ctf878 startup guide

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CTF878 Flowmeter Startup Guide


Principle of Operation

Flow

Channel 1Transmit

Channel 2Transmit

Channel 1Receive

Channel 2Receive

• Continuous wave (CW) acoustic signals are transmitted from the transmit transducers

• Flow eddies modulate the amplitude of each acoustic beam as they pass through

• Electronics console demodulates signals from both receive transducers similar to AM radio

• DSP cross-correlates similar patterns in each demodulated signal to calculate the delay – Tao between these patterns

• The distance between the transducer pairs or Tag Path is divided by Tao to obtain flow velocity


Signal Processing

Carrier UpChannel 1

Carrier DownChannel 2

Modulation UpChannel 1

Modulation DownChannel 2

Tao


Cross-Correlation

Noise

Signal

Cross-Correlation SNR = Signal AmplitudeNoise Amplitude


Obstacles to Flow Measurement


Signal Through Gas• Most of the energy remains in

the pipe wall due to the acoustic impedance (density • SOS) mismatch between the pipe and the gas. A gas with higher density (pressure) provides better Signal Strength

• Signal through gas is attenuated more with longer path length, which is compensated by lowering transducer frequency with a sacrifice in the magnitude of signal modulation

(Caution: Lower transducer frequency is for larger pipes only!)


Short Circuit Noise•Pipe wall conducts acoustic

short circuit or SC through the circumference and heavy wall pipes have more SC due to more acoustic modes generated in the thick wall

•Acoustic signal is also conducted through the pipe wall between the transducers of each path causing cross talk

•Lower frequency transducers generate more SC which excludes their application for smaller pipes

•For these reasons, the dampening material is required for all applications

Gas “Signal”

Short Circuit “Noise”


Liquid on the Pipe Wall• Liquid on the inside or outside surfaces of the pipe is a

major obstacle to CTF878– Amplitude of the acoustic SC signal traveling in the pipe

wall modulates in the presence of a liquid on the wall– SC modulation cannot be distinguished from modulation

caused by flow turbulence

• Dampening material installed outside of the clamping fixture reduces SC modulation due to rain on uninsulated pipes and SC reflected from any nearby circumferential welds


Application VerificationGas type and minimum pressure:– Dry air, oxygen, nitrogen or argon at or above ambient pressure (1 bara, 14.5 psia)– Sweet natural gas at or above 2 bara, 30 psia– Other acoustically conductive gases with density of 0.074 lbs/ft3, 1.185 kg/m3

Transducer frequency:– 0.5 MHz for ANSI (DIN) 3 (75) to 16 (400) pipes – 0.2 MHz for ANSI (DIN) 16 (400) to 24 (600)

Pipes:– ANSI (DIN) 4 (100) to 24 (600)– Non-lined steel (double minimum pressure/density for Duplex), copper and most other

metals– HDPE (High Density Polyethylene), PVC, CPVC and most other non-lined plastic pipes

(fiberglass requires demo)

Velocity Limits:– Bi-directional flow– Between 3.5 ft/s (1.1 m/s) and 150 ft/s (46 m/s)


Installation


Pipe Geometry

20D 10D

Flow

Minimum Straight Run:– 10 to 20 (preferred) diameters upstream– 5 to 10 (preferred) diameters downstream– Minimum of 20 diameters between circumferential welds

P T


Pipe SurveyThickness Variation– Measure the thickness at 5 points

along the axis of the pipe– Maximum variation should be

less than 0.01 in. (0.25 mm)

Pipe Cross-section– Measure the average OD– Measure the thickness at 8 points– Program the meter with the

average thickness value

Transducer Location– Nearest the horizontal plane– Location with the greatest

thickness difference of the opposing walls (W3 and W7 )

– Away from circumferential weld(s) or seam

1 2 3 4 5

W1

W2W8

W4

W3W7

W6

W5


Pipe Preparation Fixture Location– Remove 30 inches (750 mm) of insulation if any– Remove any loose paint and/or rust– Do not alter the curvature of the pipe if using a grinder

