
37
To restart the filtering process, the HPB must receive an IN=Reset command or a power off/on sequence.
To disable the Buoy/Wave Filtering Algorithm, the HPB must receive a DO=X command, at which time normal
pressure readings will resume. (Note: The Buoy/Wave Filtering Algorithm will not be activated until the DO=B
configuration is made permanent by using the SP=ALL command.)
(3)
(1) The HPB will be pre-configured at the factory with the Buoy/Wave Filtering Algorithm enabled, if ordered with a
-H020 suffix. Consult the factory for other custom configurations.
(2)
A=
,
B=
,
C=
,
D=
,
CK
,
F=
,
I=
,
M=
,
P=
,
S=
,
U=
,
V=
,
X=
, and
Z=
inquiries are unavailable during the wave filtering
process.
(3) To obtain accurate sensor temperature readings at the completion of the wave filtering algorithm, it is necessary
to first send a
*ddIN
command. A
*ddIN
command will also interrupt the wave filtering algorithm and return the
HPB to normal pressure readings.
_____________________________________
1
WOCE Suface Velocity Programme Barometer Drifter Construction Manual, WMO-IOC, DBCP Technical
Document No. 4, Authors: A.L. Sybrandy, C. Martin and P.P. Niiler (Scripp Institution of Oceanography)
DS Deadband and Sensitivity Control
The
D
eadband and
S
ensitivity control command allows the user to adjust the threshold value that causes a
change in pressure reading. There are two option for this,
C
and
S
.
The
C
option sets the deadband to around the center of the pressure reading that moved it last. When the
deadband is first set, the deadband will be split half above and half below the current reading. When the
pressure exceeds either limit, the new pressure value becomes centered in the deadband limits.
The
S
option sets the deadband based on the peaks and valleys of the pressure level. For instance, when a
small peak pressure is sensed, the top edge of the deadband will move to that pressure and have the entire
deadband range below this value. The output reading will be one-half the deadband below this pressure
(see Figure 7). As long as the pressure stays within the new deadband range the output will not change. If
a pressure is sensed below this range, the deadband will move so that the bottom edge will be at that pressure
and the entire deadband will be above this value.
Note:
For both the
C
and
S
options, there are instances when the transmitted pressure value can be inside the
deadband limits. This is due to the integration of the pressure value where multiple pressure samples are
used to determine a single pressure reading. If one of the samples falls outside the deadband limits and the
average of all the samples falls inside the limits then the transmitted reading will be inside the limits. To
avoid this effect, set the integration time to
I=R61
, or greater. Now the transmitted pressure output will be
based on a single sample.
To eliminate repetitive readings of the same pressure within the deadband set the
OP=U
command. See Figure 7 for
command illustrations. (Default:
DS = 00S0
)
Note:
The deadband should be set to zero when the buoy/wave filtering algorithm is enabled.
Inquiry:
*dd
DS
Action:
*dd
WE
EEPROM Store: *dd
WE
*dd
DS=
deadband
or
*dd
SP=ALL
*dd
DS=
C
n
or
*dd
DS= S
n
deadband
0
provides no deadband
1-60
provides deadband x 0.005% of full scale deadband limits
C
Center deadband around each new pressure output change.
S
Deadband Spread varies with the peaks and valleys of pressure changes.