DigitalFlow™
XGF868i

Flare gas mass flow
ultrasonic flowmeterFeaturesApplications• Measures velocity, volumetric and mass flow

The DigitalFlow XGF868i flowmeter is a complete
ultrasonic flow metering system for:• Independent of gas composition• Measures instantaneous average molecular weight• High velocity range to 120 m/s (394 ft/s)• Accurate low flow rate measurement• 4000 to 1 turndown ratio• One or two path configurations• Allows cross flow immunity in large pipes• Minimal maintenance due to no moving parts, no holes ortubes, and tolerance to dirty or wet conditions• No pressure drop
• Field-proven installation techniques• Easy serviceability• Flare gas• Track down or prevent losses from leakage with positive
material identification• Measures Net Heating Value (NHV) of vent gas in BTU/SCF,MJ/m3, or KJ/m3• Account for total plant throughput of material• Reduce cost of steam usage with proportional control• Conserve energy by eliminating unnecessary flaring• Comply with government regulations for pollution control• Vent gas• Hydrocarbon gases• Biogases• Digester gases

Flare gas mass flow meterBest technology for flare gas

The DigitalFlow XGF868i ultrasonic flow meter uses thepatented Correlation Transit-Time™ technique, digital
signal processing, and an accurate method of calculating
molecular weight. Add to these features the inherent
advantages of ultrasonic flow measurement— reliability withno routine maintenance, high accuracy, fast response, andwide rangeability, the DigitalFlow XGF868i flow meter is theclear choice for flare gas applications.

Ultrasonic flow measurement, the ideal technology forflare gas applications, is independent of gas properties,
and does not interfere with the flow in any way. All metal
ultrasonic transducers installed in the pipe send soundpulses upstream and downstream through the gas. From thedifference in these transit times between the transducers,
with and against the flow, the DigitalFlow XGF868i’s onboard
computer uses advanced signal processing and correlation
detection to calculate velocity, and volumetric and mass
flow rate. Temperature and pressure inputs enable the meterto calculate standard volumetric flow.

Compact housing
All of the DigitalFlow XGF868i’s electronic components arehoused in a compact, low cost, explosion proof/flame prooftransmitter package that can be installed close to the flow
measurement point. This greatly simplifies wiring of theflowmeter.

Simple installation
The flow meter system consists of a pair of transducers andinsertion mechanism for each channel, and an XGF868i. The
transducers can be installed as part of a flowcell, or directly into
the pipe with a hot- or cold- tapping procedure. The DigitalFlow
XGF868i meter can be located up to 1,000 ft (300 m) from thetransducers.

Wettedtransducer

FLOW

Ultrasonicsignal path

Wettedtransducer

V=Typical meter set-up for standard volumetric or hydrocarbon mass flow

Pressure

P2 (tup- tdn)
2L (tdnx tup)

QSTD = QACT xTemperature

PfPbx

TbTf

QSTD = Standard volumetric flow rate
QACT = Actual volumetric flow rate
Pf = Flowing pressure
Pb = Base pressure= Flowing temperature
TTb = Base temperature
V= Velocity
P= P ath length
L= Axial length
tup = Upstream transit time
tdn = Downstream transit time

Diagonal 45

Mid-radius 90

90-180 Diagonal

Pipe rack

Standard transducer mounting configurations

Off-diameter diagonal 45Ideal for flare gas flow measurement
The Correlation Transit-Time technique has distinct
advantages over other methods of flare gas flow
measurement, and it is used to solve a variety of difficult
problems. Typically, gas in flare stacks, headers or laterals
is a mixture of components from different sources. Flow rate
in flare systems may be unsteady or even bidirectional.
Pulsating pressure, varying composition and temperature,harsh environment, and wide flow range further complicate
the measurement. The XGF868i is designed for superior
performance under these conditions.

XGF868i with T17 transducers low flow % error

One meter, wide range of flow conditions
High flow

The DigitalFlow XGF868i meter achieves extended range
rangeability of 4000 to 1. It measures velocities from 0.1 to328 ft/s (0.03 to 100 m/s) standard in both directions, while
the extended range version measures velocities to 394 ft/s
(120 m/s) in one direction. In steady or rapidly changing
flow, it measures in pipes from 4 in to 120 in (100 mm to 3m) in diameter. With this range of operation, one DigitalFlow
XGF868i flowmeter performs measurements under theconditions that occur in a flare line on or offshore.
Low flow
For base load operation, the volumetric flow in flares is often
in the range 0.1 to 1 f/s (0.03 to 0.3 m/s) and the XGF868i flaregas flow meter improves the accuracy over that range, but
still measures at high velocity during facility relief or upset
conditions.
A single path uses a long path to achieve accurate low
flow measurements, and with the recovery angle on thedownstream transducer, the extended range high flowrate is accomplished as well.

