Greyline Instruments TTFM-6.1 Operating Manual
www.greyline.com
USER'S GUIDE
Installation & Operation
Instructions
Transit Time Flow Meter
Model TTFM 6.1
Manual Series A.1.0
Note: This page has been left blank intentionally.
TTFM 6.1 Transit Time Flow Meter
INDEX
CONNECTIONS ................................................................................................................ 4
KEYPAD SYSTEM ............................................................................................................ 6
CALIBRATION MENU ..................................................................................................... 7
ICONS ................................................................................................................................. 8
MESSAGE ICON ............................................................................................................... 9
STATUS.............................................................................................................................. 9
PASSWORD ..................................................................................................................... 10
MENU SELECTIONS ...................................................................................................... 10
UNITS/MODE .................................................................................................................. 11
SET UP ............................................................................................................................. 13
CALIBRATION ................................................................................................................ 15
RELAY PARAMETERS .................................................................................................. 16
DATA LOGGING ............................................................................................................ 17
COMMUNICATION (OPTIONAL) ................................................................................ 19
SPECIAL FUNCTIONS ................................................................................................... 20
TYPICAL SENSOR INSTALLATION ........................................................................... 23
SENSOR MOUNTING ..................................................................................................... 26
2 OR 4 CROSS INSTALLATION OVERVIEW - TMK-B1 KIT ................................... 27
2 OR 4 CROSS INSTALLATION OVERVIEW - TMK-B21 OR TMK-B22 KIT ......... 37
ENCLOSURE INSTALLATION ..................................................................................... 49
FIELD TROUBLESHOOTING........................................................................................ 50
COMMON QUESTIONS AND ANSWERS ................................................................... 53
APPLICATIONS HOTLINE ............................................................................................ 55
PRODUCT RETURN PROCEDURE .............................................................................. 55
SPECIFICATIONS ........................................................................................................... 70
APPENDIX A - CONVERSION TABLE ........................................................................ 71
PIPE CHARTS .................................................................................................................. 72
APPENDIX C – LIQUID SPEED OF SOUND ............................................................... 76
APPENDIX D ................................................................................................................... 83
IMPORTANT NOTE: This instrument is manufactured and calibrated to meet product specifications. Please read this
manual carefully before installation and operation. Any unauthorized repairs or modifications may result in a suspension of
the warranty. If this product is not used as specified by the manufacturer, protection may be impaired.
Available in Adobe Acrobat pdf format
Page 3
TTFM 6.1 Transit Time Flow Meter
CONNECTIONS:
POWER INPUT: The standard model requires AC power input between 100 to 240 VAC 50/60Hz
10VA. No adjustments are necessary for voltages within this range. Connect L (Live) N (Neutral) and
AC Ground.
Optional DC input model requires 9-32 VDC/10 Watts. Connect to + and - terminals.
Optional Thermostat and Heater modules are available rated for specifically 115 VAC or specifically
230 VAC.
IMPORTANT NOTE: To comply with electrical safety standards, AC power input and relay connection
wires must have conduit entry to the instrument enclosure. Installation requires a switch, overcurrent
fuse or circuit breaker in the building (in close proximity to the equipment) that is marked as the
disconnect switch.
Risk of electric shock. Loosen cover screw to access connections. Only qualified personnel
should access connections.
Note: Use of instrumentation over 40°C ambient requires special field wiring.
Note: User replaceable fuse is 2 Amp 250V (T2AL250V), located on the power supply.
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TTFM 6.1 Transit Time Flow Meter
100-240 VAC Meter CONNECTIONS
Page 5
TTFM 6.1 Transit Time Flow Meter
KEYPAD SYSTEM
The diagram on page 7 shows the TTFM 6.1 menu system. Arrows show the four directions to leave a
menu box. Pressing a corresponding keypad arrow will move to the next item in the direction shown.
Move the cursor (highlighted) under numerals and increase or decrease numerals with the and
keys.
To store calibration values permanently (even through power interruptions), press the button.
Page 6
TTFM 6.1 Transit Time Flow Meter
CALIBRATION MENU
Page 7
TTFM 6.1 Transit Time Flow Meter
ICONS
Page 8
TTFM 6.1 Transit Time Flow Meter
MAIN DISPLAY
MESSAGE ICON
STATUS
The Main Display shows the units selected from the Units/Mode menu, flow rate
or velocity rate being measured, totalizer, totalizer multiplier, and relay states. The
TTFM 6.1 will go to this display after start-up.
