Automating Remote Stations
Authors: Joyner J.W. , Elder B.P. 
Published: December 2007

Introduction

There is a real trend in the capabilities of industrial apparatus which precludes the need for people except for maintenance visits. This capability is often used together with suitable controls and called automation, which might be defined as the accomplishment of a specific operation entirely by machinery. Most current experiences with automation have been on a modest geographical scale. Possibly this is due to the fact that most of the major efforts along these lines have been in manufacturing, where operations are within self-contained unit plants. In petroleum production, gathering and transmission, however, there are many cases where sub-units need be operated without human attendance even though they are geographically removed from the system central control. Automation can be defined in many ways, and its meaning varies from application to application. To one engineer it can mean alarm monitoring -an elementary form of telemetry coupled with some form of supervisory control to allow safety shut-down protection. To another engineer it can mean the forced sequence starting (or stopping) of an engine-compressor. A systems engineer might think of automation as the complete manufacturing of a product from raw material to packaged form without human assistance. All definitions of logic have one common thread logic. Let us specify logic as any mechanism of decision making, whether it be a simple relay sequence or a multi-variable computer operation or a man.

General Analysis Of The Scattered Plant

If, for instance, a man is assigned to a compressor location so that upon request he will

start the motor, observe that operating speed is reached and open valve A, close valve B, a control system vested with some logic has been established (see Fig. 1).

If now, the request to start is given from a remote location by a dispatcher, based on the examination of various operating parameters brought to him by conventional telemetry, a second area of logic is introduced, together with a requirement for a channel for communication between the two areas of logic. The system control has been expanded geographically as in Fig. 2.

At the dispatch location is a sub-system which scans the telemetered data from over the operating network, compares actual values with desired values and makes decisions to continue operation or to make changes. At the remote station is another sub-system which awaits an order from the dispatch location to change something. Upon completing the change, an acknowledgment is made. So far, the entire operation is dependent upon an available channel for communication between the logic or decision making locations. By adding a local alarm at the remote station to indicate a dangerous condition (and so act as a locally originated request or a change, much as one from the dispatch location) it may be possible to continue operation for short periods of time without communication with the dispatch location. An examination of this very simple case reveals several avenues to automation, each with a unique effect on the communications channel. At the remote station, every decision so far discussed is reducible to an AND or an OR function.

JPT

P. 757^