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Reference Manual
00809-0100-4832, Rev AA
October 2004
Rosemount 3095FC
1-4
Low Power Mode Sleep mode is used to place the CPU in a low power mode. The battery
voltage is monitored by low voltage detection circuitry and the low voltage limit
value is set at 5.4 volts. During Sleep mode, sub-modules are powered down.
The 3095FC enters Sleep mode after one minute of inactivity on the
communication ports.
Wake-up from Sleep occurs when the 3095FC receives a:
• Timed interrupt from the Real-Time Clock
• Signal from one of the communication ports
3095FC Functions Most of the 3095FC functions are determined by the firmware. The features
and applications provided by the firmware, which must be configured by using
Rosemount User Interface Software, include:
• Flow calculations for an orifice meter
• Extensive historical data archival
• Memory logging of 240 alarms and 240 events
• Security with local and remote password protection
Flow Measurement
The primary function of the 3095FC 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 primary inputs used for the orifice metering flow measurement function
are DP, SP, and temperature. The DP and SP inputs are sampled once per
second. The temperature input is sampled and linearized once per second
from an RTD probe.
1992 Flow Calculations for Orifice Metering
The 1992 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 1992 flow calculation may be configured for
either Metric or U.S. units.
Flow Time
The DP stored for each second is compared to the configured low flow
cutoff. If the DP is less than or equal to the low flow cutoff or the converted
SP 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 the DP exceeded the low flow cutoff.
Input and Extension Calculation
Every second the Rosemount 3095FC stores the measured input for DP,
SP, and temperature and calculates the Integrated Value (IV) (the square
root of the absolute upstream SP times the DP).
Flow time averages of the inputs and the IV over the configured calculation
period are calculated, unless there is no flow for an entire calculation
period. Averages of the inputs are recorded to allow monitoring during no
flow periods.