PHYWE Cobra4 Oxygen Operating Instructions Manual

Operating Instru

c-

with the applicable

EC regulations

PHYWE Systeme GmbH & Co. KG
Robert-Bosch-Breite 10
37079 Göttingen

Germany

Tel. [phone]
Fax [phone]
E-mail [e-mail]
Internet www.phywe.de

Cobra4 Sensor-Unit Oxygen

12676-00

The unit complies

Fig. 1: 12676-00 Cobra4 Sensor-Unit Oxygen

TABLE OF CONTENTS

1 SAFETY INSTRUCTIONS

2 PURPOSE AND CHARACTERISTICS

3 FUNCTIONAL AND OPERATING ELEMENTS

4 OPERATING INSTRUCTIONS

5 HANDLING

6 TECHNICAL DATA

7 SCOPE OF SUPPLY

8 ACCESSORIES

8 WARRANTY

9 DISPOSAL

1 SAFETY INSTRUCTIONS

• Read the operating instructions thoroughly and com-

• Only use the unit for its intended purpose.

• The unit is intended solely for use in dry rooms where

• Protect the Cobra4 Sensor-Unit Oxygen against dust,

• Ensure that no liquid can penetrate the housing. Other-

• When using the unit outdoors, ensure that no rain or

• Do not open the unit.

• Connect the data output of the Cobra4 Sensor-Unit Oxy-

• Based on today's state of software development, it is im-

pletely prior to starting the unit. Please read also the op­erating instructions of the measurement data recording
device that is used (Cobra4 Wireless-Link, USB-Link,
Mobile-Link, or Junior-Link). This is important for your
own protection and for avoiding damage to the unit.

there is no risk of explosion.

moisture, and vapours. Clean the unit with a slightly
moist, lint-free cloth. Do not use any aggressive cleaning
agents or solvents.

wise, the Cobra4 Sensor-Unit Oxygen may be damaged.

splash water can penetrate the housing.

gen only to the intended measurement data recording
devices.

possible to guarantee that a product is completely free
from errors or defects.

This is why PHYWE Systeme GmbH & Co. KG does not
accept any liability for damage that results from the in­stallation or use of this unit.

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2 PURPOSE AND CHARACTERISTICS

The Cobra4 Sensor-Unit Oxygen is used to measure the
oxygen content in the gaseous state and the oxygen concen­tration in dissolved form.
Depending on the type of application, the Cobra4 Sensor­Unit Oxygen can be connected to one of the following meas­urement data recording devices for the transfer of the meas­urement data:

• Cobra4 Wireless-Link (12601-00) for the wireless data
transfer to a computer,

• Cobra4 USB-Link (12610-00) for the data transfer to a
computer via a USB cable,

• Cobra4 Junior-Link (12615-00) for the data transfer via
USB during student experiments,

• hand-held Cobra4 Mobile-Link (12620-10).

The front of the unit is equipped with an interface via which
the connection to the measurement data recording devices is
realised. Mechanically secure locking is ensured by way of
the lock knob and the corresponding hole.

3 FUNCTIONAL AND OPERATING ELEMENTS

3.1 Operating elements

The Cobra4 Sensor-Unit Oxygen does not have any manual
operating elements. It is controlled by way of the hand-held
Cobra4 Mobile-Link or via a computer if it is connected to a
Cobra4 USB-Link, Cobra4 Wireless-Link, or Cobra4 Junior­Link, as soon as the connection between the Sensor-Unit and
one of the three measurement data recording devices has
been established.

3.2 Measurement inputs

The front of the unit is equipped with a connector for connect­ing the oxygen probe.

5 HANDLING

This section describes the start-up of the Cobra4 Sensor-Unit
Oxygen and the recording of measurement data. Please read
this section thoroughly in order to avoid failures or operating
errors.

5.1 Starting the Cobra4 Sensor-Unit Oxygen

Software/device software update
Ensure that the current versions of the "measure" software
package and of the firmware of the Cobra4 module are in­stalled.
Cost-free software update at:

www.phywe.com > Downloads > Software:

"measure" measurement software

PHYWE firmware
A cost-free update of the software is also possible via the
"measure" DVD.

Topping-up the electrolyte solution
The lower end of the electrode can be unscrewed. This cap
covers the actual electrode. The entire cavity between the
cap and electrode must be filled with the electrolyte liquid
(KCl). Ensure that no air bubbles are entrapped. The elec­trode comes supplied in an unfilled state. In addition, the liq­uid evaporates gradually. This is why the liquid must be
topped up from time to time.