Transducer Location– Mark two correctly spaced areas on either side of the

pipe, 4 inches (100 mm) long by 2 inches (50 mm) wide– Grind off paint if it is thick or uneven without altering

the pipe curvature– Polish with fine sand paper


Dampening Installation Wrapping DMP-1 (Maximum Temperature 150 ºF, 65 ºC)– Warm up the DMP-1 if the pipe surface is below 45 ºF (7 ºC) – Apply the DMP-1 starting at the bottom– Align it parallel to the axis of the pipe– Pull DMP-1 while wrapping, taking care to minimize air pockets by

pressing it and sliding back and forth with the free hand

Removing DMP-1 from Transducer Locations– Temporarily install the clamping fixture with the yokes correctly

spaced– Install the transducers without any couplant and mark their locations– Remove the transducers and cut off the dampening material from

marked locations


High Temp. Dampening Installation

Safety Equipment and Precautions– Wear high temperature gloves and goggles – Use hardhat to avoid head injuries and burns from overhead pipes– The area must have good ventilation because of fumes and

smoke during installation

Installing the Pipe Dampening Jacket (PDJ)– Orient the PDJ to allow clearance for transducers and junction

boxes– Remove the paper liner from the inside of the PDJ– Wrap the PDJ around the pipe with the fasteners close to the

bottom– Place a metal bucket and a drop cloth under the PDJ to collect the

hot fluid runoff


Final Installation Clamping Fixture– Replace any plastic parts with metal versions for high temperature– Adjust the transducer yoke positions to correct spacing– Align fixture correctly during installation by maintaining equal distance

between pipe brackets on top and bottom and placing yokes over transducer openings

Transducers– Screw the transducers into the junction boxes and verify the

orientation – Apply a thin layer of couplant to the whole face of each transducer– CPL-01/CPL-04 for temporary normal/high temperature installations– CPL-16 for permanent normal and high temperature installations– Allow the CPL-16 to “skin” on the pipe for 15 minutes before fully

tightening the transducer hold down bolts and locking nuts


System Wiring Wiring the Preamplifier(s)– Connect the preamplifier cable in the junction box to the

Channel 1 receive or upstream transducer of the upstream path– The Channel 1 Transmit cable from the flowmeter should be

connected to the downstream transducer of the upstream path– Repeat connections for the Channel 2 (downstream path)

transmit and receive cables

Wiring the Flowmeter– If used, wire the pressure and temperature transducers to the

Analog/RTD inputs– Hook up the Analog or Frequency output and Alarms, if required– Verify that the power source is not energized and connect the

power to the CTF878 flowmeter


Wiring Diagram

Flow

P

T

Ch. 1 TX

Ch. 2 TXCh. 2 RX Ch. 1 RX

Preamplifiers (1080) installed on receiving transducersTransducer Spacing = X1 – X2

X1

X2

Tag Path

DigiFlow CTF878

g


Flowmeter Programming

DigiFlow CTF878

g


Pipe and Transducer Parameters• Transducer Selection

– Number 312/310 for 0.2/0.5 MHz up to 266°F (130 °C)– Number 318 for 0.2 MHz up to 350°F (176°C)– Number 307 for 0.5 MHz up to 450°F (232°C)– Wedge temperature is an average of ambient and gas temperatures

• Pipe Properties– Select the pipe material from the list– Program OD and wall thickness measured in “Pipe Survey”

• Gas Properties– Select the type of Fluid being measured– Use Sonicware™ or the NIST website for Kinematic Viscosity

• Transducer Spacing– Physical transducer spacing for each path must be the same as calculated by the

CTF878– Up to 0.25 inch (6.4 mm) difference from calculated spacing is allowed

• Tag Path– Tag Path or the distance between paths must be the same as calculated by the

CTF878– Based on pipe ID with minimum 5-inches (125 mm) and maximum 10-inches (250

mm)


Standard/Normal Flow Parameters

• Enabling Analog/RTD Inputs– Enable Analog inputs in the “Analog I/O” menu

• Temperature Input– Program correct “Base” temperature (check with customer)– Measure the “Fixed” temperature as close as possible to the

measurement location and under the insulation, if used– Program “Active” temperature input with appropriate limits

for the probe

• Pressure Input– Program correct “Base” pressure (check with customer)– “Fixed” pressure must be obtained from a probe as close as

possible to the measurement location without pressure drops (elbows, tees, valves or reducers) in between

– Program “Active” pressure input with appropriate limits for the probe


Error Limits• Diagnostic Parameters

– SNR Min. sets Low SNR Error (E8) trigger point, default is 10

– Carrier Limits set Carrier Under (E4) and Over (E5) trigger points, defaults are 75 mV and 1200 mV

