PROBE & MEMBRANE MAINTENANCE
The oxygen probe body is made of reinforced
plastic for maximum durability.
A thermistor temperature sensor provides tem-
perature measurements of the sample tested. It
is always recommended that the protective cap
be kept on the probe when the probe is not in use
to provide protection against damage and dirt.
To replace the membrane or refill with electro-
lyte, proceed as follows:
•
Remove the protective cap
by gently twisting and pull-
ing it off the body of the
probe (see fig. 1).
•
Unscrew the membrane
by turning it counter-
clock-wise with the other
hand (see fig. 2)
•
Wet the sensor by soak-
ing the bottom 2½ cm (1")
of the probe in electrolyte
(HI 7041S) for 5 minutes.
•
Rinse the new membrane
(HI 76407A) supplied with
the meter with electrolyte
while shaking it gently.
Refill with clean electro-
lyte.
•
Gently tap the sides of the
membrane with your fin-
ger tip to ensure that no
air bubbles remain
trapped. Do no directly
tap the bottom with your
finger as this will damage
the membrane.
TWIST
AND
PULL
fig. 1
UNSCREW
fig. 2
11
SALINITY COMPENSATION
The table below shows the influence of salt in
the measurement of oxygen.
In HI 9142 all the readouts are referred to 0 g/l
of salinity value. In fact, salinity affects D.O.
concentration decreasing its value.
For your reference the table below reports the
oxygen solubility at various temperatures and
salinity. From the table you can calculate the
quantity to be subtracted to correct your read-
ing.
35 g/l
9.0
8.6
8.3
8.0
7.6
7.4
7.1
6.9
6.6
6.4
30 g/l
9.3
8.9
8.6
8.2
7.9
7.6
7.3
7.1
6.8
6.6
°C
10
12
14
16
18
20
22
24
26
28
0 g/l
11.3
10.8
10.3
9.9
9.5
9.1
8.7
8.4
8.1
7.8
10 g/l
10.6
10.1
9.7
9.3
8.9
8.5
8.2
7.9
7.6
7.4
20 g/l
9.9
9.5
9.1
8.7
8.4
8.0
7.8
7.5
7.2
7.0
°F
50.0
53.6
57.2
60.8
64.4
68.0
71.6
75.2
78.8
82.4
Salinity (g/l) at Sea Level
10