1. Unscrew the lower end.

2. Fill the cap with the liquid.

4 OPERATING INSTRUCTIONS

Combined with the Cobra4 Wireless-Link, Cobra4 USB-Link,
Cobra4 Junior-Link, and Cobra4 Mobile-Link, the Cobra4
Sensor-Unit Oxygen fulfils the technical requirements that are
summarised in the current directives the of the European
Community. The unit must be used under the supervision of
an expert and in an electromagnetically controlled environ­ment at research, teaching, and training facilities (schools,
universities, institutes, and laboratories).
This means that, in such an environment, radio transmission
devices, e.g. mobile phones, should not be used in the direct
vicinity of the unit. The connected cables must not be longer
than 2 m.
Electrostatic charges or similar electromagnetic phenomena
(HF, bursts, indirect lightning discharge, etc.) may affect the
unit so that it will not work within the specified data range.
The following measures reduce or eliminate the potential in­terferences:
avoid carpets; provide equipotential bonding; perform the ex­periments on a conductive, earthed surface, use shields and
shielded cables. Do not use radiofrequency transmitters (ra­dio sets, mobile phones) in the direct vicinity of the unit.

3. Screw the filled cap back onto the electrode. Use a
cloth to wipe off any liquid that leaks out.

Preparation
Connect the oxygen probe (see the list of accessories) to the
connector at the front of the Sensor-Unit. Connect the Co­bra4 Sensor-Unit Oxygen with one of the four possible
measurement data recording devices via the 15-pin snap-on
connector. The Sensor-Unit is immediately ready for opera­tion since it is supplied with power via the measurement data
recording device. Please refer to the corresponding operating
instructions for more information concerning the operation
and control of the measurement data recording devices.

Calibration
It is not necessary to recalibrate the sensor for every meas­urement. Especially if only the change in oxygen content is to
be demonstrated, an already existing calibration (the last
calibration remains automatically stored in the sensor) or the
factory settings are usually sufficient. However, if absolute
values are required for your measurement, e.g. if you are de­termining the oxygen content of bodies of water, or if you
want to optimise the accuracy of your measurement, we rec­ommend calibrating the sensor. See section 5.3.

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5.2 Recording of measurement data

Measurement:
Two types of measurements can be performed with the Sen­sor-Unit Oxygen: Measurement of the oxygen content, e.g. in
the air (% by volume), and a measurement of the oxygen
concentration in an aqueous solution (mg/l or %).

a) Measurement of oxygen in the air

Remove the protective cap and select the measuring

channel "Gas". It takes approximately 1 minute for the
value to settle.

b) Measurement of dissolved oxygen

Remove the protective cap and select the measuring
channel "Fluid".

• Plunge the oxygen probe into the solution so that
the temperature sensor is also covered (approxi­mately. 5-6 cm). Do not immerse it completely in
the liquid. The handle is not waterproof.

Temperature sensor

• Record the oxygen concentration by starting a
measurement via the software/Mobile-Link or read
the current values off of the display/user interface

a) With the Cobra4 Mobile-Link:

Select "Menu", "Calibration", "One point" and confirm by
ticking.

b) With the Wireless-Link, USB-Link, or Junior-Link and via

the "measure" software
In the navigator, double-click the channel "Concentra­tion", open the tab "Calibration", and then click "Apply".

2. Dissolved oxygen

In this case, a one-point-calibration will be performed in
which the electrode is held in air that is saturated with water
(see "Info" at the end of the paragraph). This corresponds to
a saturated solution of the oxygen in water.

Procedure
Select the measuring channel "Fluid".
Fill the (supplied) calibration bottle with approximately 5 ml of
distilled water. Push the oxygen electrode through the seal of
the screw cap and screw the cap on tightly. Attention, the
sensor must not plunge into the fluid. Then, shake the bottle
with the electrode gently for approximately 10 seconds in or­der to saturate the air in the calibration bottle with water va­pour. Under these conditions, the oxygen content is assumed
to be 100% saturation. After one minute, there should be an
equilibrium (constant measurement value) and the calibration
can be performed (either with the Mobile-Link, see c), or with
another device and the software, see d)).

of the software.

• Ensure that the water sample that is to be ana-
lysed is slightly stirred in a continuous manner.
This is important since the sensor consumes oxy­gen during the measurement. Without stirring, it
would seem as if the oxygen concentration de­creases.

Measuring principle:
This sensor type is an amperometric Clark sensor with a
platinum cathode and a silver anode.
A fixed voltage is applied at the platinum electrode. When
oxygen diffuses through the membrane and to the cathode,
the latter will be reduced:

1/2 O2 + H2O + 2

e–

→

2 OH–

The reference electrode (anode) is subject to oxidation:

Ag + Cl– → AgCl + e–

Correspondingly, a current flows and this current is propor­tional to the oxygen diffusion and, thereby, to the oxygen
concentration. The current is converted into a voltage signal
that is then received by the sensor.

5.3 Calibration

Ensure to perform the calibration at a temperature that is
similar to the temperature of the sample. Like in the case of a
measurement, wait for approximately 1-2 minutes after the
connection of the sensor until the measurement value has
settled. Then, perform the calibration.

1. Oxygen in air

Select the measuring channel "Gas".
Hold the sensor in the ambient (outdoor) air since, in this
case, the oxygen content will be constantly at 20.9%. De­pending on the Link device that you use, follow the steps un-

Fig. 2: Calibration

c) With the Cobra4 Mobile-Link:

Select "Menu", "Calibration", "One point" and confirm by
ticking.

d) With the Wireless-Link, USB-Link, or Junior-Link and via

the "measure" software
In the navigator, double-click the channel "Concentra­tion", open the tab "Calibration", and then click "Apply".

Info: The calibration in water-saturated air corresponds to the
calibration in a saturated solution since the oxygen in the
electrode first passes through the electrolyte solution before it
reaches the cathode. The oxygen concentration in water­saturated air and the oxygen concentration in the electrolyte
solution will be the same. Depending on the partial pressure
of the oxygen in the air, it will correspond to Henry's law. This
relationship applies to the sensor in air and to the sensor in
the solution.

der a) or b) respectively.

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5.4 Storage

Short-term:
Leave the electrolyte solution in the cap and place the elec­trode in distilled water in between the measurements. If pos­sible, leave the measuring instrument switched on.

Several days:
Rinse the outside of the electrode with distilled water, dry it,
and put on the protective cap. This prevents the electrolyte
solution from evaporating.

Long-term:
Unscrew the cap and remove the electrolyte solution com­pletely. Clean the electrode and the cap with distilled water
and dry both. Shake the water off the membrane. Screw the
dry cap loosely onto the electrode (do not close it com­pletely!). Store in a dry and light-protected place.

5.5 Care

Membrane
Ensure not to damage the membrane and follow the storage
instructions in order to increase the service life of the elec­trode. Creases or holes in the membrane are a sign that it
does not work properly any more.
If the membrane is soiled or if it shows signs of damage (this
might be indicated by incorrect measurement values), use
the supplied spare cap with a membrane.

Cathode and anode
They must be polished with the supplied polishing cloths from
time to time. To do so, remove the cap so that the anode and
cathode can be accessed. Polish them with slight pressure
and a clean cleaning cloth (included in the scope of supply) in
order to remove any deposits from the surface. Rinse them
with distilled water and then with alcohol, shake the liquid off,
and screw the cap back on loosely.

6 TECHNICAL DATA

(typical data for 25°C)
Operating temperature range: 5 to 40°C
Rel. humidity: < 80%

O2, dissolved
Measuring range 0...20 mg/l

0...200%
Accuracy 1%

Resolution 0.01 mg/l
Max. sampling rate 100 Hz
O2, gaseous
Measuring range: 0...30 %
Accuracy 1%

Resolution 0.1%
Max. sampling rate 100 Hz

Connector: Sub-D, 15-pin-type
Dimensions (L x W x H) 110 x 70 x 30 mm
Weight: 100 g

7 SCOPE OF SUPPLY

The following items are included in the scope of supply:

• Cobra4 Sensor-Unit Oxygen 12676-00

8 ACCESSORIES

For information concerning the use of the individual ac­cessories, see the section 5.1 to 5.4.

Oxygen probe 12676-11
including 50 ml of the electrolyte liquid, a protective cap, a

calibration bottle, a spare membrane, and cleaning strips for
the cathode and anode

Electrolyte liquid (KCL-solution)

8 WARRANTY

We give a warranty of 24 months for units supplied by us in­side the EU, and a warranty of 12 months outside the EU.
The following is excluded from the warranty: Damage that is
due to non-compliance with the operating instructions, im­proper use, or natural wear.

The manufacturer can only be held liable for the function and
safety-relevant properties of the unit, if the maintenance, ser­vice, and modifications of the unit are performed by the
manufacturer or by an institution that is expressly authorised
by the manufacturer.

9 DISPOSAL

The packaging mainly consists of environmentally-friendly
materials that should be returned to the local recycling sta­tions.

Do not dispose of this product
with normal household waste.
If this unit needs to be disposed of,
please return it to the address
that is stated below for proper
disposal.

PHYWE Systeme GmbH & Co. KG
Customer Service
Robert-Bosch-Breite 10
37079 Göttingen
Germany

Tel. [phone]
Fax [phone]

4

www.phywe.de, © All rights reserved 12676-00 / 4513