| ToGa Technical details pdf copy of manual |
ToGa
Operating instructions |
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Layout |
| The ToGa is a very simple instrument, basically all you
need to do is turn it on and adjust the trim pot to the instrument reads 100%. The probe should be dry when you conduct the calibration,
there is no warm up time. |
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Measurements |
| Before immersing the probe, switch the unit on
the and check the reading. Normally it will be between 97 and 101.5%. With the probe still
dry set the display to read 100% by adjusting the trimpot. The probe can only be reset if
it is dry and has not been in water for at least 24 hour. If the probe is wet or has
recently been used, the instrument should be set to 102%. The precise setting
depends on the air temperature and water vapour pressure. Immerse the probe in the water to completely
cover the probe, leave the probe for 10 minutes and if you wish to save the battery you
can turn the instrument off during this period. After the 10 minute period note the
reading on the instrument.
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Checking the Toga |
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The membrane is the most vulnerable part and it can be checked whilst dry by
gently breathing across the probe. Your breath contains water vapour
which will increase the gas pressure, the ToGa probe will be able to
detect this slight increase in pressure and the reading will increase by
around 0.5 to 1.5%. After you have stopped breathing across the probe,
the reading should drop back down to 100%. |
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Additional Notes |
| When you measure the total gas pressure of the water, the total gas
meter is first set to read 100% with the probe dry and in the air. When the probe is
immersed into the water the reading will change depending on the dissolved gas pressure in
the water. The instrument will detect nitrogen, oxygen, argon and carbon dioxide. The most
important gas is nitrogen, however the instrument will also detect the gas pressure due to
water vapour pressure. The water vapour pressure will exert a gas pressure of 1% to 2%
depending on the temperature of the water. In a typical case with the water temperature
around 10 degrees centigrade the water vapour pressure will be about 1.5%, the higher the
temperature the higher the vapour pressure. Assuming the water is at 100% saturated with
dissolved gases, the ToGa will actually read 101.5%, with this extra 1.5% being due to
vapour pressure. It is therefore quite common to obtain readings of 101% to 102% in the
water, this gas pressure is safe for most aquatic animals It
takes 24 hours for the water vapour pressure to stabilise in the probe,
therefore if you use the instrument and then check the reading in air 1 hour
later, the probe may be dry, but the reading could have increased to 102%
with the probe in air. If the probe is then calibrated
back to 100% with the probe in air, and then left for 24 hours, the reading
would have dropped to 98%. This 2% deviation around 100% is therefore due to
water vapour and the condition of the probe during calibration.
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Operational Notes |
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It is important that all total gas meters are stored in a dry place
between use
Do not store near paints or solvents
Do not leave the probe in water
It is not necessary to perform frequent calibrations, if the instrument
has to be adjusted by more than 2% advise Dryden Aqua
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