Energy measurement
Latency in measuring the energy content of a flare gas canlead to poor combustion efficiency or fuel gas waste at
the flare tip. This can lead to excessive emissions, mostly
harmful methane, into the atmosphere, risking increased
fine associated with non-compliance and greater negative
impact on the climate. The model XGF868i has an option
for measuring the net heating value (NHV) of the flare gas
to help operators optimize their assist flares to provide
a smokeless flame and maintain a high combustion
efficiency without the latency issues or the installation andmaintenance costs of a separate analyzer. For increased
capabilities unlocking the full potential of reduced emissions
and flare control and optimization, use a GF868 or an XGF868
with flare.IQ advanced control solution.

Dual-channel model standard
For maximum accuracy, the standard two channel XGF868i
can accommodate single or dual channel operation in avariety of transducer configurations.

The 6 degree recovery angle on the downstream
transducer provides high flow rate capability.

NIST traceable test results to over 120 m/s velocity

Designed for flare gas environment
The DigitalFlow XGF868i flow meter has no moving parts toclog or wear out. Its patented ultrasonic transducers areconstructed of titanium or other metals that withstand thecorrosive environment usually found in flare gas applications.
The transducers are designed for use in hazardous locations.
In contrast to other flow meter types, the ultrasonic transittime technique does not depend on the properties of flare
gas and does not require regular maintenance.
The DigitalFlow XGF868i flow meter offers a unique
combination of rangeability, ease of installation, lowmaintenance and accuracy in a low-cost transmitter. The
all-digital XGF868i creates no pressure drop; has no moving
parts or parts that foul or collect debris; seldom requires
maintenance; and provides reliable, drift-free operation. The
flow rate can be displayed locally or transmitted to a remotesystem via an analog or digital communications link.

Patented molecular weightmeasurement method
The DigitalFlow XGF868i uses a patented method for
calculating the average molecular weight of hydrocarbon
mixtures. This proprietary algorithm extends the range formeasuring average molecular weight, while improving
accuracy and compensating for nonhydrocarbon gases
better than ever before possible. Normally sound speed ingases depends on gamma.

C=

γRT

The algorithm in the meter relates sound speed of the gases
to the average molecular weight of the gases, without adependency on gamma, for hydrocarbon gases. Molecularweight, with temperature and pressure, allows the mass flow
to be calculated.

R(T)

M =
V=A
=
ρ=
P=
T=
R=
MW =
Q =
γ=
C =

Mass flow
Actual velocityCross-sectional area
Density
Pressure (absolute)Temperature (absolute)
Universal gas constant
Molecular weight
Volumetric flow rate
Gamma: adiabatic constant
Speed of soundHigher accuracy mass flow data and more precise knowledgeof flare gas composition can improve the efficiency of plant
operation.
Leaks/lost productDetection of even a small increase in flow rate into theflare system may indicate a leak source such as a partiallyunseated relief valve. An accompanying change in theaverage molecular weight of the flare gas may be used
to help locate the leak source. Quick identification andelimination of leak sources into the flare system saves
significant amounts of potentially lost energy and productand aids in early detection of process control problems.
Steam injection/mass balance

Excess steam delivery can be a major cause of loss of
product and energy. Reducing steam injection improves theoverall efficiency in refinery and chemical plant operation.
The DigitalFlow XGF868i can help save millions of dollars in
reduced losses. Using the instantaneous average molecularweight and mass flow rate of the gas, delivery of the correct
amount of steam required at the flare tip can be accuratelycontrolled. Steam usage can be reduced. Mass flow rate
may be used to perform a mass balance calculation and tocontrol flare tip steam injection.
Emissions complianceMWρ= P(MW)

Identify leaks, reduce steam usage,
improve plant balance, and comply withemissions regulation

M=ρVA

Maintaining compliance with pollution control regulations
requires measurement at low flow and at high flow, andverification of meter performance. The sound speed andother diagnostics allow easy meter verification whilemeasuring over this wide flow range.

Low operational costs
Because the DigitalFlow XGF868i installation produces no flow
obstruction, the energy-robbing pressure drops and highmaintenance requirements characteristic of other flow meters
are eliminated. The special sealed metal transducers suppliedwith a DigitalFlow XGF868i system are immune to the erosion
and stress caused by thermal expansion cycles.
Payback for the entire DigitalFlow XGF868i installation usuallyoccurs within a matter of months.

