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Title: Digital Flow Measurement And Control
Author: A. W. Langill, Jr.
Source: 1973 Gulf Coast Measurement Short Course (Now called ASGMT)
Year Published: 1973
Abstract: This paper presents the essential of digital valves as applied to the accurate control of process fluid streams under cornnand of a digital computer or digital control system. In this context, digital valves function solely as control devices, responding directly to positioning commands originating in the control computer. However, with a few modifications in the digital valve design, and with the introduction of a small LSI-based Microcomputer-controller, a digital sub-system is formed that not only controls fluid flow rate, but also is capable of digitally measuring fluid flow. The resulting DigiCell system has the following general characteristics: (1). 0.5% accuracy over a turndown ratio of over 1000-to-l for a 10-bit unit. (2). Parallel or serial digital flow rate output. (3). Flow rate control accuracy of 0.1% for for a 10-bit unit. (4). Rapid dynamic response. The DigiCell can follow a step-function change in flow rate set point. The theory of operation of this new combined digital valve and digital flowmeter is presented. The paper concludes with descriptions of two typical applications of this new digital technique, both taken from the field of pipe line control. The first is an all-digital high-response Override Control System for liquid pipe line control - while the second is an all-digital Compressor Surge Control System for use in gas pipe lines.

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