During normal operation the front display shows the measured
valve of Do in mg/l from the attached probe.
In order to enter the menu, press the "<" key followed by the
">" key, you now have an option to either calibrate or to change the set points.
The system is menu driven from the display.
1 Calibration
There a 2 options for calibrating the probe, Fast & Slow. The
slow calibration is the more accurate but for general applications Fast
calibration is all that is required.
In Fast Calibration, the probe is calibrated in air,
referenced to the water temperature, and must be undertaken after two minutes of
the probe being removed from the water. A 120-second countdown timer is
activated when Fast Calibration is selected. After the 120 second count down you
can add the temperature of the water.
In Slow Calibration, the probe is calibrated with reference
to the air temperature, and must be undertaken after 20 minutes of the probe
being removed from the water. A 1,200-second countdown timer is activated when
Slow Calibration is selected, after which the temperature of the air is inserted
To alter a value, eg, salinity, altitude, temp, press the Alt
key, which will highlight a block cursor, then press OK. Use up and down arrow
keys to enter the first value, then left/right arrow keys to move across the
next number. When the correct value is entered press OK to accept, and Alt to
remove the block editing cursor. Press Next to go to the next value, and alter
as above.
The calibration of the probe will normally give a value of
around 10mg/l +/- 3mg/l. The raw data value relates to the mv out-put from the
probes which equates to 1 mg/l of oxygen. The raw data is used to make sue the
probe is okay, the value will normally be 9 +/- 4, if it is out-with this range
there may be a problem with the probe such as a damaged membrane.
- Set Points
There are three set point settings available on the
programmer, and these will operate as follows:
HH/LL set point
This is a high-high-low-low set point which activates the
alarm output contacts. The normally open contact will change over at a reading
below the HH/LL set point, and reinstate at a reading above this set point.
Hi set point
At this set point the oxygen/air valve will close.
Lo set point
At this set point the oxygen/air valve will open.
It is important to make sure that the values are not less
than 0.5 mg/l apart, to allow adequate hysteresis on the switching point and
prevent the valve from constantly opening and closing.
