YSI SonTek ADVField, Technical Documentation Manual

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Using Frequency Pressure Sensors with SonTek/YSI Systems (December 2001)
1
SonTek/YSI Support Documentation
6837 Nancy Ridge Dr., Suite A
•
San Diego, CA 92121
•
Telephone (858) 546-8327
•
Fax (858) 546-8150
•
Internet: support@sontek.com
Using Frequency Pressure Sensors with
SonTek/YSI ADPs, Hydras, and Argonauts
This document describes the use of frequency pressure sensors with SonTek acoustic Doppler
current meters. SonTek supports two types of frequency pressure sensors: (1) the Druck RPT, a
silicon resonant transducer (referred to as
DRUCK
) manufactured by Druck, Inc. and (2) the Paro-
scientific digiquartz transducer (referred to as
PAROSFREQ
) manufactured by Paroscientific, Inc.
1. Overview
Typically, SonTek instruments include analog pressure sensors (e.g., strain gage) that provide
sufficient accuracy and stability (0.1 to 0.25 %) at a moderate cost. These sensors are usually in-
stalled within the system head (Figure 1). They are internal to the system and are usually referred
to as
PRESSURE
or
PRESSURE SENSOR
within our documents and system command interface.
Some applications, however, require better long-term stability (e.g., tide studies, wave interaction
with topography, long-term water-level monitoring, etc.). To accommodate these needs, SonTek
has integrated
frequency pressure sensors , which offer an order of magnitude better accuracy and
stability (0.01%). The first supported sensor was the Paroscientific digiquartz with a serial inter-
face (
PAROS
). These sensors, because of their size did not fit inside our systems and were
mounted externally (Figure 1). The next supported sensor, the Druck RPT, did fit inside an ADP
or ADVOcean head. However, for historical purposes, all
non-strain gage sensors are usually re-
ferred to as
EXTERNAL PRESSURE SENSOR
within our documents and system command interface.
2. Serial External Pressure Sensors (PAROS)
As mentioned, the first external pressure sensor supported by SonTek was the Paroscientific digi-
quartz with serial interface (
PAROS
). The
PAROS
is connected to a system by a 1 to 2-m cable.
The
PAROS
is available for ADP, PC-ADP, and Hydra systems. The differences, when compared
with a strain-gage sensor, are as follows:
•
The
PAROS
is an absolute sensor. It reads 1 dbar in air; a strain gage reports 0 dbars in air.
•
Sampling rate is limited to 4 Hz (ADVs and Hydras) due to serial interface limitations.
External Paroscientific
Pressure Sensor
Power and
communication cable
Internal pressure sensor
(strain-gage or Druck RPT)
SonTek ADP
External Paroscientific
Pressure Sensor
Power and
communication cable
Internal pressure sensor
(strain gage or Druck RPT)
SonTek ADVO
Figure 1: ADP and ADVOcean with external pressure sensors.