CTD90 manual V3-1 12-12-2006
CTD90 – Probe
Manual and operating instructions
Version 3.1
12.12.2006
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Contents
1. General description
2. Mechanical characteristics
2.1.
2.2.
2.3.
2.4.
2.5.
Pressure tube
Probe base
Probe lid
Sensor protection cage
Measurements and weights
3. Sensors
3.1
3.2
3.3
3.4
3.5
3.6.
3.7.
3.8.
3.9.
Pressure sensor
Ground runner
Temperature sensor
Conductivity cell
Oxygen sensor
pH and redox sensor
SEAPOINT Turbidity sensor
TURNER Cyclops7 fluorometer
Multirange sensors
4. Sensor replacement, opening the probe
5. Probe electronics
6. Connector pin assignment, power supply and interfaces
6.1.
6.2.
Operation with multicore cables
Operation with single conductor cables
7. Service and maintenance information
7.1.
7.2.
7.3.
7.4.
7.5.
7.6.
Underwater connector
Pressure sensor
Temperature transducer
Conductivity cell
Ph/Redox sensor
Oxygen sensor
8. Probe data format
9. Calculation of the physical data
10. Spare parts and accessories
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General description
The CTD90 is a small and handy microprocessor controlled multiparameter
probe for precise online measurements of chemical, physical and optical
parameters. The housing of the probe is pressure resistant up to 500 m (2000
m optional) depth; the maximum allowable operation depth depends on the
sensors line-up. Due to its handiness and its low weight it is particularly
suitable for portable employment without the use of a winch.
The small housing diameter of 90 mm only allows a maximum of 9 sensors
that can be accommodated to the sensor base. Additional sensors or
instruments can be attached externally to the probe via underwater
connectors (maximum of 5 external instruments). The CTD90 is able to
release multi water samplers and plankton multi nets and to recognize the
status of these units (number of bottles closed or number of net changes).
The CTD90 runs on standard single conductor cables with constant current,
the measurement readings are transmitted as FSK-signals modulated on the
DC supply. This method of operation requires a specific probe interface,
which generates the constant current and converts the FSK-signals into PCcompatible RS232-signals. This kind of data transmission can bridge some
kilometres of cable without data errors or disturbances.
For shorter distances (several hundred metres) a multicore cable can be
used. The probe is then supplied with constant voltage (battery or DC power
supply). The PC received data directly from the probe as RS-232C signal. A
specific interface is not required by this mode of operation.
The CTD90 is equipped with a 16-channel data acquisition system with 20-bit
resolution. A high long-time stability and automatic self-calibration of the
analogue digital converter guarantees stable and precise CTD measurements
for many years.
A very important feature is that the CTD90 is nearly free of corrosion, since all
mechanical parts and sensors are made of titanium except screws and
pressure transducer. This fact guarantees long lifetime and proper function of
all mechanical components even under worst ambient conditions.
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Mechanical characteristics
All parts of the probe, which are exposed to seawater, are made of corrosionproof metals or plastics. Essentially the probe consists of the following
mechanical structural components:
Housing: - Pressure tube
- Probe base
- Probe lid
Sensor protection cage
Sensors
The sensors are described in a separate chapter. The underwater housing
consists of a cylindrical tube closed on both ends with caps and sealed with
two O-rings each.
2.1
Pressure tube
The pressure tube is made of a solid-drawn seamless titanium tube with an
external diameter of 89 mm, a wall thickness of 3 mm and is able to withstand
500 m water depth. There are 4 drill holes in 90° graduation situated 11 mm
away from each tube-end. These holes are used for fixing of base and lid to
the pressure tube with 4 stainless steel screws M3*6mm. The inside of the
tube ends are slightly bored so that both of the inner o-rings fit neatly.
2.2
Probe base
The probe base is made of solid titanium and is used for the attachment of
nearly all sensors. Fig.1 shows the principle arrangement of the sensor
positions.
Standard probe
The base has room for 9 sensors: the pressure sensor is always mounted in
the centre position. For the remaining sensors there are 8 fits. The sensors
are inserted into these fits; the M4-tapped holes situated between the fits are
for fastening the sensor flange with M4-screws. All sensors (except the
pressure sensor) have identical flanges. The pressure transducer is inserted
to the base inside and held by a M18*1 nut against the pressure from outside.
A ¼“UNF28THD tapped hole is for connecting the base to a pressure gauge
so that the pressure sensor can be calibrated when installed.
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Figure 1
CTP90 standard bottom
8
5
1
1/4" UNF 28THD
connection to
pressure gauge
2
4
8 standard fits for
bottom mounted sensors
3
7
6
CTP90 bottom with
integrated currentmeter, transmissiometer or Cyclops7
fit for currentmeter
or transmissiometer
or Cyclops7-fluorometer
5
6
4
standard fits for
C,T,P,O2,pH,Red,Turb
2
3
1
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CTD90 probe with integrated current meter or transmissiometer
The flange of the current meter and transmissiometer has a diameter of 40
mm and requires more space on the bottom than the standard sensors
(approximately 25 mm diameter). It is not possible to mount the pressure
transducer in the centre position. Hence the pressure sensor get its own
housing and is plugged in one of the five remaining standard fits. The
calibration connection thread for the pressure gauge has the ISO size M8 *
1,25 mm.
