SonTek/YSI
Using Frequency Pressure Sensors with SonTek/YSI Systems (December 2001)
2
3. Frequency External Pressure Sensors
3.1. The Druck RPT (DRUCK)
Although the
PAROS
provides the required accuracy, its size and external location cause addi-
tional complications when mounting and deploying a system. SonTek, in collaboration with
Druck, Inc., now offers the Druck RPT (resonant pressure transducer) sensor. This sensor is very
compact and fits inside the same mounting socket as the regular strain gage (Figure 1). The
DRUCK
sensors are available for ADP, PC-ADP, Argonaut SL/XR, and Hydra systems. The dif-
ferences, when compared with a strain-gage sensor, are as follows:
•
The
DRUCK
is an absolute sensor. It reads 1 dbar in air; a strain gage reports 0 dbars in air.
•
Requires a special interface to sample the frequency signal.
•
Sampling rate is limited to 10 Hz (ADVs and Hydras) because of the time required to sam-
ple the frequency signal with sufficient precision.
•
Requires calibration matrix (specific to each sensor) to be loaded into the processor (system
CPU or a user PC) to obtain valid pressure readings.
•
Available in 50-psia pressure rating only (equivalent to
≈
22 dbar strain gage).
3.1.1. Sensor Calibration Template
Each current meter purchased from SonTek that has the
DRUCK
sensor installed already has the
appropriate calibration coefficients loaded into the processor. If this information is lost, you can
use the calibration sheet provided by the pressure sensor vendor to construct your own calibration
file. The structure of the
DRUCK
calibration file, required by SonTek systems, is as follows.
•
Pressure Sensor Serial Number
•
Oscillator Frequency (in Hz)
•
X
•
Y
•
Low end of temperature range
•
Corresponding voltage of the diode
•
Diode sensitivity
•
K00 K01 K02 K03
•
K10 K11 K12 K13
•
K20 K21 K22 K23
•
K30 K31 K32 K33
•
K40 K41 K42 K43
•
K50 K51 K52 K53
Example – Druck calibration file
1145118.drk
:
1145118
12.0000000E+06
+8.8880000E+03
+5.5200000E+02
-10
622
-2.21
+1.6214761E+03 -2.0699499E-02 +5.5220000E-05 -5.6160001E-08
+1.8251241E+00 -5.8612000E-06 +3.6197001E-08 -3.8715001E-10
+3.8615943E-04 -1.5274000E-09 -4.7059999E-12 -1.3233001E-13
+7.0553313E-08 -1.9064000E-12 -4.0058001E-14 +9.0119996E-16
+1.7913088E-11 -1.3525000E-15 +1.7647000E-17 +3.8552999E-19
+3.7756621E-15 +1.9573000E-19 +3.6951001E-20 -3.3300999E-22
ote: The X, Y, and K coefficients can
be found on the Druck calibration sheet.
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