pg
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15
Depth
Sensor Overview
EXO measures depth of water with a non-vented strain gauge. A differential strain gauge transducer
measures pressure with one side of the transducer exposed to the water and the other side exposed to a
vacuum. We calculate depth from the pressure exerted by the water column minus atmospheric pressure.
Factors influencing depth measurement include barometric pressure, water density, and temperature.
Calibration in the atmosphere “zeros” the sensor with respect to the local barometric pressure. A change in
barometric pressure will result in a zero shift unless the transducer is recalibrated to the new pressure.
EXO sondes have intake openings to allow water to act on the strain gauge. The EXO1 intake is located in
the yellow section between the battery compartment and
label of the sonde. The EXO2 intake openings are two small
holes on the face of the sonde bulkhead.
Location of Depth Sensor
Depth sensors are not on center. When deploying the sonde
vertically,
take care to ensure the sonde is redeployed in
same position. Often a marker pin inside a PVC pipe is
used. In
horizontal
deployments, take care to ensure the
redeployments are always in the same orientation. This is
especially important for the EXO2 sonde because the depth
sensor is off-axis.
1.6
(continued)
EXO 2 Depth Intake
EXO 1 Depth Intake
Specifications
Units
PSI, Depth (m, ft, bar)
Temperature
Operating
Storage
-5 to +50°C
-20 to +80°C
Range
Shallow:
0 to 33 ft (10 m)
Medium:
0 to 328 ft (100 m)
Deep:
0 to 820 ft (250 m)
Accuracy
Shallow:
±0.04% FS (±0.013
ft or ±0.004 m)
Medium:
±0.04% FS (±0.13 ft
or ±0.04 m)
Deep:
±0.04% FS (±0.33 ft or
±0.10 m)
Response
T63<2 sec
(see pg 12)
Resolution
0.001 ft (0.001 m)
Sensor Type
Stainless steel strain gauge
Depth Sensor Location
27.2 cm to WQ Sensors
Depth Sensor Location relative
to other water quality sensors
(see EXO sonde label)
