EF-Series Instruction Manual
Rev 2/01 2-3
2.3 PRODUCT FUNCTIONS
This section describes the functions of the eFlow EF-Series flow computer, most of which is deter-
mined by firmware. The features provided by the firmware, much of which must be configured by
using the ROCLINK configuration software, are:
♦
Flow calculations for an orifice meter.
♦
Archival of data for up to 15 history points.
♦
Memory logging of 240 alarms and 240 events.
♦
Security with local and remote password protection.
♦
Power cycling control for a radio.
♦
Report-by-exception (RBX) capability.
2.3.1 Flow Measurement
The primary function of the EF-Series Unit is to measure the flow of natural gas through an orifice in
accordance with the 1992 American Petroleum Institute (API) and American Gas Association (AGA)
standards. The flow calculation is in accordance with ANSI/API 2530-92 (AGA Report No. 3 1992),
API Chapter 14.2 (AGA Report No. 8 1992 2nd printing 1994), and API Chapter 21.1. The flow
calculation may be configured for either Metric or English units.
The primary inputs used for the orifice metering flow measurement function are differential pressure,
static pressure, and temperature. The differential and static pressure inputs, which are sampled once
per second, come from the Flow Sensor. The temperature input, which is sampled and linearized once
per second, comes from an RTD probe.
Flow Time
The differential pressure stored for each second is compared to the configured low flow cutoff. If the
differential pressure is less than or equal to the low flow cutoff or the converted static pressure is less
than or equal to zero, flow is considered to be zero for that second. Flow time for a recalculation
period is defined to be the number of seconds for which the differential pressure exceeded the low flow
cutoff.
Input and Extension Calculation
Every second the EF-Series unit stores the measured input for differential pressure, static pressure, and
temperature and calculates the flow extension (defined as the square root of the absolute upstream
static pressure times the differential pressure).
Flow time averages of the inputs and the flow extension over the configured recalculation period are
calculated unless there is no flow for an entire recalculation period. If there is no flow, averages of the
inputs are recorded to allow monitoring during no flow periods.
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