Sea-Bird Electronics SBE 38 Manual de usuario descargar pdf (Pagina 20)

Section 2: Description of MicroTSG SBE 45

Baud Rate, Cable Length, Power, and Data Transmission Rate

Baud Rate, Cable Length, and Data Transmission Rate

The rate that data can be transmitted from the MicroTSG is dependent on the

amount of data to be transmitted per scan and the serial data baud rate:

Time 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 Format in Section 4: Setting Up MicroTSG).

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.

Include decimal points, commas, and spaces when counting the

number of characters.

Note that the MicroTSG transmits data after it has completed the previous

sample and before it starts the next sample. See Sample Timing above for

information on sampling time.

The length of cable that the MicroTSG can drive to transmit real-time data is

also dependent on the baud rate. The allowable combinations are:

Maximum Cable Length (meters) Maximum Baud

800 1200

400 2400

200 4800 (factory set default)

100 9600

50 19200

25 38400

Notes:

• Baud rate is set with Baud=.

• Real-time output rate is set

with Interval=.

• Output format is set with

OutputCond=, OutputSal=, and

OutputSV=.

See Command Descriptions in

Section 4: Setting Up MicroTSG for

command details.

Example –

What is the minimum transmission time over 100 m of cable with OutputCond=Y, OutputSal=Y, OutputSV=Y, and

OutputFormat=0?

With 100 meters of cable, the MicroTSG requires a baud rate of 9600 or less.

Number of characters (from Data Output Format in Section 4: Setting Up MicroTSG) =

8 (T) + 2 (comma & space) + 8 (C) + 2 (comma & space) + 8 (salinity) + 2 (comma & space) + 8 (sound velocity)

+ 2 (carriage return & line feed) = 40

Time required to transmit data = (40 characters * 10 bits/character) / 9600 = 0.042 seconds = 42 msec

What is the minimum total time required per sample (Interval=), if averaging 4 measurements/sample (NCycles=4)

and operating in Autonomous Sampling Mode?

In Autonomous mode, time to acquire T and C (from Sample Timing above)

= (NCycles * 0.1336) + 0.287 = (4 * 0.1336) + 0.287 = 0.82 seconds

Total sampling time

= time to acquire T and C + time to compute parameters (from Sample Timing above) + time to transmit data

= 0.82 + (.0088 + .0154 + .083 + .035) + .042 = 1.00 second

Therefore, set Interval=1, transmitting 1 sample every second.

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Sea-Bird Electronics SBE 38 Manual de usuario Pagina 20

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