GREISINGER GOX 91 Brief Operating Manual

Brief Operating Manual for Digital Oxygen Meter GOX 91

Specification

Measuring range: 0.0 to 30.0 mg/l O2

0 to 199 % O2 saturation

0.0 to 45.0° C

Accuracy: ~ 1.5 % +/- 1 digit (from 5 to 35° C)

Temperature compensation: Automatic

Adjustment of atmospheric pressure: Via turning knob from 800 to 1100 mbar absolute

Ambient temperature: 0 to 45°C

Display: 3 1/2 digit LCD, approx. 13 mm high

Electrode: Active oxygen electrode with automatic pressure compensation,

approx. 4 m of cable with plug

Analog output: 1 mg/l = 100 mV, connection via monoplug, dia 3.5 mm

Power supply: 9 V-battery type JEC 6F22 (included in scope of supply) and

lateral mains supply socket for 2.5 mm dia monoplug (automatic
battery disconnection as soon as mains supply unit is plugged in)

Battery service life: Approx. 150 operating h

Low battery warning: Automatic; "BAT" displayed in case of low battery voltage

Dimensions of housing: Approx. 150 x 86 x 30 mm (height x width x depth); impact resistant

ABS plastic housing with integrated pop-up clip for table-top or
suspended operation.

Weight: Approx. 450 g (incl. battery and electrode)

Points to be observed prior and during measuring:

Prior to measuring make sure that the electrode has assumed water temperature. To test please proceed as
follows: switch device to temperature indication and move electrode around in water until stable temperature is
displayed. The electrode is now ready for oxygen measurements.

When conducting O2 measurements, fresh water samples must constantly be fed to the electrode membrane
with a minimum flow velocity of approx. 30 cm/sec.
This flow is achieved by stirring the water samples with the electrode or by using a flow generator. The
minimum flow velocity has been reached if faster stirring does not result in a higher value on the display.

For measuring proceed as follows: 1. Put electrode in measuring media and wait till it has assumed medium

temperature.

2. Set pressure compensation of the unit to current atmospheric pressure

(required only if values are to be displayed in %) by means of the "mbar"
potentiometer

3. Switch on device and set to temperature display. Check if electrode has
assumed water temperature by slightly stirring the water with the
electrode.

4. Switch over to oxygen measuring.

Generate required flow velocity by stirring measuring media with
electrode and read off measuring value as soon as stable value
appears on display.

Air calibration:

Each measuring device has been subjected to a series of tests demanding maximum quality standards in all
stages of manufacture and has been calibrated before leaving the factory.
Nevertheless, the user should carry out the following procedure to check the calibration prior to every
measuring process:
Place measuring device and electrode on a table and wait for approx. 30 minutes for electrode to assume
ambient temperature. Make sure not to subject electrode to any other heat source (lamp etc.).
Switch on measuring device and set to temperature measuring using the turning knob (on front side of unit)
and look up oxygen value corresponding to temperature in the following table. Switch unit to O2 measuring
(slide switch position: mg/l) and check oxygen value displayed. If value deviates too much it can be adjusted by
means of the "slope" potentiometer.

Table for air calibration

Air temp.

in ° C

O2 value

in mg/l

Air temp.

in ° C

O2 value

in mg/l

Air temp.

in ° C

O2 value

in mg/l

Air temp

in ° C

O2 value

in mg/l
0 13.8 10 11.6 20 9.7 30 8.1
1 13.6 11 11.4 21 9.5 31 8.0
2 13.4 12 11.2 22 9.3 32 7.8
3 13.2 13 11.0 23 9.1 33 7.7
4 12.9 14 10.8 24 9.0 34 7.6
5 12.7 15 10.6 25 8.8 35 7.5.
6 12.5 16 10.4 26 8.6 36 7.4
7 12.2 17 10.2 27 8.5
8 12.0 18 10.0 28 8.3
9 11.8 19 9.9 29 8.2

Customer may, of course, choose one of the two methods of calibration at his own discretion: simple calibration
in air or conventional wet calibration in saturated water.

Water calibration

Although cold water usually absorbs more oxygen, it is much more difficult to determine its actual degree of
saturation without using a WINKLER-test as there is a permanent risk of over-saturation.
We, therefore, recommend using warm water at a temperature of 25 to 30° C. In order to prepare water
saturated with air, we recommend to pour water from one container into another one from approx. 50 cm
height and repeat the procedure about 20 times. Before finally calibrating the electrode to 100 % you should
wait another 5 minutes to allow any oversaturation in the water to escape.
Do not forget to stir water when carrying out the setting-up.

Re-checking of calibration after measuring:

We would like to point out that membranes behave quite differently in water than in air when first subjected to
it. It is only after the electrode has been subjected to air for a considerable period of time (approx. 30 minutes)
that it will find its equilibrium. It is vital, however, that the tip of the electrode is really dry.

The electrode adjusts much more quickly when changing from air to water, ie 90 % of the final value within a
few seconds only.

Care and maintenance of the electrode

Please refer to the schematic drawing of the elctrode on the last page of this manual.
The following points should be observed: