wtw MultiLine FDO 925 User manual

FDO®925
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Operating manual
Optical D.O. sensor

FDO®925
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Note
The latest version of the present operating manual can be found on the
Internet under www.WTW.com.
Copyright ©Weilheim 2010, WTW GmbH
Reprinting - even as excerpts - is only allowed with the explicit written
authorization of WTW GmbH, Weilheim.
Printed in Germany.

FDO®925 Contents
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Contents
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1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.1 Structure and function . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.2 Recommended fields of application . . . . . . . . . . . . . . . . 22
2 Measuring / Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1 General information on the handling of the sensor cap . 23
2.2 Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3 Measuring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4 Function check and user calibration . . . . . . . . . . . . . . . . 24
2.5 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3 Maintenance, cleaning, replacement . . . . . . . . . . . . . . . . 25
3.1 General maintenance instructions . . . . . . . . . . . . . . . . . . 25
3.2 Exchanging the sensor cap . . . . . . . . . . . . . . . . . . . . . . . 26
3.3 Cleaning the sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.4 Checking the zero point of the sensor . . . . . . . . . . . . . . . 28
4 What to do if... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6 Wear parts and accessories . . . . . . . . . . . . . . . . . . . . . . . 32

Contents FDO®925
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FDO®925 Overview
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1 Overview
1.1 Structure and function
Structure
Sensor cap with
memory chip
A memory chip is integrated in the sensor cap. The following data are stored
on the memory chip:
zType designation of the sensor cap
zSeries number
zData of the factory calibration or user calibration
Intelligent mem-
brane (IQMC tech-
nology)
For each membrane, the individual calibration values are determined by a
factory calibration process and stored to the memory chip of the sensor cap,
ensuring maximum accuracy over the whole lifetime of the sensor.
1Shaft
2Connection head
3Fixing ring
4Sensor membrane
5SC-FDO®925 sensor cap with memory chip
6Gold-plated contacts for the memory chip of the sensor cap
7Locking device
8Measurement window
9O-ring
10 Thermistor enclosure with temperature sensor
12
5
7
3106984

Overview FDO®925
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Automatic sensor
recognition
The data of the sensor and sensor cap is recalled by the meter when the
sensor is connected and is used for measurement and for measured value
documentation. The calibration data are stored in the sensor cap. Thus, the
calibration is automatically retained if the sensor or meter are exchanged.
The digital transmission technique guarantees the failure-free communi-
cation with the meter even with long connection cables. If the sensor firmware
is enhanced by WTW, it can be updated via the meter.
1.2 Recommended fields of application
Recommended
fields of applica-
tion
zOn site measurements in rivers, lakes and wastewater
zApplications in water laboratories
zBOD measurements

FDO®925 Measuring / Operation
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2 Measuring / Operation
2.1 General information on the handling of the sensor cap
Despite its exterior robustness, the sensor is a high precision optical instru-
ment. Therefore, you should take the following precautions when dealing with
the FDO®925:
zPlease do not touch the sensor membrane with your fingers
zAvoid any great mechanical stress of the sensor membrane (pressure,
scratches).
2.2 Commissioning
Scope of delivery zD.O. sensor FDO®925 with sensor cap
zCheck and storage vessel, FDO®Check
zOperating manual
Preparing the sen-
sor for measure-
ment
Connect the sensor to the measuring instrument. The sensor is immediately
ready to measure.
2.3 Measuring
Minimum immer-
sion depth
Observe the required minimum immersion depth (see chapter 5 TECHNICAL
DATA).
Indicent flow The FDO®925 D.O. sensor enables precise measurements without any
incident flow.
However, an incident flow of the sensor membrane improves the responding
behavior of the sensor (see chapter 5 TECHNICAL DATA). The incident flow can
be provided in different ways, e. g.:
zThe flow of the water to be measured is sufficient (aeration tank, water
pipe, stream)
zSlowly pull the sensor through the water by hand (lake, container), or
zUse a flow aid such as a magnetic stirrer with stirring device (see
chapter 6 WEAR PARTS AND ACCESSORIES)

