1.0 Objective:
To provide written
procedure for the operation of DO Meter.
2.0 Scope:
This SOP covers
operation of DO Meter in Environment Department.
3.0 Responsibility:
Jr. Research Officer, Research Officer: Responsible for operation,
calibration and maintenance of the instrument as per procedure.
QA Officer / QA
Manger: Review the records and governing the documents.
3.0 Dissolved Oxygen (DO) Measurements:
3.1 ON/OFF : This switch is used to switch ON the
instrument at the time of use.
It should be switched OFF when not in use.
3.2 SET ZERO :
This is used for setting 000 on the display when electrode is put
in sodium sulphite solution.
3.3 Temp. ºC. :
The knob is kept at a position equivalent to the temp of the
solution. It compensates for the variation of temperature.
3.4 CAL
standard solution.
4.0 DO Probe Assembly:
DO Probe consists
of a silver and gold Electrode cells and an electrolyte tube with a ring.
The following
procedure may be followed for assembly of DO Probe.
4.1
Place one membrane on the lower
part of the electrolyte tube. Be careful to handle
its membrane.
4.2
Fix the ring on the electrolyte
tube covering the sides of the membrane. Make sure that there are no wrinkles
in the membrane & that it does not get puncture.
4.3
Fill potassium chloride
solution (7.5%) in the electrolyte tube to its top.
4.4
Insert the electrode in the
electrolyte tube and tightly screw it up. Now the probe is ready for use.
5.0
PRECAUTIONS:
5.17
.5% KCL solution acts as a good electrolyte
in DO Probe. Presence of any other salt in
electrolyte
solution may damage the probe.
5.2
The electrolyte tube should not contain any
air bubble, if it is present, it will cause
fluctuations in the reading
6.0
DO OPERATIONS:
6.1 Set the SET ZERO
Knob to the extreme left position and CAL Knob
position
6.2
Place the DO Probe in 2% sodium
sulphite solution allow the display to settle. If it does not read 000set the
SET ZERO Knob to bring the display to read 000 by keeping the
temp.ºC knob at the solution temp. CAL Knob
6.3 Now
calibrate the instrument with a known value of DO solution (say distilled
water)
6.4 Take 250 ml flask and fill 2/3 of it with distilled water.
6.5 Stopper the flask and shake it for 30seconds.
Remove the stopper back and
swirl the water back and repeat the
procedure 4 times.
6.6
Measure the temperature of the water
and set the Temp. ºC knob at temperature
of the water in flask.
6.7
Hold DO probe in the flask and agitate
the water. Note the reading in the table 1
given below for given temperature.
If necessary adjust the meter reading with
display should read 7.5 in distilled water)
Note: Please refer to the saturation value of the dissolved oxygen in
distilled water as
given in table-1. It shows the value
for dissolved oxygen which will be obtained
when shaking the distilled water
at a given temperature in the air.
6.8
Now the instrument is ready to take
measurement of DO value of any unknown
7.0
Caution:
1) Since the measurement is based
on the diffusion process, the agitation of the solution is must. Hand shaking of the solution may not given accurate readings.
Magnetic stirrer is recommended for this process.
2) Movement of the solution be about 2
ft. /sec for accurate measurement.
TABLE – 1
DO
SATURATION VALUES OF DM WATER
ºC
|
ppm
|
ºC
|
ppm
|
ºC
|
ppm
|
ºC
|
ppm
|
0
|
14.3
|
13
|
10.3
|
26
|
8.1
|
39
|
6.6
|
1
|
13.9
|
14
|
10.1
|
27
|
7.9
|
40
|
6.5
|
2
|
13.6
|
15
|
9.9
|
28
|
7.8
|
41
|
6.4
|
3
|
13.2
|
16
|
9.8
|
29
|
7.7
|
42
|
6.3
|
4
|
12.9
|
17
|
9.6
|
30
|
7.5
|
43
|
6.2
|
5
|
12.5
|
18
|
9.4
|
31
|
7.4
|
44
|
6.1
|
6
|
12.2
|
19
|
9.2
|
32
|
7.3
|
45
|
6.0
|
7
|
11.9
|
20
|
9.0
|
33
|
7.2
|
46
|
5.9
|
8
|
11.6
|
21
|
8.9
|
34
|
7.1
|
47
|
5.8
|
9
|
11.3
|
22
|
8.7
|
35
|
7.0
|
48
|
5.7
|
10
|
11.1
|
23
|
8.4
|
36
|
6.9
|
49
|
5.6
|
11
|
10.8
|
24
|
8.3
|
37
|
6.8
|
50
|
5.5
|
12
|
10.6
|
25
|
8.2
|
38
|
6.7
|
51
|
5.4
|
8.0 HISTORY OF REVISION:
Revisiom No
|
Effective Date
|
Revision Date
|
Reason for revision
|
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