The printed circuit boards (PCB) are screwed on a bedplate made of 1,5 mm
aluminium sheet which is mounted on the inside of bottom cap.
Lid and pressure tube are sealed by two O-rings 76 * 2,5mm and are bolted
onto the side with 4 screws M3*4.
2.3
Probe lid
The lid has the same dimensions as the base and is also made of titanium.
Fastening and sealing are identical to that of the base. Screwed into the lid is
a supporting bolt with a loop for hanging it onto a shackle. The standard
version includes one underwater bulkhead connector in the lid. In all a
maximum of 6 plugs (SUBCONN MICRO series) can be accommodated next
to the suspension bolt so that 5 additional instruments or sensors can be
connected to the CTD90.
A circular board is situated on the inside of the lid. It contains the DC-DCconverter, the cable-driver and the FSK modulator. The connection to the
sensor electronics is established by a separable cable-connection on the lid.
2.4
Sensor protection cage
A sensor protection cage made of 6 mm titanium rods with a diameter of 120
mm and a length of 220 mm is delivered with the standard version. The
protection cage protects the sensors on the water-floor against shocks and
ground contact and guarantees a fine water-flow through the sensors. The
protection cage is fastened with a single screw at the lower end of the
pressure pipe. As option any other size can be supplied. The version with
integrated current meter is supplied with a big size protection cage of 780mm
length and 220 mm diameter covering the complete probe.
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CTD90 dimensions and weights
Standard CTD90
-
pressure tube length
tube diameter
protection cage diameter
protection cage length
gross length
gross weight
340 mm
89 mm
120 mm
220 mm
630 mm
3,5 kg
2000 m version:
-
tube
total weight
89 * 5,5 mm titanium
4,4 kg
6000m version:
tube
total weight
89+7,62 mm titanium
5,5kg
CTD90 with current meter (2000 m)
-
protection cage diameter
220 mm
Protection cage height
780 mm
gross weight (probe)
5,7 kg
gross length (probe)
700 mm
weight with protection cage
7,1kg
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Sensors
The CTD 90 has a maximum of 16 analogue channels and 8 digital inputs or
outputs for the connection of different sensors. A maximum of 9 sensors fit
onto the bottom. The other sensors or instruments have to be connected
externally via additional underwater plugs in the sensor lid.
The following sensors can be accommodated in the sensor-base (bottom
mounted sensors without cable connection)
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Pressure transducer
Ground runner
Temperature sensor Pt 100
Conductivity cell
Oxygen sensor
Ph and redox sensor
Seapoint turbidity meter
The standard sensors have the same flange with an integrated six-pin glass
feed through (400 bar) equipped with a small six-pin round connector (see
figure below). All of these sensors can therefore be removed from the outside
and can easily be replaced without having to open the probe.
standard
sensor
flange
2x O-rings 16x1.5
O-ring 13x1
6 pin glass
feedthrough
LEMOSA 6pin connector
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External sensors
with analogue outputs and cable connection to the top cap of the CTD90
fluorometer (Seapoint, TRIOS, Cyclops7)
current meter (hs engineers)
transmissiometer
light sensors (LI-COR)
multi water samplers (Hydro-Bios)
multi plankton nets (Hydro-Bios)
fast oxygen sensor (AMT), also available with standard flange
H2S sensor (AMT), also available with standard flange
methane sensor (CAPSUM)
can be attached and operated as external sensors. Power for external
sensors has to be supplied by the CTD90. Standard supply voltage is 12 volt;
supply up to 26 VDC is possible.
3.1
Pressure transducer
A piezo-resistive full bridge in OEM version with a diameter of 15 mm and a
total height of 6 mm is used as pressure transducer (produced by the Swiss
manufacturer KELLER). The casing and diaphragm are made of alloy C276.
The transducer is delivered with a small SMD-PCB and includes a
temperature compensation of the pressure measurement. The sensor is
mounted in the base of the probe; the SMD-board has contacts and is
plugged onto the main board of the probe.
Pressure transducer
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Technical characteristics
-
Manufacturer
Model
-
Dimensions
Full scale range
Bursting pressure
Repeatability
Hysteresis
Zero drift
-
Precision
3.2
Ground runner
KELLER, Switzerland
PA7-XXX Progress
(XXX:= full scale range in bar)
15 mm diameter, 5,6 mm height
1, 2, 5, 10, 20, 50, 100, 200 bar
150 % of FS range
0,1 % of FS range
0,1 % of FS range
0,01 %/°C
reduced to 0,1%FS by Progress
0,1 % in the range of –5°...35°C.
The function of the ground runner is to recognize the sea floor in time during
profiling. It helps avoiding damage to the sensors through ground contact.
The ground runner mainly consists of a mobile magnet and a reed contact,
which are held together by spring tension. During a profile the magnet is
pressed against the spring tension by a control weight on a line and so kept
away from the reed contact, the contact is open. If the control weight has floor
contact the spring release the tension and presses the magnet to the reed
contact which is then closed by the magnetic field.
The reed contact produces a digital signal, which is interrogated by the microcontroller and serially, transmitted to the PC.