Press from the Main Display to view status of the data logger and
error/warning messages provided by the instrument. The Message Icon will
appear on the Main Display if error messages are being generated by the
instrument. Press to return to the Main Display.
Press from the Main Display to view instrument Status.
Velocity Displays flow velocity in ft/s or m/s.
Tot Displays total volume in units selected in the
Units/Mode menu.
Signal Strength Displays magnitude of signal being received by the
ultrasonic sensor. 100% is the ideal signal strength.
Signal strengths less than 100% could indicate poor pipe
conditions (corrosion), highly aerated water, or
programmed setup parameters which don’t closely
match field conditions. Consideration should be made to
use 1-cross installation method in such cases, if not
already using it.
Relays Displays current state of the relay outputs. Energized
relays will display as a white character on a black
background.
Adj. SOS Displays measured sonic velocity of the fluid in ft/s or
m/s.
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TTFM 6.1 Transit Time Flow Meter
24 HR LOG
PASSWORD
MENU SELECTIONS
Press from the Main Display to view a formatted flow report. Press to scroll
down one day or repeatedly to scroll to a specific date. Up to 365 days will be
stored. Newest date will overwrite the oldest. Press to return to the Main
Display.
The Password (a number from 0000 to 9999) prevents unauthorized access to the
Calibration menu.
From the Main Display press the key to get to
password is 0000 and if it has not been changed, this screen will be bypassed
completely.
A new password can be stored by going to the
Password
If a user password is required, press to place the cursor under the first digit and
or to set the number, then to the second digit, etc. Press or to proceed
to the Menu Selections screen.
menu.
Password. Factory default
Special Functions New
The Menu selections page is used to navigate to specific menus which are
described in more detail on the following pages.
Press or to navigate to different menus, and to enter the selected menu.
Page 10
TTFM 6.1 Transit Time Flow Meter
UNITS/MODE
At
press the key and then the or to select your units of
At
, press the and then the or to select units for volume. Note:
next menu item.
At
, press the and then the or to select the totalizer
as an example. Press to store your selection then to the next menu item.
At
, press the and then the or to select the engineering
selection then to the next menu item.
At
, press the and then the or to select the engineering units for
flow rate. Press to store your selection then to the next menu item.
Available Flow Rate Engineering Units:
Abbreviation
Description
Abbreviation
Description
USG/d
US gallons per day
L/d
liters per day
USG/h
US gallons per hour
L/h
liters per hour
USG/m
US gallons per minute
L/m
liters per minute
USG/s
US gallons per second
L/s
liters per second
ft3/d
cubic feet per day
m3/d
cubic meters per day
ft3/h
cubic feet per hour
m3/h
cubic meters per hour
ft3/m
cubic feet per minute
m3/m
cubic meters per minute
ft3/s
cubic feet per second
m3/s
cubic meters per second
bbl/d
barrels per day (1 bbl = 42 USG)
IG/d
Imperial gallons per day
bbl/h
barrels per hour (1 bbl = 42 USG)
IG/d
Imperial gallons per day
bbl/m
barrels per minute (1 bbl = 42 USG)
IG/d
Imperial gallons per day
bbl/d
barrels per second (1 bbl = 42 USG)
IG/d
Imperial gallons per day
USMG/d
US million gallons per day
IMG/d
Imperial million gallons per day
USMG/h
US million gallons per hour
IMG/h
Imperial million gallons per hour
USMG/m
US million gallons per minute
IMG/m
Imperial million gallons per minute
USMG/s
US million gallons per second
IMG/s
Imperial million gallons per second
At
Mode, press the and then the or to select Flow or Velocity. Flow
mode displays the flow rate in engineering units (e.g. gpm, litres/sec, etc.) Press
the to store your selection then the to the next menu item.
Linear
measurement. The Linear units define what units the pipe dimensions and sensor
spacing will be displayed in. Typically inches or mm is selected.
store your selection then the to the next menu item.
Volume
“bbl” denotes US oil barrels. Press the to store your selection then the to the
Multiplier
multiplier. Multipliers are used when resolution down to single digit is not
required, or when you don’t want to convert from gallons to thousands of gallons,
Press the to
Velocity
units for flow velocity and sonic velocity of the fluid. Press to store your
Flow
Page 11
TTFM 6.1 Transit Time Flow Meter
UNITS/MODE (cont.)
