Flow (dP) transmitter speed of response to meet API 670 5th Edition requirements.
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The new API Standard 670, that covers Machinery Protection Systems, was updated in the 5th edition in November 2014 to include a section on surge detection for centrifugal and axial compressors. Moreover, in the standard’s informative Annex K, there is a well-written distinction between an antisurge control system and a surge detection system.
One common aspect of both the surge control and surge detection applications is the selection of the differential pressure transmitters used to provide the compressor flow signal, and which must have a sufficiently fast response. In some cases, the two systems (surge detection and surge control) may share the same transmitter signals.
This article analyzes a typical behavior of the differential pressure transmitter signal from a flow measuring device during compressor surge and derives practical guidelines for selecting adequate transmitter dynamic response characteristics.