Sensor Components; Basic Principle Of Operation - Hach LANGE ORBISPHERE C1100 User Manual

3.2 Sensor components

The following illustration shows the assembled sensor with the storage cap and sensor collar
removed and the exploded view of the main sensor components. To remove the storage cap,
you will first have to unscrew and remove the sensor base.
1 - Protection cap locking washer
2 - Protection cap
3 - Dacron
4 - Cartridge containing electrolyte and membrane

3.3 Basic principle of operation

In its simplest form, the electrochemical sensor consists of one center electrode (cathode) and
one counter electrode (anode) immersed in an electrolyte solution which is separated from the
liquid sample by a gas permeable membrane. An electronic circuit is linked to the anode and
cathode. Through an applied voltage, current will flow between the anode and the cathode.
A guard ring electrode surrounds the center electrode in order to reduce the influence of other
gases on the center electrode, and therefore improving analysis stability. The sensor head is
covered with a protection cap to protect the membrane.
Ozone penetrating through the membrane into the cell reacts with the electrolyte which then
undergoes a reaction at the cathode, causing a measurable electric current to flow. This current
is proportional to the amount of gas entering the cell, which in turn is proportional to the partial
pressure of gas in the sample outside the cell.
The result is shown as gas concentration, which can then be displayed with a choice of several
measuring units, according to instrument setup.
The sensor also includes "smart sensor technology", implemented using an RS485 interface.
The sensor electronics perform four functions:
• Apply constant voltage to the anode
• Measure the current flowing through the sensor
• Compensate for temperature variation in the liquid sample
• Convert the cell's electric current into an analog signal for sensor output
Figure 6 Sensor components
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mesh patch
5 - Cotton washer
6 - Sensor body
7 - Plastic base
Introduction
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