Use & Limitations of Oxygen Analyzer on Oil Tankers:
The instrument is used to check the O2 content of the atmosphere within a tank or other confined space. Samples of the atmosphere are drawn by means of a rubber aspirator bulb and passed over a sensor.
The sensor is the most important part of the instrument and can be of various types:
- Paragmagnetic Sensor:-
- The magnetic properties of oxygen is used to deflect a light, metal body suspended in a magnetic field. When the gas is drawn through the cell, the suspended body experiences a force proportional to the magnetism of the gas. An equal and opposing force is produced by an electric current passing through a coil would round the suspended body. This equalizing current is proportional to the magnetic force of the gas which depends on its O2 content.
- Electrolytic Sensor:-
- In this type of oxygen is passed into an electrolytic cell causing a current to flow between two electrodes separated in a liquid electrolyte. The current flow between the electrodes is directly proportional to the O2 concentration in the sample. In this type, certain gases may affect the sensor or poison the electrolyte giving rise to false readings.
- Chemical absorption liquid:- in this type a known volume of the sample gas is brought into contact with a measured volume of a liquid which absorbs O2 causing a change in its volume. The change in volume is a measure of the O2 content of the sample.
- Can only measure O2 content.
- Regular calculation prior every use.
Properties of Oxygen Analyzer:
These analyzers come in various makes and models and we will be studying about one such analyzer namely the continuous reading type analyzer.
The main property of oxygen which helps in its detection and measurement of its percentage in the given sample of air is that of Para-magnetism. Basically this means that oxygen gets attracted towards a magnetic field. The set up for measuring oxygen content using this property can be understood from the image shown below.