3.3
Temperature sensor
The temperature sensor is a platinum resistor Pt100 in a tiny ceramic carrier
of 15 mm length and 0,9 mm diameter. It is fitted in a slender titanium tube
1,2 * 0,1 mm, about 30 mm long. This delicate tip is resistant to a pressure of
600 bar but it is extremely sensitive to knocks and inflection. Therefore the tip
is surrounded by a titanium perforated shield tube, which is mounted onto the
standard flange. The platinum resistor is connected in 4-wire technique.
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Technical data
Manufacturer
Type
Measuring range
Response time
Repeatability
Accuracy
Maximum depth
3.4
SST
Merz Pt 100/1509
-2°C – 35°C
approx. 150 msec.
< 0,001°C
0.005°C
6000 m
Conductivity cell
Short description of measuring principle
All models of conductivity sensors use 7 electrodes in a cylindrical arrangement. The cell is always constructed symmetrically as depicted in the
following sectional drawing.
The central electrode D is used to impress alternating current of 500 Hz to 1
kHz frequency (square wave) into the water volume while both outside
electrodes A and G are the current return leads, which are held on a constant
potential. There exist two pairs of sensing electrodes (B, C and E, F), which
measure the voltage drop across them. The electrical field in a homogeneous
medium is symmetrically divided on both half-cells. The constant potential on
the outer electrodes limits the electrical field to the inside of the cylinder and
prevents any influence from boundary conditions outside the cell. The
conductivity electronic is mainly an automatic closed AC control loop which
hold the voltage drop across the sensing electrodes on a constant level, while
the current is proportional to the actual conductivity value.
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Conductivity sensor for profiling
The conductivity cell consists of a quartz glass cylinder with 7 platinum
coated electrodes. Because of the small inner diameter of 8 mm the cell
needs a minimum vertical flow velocity to obtain full accuracy. The cell is
vulcanised with rubber in a mould. The cleaning procedure must be carried
out very carefully hence the glass cylinder is sensitive against shock and
impact.
Technical characteristics:
Manufacturer
Model
Cell factor
Ranges
Response time
Reproducibility
Accuracy
Maximum depth
Min. flow through the cell
ADM
7-pole electrode cell
K= 1,2
0 – 6 mS/cm – 65ms/cm
100 msec at 0,5 m/sec flow
< 2µS/cm
20 µS/cm
1000 m
10 cm/sec
Conductivity sensor (6000 m)
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3.5. Oxygen sensor
The oxygen sensor measures the dissolved oxygen in the water using
polarographic methods. The platinum cathode has a diameter of 4mm and is
encased with a teflon membrane. The oxygen current consumption ranges
from 0 to 12 µA due to the big diameter of the platinum wire. The relative high
current consumption requires a minimum current flow of 10 cm/sec in order to
avoid qxygen depletion in front of the membrane.
Technical data:
Manufacturer
Type
Polarisation voltage:
Range
Oxygen current
Temperature range
Response time
Accuracy
Maximum depth
SST/Oxyguard DO522M18
Clark electrode, self galvanizing
-0,7 VDC
0 – 200 %
0 – 30 µA
-2°C – 30°C
approx. 10 sec (98%)
+ /-3%
2000 m
Oxygen sensor without protection cap
Oxygen sensor with protection cap
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3.6. pH and Redox sensors
3.6.1 Depth range 0..160m
pH and redox combined electrodes are industrial sensors using a solid
reference system (stiff polymer mass containing KCl) and an aperture
diaphragm which allows direct contact between reference electrolyte and
sample medium. Regeneration of the glass membrane or filling up electrolyte
is not possible. When the lifetime of the sensor is over, it has to be replaced
by a new one. The sensor has a thread PG 13,5 and is screwed into a flange.
A coaxial socket makes the electrical contact in the flange. Sealing between
sensor and flange is achieved by an O-ring, which is part of the sensor.
Technical data:
Manufacturer
Model
Measuring range
Maximum depth
Shaft diameter
Length with flange
Response time
pH
METTLER-TOLEDO
405-DXK-S8/120
4-10
160m
12 mm
167 mm
approx. 1 sec
Redox
METTLER-TOLEDO
Pt 4805-DXK-S8/120
-2000mV – 2000 mV
160 m
12 mm
167 mm
approx. 1 sec.
3.6.2. Depth range 0..500 m
pH and redox combined electrodes based on the same principles as
described in §3.6.1 but more pressure resistant.
Technical data:
pH
Redox
Manufacturer
Model
Maximum depth
Hamilton
Polylite PRO 120 XP
500m
Hamilton
Polylite RX 120 XP
500m
Other technical data same as above (see picture next page).
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3.6.3. Depth range 1200m
This pH/ORP Sensor uses a pressure-balanced glass electrode with a
reference to provide in-situ measurements up to 1200m depth. The sensor is
equipped with a reference system using a solid gel (stiff polymer mass
containing Ag+-free KCl) and a ceramic pore diaphragm and with a pressure
stable pH-sensitive glassy electrode.The pH probe is permanently sealed and
supplied with a soaker bottle attachment. The bottle contents must be 3 mKCl
solution (pH 4) that prevents the reference electrode from drying out during
storage.
This sensor is absolutely H2S resistant.
