GREISINGER GOX 91 User 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)
Temperaturecompensation: Automatic
Adjustmentofatmosphericpressure: Via turning knob from 800 to 1100 mbar absolute
Ambienttemperature: 0 to 45°C
Display: 3 1/2 digit LCD, approx. 13 mm high
Electrode: Active oxygen electrode withautomatic pressure compensation,
approx. 4 m of cable with plug
Analogoutput: 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
Dimensionsofhousing: 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. batteryand 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 anyother 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.
Watercalibration
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:

For storage purposes place electrode in a container with dechlorized water up to the cable connection point.
Make it a rule to unscrew the protection cap and to clean the membrane with a clean soft tissue before each
measuring series.
Exchange electrolyte every 6 months.
In case of damage to the membrane, both membrane and electrolyte will have to be exchanged.
Exchanging ofmembrane:
When do you have to exchange the membrane ?
1. Immediately after inadvertently knocking the electrode tip against a hard object, thus causing damage.
2. If the measuring value displayed is continuously falling, this is normally an indication for a defective
membrane.
The damage may be a hairline crack too small to be noticed with the naked eye through which the electrolyte
film
slowly evaporates; this resulting in a reduced conductivity and a slowly but continuouslydecreasing measuring
value being displayed.
A membrane exchange is easily done and can, therefore, be carried out by the user himself:
1. Unscrew protection cap.
2. Take off first red neck ring.
3. Take off O-ring and second red neck ring. (This is easily done by slightly turning the rings with a tissue.)
4. Remove damaged membrane.
5. Remove cover screw and empty out old electrolyte (attention: electrolyte is caustic).
6. Top up with new electrolyte (brimful) holding electrode slightly askew to allow air bubbles to escape.
Lightly tapping the electrode shaft also helps to remove air bubbles.
Electrolyte does not have to be exchanged if new or if membrane has been damaged whilst putting it on
7. Re-place cover screw. Screw to be fingertight only.
8. Hold electrode vertically and check the four channels for droplets. If no droplets can be seen use your
thumb to make pumping movements on the pressure balance membrane till electrolyte is showing.
9. Turn electrode round holding it vertically pointing upwards.
10. Wipe off silver cathode with a paper tissue till clean, but do not polish. The "scratches" on the silver
surface have been deliberately made as scuffing assists the formation of an electrolyte film.
11. Put one drop of electrolyte on the silver plate, put new membrane on top and re-position first red neck ring.
Make sure to draw the 4 edges of the membrane slightly downwards to avoid excessive wrinkling. Pull ring
down until O-ring groove re-appears. Re-place O-ring avoiding any risk of damaging the membrane with
your finger nails. Put on second red neck ring and cut off excessive Teflon material with razor blade or
sharp knife.
12. Re-place and fasten protection cap.
It is vital that no wrinkling occurs when fitting the new membrane. We, therefore, recommend that the Teflon
material be gently drawn down after re-positioning of the first neck ring to smooth any wrinkles. Make sure not
to twist membrane !!
Utmost care must be employed in conducting this procedure. There must not be any pressing, pushing or
turning in the opposite direction as the membrane tension would thus be relieved never to allow trouble-free
operation of the membrane.
If you do not succeed in replacing the membrane at the first attempt, please repeat procedure. If membrane is
not fitted tight enough, twisted or wrinkling, this may lead to incorrect measurements.
Make sure to use a new piece of Teflon for each attempt as a piece of material that has once been stretched and
twisted can never again be made into a well-positioned membrane.
To check if membrane in electrode is tight enough, hold electrode with tip pointing upwards, switch on unit
and wait for display to show stable value. Then move electrode downwards with a jerk. In case of deviations on
the display of approx. 2 mg/l or more, the membrane has not been fitted tight enough and will have to be
replaced.

After re-positioning, rinse membrane with water. We highly recommend to wait at least 30 to 45 minutes
before starting to re-calibrate the unit. In order to make absolutely sure that measurements will be correct, allow
electrode to stabilise for 12 hours (during the night) before re-calibrating as Teflon material, which is easily
overstretched during positioning, will without fault return to its original state after some time.
Once this state has been reached again, this can be seen at the display of the unit as immediately after replacing
the membrane a relatively high value is displayed; due to the tension in the material being relieved the value on
the display will fall accordingly.
Please note that our experience has shown that in most cases inaccurate measurements are the results of the
membrane being incorrectly replaced and/or the unit being incorrectly calibrated. Please make sure to emplay
utmost care when replacing the membrane or calibrating the unit.
In the course of the time and due to temperature differences during measurements the membrane will loose its
elasticity and, if electrode has not been stored in water, will have to be replaced after 3 months regardless of its
being defective or not.