YSI SonTek ADVField, Technical Documentation Manual

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SonTek/YSI
74 ADVField Operation Manual (September 1, 2001)
4.8. Optional Sensors (Internal): Temperature and Pressure
All ADVField systems (16/10/5-MHz) can include temperature and pressure sensors in the signal
conditioning module as described in §1.1.2 and §1.1.3. The temperature sensor is used for sound
speed corrections. The pressure sensor provides simultaneous pressure and 3D velocity meas-
urements (PUVW for directional wave spectra).
The temperature sensor uses a thermistor installed in the conditioning module end cap coupled to
a titanium pin that is exposed to the water. A titanium pin is used to eliminate any corrosion con-
cerns. This design allows the thermistor to be mounted internally, while avoiding the insulating
effect of the plastic housing. Even with this coupling, the temperature sensor does require some
time (
≈ 5 minutes) to stabilize to the true water temperature. The pin is mounted through a hole in
the end cap. The back of the hole (leading into the conditioning module) is filled with epoxy to
create a watertight seal. The two wires from the temperature sensor are connected to the pressure/
temperature sensor board as described below.
For the temperature sensor to function properly, the entire conditioning module must be sub-
merged. Under normal operating conditions, the temperature sensor has a specified accuracy of
±
0.2
°
C over the range of -5.0 to 50.0
°
C. Temperature data is stored with a precision of 0.01
°
C.
The specified accuracy corresponds to a sound speed accuracy (for temperature considerations
only) of less than
±
0.1%.
The pressure sensor is mounted
in the conditioning module end
cap (Figure 23). The sensor is
recessed within the end cap and
isolated from the water for cor-
rosion protection by a dia-
phragm and silicon-oil reser-
voir. The diaphragm is held in
place by a plastic retaining plug
that screws into the end cap.
The sensor forms a watertight
seal using a bore seal o-ring.
For added leak protection, the
path into the conditioning
module is filled with epoxy.
The two wires from the temperature sensor and the six wires from the pressure sensor go into a
10-pin connector that mates with the pressure/temperature sensor circuit board. This board condi-
tions the signals from the sensor before going through the cable to the processing module. A 5-
pin connector from the pressure/temperature sensor board goes to the conditioning module con-
nector and to the processing module. See §4.7.3 for more information about the internal wiring of
the signal conditioning module and the mounting of the pressure/temperature sensor board.
Pressure sensor data is stored in units of counts that must be converted to physical units (dBar)
using two calibration constants. Pressure is stored as counts to maintain high resolution for a
wide range of pressure sensors (from 10 to 6000-m depth ratings). Pressure is converted to dBar
using the following formula.
Retaining Plug
Diaphragm with
Silicon Oil Reservoir
Pressure Sensor
with Bore Seal O-Ring
Sensor Wires
Cross Section of Conditioning Module End Cap
Pressure Sensor Installation
Figure 23 - ADV Pressure Sensor Installation