PH
Manufacturer
Measuring range
Maximum depth*
Shaft diameter
Shaft material
Bulkhead material
Thread
Shaft length
Length with flange
Response time
AMT GmbH
4-10
1200m
12 mm
transparent plastic
Stainless steel
G1/4 (ISO228)
84mm
117 mm
approx. 1 sec
Redox
AMT GmbH
-2000mV.. – 2000 mV
1200 m
12 mm
transparent plastic
stainless steel
G1/4 (ISO228)
84mm
117 mm
approx. 1 sec.
* This sensor is pressure resistant up to several thousand meters depth
with a slight increase of pH/ORP values.
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3.7. Seapoint turbidity sensor
The bottom mounted turbidity sensor is based on the SEAPOINT turbidity
meter in the bulkhead version, which is screwed onto a standard flange.
Electrical connection is achieved by a separable 6 pin round connector. For
further details please refer to SEAPOINT´s manual.
The Turbidity sensor measures the concentration of suspended matter. It is
equipped with a pulsed infrared light transmitter and detects the scattered
light from the particles suspended in water. Transmitter and detector
arrangement uses 90° scattering at a wavelength of 880 nm. The output
signal is proportional to the particle concentration in a very wide range. For
detailed description of Seapoint turbidity meter refer to the special user
manual.
Specifications:
Power: 7 – 20 VDC, 3,5 mA average
Signal: 0...5 VDC (each range)
Scatterance angle: 90° avg. (15...150°)
Light source wavelength: 880 nm
Linearity: 2%
Depth capability: 6000 m
Size: 2,5 cm diameter, 11 cm length
Ranges: 0-25, 0-125, 0-500, 0-2500 FTU
Picture shows the bulkhead version with flange
The turbidity sensor is available in two different versions: standard version
has an underwater plug, is connected to the probe via a 6-wire cable and has
to be fixed to the probes protection cage with a clamp. The Bulkhead version
is plugged into a fit of the bottom cap of the probe and hence needs no
underwater connection cable. The range can be selected by hardwiring
according to the customers requirements.
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3.8. Cyclops7 Fluorometer
There is one version of CTD90, that allows the adaption of Turner`s cyclops7
fluorometer into the bottom cap of the probe. The cyclops7 is integrated
without any modification of the fluorometer housing. To avoid corrosion
problems the cyclops7 housing must be made of titanium. The gain setting
lines are fixed to a gain of 10 which corresponds to a range of approximately
0-50µg/l. Internal wiring is depicted in drawing 015 M08 04A (see appendix).
Modification and change of gain setting requires opening of the CTD90
housing.
For details and hints for application please refer to turner´s user manual.
3.9. Multirange sensors
There are a number of sensors, which have several measuring ranges with
different sensitivities on a single analogue output. The CTD90 supports these
multirange sensors by automatic range switching and transmits measurement
values and range information to the board unit in a single 16 bit word.
Analogue values have 16-bit resolution. The range code consists of 2 bits and
occupies the two least significant bit of the 16 bit measuring value. This limits
the real resolution of the multirange sensors to 14 bits. But since all these
sensors doesn’t need CTD resolution the overall accuracy is not affected by
this procedure.
3.9.1. Seapoint turbidity meter
Description is given in §3.7. Beside the hardwiring of the selected range the
CTD90 offers the possibility of automatic range switching.
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Both versions have 4 ranges, which are controlled by two independent gain
control lines A and B:
range
B
A
gain
calibration range
0
1
2
3
0
1
0
1
0
0
1
1
*1
*5
*20
*100
0...2500 FTU (linear up to 1000 FTU)
0.....500 FTU
0 125 FTU
0
25 FTU
0:= line tied to GND
1:= line left open
The CTD electronic monitors the signal output of the turbidity sensor and
selects automatically the next suitable range if a certain limit is exceeded or
dropped. The limits are approximately 10% resp. 90% of the current range.
The instrument is factory calibrated with a formazine turbidity standard.
3.9.2. LI-COR Quantum sensor
is used for measuring Photo synthetically Active Radiation (PAR) in aquatic
environments. Due to its 400 – 700 nm quantum response it is a suitable
sensor for investigation of the primary production. LICOR offers two different
underwater sensors:
LI-192SA cosine corrected quantum sensor (following Lambert’s cosine law)
measures the Photosynthetic Photon Flux Density (PPFD) through a plane
surface (photon or quantum irradiance between 400 and 700 nm)
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LI-193SA spherical quantum sensor determines specifically the
Photosynthetic Photon Flux Fluence Rate (PPFFR), the number of photons in
the visible range incident per unit time on the surface of a sheer divided by its
cross sectional area.
Both instruments are calibrated in µmol/s*m2 (µE) where 1 µmol is 6,023 *
10-17 photons.
Specification:
Detector: silicon photodiode
Range: 0 ... 10000 µmol/s*m2
Calibration accuracy: 5%
Linearity: 1%
Long term stability: 2% per year
depth capability: 350 m (LI-193SA) / 550 m (LI-192SA)
Sensitivity: typical 3 µA / 1000µE
Both sensors will be connected to the probe by a 2 wire underwater cable.
Please note: the light sensors must be mounted on the top of the probe to
avoid shade of neighboured instruments.
