Precautionary Labels; Product Overview; Operating Principle - Hach ORBISPHERE GA2 00 Series User Manual

Indicates a situation which, if not avoided, may cause damage to the instrument. Information that requires special
emphasis.

2.1.2 Precautionary labels

Read all labels and tags attached to the instrument. Personal injury or damage to the instrument
could occur if not observed. A symbol on the instrument is referenced in the manual with a
precautionary statement.
This is the safety alert symbol. Obey all safety messages that follow this symbol to avoid potential
injury. If on the instrument, refer to the instruction manual for operation or safety information.
This symbol indicates the need for protective eye wear.
This symbol indicates the need for protective hand wear.
Products marked with this symbol indicates that the product contains toxic or hazardous substances
or elements. The number inside the symbol indicates the environmental protection use period in
years.
Electrical equipment marked with this symbol may not be disposed of in European domestic or
public disposal systems. Return old or end-of-life equipment to the manufacturer for disposal at no
charge to the user.

2.2 Product overview

2.2.1 Operating principle

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 gaseous
or 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 and, in some applications, a grille to protect the
membrane. Materials used for the components of the sensors differ with the application.
Gas penetrating through the membrane into the cell dissolves in the electrolyte. It 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 gaseous or liquid sample
• Convert the cell's electric current into an analog signal for sensor output
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