Section 4: Deploying and Operating SBE 19plus V2
33
Real-Time Setup
Baud Rate and Cable Length
Without a Sea-Bird Deck Unit
The rate that real-time data can be transmitted from the SBE 19plus V2
is dependent on the amount of data to be transmitted per scan and the serial
data baud rate:
Time required to transmit data =
(number of characters * 10 bits/character) / baud rate
where
Number of characters is dependent on the included data and output
format (see Data Output Formats).
Add 2 to the number of characters shown in the output format, to
account for the carriage return and line feed at the end of each scan.
For decimal output (OutputFormat=2, 3, or 5), include decimal
points, commas, and spaces when counting the number of characters.
Time required to transmit data must be less than the real-time output rate.
The length of cable that the 19plus V2 can drive is also dependent on the baud
rate. The allowable combinations are:
Maximum Cable Length (meters) Maximum Baud Rate
1600 600
800 1200
400 2400
200 4800
100 9600
50 19200
25 38400
Notes:
• Set baud rate with BaudRate=.
• Set data storage and real-time
output rate with NAvg= (for Profiling
Mode) or SampleInterval=
(for Moored Mode).
• Include auxiliary A/D sensors in the
data stream with VoltN= commands.
Include auxiliary RS-232 sensors in
the data stream with SBE38=,
GTD=, or DualGTD= commands.
• Set output format with
OutputFormat=.
• Real-time data is automatically
output in Profiling Mode.
In Moored Mode, set
MooredTxRealTime=Y
to output real-time data.
• If using external power, see External
Power in Section 2: Description of
SBE 19plus V2 for power limitations
on cable length.
Example 1 - 19plus V2 without a Deck Unit. Profiling Mode, strain-gauge pressure, configured with 2 external voltages.
What is the fastest rate you can transmit real-time data over 800 m with OutputFormat=0 (raw hexadecimal data)?
With 800 meters of cable and no Deck Unit, the 19plus V2 requires a baud rate of 1200 or less.
Number of characters for OutputFormat=0 (from Data Output Formats) =
6 (T) + 6 (C) + 6 (P) + 4 (P temperature compensation) + 2*4 (external voltages) + 2 (carriage return & line feed) = 32
Time required to transmit data = (32 characters * 10 bits/character) / 1200 =
0.267 seconds > 0.25 seconds (4 Hz, maximum sampling rate).
Therefore, set NAvg=2, averaging 2 measurements/sample and storing and transmitting 1 sample every 0.5 seconds.
Example 2 - 19plus V2 without a Deck Unit. Moored Mode, strain-gauge pressure, configured with 4 external voltages,
10 measurements/sample (NCycles=10), pump running during sampling (MooredPumpMode=2), and a 15-second
delay before sampling (DelayBeforeSampling=15). What is the smallest sample interval you can use if you want to
transmit real-time data over 800 m with OutputFormat=0 (raw hexadecimal data)?
With 800 meters of cable, the 19plus V2 requires a baud rate of 1200 or less.
Number of characters for OutputFormat=0 (from Data Output Formats) =
6
(T) + 6 (C) + 6 (P) + 4 (P temperature compensation) + 4*4 (external voltages) + 8 (time) + 2 (carriage return & line feed) = 48
Time required to transmit data = (48 characters * 10 bits/character) / 1200 = 0.4 seconds
Minimum time required for each sample =
15 seconds (delay after turning on power) + 2.5 second sampling time + [(10-1) * 0.25 seconds] +
0.4 seconds to transmit real-time + 3 seconds to go to sleep between samples = 23.15 seconds, round up to 24
Therefore, set SampleInterval=24, storing and transmitting one sample every 24 seconds.
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