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The dynamic measuring range (sensitivity of the photodiode) covers approximately 7 to 8 decades of light intensity. Logarithmic amplifiers have a different
resolution depending on the current value. To avoid this disadvantage the
complete range is divided into 4 decades each with 14-bit resolution.
range
0
1
2
3
range code
0
1
0
1
0
0
1
1
current [µA]
0.....0,05
0 0,5
0.....5
0 50
PPFFR / PPFD (*)
0........12
0......125
0....1250
0..12500
(*) calculated for LI-multiplier of 250
The result is a linear response from 0,001 up to 10000 µmol/s*m2.
Range switching is executed automatically when the measuring value
increases the 95% full scale level or decreases 5% FS of the current range.
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3.9.3. Seapoint Fluorometer
measures chlorophyll A concentration in 4 different ranges, which are selected by two control lines A and B
range
range code (B/A)
0
1
2
3
0
1
0
1
Concentration [µg/L]
0
0
1
1
0....150
0
50
0
15
0........5
The range switching procedure is similar to the turbidity meter; the limits are
90% and 10% of full scale.
The instrument has a six pin underwater plug (Impulse AG306) and has to be
connected by a cable to the CTD.
Specifications:
Power: 8 – 20 VDC, 15 mA average
Signal: 0 – 5 VDC (each range)
Light source: blue LED 470 nm
Detector: photodiode 680 nm
Min. detection level: 0,02 µg/l
Depth capability: 6000 m
Size: 64 mm diameter, 168 mm length
The instrument is also available in a version to measure DOC (dissolved
organic matter or yellow substances).
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Replacement of sensors, opening the probe
When replacing a sensor the probe generally doesn’t have to be opened
(exception: pressure sensor). Proceed as follows:
-
remove both of the M4-screws which hold the flange
carefully remove the respective sensor whilst gently turning it out of its
fitting in the base
disconnect the plug contacts (pull lightly).
Reassemble in opposite order. To remove the pressure sensor the probe has
to be opened. This is done in the following order:
-
-
remove the protection case
take the lid off: first of all unscrew the 4M3-screws on the side of the
tube-end and then pull the lid off whilst gently turning it without tilting it
detach the base from the tube (as with the lid)
disconnect all of the sensor plugs, unsolder the pressure sensor cable
on the main board
detach the bedplate from the base, unscrew the pressure sensor
holding screw
pull the sensor out carefully by its cable (from 100 m range upwards
blow it out, if necessary, with compressed air from the front side)
Attention: When replacing the pressure sensor the progress-print must
always be replaced as well because it contains the temperature
compensation for the specific pressure sensor. When inserting the new
pressure sensor grease the O-ring thoroughly. Reassembling is done in the
opposite sequence.
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Probe electronics
The electronics of the basic version consists of two printed circuit boards
1.
2.
3.
5.1
Power supply and cable driver
Main board and plug-in modules.
Expansion board
Probe power supply
is situated on a small circular board (50 mm diameter), which is screwed to
the inside of the lid. This board contains the DC-DC-converter for the probes
operating voltages (5 volt and –5 volt), the FSK modulator, the cable driver
and the zenerdiode for constant current supply. Components, which produce
a considerable heat, are screwed onto the lid, thus using the good thermal
contact for heat abduction to the metal housing and seawater (cable driver
transistor, zenerdiode). The wires of the probes underwater connector are
soldered onto this board; the connection to the main board is separable by a
plug.
5.2
The main board
Measures 250 mm * 50 mm and contains the following circuitry:
-
Data acquisition module as SMD plug-in board
8 channel analogue multiplexer
RS-232 driver
Water sampler releaser
Temperature bridge
Conductivity control circuit
Pressure amplifier (with Progress-print as plug-in module)
Oxygen amplifier
Redox amplifier
PH amplifier
Differential amplifier for sensors with analogue output
The main board has an expansion plug which contains all necessary signals
for a system extension to 16 sensors. On the backside of the bedplate a
further same sized additional printed circuit board can be attached which
incorporates the electronics for further sensors.
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ADC Module
The heart of the probe is a microprocessor controlled 20-bit analogue digital
converter, which generates an auto calibration cycle each time the probe is
switched on. This results in an exceptionally good long-term stability. This is
especially important for the stability and precision of the CTD sensors.
5.3. Expansion board
The expansion board is equipped with a second 8-channel analogue
multiplexer for the upper address range from 8 to 15. This board provides the
plug in position for all multirange sensor electronics and the interface circuitry
for current meter and compass.
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Power supply, connector pin assignment and interfaces
The CTD90 has a 4-pin underwater connector, which allows the probe to be
operated in different modes. The standard connector is SUBCONN MCBH4M
made of titanium. For compatibility to existing systems a SUBCONN BH4M
can also be used.
Pin assignment:
BH4M
MCBH4M
Bulkhead connector
Pin1
Pin2
Pin3
Pin4
6.1
+Ik / FSK signal
TxD (RS232)
-Ik / -Ub / GND
+ Ub
4
1
3
2
Operation with multicore cables
The use of multicore cables is advisable for shorter distances between probe
and PC and particularly in a laboratory. The probe is then supplied either by a
battery or a regulated power supply. The voltage is applied to Pin3 (negative)
and Pin4 (positive). Data transfer to the PC is via pin2 (Transmit data TxD)
and pin3 (GND). The wiring of such a cable is described below.
