Sea-Bird Electronics SBE 38 Manual do Utilizador descarregar pdf (Página 36)

Manual revision 006 Section 4: Deploying and Operating SBE 19plus V2 SBE 19plus V2

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.

In Profiling Mode, the time required to transmit data must be less than the

real-time output rate. In Moored Mode, the time required to transmit data plus

the time required to make the measurements must be less than the

(interval between samples – 5 seconds) for Autonomous Sampling, because

the 19plus V2 goes to sleep for a minimum of 5 seconds between each sample.

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)

1600

800

400

200

100

Maximum

Baud Rate

600

1200

2400

4800

9600

19200

38400

Notes:

• See External Power in Section 2:

Description of SBE 19plus V2 for

cable wiring on the ship.

• 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) =

(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 + 5 seconds to go to sleep between samples = 25.15 seconds, round up to 27

Therefore, set SampleInterval=27, storing and transmitting one sample every 27 seconds.

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