At
, press the and then the or to select units for
Temperature
temperature. Press the to store your selection then the to go back to another
menu item, or to exit back to the Menu Selection screen.
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TTFM 6.1 Transit Time Flow Meter
SET UP
Sensor
Choose SE16B.
Type
Select transducer Type which matches the transducer pair
Fluid
Select fluid type.
Vel@25C
When Fluid = Other, enter the fluid velocity at 25C from table or
dV/C
When Fluid = Other, Enter fluid velocity adjustment factor over
Temp Mode
Choose Fixed.
Temp
Enter fluid operating temperature in displayed engineering units.
Pipe
Select pipe material.
Pipe Vel
When Pipe = Other, enter pipe material speed of sound (consult
OD
Highlight the digits and then or to change the numbers and
Wall
Enter pipe wall thickness. Pipe wall thickness should be entered
Lining
Select liner material.
Press or to position curser at Setup, and to enter. Use or to position
cursor before each menu item and to enter. When settings are completed press
to store and again to return to the Main Menu.
Select
connected to the TTFM. Options: 35, 37, 39, and 41.
Type is determined by the part number on the SE16-B transducer
label. Guide:
Part Number on SE16-B Label Corresponding Angle
SE16-B1 35
SE16-B2 37
SE16-B3 39
SE16-B4 41
other reference. Engineering units may be m/s or ft/s depending
on Units menu programming.
change in temperature in units of m/s or ft/s per °C.
factory).
decimal point. Pipe OD should be entered as the exact outside
diameter of the pipe where the sensor is mounted. Refer to the
Pipe Charts Appendix in this manual for outside diameter of
common pipe types and sizes.
as the exact wall thickness of the pipe where the sensor is
mounted. Refer to the Pipe Charts Appendix in
this manual for wall thicknesses of common pipe types and
sizes.
Page 13
TTFM 6.1 Transit Time Flow Meter
SET UP (cont.)
Vel
When Lining = Other, enter speed of sound of liner (consult
Thick
When Lining ≠ None, enter liner thickness.
Crossings
Zero Tare
Used to calibrate zero-flow measured by the TTFM 6.1 in
Sens Space
After sensor, angle, fluid, and pipe material are defined, this
Velocity
Displays the measured velocity after the sensors have been
Signal
Displays magnitude of signal being received by the ultrasonic
method if this is not the current mounting mode.
factory).
Crossings 1 = Z mounting
Crossings 2 = V mounting
Crossings 4 = W mounting
Strength
NOTE: Not all Crossings selections will be available at the
same time. The meter will limit selections based on
parameters like pipe size and material.
process. Flow in the pipe should be confirmed as 0 before
enabling, or significant errors in flow accuracy could occur.
Set Calibration/Damping to 5%, and under no flow conditions
and with a full pipe, select
Yes to force readings to zero.
displays the calculated sensor spacing. Also called the
separation distance. The sensors will be set to this dimension
when installed on the pipe, as described later in this manual.
connected at the specified separation distance.
sensor. Should be 100% under ideal operating conditions.
Signal strengths less than 100% do not indicate that the meter
is not reliable, however, the meter may be more susceptible to
complete signal loss should process conditions like entrapped
air worsen. When signal strength is less than 100%,
consideration should be made to using 1-cross mounting
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TTFM 6.1 Transit Time Flow Meter
CALIBRATION
Mode
Displays the Mode which was selected in the Units/Mode
20mA
Press then or to change the numbers and decimal point
4mA
Press then or to set the flow rate corresponding to
Min Flow
Flow rates below this setting will be displayed as zero flow.
Damping
Increase damping to stabilize readings under turbulent flow
Cal
Calibration constant defined when the TTFM was calibrated at
Press to return to Menu Selections.
Press or to position curser at Calibration menu, and to enter. Use or
to position cursor before each menu item and to enter. When settings are
completed press to store and again to return to the Main Menu.
menu. This is read-only.
position. Use this menu to set the corresponding flow rate that
will be represented by 20mA analog output. If maximum flow
is unknown, enter an estimated flow rate and observe actual
flow to determine the correct maximum value. Any velocity or
flow rate up to +40 ft/sec (12.0 m/sec) may be selected.