Inline cable IL4F
signal
9-pin SUB-D plug DB25S
Pin 2
Pin 3
Pin 3
Pin 4
TxD
GND
- Ub
+ Ub
Pin 3
Pin 5
banana plug black
banana plug red
MCIL4F with locking sleeve
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The supply voltage ranges from 9 to 26 volt DC. The probe is designed for
connection to 12-volt batteries or to regulated power supply. The current
consumption is about 50 mA for a C,T,D,O2,pH,ORP.
The maximum supply voltage is 26 volt. Higher voltages cause destruction of
components. Damage due to overvoltage is not covered by the guarantee.
Connection to unregulated power supplies, in particular motor-driven emergency power supplies, is not advisable.
The maximum length of the multicore cables depends mainly on the cable
resistance and can at best be several hundred meters. An advantage is that a
specific interface between probe and PC is not necessary.
6.2
Operation with single conductor cables
The standard application of CTD-probes is profiling performed via winches
with slip rings and single conductor cables. Constant current then supplies
the CTD90; the FSK signal is impressed on the constant current as voltage
modulation. An interface between PC and winch (probe) produces the
constant current and converts the FSK-signal from the probe into PCcompatible V24 data. The maximum voltage of the current source depends
on the cable resistance (cable length). The wiring is as follows:
Inline cable
Signal
cable
Pin 1
Pin 3
+ Ik/FSK-signal
-Ik
internal wire
shield
The basic version has a constant current of about 60 mA; this can be
distinctly higher when external devices are connected. The voltage drop
between Pin 1 and Pin 3 is approximately 17-18 volt. The FSK signal is a
sinusoidal signal of approx. 5Vss and modulated on the constant level. A
logical LOW-level is the equivalent to the low frequency; a HIGH-level is
equivalent to the higher frequency. The frequencies are 35kHz and 45 kHz.
The TxD signal on pin 2 of the probe connector is identical with the RS-232
output of the probe interface.
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7 Service and maintenance
The best maintenance for the probe is to handle it with care. Despite the fact
that the probe is sturdily and stabile designed, unnecessary strains like
knocking and shocks should be avoided. Apart from that, there are only few
instructions and maintenance rules, which should be heeded or met to, so as
to ensure a longer life span and correct measuring, results.
7.1
The underwater connector
Is actually maintenance-free. However it has proved itself to be advisable to
lubricate the sealing surfaces of the pins with sea waterproof grease. This
reduces wear whilst plugging and unplugging. Further tips:
-
7.2
clean the plugs with warm soapy water. They do not have to be dried.
Chemicals should be avoided.
To avoid corrosion never plug or unplug whilst under water
To conserve the cable plug never unplug by pulling on the cable. Avoid
bending radiuses and above all narrow, sharp kins.
Plugs that are not in use should never be left blank. They should always
be protected against corrosion by a dummy cap.
Pressure sensor
The pressure sensor doesn’t require special attendance or maintenance.
Personnel experience has shown however, that the pressure sensors should
never be tested by pressing a pin onto the membrane. This often causes
damage to the membrane or dents it, which can lead to pressure reading
mistakes or to a total damage. Pressure sensors damaged in such a way are
not covered by the guarantee.
7.3
The temperature sensor
The temperature sensor is maintenance free. Dirt and plant cover only
prolong the time constant but have no effect on the precision. When cleaning
the sensor take special care of the sensitive tip, which should not be bent.
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7.4. The conductivity cell
Is principally not maintenance free. It must regularly be inspected for plant
cover and electrolytic calcification. Both effects reduce the measured
conductivity. It is appropriate if the probe is rinsed on deck with fresh water
after each application. This prevents the formation of salt crystals on the cell
surface. Calcareous deposits, which originate from the electrical current flow
in the cell, are easily removed if the cell is immersed for a few minutes in a
diluted acid. The quantity of rising CO2-bubbles gives information on the rate
of calcification. The cell is completely decalcified when the bubble formation
has ceased. Afterwards the cell has to be rinsed with fresh water. Depending
on the operating time this procedure is only necessary every few months.
Cleaning is more difficult after long-time application especially during warm
months, when heavy sea-pest growth densely populates the cell within a
short time (2 weeks). In this case the cell has to be placed into diluted acid (if
necessary for a longer time) and then a plastic bottlebrush has to be pushed
through it. This procedure may have to be repeated until the cell is completely
cleaned. Then the cell is rinsed with fresh water. Particular care has to be
taken, that the metal components on the electrode surfaces are not
scratched, nor must they come into contact with other metals. Otherwise the
lifetime of the cell and the long-time stability of the conductivity
measurements will be impaired. After the electrodes have been treated with
acid a short-term increased conductivity reading may occur, this should
normalize itself within an hour.
7.5. Oxygen sensor
The oxygen sensor requires some attention from time to time. All the
necessary maintenance like exchange of electrolyte and membrane is
described in an OxyGuard leaflet in the appendix of this manual.
The red O-ring has two different positions:
1. in the front position (shown in the picture below) the O-ring prevents
leakage of the electrolyte through the thread during storage. This
position should not be used for measurements but only for
storage.
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2. in the backward position it allows the electrolyte to build a high
impedance electrolytic connection between medium (sea water) and
electrolyte room behind the membrane. This connection is necessary
for proper measurements. Please take care that during
measurements the O-ring takes always the backward position
The Oxyguard DO sensor is supplied by us with a sensor protection cap
made of plastic . To achieve a tight fit to the sensor head the cap is equipped
with an O-ring 21*1 mm and a 2mm hole in the center of the bottom (see
photo). The cap should be used as protection for the membrane and sensor
head as well as useful tool for oxygen field calibration.