XGF868i specifications
Operation and performance
Fluid types
Flare and vent gases
Pipe materials
All metals, fiberglass. Consult Panametrics
for other materials.
Flow accuracy (velocity)
Dependent on pipe diameter, and gas species.
See table below for more informationElectronics
Flow measurement
Patented correlation transit-time mode
Enclosures• Standard: Epoxy-coated aluminum weatherproof
Type 4X/ IP66 						Can be configured for Class I, Division 2, Groups ABCD,
NEC & CEC
• Optional: Stainless steel, weatherproof 			
Type 4X/ IP66 						Can be configured for Class I, Division 2, Groups ABCD,
NEC & CEC 						Explosion proof 					Class I, Division 1, Groups BCD, NEC & CEC 			Ex d IIC T6 Gb, IECEx & ATEX (II 2G)
Dimensions (h x d)Standard: Size 8.2 in x 6.6 in (208 mm x 168 mm)
Weight10 lb (4.5 kg)
ChannelsStandard: Two channels (for two-path averaging)
Display
2 line x 16 character backlit LCD display, configurable todisplay up to four measurement parameters in sequence
KeypadBuilt-in magnetic six-button keypad for full functionality
operation
Power supplies• Standard: 100-240 VAC ±10%
• Optional: 12 to 28 VDC, ±5%Note: For DC-powered meters, Class 2 rated supplies must be used for theline power.

Power consumption
20 W maximumOperating temperature–40°F to 140°F (–40°C to 60°C)
Storage temperature–67F° to 167°F (–55°C to 75°C)
Standard inputs/outputs
TTwo 0/4 to 20 mA isolated outputs, 600 Ω max. load
Two 4 to 20 mA isolated inputs, 24 VDC loop power, orOne 4 to 20 mA isolated inputs, 24 VDC loop power, one
direct three-wire RTD (temperature) input,–148°F to 662°F (–100°C to 350°C), 100 Ω platinum
Optional inputs/outputs• Two frequency outputs, optically isolated, 3 A maximum,
100 VDC maximum, 1 W maximum, from DC to 10 KHzmaximum
Digital interfaces
Standard: RS232 (PanaView PC software) HART®7 protocol on
4-20 mA output• Optional: Modbus® RS485 or TCP/IP• Optional: Ethernet• Optional: OPC server• Optional: Foundation Fieldbus®

• Optional: Namur NE107 compliant
European compliance
Complies with• 2014/30/EU EMC - Industrial EM Environments• 2014/35/EU LVD - Equipment Class I, Pollution Degree
2,Overvoltage Category II• 2014/34/EU ATEX (optional) - II 2G• The GF868 is intended for inclusion in large-scale fixedinstallations (LSFI) and are therefore outside of the scopeof Directive 2011/65/EU RoHS.

T5MAX wetted flow ultrasonic transducers

Insertion mechanism

Temperature range
Normal Temperature (NT): -55 C to 150 C

Standard and extended range

Pressure range
Standard: -2 psig to 1500 psig (87.6 to 10300 kPa)
Transducer Material
Standard: Titanium
Optional: Hastelloy® alloy or SS316 (Consult factory)
Process connections
Flanged and compression fittings
Hazardous Area Classifications
Explosive-proof Class I, Division 1, CD
Optional: Group B upon request
Ex d IIC T4.T3 or T2 Gb, IECEx & ATEX (II 2G)
An integrated XAMP preamplifier may be installed in thecertified assembly.

T5/T17 wetted ultrasonic flow transducers
Temperature range
Normal Temperature (NT): -55°C to 150°C
Low Temperature (LT): -220°C to 100°C
High Temperature (HT): -50°C to 250°C
Extremely High Temperature (XT): -180°C to 300°C
Pressure range
Standard: -2 psig to 1500 psig (87.6 to 10300 kPa)
Transducer Materials• Standard: Titanium• Optional: Monel® or Hastelloy® alloys or SS316
Process connections
Flanged and compression fittings
Hazardous Area classifications
Explosion proof Class 1, Division 1, Group C, D 		Optional: Group B upon request
ATEX II 2 G Ex db IIC T6…T2 Gb IP66
IECEx Ex db IIC T6…T2 Gb IP66

• 2 in (50 mm) and 3 in (76mm) flange mounted packing
gland and valve.

Preamplifier
In-line XAMP preamplifier with BNC connections; oneper transducer.
Gain• Standard: 20 and 40• Optional: 2, 10 (factory selected)
Preamp temperature range-40°C to +60°C (-40°F to +140°F)

Location
Installation of the XAMP in the transducer assembly iscovered by the transducer’s hazardous area certification,subject to the above temperature limits.
Alternately, the XAMP may be installed separate from thetransducer – remote mounted – with the following rating.
Explosion-proof Class I, Division 1, CD or BCD
Ex d IIC T6 Gb, IECEx & ATEX (II 2G)Transducer cables• Standard: (per pair of transducers)­ One pair of coaxial cables, type RG62 A/U, preamplifier to
XGF868i electronics, lengths 3 m (10 ft) to 330 m (1000 ft)
maximum• Optional: flame retardant, armored cable

Additional options
PanaView™ PC-interface software
The DigitalFlow XGF868i communicates with a PC through aserial interface and Windows® operating systems. Features
include site files, logs and other operations with a PC.