– DMod Limits set Modulation Under (E6) and Over (E7) trigger points, defaults are 75 mV and 1500 mV

• Flow Parameters– Velocity Limits set Velocity Range Error (E9) trigger point

which should be programmed to application maximum and minimum

– Acceleration Limit sets Acceleration Error (E10) trigger point, decrease if flow will not change a lot and increase otherwise to improve response


Signal Setup Parameters• Signal Menu

– Reverse Flow should be checked to reverse the flow reading – Zero Cutoff is the lowest measured velocity, lower values will be

displayed as zero– Velocity Averaging is the number of readings that are averaged

together, the greater the number, the slower the response– Errors Allowed sets the number of errors that is allowed before an error

message is displayed, the default is 2• AGC/MGC Menu

– Gain control should always be set to AGC or automatic, manual control or MGC is used for diagnosis of problems

– Carrier set point limits HFHI and HFLO for AGC should be set to 1000 mV and 200 mV

– Modulation or low frequency set point LFSP should be set to 590 mV• Cross-Correlation (CC) Averaging

– CCorr Average should be set to 75%, increase to improve SNR for low flow

• Low Pass (LP) Filter– Electrical (Elec.) System should be set to the frequency of the AC power

system


Calibrating Analog I/O• Calibrate Analog Output(s) for Data or Input

Calibration– Connect DMM or Calibrator to the Output being calibrated– Select “Main Board (0)” or Slot # corresponding to the Analog

Output option card in the “Calibrate/Test” submenu from the “Service menu”

– Calibrate upper and lower limits then repeat for the other output(s)• Calibrate Analog Input(s)

– Connect a Calibrator or Analog Output A to Input (A)– Select the appropriate Slot number– Select the appropriate Analog Input in the “Calibrate/Test” submenu

from the “Service menu”– Calibrate upper and lower limits then repeat for the other input(s)

• Calibrate RTD Input(s)– Connect RTD Calibrator to the appropriate RTD Input on the Option

Card– Select the appropriate Slot # and Input in the “Calibrate/Test”

submenu– Calibrate upper and lower limits for each RTD Input used


Operation Verification and Troubleshooting


Signal Verification• Cross-Correlation SNR (CC SNR)

– CC SNR should be greater than 10– If not, the flow is too low

• Carrier Amplitude and Gain– Carrier Amplitude should be between 75 mV and 1200 mV– If Carrier Gain is close to –6 dB and Amplitude is high, the carrier may

be saturated – remove the preamplifiers and disable preamplifier power– If Carrier Amplitude is below 75 mV and Gain is 31 dB, the carrier is too

weak, add preamplifiers or use 0.2 MHz transducers and receiver card

• Modulation (Mod) Amplitude and Gain– Mod Amplitude should be between 75 mV and 1500 mV– If Mod Amplitude is below 75 mV and Gain is 31.5 dB, the Carrier is

weak– If Mod Amplitude is above 1500 mV and Gain is –16.5 dB, there is

inadequate straight run upstream or high liquid content in the gas


Flow Measurement Verification

• Delay (Tau)– Tau should be stable and reasonable– Unstable Tao could be caused by low CC SNR

• Velocity/Volumetric Accuracy– Check the physical Tag Spacing and programmed setting

consistency– Check the Temperature and Pressure settings or probe parameters– Check whether there is enough straight run of pipe and no

disturbances upstream

• Sanity Check– Reverse the transducer cables between channels – Verify that Tau and velocity/volumetric are negative with the same

magnitude– The sum of Carrier and Demodulation gains for Channel 1 should be

equal to Channel 2, which indicates that the cross-talk is cancelled out


Troubleshooting Flow ChartCARRIER UNDER (E4) CARRIER OVER (E5) MOD UNDER (E6) MOD OVER (E7)

XDCR SPACING?

COUPLANT?

GAS DENSITY LOW?

ADD PREAMPS

CHANGE TO 0.2 MHz

DAMPENING?

CHANGE TO 0.5 MHz

TAG PATH?

COUPLANT?

LOW VELOCITY?

CHANGE TO 0.5 MHz

REMOVE PREAMPS

CHANGE TO 0.2 MHz

LIQUID CONTENT?

LOW SNR (E8)

CARRIER GAIN < 0?

MOD GAIN < 0?

STRAIGHT RUN?

DAMPENING?

REMOVE PREAMPS

YesNo

YesNo

LOW VELOCITY?

ctf878 startup guide

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