If the membrane tension is dropping during operation or time the sensors
output signal is changing too. The zero point of the oxygen sensor remains fix
during its lifetime but the sensivity (slope) can vary. The user can execute a
field calibration after each membrane exchange or when he doesn´t trust the
measured values anymore.
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Field calibration
The SDA software offers the possibility to perform a field calibration and to
change the reading automatically. Let the SDA program run with the probe
connected to the PC. The field calibration procedure is very simple:
-
-
Keep the membrane of the DO sensor dry
Put the red o-ring in the backward position
plug the protection cap onto the sensor head with a proper fitting o-ring
Fill a small plastic cup with water and immerse the sensor head up to the
flange (small white plastic cup is part of the delivery)
after a short time the enclosed air in the cap is water vapour saturated and
the the oxygen reading should have 100% partial pressure.
If the oxygen reading is stable click menu point Calibrate and 02 Field
Calib
When O2 Field Calib is selected, the current oxygen reading is
automatically stored. The default value 100% is accepted when clicking on
the button Calculate slope now.
The SDA programm calculates the new oxygen Field calibration coefficient
(originally 1) and the reading is now 100%.
The field calibration method works in any basin or tank and the result is
independent of the salinity. When putting the complete probe into a basin you
have to estimate the immersion depth of the oxygen sensor (measured from
the membrane to water surface). Every 10 cm immersion depth lead to an
increase of the oxygen reading of 1%. So e.g. if the procedure is executed
with the DO sensor 30cm below the water surface, the default value in the
button field Enter desired value has to be changed to 103%.
7.6. pH and Redox sensor (160m + 500m)
Both sensors are principally maintenance free. After its life span has ended
the corresponding sensor has to be replaced. When unscrewing the sensors
no moisture (e.g. water drops) what so ever must reach the contacts (dry
beforehand). A single drop of saltwater is enough to cause long-lasting
incorrect measurements – this is due to the high output impedance of 100 –
400 MΩ. So only replace sensors under clean and dry conditions please.
The life span of the sensors ceases when the time constant of the pH or
redox measurement drastically increases. The life span has also ended when
the reference electrolyte is dissolved down to the screw thread rim. Water can
then possibly leak in through the bolting. The pH and Redox sensors are
particularly endangered when they come into contact with H2S in water.
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Some minutes in hydrogen sulphide is enough to irreparably ruin the sensor.
In most cases stable-measuring results cannot be achieved anymore despite
lengthy rinses with cleansing or buffer solutions. If measurements in H2Sconcentrations are necessary we recommend to remove the sensors and to
screw on locking caps (or to use the 1200m sensor; refer to 7.7.)
Special care has to be taken that before using the sensor no air bubble is to
be found in the pH electrolyte directly behind the ion-permeable glass layer
because it would interrupt the internal electrical connection to the pH
electrode. The air bubble has to be shaken out – similar to the shaking of a
thermometer. The air-bubble often occurs when the sensor has been stored
horizontally for a longer time.
7.7 pH/ORP sensor (1200m, H2S resistant)
Do never touch the sensitive tip. Protect the pH-sensor with the delivered
soaker bottle containing the storage solution and avoid any dry out of the
sensitive tip.
Avoid any air inside the bottle, fill completely with 3 M KCl. Make sure, that
only 3 M KCl with pH 4 buffer is used for storage. It is not allowed to use
other wetting caps in order to avoid any air pressing into the diaphragm
leading to sensor malfunctions or damage. Damage because of using other
wetting caps or storage without any wetting cap is not covered by guarantee.
The pH sensor has to be rinsed carefully with fresh water after finishing the
measurements.
The pH sensor is a replacement part and has to be changed , if the sensor
has reached the lifetime. The sensor has a stainless steel thread G1/4A
(titanium on request) which is screwed into a flange. The electrical contact is
made by a socket in the flange. Sealing between sensor and flange is
achieved by an O-ring which is part of the sensor. After the sensor’s life span
has ended, the sensor has to be replaced.
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7.8. Seapoint turbidity meter
The turbidity sensor has to be cleaned from time to time. Especially the
optical sensitive flat surfaces have always to be kept clean. Avoid the use of
chemical solvents. Make use of the protection cap if the sensor is not in
operation.
8. Probe data format
The probe data can be fed into the PC serial ports COM1 to COM4. The
standard settings of the probe are:
Baud rate
Character length
Number of stop bits
Parity
Protocol
Signals
1200 (2400, 4800, 9600)
8
1
odd
non, asynchronous
GND, TxD
The data is transmitted as binary data. 3 bytes (24 bit) per sensor are
required, 16 bits are measuring values, 5 bits are address and 3 are status
bits. The transmission format is presented in the following chart:
Sensor
1. Byte
2. Byte
3. Byte
LSB
H D0 D1 D2
H D7 D8 D9
L D14 D15 A0
MSB
D3 D4 D5 D6
D10 D11 D12 D13
A1 A2 A3
A4
DO – D15
AO – A4
H, H, L
16 bit binary data (decimal value 0 – 65535)
5 bit binary address (decimal sensor address 0-31)
3 status bits 1,1,0
A sensor data transmission starts with the 1. Byte (LSB first) and ends with
the third byte (MSB last). Every sensor in the probe has a specifically
assigned binary address which identifies the kind of sensor. The status bits
are useful for the PC data acquisition programmes to compile the 3 bytes in
the correct sequence.
