Halul homes in on digital radio shutdown
  from: Offshore Engineer
  by: Gerard Mallee
  Monday, April 07, 2008

A digital radio communication network serving Qatar Petroleum is designed not only to provide reliable two-way voice communication but also to facilitate remote shutdown of the company’s Halul Island oil loading facility in the event of an emergency. IHC Systems’ Gerard Mallée describes the novelties and niceties of this state-of-the-art system.

Consisting of a fixed radio base station installation at Halul Island, the Single Buoy Mooring (SBM) Digital Radio Shutdown System (DRSS) operates with a mix of handheld, mobile and fixed mobile radio units provided to authorized personnel for berthing of oil tankers prior to the oil loading operations at two mooring buoys, SBM-1 and SBM-2.

The main purpose of this system is two-way reliable voice communication. A second purpose is to enable authorized personnel to remotely shutdown the turbine oil pump facilities for safety reasons, should an oil spill, fire or some other emergency occur during loading operations.

The 1.5km² Halul Island is some 80km northeast of Doha, the Qatari capital, and has all the facilities of a major international oil terminal. The island is home to 11 large crude oil storage tanks with a total capacity of 5 million barrels, crude oil pumping facilities, power generation and water desalination plants. Oil is blended and exported from Halul to customersf oil tankers moored offshore via the two SBM buoys.

Situated respectively 3.9km and 5.1km from Halul in the deepwater area to the southeast, these moorings enable tankers to weathervane around their turrets with a rotational freedom of 360 degrees.

System layout

The SBM Digital Radio Shutdown System provides three radio traffic channels (semi-duplex) for remote shutdown of the SBM-1 and SBM-2 pumps, normal voice communication, and berthing. Every mobile radio has the possibility to generate a shutdown command for SBM-1 or SBM-2, achieved by means of a specific, programmable and unique tone code.

All radio communications take place via five centralized duplex base stations. The following channel assignment applies:

• channel 1: main and standby (SBM-1 shutdown and voice); 
• channel 2: main and standby (SBM-2 shutdown and voice);
• channel 3: main (berthing).

The base stations (including the shutdown system) are located in the radio equipment room around 50m from the radio tower.

The operating procedure is as follows: handheld/mobile sends a shutdown command over the dedicated channel; reception of the command is acknowledged by the system to the handheld/mobile (after a programmable delay); system decodes the shutdown command signaling tone and (after a programmable delay) activates the relay in the SBM instrumentation panel in the control room.

The pump shutdown relays are located in the auxiliary room and are currently being controlled by relays in the SBM instrumentation panel in the control room by a low voltage digital signal. The system is interfaced to the existing radio dispatch panel (in the radio room). Operators are able to manually switchover between the main and standby base stations for every channel, and also carry out a reset function for the shutdown status. On this radio dispatch panel signaling takes place (LED and buzzer) of every received shutdown command. The mobiles (SRM2000) and handheld portables (MPT 700) are able to generate a shutdown command without interference of the console operators. Blocking of the shutdown command by operators can only take place via the SBM instrumentation panel (and not via the radio shutdown system). Every shutdown command is logged, with sender ID and time & date stamp.

All equipment (monitors, computers and radio communication) is powered by its own uninterruptible power supply unit. The total system is resistant to a power failure for eight hours.

Trunking system

The supplied digital radio system consists of a Tetra (Terrestrial Trunked Radio) system. The Compact Tetra is a new design using distributed intelligence and latest state-of-the-art technology. Tetra is an ETSI-standard for digital mobile radio communication for both voice and data traffic. A growing number of companies in the industrial and transport sector are changing from analogue (trunking) systems to Tetra.

Tetra is a trunking system, which implies that no fixed channel assignment is required. A free traffic channel is assigned to any authorized user requesting access to the system. Theoretically, four user-groups can use one Tetra radio carrier simultaneously, as Tetra is a four-slot TDMA (Time Division Multiple Access) system. In trunking radio networks two types of channels exist. The traffic channels normally carry voice communication, and the control channel is used for (user) access control and short data messages.

