Tank Gas Testing Equipment
A sample of gas is drawn into the sample chamber using the hand pump. Any combustibles land on the surface of the hot wire and burn increasing the temperature of the wire thereby increasing the resistance. This causes an imbalance in the wheatstone bridge arrangement indicated on the display. This display is scaled in percent lower explosive limit and is calibrated for hydrocarbons. Note that the unit will operate against any combustible gas although the readout would be erroneous.
calibration gas is used to check the accuracy of the meter. In addition the unit must be landed on a regular basis for formal calibration.
The teflon is semipermeable letting in gasses and not moisture.
The instrument functions by the oxidation of the electrolyte which increases or decreases the conductivity of the cell depending on the oxygen content.
The off centre ball is further forced off centre when the oxygen moves in the lines of the magnetic field. This movement is detected.
A mirror is mounted on the arm. A light source is reflected off the mirror to a pair of photelectric cells. The position of the arm governs the light falling on the cells. The unit balances the light by adjusting the current in the righting coil. This current forms the measured value and is directly related to the oxygen in the sample.
Dirt and moisture can be extremely destructive for these instruments and as such should be left on rather than switched off. For fixed installations the cell is kept at 60'C