Streaming operation

Overview

The MLM system is standard save for the capability of external power being able to power both the SSM and the attached RBR logger.
A 2 conductor power cable nominally supplying 12V DC (Min 9V, max 14V) is connected to the sub-surface modem (SSM). Power is supplied to the logger via the interconnect cable included with the modem system (6 pin connectors).

The modem has been configured for an application where the modem system is connected to a streaming RBR logger that is sampling at 6Hz. (NOTE: The RBR logger’s serial baud rate must be set to 2400). The configuration of the programmable modem parameters (below) reflects this application.

A typical scenario would be that the computer connected to the Head- End modem (HEM) would establish a link to the SSM (Using the SSM’s serial number as the address) and then put the system in “transparent mode”. Once in transparent mode, the computer connected to the HEM would effectively be talking directly to the logger connected to the SSM. The logger would subsequently be controlled by issuing commands from the “OEM command” set.

E.g.

• establish link to SSM

• enter transparent mode

• clear logger memory

• enable logging
  
  

The logger would be streaming output data at 2400 baud to the SSM.

The SSM would transmit data to the HEM in blocks of 256 bytes. Therefore the HEM would transmit data to the host computer in blocks of 256 bytes (256 set by the buffer size) on a continuous basis.
Sending the “stop” command to the logger would end the streaming of data and then the SSM link could be cleared down or let to timeout. The system would then be idle.

Benchtop testing and a “simulated mooring line”

When performing benchtop testing, the user would normally thread a wire loop through the toroidal transformer mooring line couplers.
It is important to put a resistance in series with the wire loop that simulates conduction through the mooring line.

The value of this resistance should be in the range 20 to 100 ohms.

Ensure there is a mooring cable transmission line (See Bench Top Testing and Simulated Mooring Line below).

HEM data connector pinout

Programmable modem parameters

All parameters are at their default values with the following exceptions:

Head-end modem

- TPCTOEN; Transparent character timeout enable; Set to 1 (Enable) - TPESCTOEN; Escape sequence guard time ; Set to 0 (Disable)
- TPCTO; Trigger character timeout; Set to 100 (1 second)
- TPMXC; Transmit buffer trigger size; Set to 256

- TPSNDC; Trigger character; Set to 0A
- BAUD;115200 (This is the default), but no less than 19200 for this application.
- Polling command set to <bs>FETCH<cr><lf>; (ee pcmd s 08 46 45 54 43 48 0D 0A)

Subsurface modem

- TPCTOEN; Transparent character timeout enable; Set to 1 (Enable) - TPSNDEN; Transparent send character enable; Set to 0 (Disable)
- TPESCTOEN; Escape sequence guard time ; Set to 0 (Disable)
- TPCTO; Trigger character timeout; Set to 100 (1 second)

- TPMXC; Transmit buffer trigger size; Set to 256
- TPSNDC; Trigger character; Set to 0A
- BAUD; 2400
- ZTO; Sleep timeout after end of serial activity; Set to 500 (5 second timeout)

- LIDEN; RBR logger ID retrieval ; Set to 0 (Disabled).