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A complete data set begins with the lowest address and ends with the highest
address. All addresses between 0 and 31 may occur. The transmitted
physical addresses are identified by the data acquisition program and
compared to those registered in the configuration file. As an example the
addresses for the CTD90:
Address 0
Address 1
Address 2
Address 3
Address 4
Address 5
Address 6
Address 7
light transmission
probe serial number, ground runner)
pressure
temperature
conductivity
oxygen
pH
redox
The remaining vacant addresses can be used for external probes or sensors.
Adress 1 Housekeeping data
The ground runner is always transmitted on the address 1 as LSB:
D0 = LOW
D0 = HIGH
no floor contact
floor contact
If the probe number transmission is activated it will be transmitted on the
upper 15 bytes of the address 1: D15…D1.
Multirange sensors:
A multirange sensor with databits D15…D0 carries the range information
in the least significant two bits D1, D0:
range
D0 D1
Range 0
Range 1
Range 2
Range 3
(0, 0)
(1, 0)
(0, 1)
(1, 1)
The true resolution of a multirange sensor is therefore 14 bit , but the sensor
data is handled by the SDA program like any other 16 bit value. The range
information is used by the SDA software to load the correct calibration
coefficients for the calculation of the engineering units.
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9 Calculation of the physical data
Data transmission and data storage when online are performed solely in
binary dates. The PC-data acquisition program carries out the calculation of
the physical values from the raw data and their display. The calculation of
physical values for standard sensors is made by a polynomial of n.th order:
Measurement value: =
Ai * ni
Ai calibration coefficients
i = 0...4
Normally imax = 1 or imax = 2. The coefficients are determined by calibration
measurements against a normal or subnormal and subsequent regression
calculations.
Further calculations such as the absolute oxygen concentration, salinity,
density and sound velocity are carried out with the current UNESCOformulas.
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10. Spare parts
10.1. Sensors
-
pH senor 160m
Redox sensor 160m
PH sensor 500m
ORP sensor 500m
PH and ORP 1200m
Pressure sensor
METTLER-TOLEDO HA405-DXK-S8/120
METTLER-TOLEDO Pt4805-DXK-S8/120
HAMILTON Polylite PRO 120 XP
HAMILTON Polylite RX 120 XP
on request
KELLER PA7-XXX Progress 0,1 - 2 Volt
(XXX Full scale range in bar)
10.2. O rings
-
Base and lid
Sensors (flange)
pressure sensor
76 * 2,5 mm
16 * 1,5 mm
13 * 1 mm (stainless Steel 316L)
12 * 1,5 mm (alloy C276)
PH/Redox sensor
12 * 1,5 mm (160m, 500m)
Underwater connector 12,42 * 1,78 mm
10.3. Plugs and cables
-
Dummy cap
Locking sleeve
Inline connector
SUBCONN MCDC4F / DC4F
SUBCONN MCDLS-F / DLSA
SUBCONN MCIL4F / IL4F
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Appendix
Corrosion protection for pressure transducer
Standard application for CTD 90 is profiling. If the probe is used for long-term
measurements like permanent monitoring or mounted stationary on ships,
special care should be taken with the pressure transducer. Exposed for a
long time to seawater, problems may rise with corrosion of the welded seam
between the transducer’s diaphragm and housing. Especially low oxygen
concentrations increase the danger of corrosion.
To solve the problem and to ensure a long lifetime of the pressure transducer,
we recommend to use the small ¼“UNF(M8) adapter, which is depicted
below. This plastic adapter is screwed into the calibration connection thread
and sealed with an O-ring 6*1 mm, the other end is closed by a pressure
balance membrane held by two 0-rings 8*1,5 mm. The inside is filled with
silicone oil AK350. The performance and accuracy of the pressure
measurement is only slightly increased.
2 x O-Ring 8 x 1,5
silicone oil AK 350
Pressure balance membrane
EYDAM 9072681
1/4" UNF 28THD
O-ring 6*1mm
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Appendix
CTD90 Sno.20, current meter and compass
Definition of terms
The instrument axes of current meter and compass integrated in the CTD90
are defined by an orthogonal co-ordinate system depicted in the diagram
below:
Y
top view
O2
P
C
X
T
V
Turb
Since the OEM current meter and compass are mounted on the bottom cap
of the probe, the arrangement of the fits on the bottom determines the axis
directions.
The SDA menu allows the acquisition of the 4 measuring parameters Vx, Vy,
Hx, Hy for the current velocity and magnetic field intensities. The user can
select between 3 different calculated directions:
MDIR
CDIR
CMDIR
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The angles are counting clockwise against the North direction (see picture
below):
N
Y
CMDIR
MDIR
V
CDIR
X
MDIR angle between North direction and positive Y-axis
CDIR angle between current vector and positive Y-axis
CMDIR angle between current vector and magnetic north
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Picture of the hs engineers inductive current meter type ISM-2001F
Example: CTD90 probe with current meter and deep-sea conductivity sensor
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