Sea-Bird Electronics SBE 38 Uživatelský manuál stáhnout pdf (Strana 17)

Manual revision 006 Section 2: Description of SBE 19plus V2 SBE 19plus V2

External Power

The SBE 19plus V2 can be powered from an external source (9 - 28 volts DC)

through the Y-cable connected to the Data I/O, Pump, and External Power

bulkhead connector on the sensor end cap. The internal battery pack is diode-

OR’d with the external source, so power will be drawn from whichever

voltage source is higher. The 19plus V2 can also be operated from the external

supply without having the internal battery pack installed. Electrical isolation of

conductivity is retained in units powered externally, preventing ground loop

noise contamination in the conductivity measurement.

On the ship, cables longer than 3 meters should be installed inside an earthed

metal conduit by a qualified electrician. This minimizes the potential for

external signals to disrupt communication and ensures that high voltage lines

(such as the sea cable) are sufficiently protected. Cables shorter than 3 meters

can be used without shielding when installing or bench testing the instrument.

Cable Length and External Power without Deck Unit

There are two issues to consider if powering the 19plus V2 externally:

• Limiting the communication IR loss to 1 volt if transmitting real-time

data; higher IR loss will prevent the instrument from transmitting real-

time data because of the difference in ground potential.

• Supplying enough power at the power source so that sufficient power is

available at the instrument after considering IR loss.

Each issue is discussed below.

Limiting Communication IR Loss to 1 Volt if Transmitting Real-Time Data

The limit to cable length is typically reached when the maximum current

during communication times the power common wire resistance is more than

1 volt, because the difference in ground potential of the 19plus V2 and ground

controller prevents the 19plus V2 from transmitting real-time data.

limit

= 1 volt = IR

limit

Maximum cable length = R

limit

/ wire resistance per foot

where I = current required by SBE 19plus V2 during communication. The

current varies, depending on operating mode:

• Profiling mode – The 19plus V2 samples and transmits data continuously.

Use the total current required for sampling (sampling, pump, auxiliary

sensor current, and communication current) in the calculation.

• Moored mode – The 19plus V2 samples, and then transmits data. Use the

communication current, 65 mA, in the calculation.

Note:

See Real-Time Setup in Section 4:

Deploying and Operating

SBE 19plus V2 for baud rate

limitations on cable length if

transmitting real-time data.

Note:

Common wire resistances:

Gauge Resistance (ohms/foot)

12 0.0016

14 0.0025

16 0.0040

18 0.0064

19 0.0081

20 0.0107

22 0.0162

24 0.0257

26 0.0410

28 0.0653

Profiling Mode Examples - for 19plus V2 with standard SBE 5M pump and no auxiliary sensors

Example 1 – For 20 gauge wire, what is maximum distance to transmit power to 19plus V2 if transmitting real-time data?

Current = 70 mA (sampling) + 100 mA (pump) + 65 mA (communication) = 235 mA

limit

= V

limit

/ I = 1 volt / 0.235 amps = 4.3 ohms

For 20 gauge wire, resistance is 0.0107 ohms/foot.

Maximum cable length = 4.3 ohms / 0.0107 ohms/foot = 402 feet = 122 meters

Example 2 – Same as above, but there are 4 instruments powered from the same power supply.

limit

= V

limit

/ I = 1 volt / (0.235 amps * 4 instruments) = 1.1 ohms

Maximum cable length = 1.1 ohms / 0.0107 ohms/foot = 103 feet = 31 meters (to 19plus V2 furthest from power source).

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