Installation flowcells
Transducers and flowcells for specific applications areavailable. Consult Panametrics for details.

Flow Accuracy

T5 Transducer

Tranducer Type

T17 Transducer

T5 Wetted Transducer

Number of Paths

T17/T5MAX (see note 1)

One Path

Two Paths

One Path

Two Paths

Flow Measurement Range
Standard Range-328 to 328 ft/s (-100 to 100 m/s) - bidirectional

Extended Range.1 to 394 ft/s (0.03 to 120 m/s) - non-bidirectional
Applicable Pipe SizesDiagonal 45

3 in to 14 in (50 to 350 mm) OD

14 in to 120 in (350 to 3000 mm) OD

Note 1 & 2

Not Applicable

Bias 90

Design Velocity Accuracy from 1 to 394 ft/s (0.3 to 120 m/s) - see notes 2 and 3Transducer TypeT5 Wetted Transducer

Number of Paths

One Path

T17/T5MAX Wetted Transducer
Two Paths

One Path

Two Paths

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

Pipe Dia. </= 6 in.
(150mm)+-2.5%+-2.0%+-2.0%+-1.5%NANANANA

Pipe Dia. >/= 6 in(150mm)+-2.0%+-2.0%+-1.5%+-1.5%+-2.0%+-2.0+-1.5%+-1.5%

Calibrated Velocity Accuracy from 1 to 394 ft/s (0.3 to 120 m/s) — see notes 3 and 4Transducer TypeT5 Wetted Transducer

Number of Paths

One Path

T17/T5MAX Wetted Transducer
Two Paths

One Path

Two Paths

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

1 ft/s (0.3 m/s)

>3 ft/s (1 m/s)

Pipe Dia. </= 6 in.
(150mm)+-1.5%+-1.0%+-1.0%+-0.75%

NANANANA

Pipe Dia. >/= 6 in
(150mm)+-1.0%+-1.0%+-0.75%+-0.75%+-1.0%+-1.0%+-0.75%+-0.75%Mass Flow Accuracy
2 to 120 kg+-4.0%+-3.1%+-2.7%+-2.3%

Molecular Weight Accuracy
2 to 120 kg/kmole+-1.8% to +-2%
Net Heating Value (NHV) Accuracy - refer to note 4

Typical accuracy2% - 5%
Flow Velocity Sensitivity from .1 to 1 ft/s (0.03 to .3 m/s)

Pipe Dia. = 10 in.
(250mm)±0.12 in/s(±0.004 m/s)

±0.08 in/s( ±0.003 m/s)

NANA

Pipe Dia. = 14 in.
(250mm)±0.12 in/s(±0.004 m/s)

±0.08 in/s( ±0.003 m/s)

±0.08 in/s(±0.003 m/s)

±0.06 in/s( ±0.002 m/s)

Pipe Dia. >/= 20 in.
(500mm)±0.12 in/s(±0.004 m/s)

±0.08 in/s( ±0.003 m/s)

±0.06 in/s( ±0.002 m/s)

±0.04 in/s(±0.0015 m/s)

Note 1: T17 available in NT/HT/LT/XT; T5MAX only available in NT.
Note 2: Accuracy and sensitivity are dependent on pipe diameter, molecular weight and temperature. All accuracy specs assume molecular weights greater than 24 kg/kmole andtemperatures less than 100 °F (38 °C)
Note 3: All accuracy specs assume a fully developed flow profile. This typically requires 20D upstream and 5D downstream. Desired accuracy can also be achieved with shorter straightruns as little as 5D upstream and 2D downstream through correction factors from Computational Fluid Dynamics (CFD) analysis loaded to XGF868 meters. Consult factory for details.
Note 4: Assuming known N2 concentration. Consult factory for details.

Repeatability±0.5% at 1 to 394 ft/s (30 cm/s to 120 m/s). Consult factory for details.

General installation straight run requirement
20D upstream and 5D downstream without CFD analysis.
5D upstream and 2D downstream with CFD analysis. Consult factory for details.

Panametrics, a Baker Hughes business, provides solutions in
the toughest applications and environments for moisture,oxygen, liquid and gas flow measurement.
Experts in flare management, Panametrics technology also
reduces flare emissions and optimizes performance.
With a reach that extends across the globe, Panametrics’
critical measurement solutions and flare emissions
management are enabling customers to drive efficiency
and achieve carbon reduction targets across criticalindustries including: Oil & Gas; Energy; Healthcare; Water andWastewater; Chemical Processing; Food & Beverage andmany others.
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