The smallest system, CTS100, has two carriers, providing a maximum of seven traffic channels and one control channel, and contains two transceivers in a redundant configuration.

The system installed by IHC Systems, with Consolidated Gulf Company (CGC) as local contractor and Getronics (K&H) as subcontractor, is a CTS100 Compact Tetra, which can easily be expanded for future developments. In the SBM DRSS, the shutdown commands consist of short data messages. Since these are transported via the control channels, shutdown commands will not affect the availability of free voice traffic channels.

The Tetra systems provide many security functions (user authorization and access) and show very high availability figures, providing a high degree of resilience through their inherently distributed architecture. They can tolerate the failure of individual components and links, without employing expensive centralized redundancy concepts. Equipment failures have only a limited effect on system operation; should a transceiver fail, another one will take over. The system uses digital voice coding throughout the network. This results in the best possible end-to-end voice quality and the fastest possible call set-up times. Extensive monitoring and control facilities ease initial system set-up and reduce cost of ownership. Online monitoring functions and extensive logging and tracking facilities are used.

The Compact Tetra Gateway (CTG-1/2) computers (main and standby) are needed as an interface between the Compact Tetra infrastructure, the Compact Tetra Dispatcher (CTD-1) and local data network. The gateways act as a database for logging activities for all kinds of data generated by the system. All data are presented in raw form and need to be handled by dedicated software to show this data in an orderly fashion to be handled for maintenance purpose. The Compact Tetra Dispatcher (CTD-1) will run the management, maintenance, service, monitor and data logging applications from the SBM system.

Operator workstations

The two operator workstations (graphic dispatcher) are also important components in the system. At two locations (radio & control room) the operator workstation monitors and controls all activities in the system. One of the operator workstations (GD-100-1) is in the radio room near the equipment room. The other (GD-100-2) is 450m away, in the control room close to the shutdown equipment in the auxiliary room. To overcome communication failures a redundant optical fiber connection is used between the equipment room and the auxiliary room. Communication between the workstations and the CTG-1/2 dispatchers is based on a 100TBase network.

Both operator workstations are equipped with a 17in LCD touch monitor. This monitor combines the reliable performance of touch technology with the latest advances in LCD display design. Operators are able to monitor the following functions: 

• monitoring talk group communication;
• breaking in on going on communications;
• selecting one group to communicate while monitoring others; 
• monitoring activation of shutdown command; and
• resetting shutdown procedures, and manual switch over main/standby radio.

The handheld radios can transmit and receive SDS (Short Data Service) messages, as well as normal voice communication. This SDS and voice communication is relayed via the Compact Tetra base station to the SBM instrumentation panel.

To overcome disturbances in radio communications the antennae have been placed in space diversity. (Space diversity relies on the fact that fading is different at different points on the earth, so two aerials a few wavelengths apart will have uncorrelated fading.) Using multiple receiver antennae and multiple transmitting antennae, this transmission technique enables the informationcarrying signal to be transmitted along several different propagation paths.

Space diversity reception techniques have been used for several years to improve uplink performance. To bring about improvements from horizontal spacing, two antennae are placed at least 10 wavelengths apart, working on the basis that a deep fade at one antenna location will not be as severe at the other receiver-antenna location. Clear benefits flowed from the application of space diversity on the Halul Island project. It offers proven enhancement in uplink performance for reception of both mobiles and portables.

Training

After the commissioning period in October 2005, workstation operators were put through a comprehensive technical training program.

Halul Island has its own fully equipped electronics department, where groups of people work in shifts and are able to do all the first line maintenance. Following intensive training, the two groups of technicians on site are qualified and able to repair, exchange, program all mobiles and handheld radios, as well as changing settings in the complete SBM DRSS.

Since its start-up, the system has run without any breakdowns. OE

About the author

Gerard Mallée is manager of the survey department of IHC Systems in The Netherlands. After early experience in the electronics industry with Siemens, Philips and the Unilever Research Lab, he switched to the marine dredging and hydrographic sector with Ballast Nedam in 1976. After studying marine radio positioning at Delft University and global positioning at Nottingham University, he joined IHC Systems in 1991.

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