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POLLED CUSTOM
POLL CUSTOM format allows the sensor to be polled for a
measurement. See CUSTOM for details on constructing the output
string. Poll by sending MA! (where 'A' is the POLL CHARACTER
ADDRESS).
After a measurement has completed, the sensor responds with the
POLL CHARACTER followed by the custom serial output string.
Up to 32 sonic anemometers may be networked using the RS-485
connection. By assigning a unique address to each device, multiple
units may run on the same network and respond individually only
when polled.
POLLED BINARY
POLLED BINARY starts a measurement and sends serial data in
binary rather than ASCII format. The advantage of using POLLED
BINARY output format is that data output strings are shorter and data
does not have to be parsed and converted from ASCII characters
to numeric values. The disadvantage is that the output cannot be
examined directly as text. The 18-byte binary output string description
appears below.
Byte
Index
Description
0
U vector cm/s (signed integer)
2
V vector cm/s (signed integer)
4
W vector cm/s (signed integer)
6
T Sonic temperature K x 100 (unsigned integer)
8
V1 Input 5V Full Scale (unsigned int 0-4000)
10
V2 Input 5V Full Scale (unsigned int 0-4000)
12
V3 Input 1V Full Scale (unsigned int 0-4000)
14
V4 Input 1V Full Scale (unsigned int 0-4000)
16
Status (byte, non-zero = error)
17
Checksum (byte, XOR of all chars, hex val)
The POLLED BINARY format may be employed using one of two
different methods.
The first method uses the MA! command to initiate a sonic
measurement ('A' is the sensor POLL CHARACTER ADDRESS,
see section 6.6). When the measurement is complete, the sensor
automatically transmits measurement data in binary form. The
delay between the start of the measurement and data availability
is determined by the OUTPUT RATE parameter (see section 6.5)
The second method uses separate trigger and data-retrieval
commands. Any sensor that receives a Tr! command while set
for POLLED BINARY operation will immediately start a sonic
measurement. The command is not address‑specific. When the
measurement is complete, data will be available for retrieval using
the RA! command ('A' is the unique POLL CHARACTER ADDRESS,
see section 6.6).
The time required to complete a measurement after the Tr! command
depends on OUTPUT RATE. Also, if multiple sensors are connected
on a shared RS-485 bus, each RA! command and its reply must be
given enough time to complete. The time constraints are shown in
the table below:
Output
Measurement
Rate (Hz)
Complete (ms)
4
225
5
175
8
115
10
90
16
58
20
45
32
25
81000V-90(L)
Minimum Delay between
bussed RA! cmds (ms)
33
23
13
11
8
8
8
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The Tr!/RA! trigger/retrieve method is useful for synchronizing
simultaneous measurements with multiple 81000 sensors. After
completing a measurement triggered by the Tr! command, data
from each sensor (uniquely addressed) can be retrieved with the
RA! command. Data rates up to 10 Hz with six sensors on a single
full-duplex bus have been demonstrated (38.4k baud). Faster rates or
more sensors may be configured by adjusting operating parameters.
6.8 THRESHOLD
THRESHOLD sets wind speed threshold for the following output
formats only: NMEA, SPEED AZIMUTH ELEVATION. UVW outputs
are unaffected. Setting THRESHOLD greater than 0 prevents
fluctuating azimuth and elevation values at wind speeds near zero.
While these values are correctly derived, they are meaningless or
distracting in some applications.
When wind speed is at or above threshold, all output values are
updated normally. When speed is below threshold, speed and
elevation outputs are set to zero and the azimuth output is held at its
last value. Setting THRESHOLD to 0 effectively disables the feature.
Note that units are cm/sec.
THRESHOLD (cm/s) : 20
ENTER NEW THRESHOLD (cm/s, 0-500) :
6.9 UNITS
UNITS sets wind speed units for CUSTOM serial output. Resolution
associated temperature units are as follows:
Wind Speed
Temperature
units and resolution
units and resolution
cm/s 1
K
0.01
m/s
0.01
C° 0.01
mph
0.1
F°
0.01
km/h 0.1
C° 0.01
knots 0.1
F°
0.01
UNITS 2
-------------------
1) cm/s
2) m/s
3) mph
4) km/h
5) knots
X) EXIT TO MAIN MENU
6.10 WAKE CORRECTIONS
WAKE CORRECTION enables or disables real-time correction
algorithms. To compensate for flow distortions in the wake of support
struts and other mechanical features, each 81000 is individually
calibrated in the YOUNG factory wind tunnel (NIST traceable)
to generate a unique correction table which is stored in the unit.
Additional compensating algorithms correct for
distortions and crosswind effects on speed of sound.
WAKE CORRECTION: YES
USE WAKE CORRECTION? (Y/N):
elevation angle
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