Emerson Process Management ControlWave EFM 3808 - Manual (Page 38)

1-22 / Introduction CI-ControlWave EFM
• AGA7 with selectable AGA8 Gross or AGA8 Detail
• Auto Adjust AGA7/NX-19
• Auto Adjust AGA7 with selectable AGA8 Gross or AGA8 Detail
• Includes run switching
• Includes an auto-selector, PID flow/pressure control algorithm per run or per station
• Interfaces to a chromatograph and provides energy throughput as well as composition
information (requires the optional Expansion Communications Module)
• Resides on a BSAP SCADA network
• Supports samplers and odorizers
• Provides audit trail and archives
• Includes a nominations function
• Allows the user to select engineering units, including English and metric
The primary function of the ControlWave EFM is to measure the flow of natural gas in
accordance with API (American Petroleum Institute) and AGA (American Gas Association)
standards. Items below implement and supplement the primary function:
• Data acquisition (see Section 1.5.1)
• Flow calculations (see Section 1.5.2)
• Data archives (see Section 1.5.3)
• Audit trail archives (see Section 1.5.3.4)
• Local display (see Section 1.5.4)
• Communications (see Section 1.5.5)
• Control outputs (see Section 1.5.6)
• Status inputs (see Section 1.5.6)
• Self test and diagnostics (see Section 1.5.7)
1.5.1 Data Acquisition
The process inputs used by the ControlWave EFM are static pressure, differential
pressure, and temperature for orifice measurement, or static pressure, temperature, and
frequency input for positive displacement (PD), turbine, or ultrasonic meters. Static
pressure and differential pressure may be obtained from the Multivariable Transducer
connected to the ControlWave EFM System Controller Module (SCM). The inputs may
also be derived from external smart Multivariable Transmitters using either the BSAP or
MODBUS protocols. Alternatively, the inputs may be obtained via the local I/O Modules
using analog transmitters. The standard ControlWave EFM application program allows
any combination of inputs to be selected, for up to four runs of measurement.
Regardless of the operating mode or the calculation interval, the ControlWave EFM
acquires samples as follows:
a. Differential pressure once per second
b. Static pressure once per second
c. Flowing temperature once per second
d. All self-test and compensation values at intervals of 4 seconds or less
1.5.2 Flow and Volume Calculations
The ControlWave EFM performs a complete flow calculation using the process variables
every second. Each calculation includes instantaneous rate according to API 14.3,
compressibility according to AGA 8 Detail or Gross method, and updates of all volumes,