Measuring / Operation FDO®925
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2.4 Function check and user calibration
Factory calibration The FDO®925 is factory calibrated. In the recommended application (see
page 22), the measuring characteristics of the sensor cap remain stable for
the specified service life. Thus, a user calibration is not usually required.
When does a func-
tion check or user
calibration make
sense?
A function check or user calibration can be useful in the following special
cases:
zIf the measured values appear to be implausible and it is assumed that the
service life of the sensor cap is over
zRoutinely within the framework of the company quality assurance.
Check or calibra-
tion medium
The check and user calibration take place in water vapor-saturated air. The
suitable conditions are easily provided with the aid of the check and calibra-
tion vessel, FDO®Check. For this purpose, moisten the sponge inside the
vessel. Then insert the sensor in the vessel as far as it will go. The sensor
membrane must be clean and dry for this.
Moisten the sponge:
zRemove the cap (1).
zTake out the sponge (2), wet it, then slightly squeeze it out.
zInsert the sponge again and close the calibration and storage vessel with
the lid.
After inserting the sensor, wait for the temperatures of the sensor and
calibration vessel to adjust.
Note
The steps of the check or user calibration are described in detail in the oper-
ating manual of the meter.
2.5 Storage
Always store the sensor in the check and storage vessel (FDO®Check) at a
temperature in the range 0 ... 50 °C (32 ... 122 °F).
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FDO®925 Maintenance, cleaning, replacement
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3 Maintenance, cleaning, replacement
3.1 General maintenance instructions
Handling of the
sensor cap
Despite its exterior robustness, the sensor is an optical high precision instru-
ment. Therefore, special care should be taken when doing any maintenance
or cleaning work:
zDirt and moisture under the sensor cap can affect the functioning and
shorten the service life of the sensor cap. Therefore, make sure the work-
ing environment is clean and dry prior to removing the sensor cap.
zPlease do not touch the outer sensor membrane with your fingers. Touch
the sensor cap at the sides only (arrows in figure on the left).
zAvoid any great mechanical stress of the sensor membrane (pressure,
scratches).
zExposure to light, particularly daylight, of the interior of the sensor cap will,
by-and-by affect the measurement characteristics and shorten the service
life of the sensor cap. Therefore, the interior of the sensor cap should not
be exposed to direct sunlight. Avoid any exposure to light that exceeds the
extent required for necessary maintenance and cleaning activities. Store
dismantled sensor caps in a light-protected environment only.

Maintenance, cleaning, replacement FDO®925
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3.2 Exchanging the sensor cap
Note
Before removing the sensor cap, observe the general maintenance instruc-
tions in section 3.1.
To exchange the sensor cap, proceed as follows:
Removing the sen-
sor cap
Mounting the sen-
sor cap
1Pull the sensor out of the sample.
2 Clean the outside of the sensor (see section 3.3.1).
3Unscrew the fixing ring from the sensor by hand.
4 Thoroughly clean and dry the sensor head once again.
5Grasp the sensor cap on the sides (arrows in figure on the left) and
remove it by pulling it away from the sensor in a straight upward
direction.
Caution:
Do not push any tools or other sharp objects between the sealing sur-
faces. This would damage the sealing surfaces and sealing ring.
6Check the front surface of the sensor for absolute cleanness and
clean it if necessary (see section 3.3.2).
7 Thoroughly clean the thread of the fixing ring.
8Check the sealing ring for intactness and correct position.
The sealing ring has to be replaced if it is damaged.
9 Aim the sensor head upwards and place the new sensor cap on the
sensor. The locking device on the sensor head must be inserted into
the receptacle on the inside of the sensor cap (see figure on the left).
10 Put the fixing ring on the sensor head and screw it tight by hand as
far as it will go. A gap of approx. 0.8 mm remains between the fixing
ring and sensor.
The sensor is immediately ready to measure.