside a disposable protective stainless
steel sleeve (WPI # 5436 ) which must contain fresh electrolyte (WPI # 7325 ), and is
separated from the external environment by a gas permeable polymeric membrane
covering the end of the stainless sleeve. The other end of the sleeve is flanged.
The locking cap is used to attach the sleeve to the probe handle.
When the sensor is fully assembled ( i.e., with locking cap and sleeve in place) the
internal electrode should be seen to press gently against the polymeric membrane,
which will then be slightly stretched. This ensures that the electrolyte diffusion layer
will be as thin as possible, which is necessary to minimize sensor response time.
Once a membrane is stretched it is permanently deformed and cannot usually be
reused if the sleeve is removed from the electrode. Four additional membrane
sleeves accompany the ISO-NOP in the start-up kit, together with a MicroFil™
electrolyte filling needle (WPI # MF28G67-5 ) and 1 mL syringe. Additional sleeves
combination
working / counter
electrode
probe
handle
stainless steel
sleeve
gas permeable
membrane
connection
to meter
locking cap
Figure C6 —
Basic probe
structure of ISO-
NO sensor