4mA analog output. This setting may be left at zero or can be
raised to any value less than the 20mA setting, or lowered to
any velocity or corresponding flow rate down to -40 ft/sec (-12
m/sec).
Constant
Default flow rate is ∼ 0.1 ft/sec for the pipe size programmed
in the Setup menu.
conditions. Decrease for fast response to small changes in
flow. Damping is shown in percentage (maximum is 99%).
Factory default is 10%.
the Greyline factory.
Page 15
TTFM 6.1 Transit Time Flow Meter
RELAY PARAMETERS
Relay
Press and or to select a corresponding relay number (2
Function
Press or to select
, On,
or
.
Flow
Mode Select
,
or
.
Pulse
Press and set digits to the flow volume increment required
Press to return to
.
Press or to position curser at Relay Parameters, and to enter. Use or
to position cursor before each menu item and to enter. When settings are
completed press to store and again to return to the Main Menu.
relays are standard, 4 additional are optional).
Pump
Off
Low Alarm
Pulse
Hi Alarm
Flow
Pump mode provides separate On/Off settings where the
relay will energize at one flow rate and de-energize at another.
On Highlight the numerals and press or to set digits to
the required relay
On set point.
Off set digits to the required Off set point.
Low Alarm mode relay will energize at a programmable
flow rate and remain energized with flow below the set point.
When flow rises above the set point, the relay will de-energize.
Hi Alarm mode relay will energize at a programmable
flow rate and remain energized with flow above the set point.
When flow falls below the set point, the relay will de-energize.
between relay pulses. Use this feature for remote samplers,
chlorinators or totalizers. Minimum time between pulses is
2.25 seconds and pulse duration is 350 milliseconds.
Return to
Relay and change settings for each relay
number.
Menu Selections
Page 16
TTFM 6.1 Transit Time Flow Meter
DATA LOGGING
Press or to position curser at Data Logging, and to enter. Use or to
position cursor before each menu item and to enter. When settings are
completed press to store and again to return to the Main Menu.
Log Site ID Enter a number from 00 to 99. The site ID will become part of
the downloaded file name to help distinguish downloads from
different instruments. Press to store the setting.
Mode Select Velocity (e.g. ft/sec or m/sec) or Flow (e.g. USGPM or
l/sec). Press to store the setting.
File Format Choose .LG2 to download data in .lg2 format for viewing on
Greyline Logger software. Choose .CSV to download data in
.csv format for import directly to Excel. This menu option can
be changed at any time without adversely affecting existing
data.
Date Press , and or to scroll and select Month, Day and
Year. Press to store the setting.
Time Press , and or to select the current time in Hours,
Minutes and Seconds. Press to store the setting.
Interval Press or to select the logging interval. Press to store
the setting. Greyline recommends choosing an interval which
will give you as much resolution as required and no more.
Choosing too often of an interval for what is required will
result in excessively large data files which take a long time to
download to USB. In critical installations, data should be
downloaded often.
Data Log Stop, Start or Delete the log file. Press or to select Delete
and to delete the log file. Press or to select Start and
to start the logger.
Important Note: You MUST Delete an old log and S
tart a new log AFTER
having made changes to Log Site ID, Mode, Date, Time and/or Interval for those
changes to be applied.
Important Note: Changing any of the parameters in the Units/Mode menu will
start a new log. It is recommended that you Delete and start a new log after
changing any Units/Mode settings.
Page 17
TTFM 6.1 Transit Time Flow Meter
RETRIEVING LOG FILE
Plug a USB Flash Memory Drive (not supplied by Greyline) into the USB output
port on the Panel of the meter. The instrument display will show the data
download icon until the log file is transferred to the memory card. The USB flash
drive may be removed when the icon for download successful appears.
Download file names will appear in this format:
Tag is set according to the
Logging
Download letter will be A for the first download from an instrument. B for the
second, then C etc. At the letter Z a - character will appear indicating that the
maximum number of downloads for that instrument are on the USB flash drive.
Older files can be erased or moved from the flash memory drive or a new memory
drive can be used.
Note: Downloading files in .lg2 format will take approximately 35 seconds per
Downloading files in .csv format will take approximately 8 minutes per 1%
OPENING .LG2 FILES
Install Greyline Logger on your PC or laptop. Select File/Open/Instrument Log
(.log) to open the log file from your USB flash drive. Greyline Logger software is
available on Greyline’s website, www.greyline.com
.CSV via Greyline Logger software.
