8
1.5.2 Analyzer operating principle
The analyzer uses an amperometric sensor operating as a closed-type
polarographic cell. The electrodes are submerged in an internal electrolyte solution
which is separated from the analyte by a membrane penetrable for oxygen but im-
penetrable for liquid and water vapor. From the analyte, oxygen diffuses through
the membrane into a thin layer of electrolyte between the electrodes and the mem-
brane and undergoes an electrochemical reaction on the surface of the cathode
which is polarized by external voltage applied cross the electrodes. In the process,
the sensor generates a DC signal which is at a fixed temperature proportional to
DOC in the analyte.
The analyzer features a temperature sensor (platinum thermal resistor) to
measure temperature and to automatically compensate for the temperature de-
pendence of the oxygen sensor signal. The temperature sensor signal is supplied
to the ADC input.
The ADC converts signals of the oxygen sensor and the temperature sensor
into codes incoming the microcontroller.
The microcontroller processes the codes received and shows the information
on the digital LCD display.
1.5.3 Analyzer design
The analyzer is shown in Fig.1.1
а
.
а
b
Fig. 1.1
1
3
15
2
4
5
12
11
13
14
8
9
10
7
16
17
MODE
CAL
ENTER
6
