Hach-Lange ORBISPHERE 3650 - Manual (Page 29)

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Operating Information
4.2 Taking measurements
Once the system is calibrated, you should be able to begin taking measurements. Connect the
top-mounted inlet to accept your sample, typically this is accomplished by connection to a
sampling valve. The sample flow can be regulated by adjusting the knurled stainless steel knob
on top of the flow chamber.
Minimum flow rates, measurement limits and response times for the various available
membranes are given in the accompanying Sensor Manual.
The LCD includes a right-side marker to distinguish between gas concentration measurements
and temperature. This marker also indicates the measurement display units (ppm, ppb, %, kPa
or mbar depending on the instrument model).
To switch between gas measurement and temperature measurement, press the Up/Down
Arrow buttons.
To backlight the LCD for approximately three minutes, press the Backlight button.
Note: For measurements of gaseous samples in % units, you must open the barometric pressure sensor
relief valve switch on the top of the instrument from time to time, to allow the pressure inside the instrument
to equilibrate to the barometric pressure.
4.2.1 Preconditioning sensors
You can expect a more rapid and accurate first result if you precondition the sensor before you
take readings.
To precondition, connect the flow chamber to a convenient sampling source at or below
expected O
2
or H
2
levels. If measurements take place in carbonated samples, precondition with
carbonated water. Open the sampling valve on the flow chamber, just enough for a trickle. Then,
switch on the instrument and watch the LCD. You will see the values drop.
Typically for oxygen, if you are measuring in the 0.1 ppm range, then only a short time is
required for the display to fall to this level, whereas ppb level measurements may require the
sensor to remain exposed to the sample for half an hour or more. You will establish your own
requirement with experience.
Once the LCD displays the expected level of O
2
or H
2
, close off the sample. The sensor is now
preconditioned and ready to use.
You may want to precondition prior to each series of measurements, depending on frequency of
use.