OPENING .CSV FILES
Use a datasheet program such as Microsoft Excel® to import data in a comma
delimited format. Use Excel to manipulate or graph data.
menu.
1% of internal log memory used.
of internal log memory used.
Log Site ID entered in the instrument Data
. Data can be converted to
Page 18
TTFM 6.1 Transit Time Flow Meter
COMMUNICATION (Optional)
Press or to position curser at Communication, and to enter. Use or
to position cursor before each menu item and to enter. When settings are
completed press to store and again to return to the Main Menu.
MODBUS Protocol Information:
Transceiver: 2-wire, half-duplex
Data format: 8 Data Bits
Floating Point Byte Order: ABCD
Termination: Jumper selectable 120Ω resistor. TB1 & TB2 = OFF, TB2 & TB3
= ON
Biasing: None
Protocol Choose MODBUS.
Address Device address for the TTFM. Valid range: 001-247 (Default:
001). This number should be unique across the bus. Press or
to scroll, to select digits, and press to store the setting.
BPS Baud rate for the MODBUS communications. Press or to
select, and to store the setting. Options: 4800, 9600, 19200,
38400, 57600, 76800, and 115200 (Default: 9600).
Parity Error checking parity for the MODBUS communications. Press
or to select, and to store the setting. Options: None, Even,
and Odd (Default: Even).
Stop Bits Press or to select, and to store the setting. Options: 1 or 2
(Default: 1).
Page 19
TTFM 6.1 Transit Time Flow Meter
SPECIAL FUNCTIONS
Language
Select
,
or
Analog Out
Select 4-20mA or 0-5V mode for the analog output.
Backlight
Select
,
or
for
Select
for high backlight lasting 1
Select
,
or
for backlight
Reset Totalizer
Select
to erase and restart the totalizer at
Negative Totals
Select
to have reverse flow readings
Capture WF
This function should only be used when instructed by
ready to be sent to Greyline.
Restore Defaults
Select
to erase all user settings and return the
Press or to position curser at Special Functions, and to enter. Use or
to position cursor before each menu item and to enter. When settings are
completed press to store and again to return to the Main Menu.
English
French
Spanish
High
Medium
Low
continuous backlight brightness.
Key Hi/Lo
minute after a keypress, and then Lo backlight
until a key is pressed again.
Key High
Med
Low
lasting 1 minute after a keypress and then backlight
off until a key is pressed again.
Yes
zero.
Yes
deducted from the totalizer. Select No to totalize
forward flow only and ignore reverse flow.
a Greyline representative to do so. The function
captures the ultrasonic signal, as measured by the
processor, for evaluation.
Select Yes to start the waveform download
process. After pressing
message
screen, connect a flash drive to the USB port on the
front of the meter. The screen will flash
for a couple seconds, and then return to
waveform is now stored on your flash drive and
instrument to factory default settings. Note: does not
reset factory calibration values.
Page 20
Yes , the screen will flash
Working for approximately 40 seconds, until the
Done appears. When Done is on the
Saving
No . The
Yes
TTFM 6.1 Transit Time Flow Meter
SPECIAL FUNCTIONS (cont.)
New Password
Select any number from 0000 to 9999. Default
Press to return to
.
setting of 0000 will allow direct access to the
calibration menus. Setting any password other than
0000 will require the password to be entered to
access the calibration menus.
Menu Selections
Page 21
TTFM 6.1 Transit Time Flow Meter
SIMULATION
screen.
Press or to position curser at Simulation, and to enter. Use or to
position cursor before each menu item and to enter. When settings are
completed press to store and again to return to the Main Menu.
Changes made in the Simulation menu exercise the 4-20mA output, digital display
and control relays.
Simulate a
the simulated output. Press to begin simulation. The 4-20mA output and relay
states will be displayed on the screen below.
Press the to terminate simulation and return to the Menu Selections
Flow /Velocity reading. Press and then or to change
Page 22
TTFM 6.1 Transit Time Flow Meter
TYPICAL SENSOR INSTALLATION
Page 23
TTFM 6.1 Transit Time Flow Meter
Pipe Preparation and Bracket Mounting
Prepare an area 2" wide by 4" long (50mm x 100mm) for each sensor bonding by removing loose paint,
scale and rust. The objective of site preparation is to eliminate any discontinuity between the sensor and
the pipe wall, which would prevent acoustical coupling.
