SUMMARY This paper describes a Subsea Distributed Data Acquisition Bus for the Subsea Hydrocarbon Production Control environment. This will have many advantages in terms of flexibility, maintainability, fault tolerance, data confidence and overall cost An outline is given of the development project describing the contents of each of its four phases. The product of this project will be a standard definition of the bus which will be non-exclusive, non-proprietary and vendor independent A system overview is presented with descriptions of typical components. An outline of the relevant areas of the MIL STD 1553B bus standard is given. This bus has been selected to be the basis for the subsea design. Other topics covered in the overview include typical system configurations, connection methods and power and signal distribution. Options are proposed for further investigation during the development project The final section of the paper gives a brief description of three of the many possible applications of the proposed subsea digital communication and power distribution bus INTRODUCTION Subsea control systems for the production of hydrocarbons are typically made up of an operator Interface on a platform, a subsea communications and power distribution system, a number of subsea control modules and subsea instrumentation Hydraulic power is supplied to the control module. On command from the surface solenoid piloted electro hydraulic valves are operated via the communications network that direct this supply to control actuators on the well Xmas tree Instrumentation mounted on the tree, and also sometimes downhole, provide signals that are digitised in the control module This data is passed to the operators console on the surface to provide information on the state and performance of the well Figure 1 is a block diagram showing the typical existing data acquisition system setup Each sensor is connected by a dedicated jumper and connector back to the control module Each analog channel therefore requires a connector mounted on the control module which adds to its overall weight and size An alternative proposed system of data acquisition for subsea control systems is illustrated in Figure 2 This involves the use of a digital communication and power distribution bus, and digital sensors The subsea control module is connected to the sensors via the dual redundant bus Systems of this sort are finding increasing use and acceptance in industrial process and control applications These are commonly referred to as Field buses The major difference between the existing and proposed subsea data acquisition systems is that in the new system the analog signals are converted to digital data in the sensor as opposed to being transmitted back to the control module for conversion. The digital sampled data is then requested from the sensor by the control module. Transmission of digital data is far more tolerant of noise and line degradation than for example 4 to 20 mA, so the repeatability of the proposed bus system is much improved Confidence in the data received at the module and hence at the surface is therefore increased.