A Sensor Mounting Kit is supplied with each Greyline flow meter. It includes recommended coupling
compound and a stainless steel mounting bracket with adjustable pipe straps. Use the Alignment Bar
(included) to align sensor brackets for V and W mode mounting.
IMPORTANT: The SE16-B transit-time transducers have arrows on the top of them. These should face
each other at installation.
Page 24
TTFM 6.1 Transit Time Flow Meter
SENSOR COUPLING
For permanent or temporary bonding, the following are recommended:
a) Super Lube® (supplied)
Additional supply: order Greyline Option CC-SL30 or your local home improvement store.
b) Water-based sonic compound: Order Greyline Option CC30
c) Electrocardiograph gel
d) Petroleum gel (Vaseline)
The above are arranged in their order of preferred application. Option d is only good for temporary
bonding at room temperature. DO NOT USE: Silicon RTV caulking compound (silicon rubber).
Use the pipe clamp and rail (supplied) as illustrated on previous page. Apply
Super Lube® to the colored face of the sensor. A bead, similar to toothpaste on
a toothbrush, is ideal. Do not overtighten (crush the sensor).
The sensor must be fixed securely to the pipe with coupling material
between the sensor face and the pipe. Sensor installation with
excessive coupling compound can result in gaps or voids in the
coupling and cause errors or loss of signal. Insufficient coupling
compound will create similar conditions.
Over time temporary coupling compounds (e.g. Petroleum Gel) may gradually sag away from the sensor
resulting in reduced signal strength and finally complete loss of signal. Warm temperatures, moisture
and vibration will accelerate this process. Super Lube® as supplied with the TTFM 6.1 (and available
from Greyline Instruments or home improvement stores) is recommended for permanent installations.
Transducer Installation in Wet Locations
The TTFM 6.1 Transit Time Flowmeter transducers are
rated for accidental submersion up to 10 psi (0.75 bar). The
flowmeter will continue to operate and measure flow
accurately during periods of submergence. Plastic seal
jackets on the cables must be filled with coupling compound
to provide additional moisture protection for the BNC cable
connectors.
Page 25
TTFM 6.1 Transit Time Flow Meter
SENSOR MOUNTING LOCATION
The position of the sensor is one of the most important considerations for accurate flow measurement.
The same location guidelines apply to Transit Time as most other flow meter technologies.
VERTICAL OR HORIZONTAL PIPE - Vertical pipe
runs are acceptable, and the transducers can be
mounted in any orientation around the pipe.
Downward flow should be avoided in case the pipe
becomes partially filled or aerated. On Horizontal
pipes and liquids with high concentrations of gas or
solids, the sensors should be mounted on the side (1 to
5 o’clock positions) to avoid concentrations of gas at
the top of the pipe, or solids at the bottom.
STRAIGHT RUN REQUIREMENTS – For best
results, the transducers must be installed on a straight
run of pipe, free of bends, tees, valves, transitions,
insertion probes and obstructions of any kind. For
most installations, ten straight unobstructed pipe
diameters upstream and five diameters
downstream of the transducers is the minimum
recommended distance for proper operation.
Additional considerations are outlined below.
• Do not, if possible, install the transducers downstream from a throttling valve, a mixing tank, the
discharge of a positive displacement pump or any other equipment that could possibly aerate the
liquid. The best location will be as free as possible from flow disturbances, vibration, sources of heat,
noise, or radiated energy.
• Avoid mounting the transducers on a section of pipe with any external scale. Remove all scale, rust,
loose paint, etc., from the location prior to mounting the transducers.
• Do not mount the transducers on a surface aberration (pipe seam, etc.).
• Do not mount transducers from different ultrasonic flow meters on the same pipe.
• Do not run the transducer triaxial cables in common bundles with cables from other instrumentation.
You can run these cables through a common conduit ONLY if they originate at the same flow meter.
• Never mount transducers under water.
IMPORTANT NOTE: In some cases, longer straight runs may be necessary where the transducers are
placed downstream from devices which cause unusual flow profile disruptions or swirl. For example:
modulating valves, or two elbows in close proximity and out of plane.
Page 26
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