
TRANSIT TIME ULTRASONIC 
FLOWMETER
FDT-81
Standard
FDT-81 shown 
smaller than  
actual size.
Comes with AC and 
automobile power adaptors, 
compartmentalized padded 
carrying case, coupling 
grease, standard sensors, 
straps, cables, mounting 
track, and complete 
operators manual.
U Automatic Reynolds Number 
Compensation
U 24 Hour Integral Rechargeable Battery 
U AC and Automobile Power 
Adaptors Included
U  User-Configurable Rate 
and Totalizer Units
U Designed for Clean and 
Ultraclean Liquids
U Non-Invasive Clamp-on Transducers
The FDT-80 Series of portable transit time flowmeters 
feature the world’s most advanced non-invasive flow 
measurement technology, providing a measuring system 
with unsurpassed accuracy, versatility, ease of  
installation and dependability. Although designed  
primarily for cleaner liquids, the flowmeter can also  
reliably measure liquids containing moderate amounts  
of suspended solids or aeration.
FDT-80 is designed for long or short term flow  
measurement surveys on full-pipe liquid systems  
and is ideal for verifying calibration of permanently 
mounted flowmeters of all types. The flowmeter  
features a tactile keypad, 24-hour battery (rechargeable), 
and a 128 x 64 pixel, back-lit graphics display–all 
integrated into a rugged, watertight enclosure. The  
FDT-80 systems utilize proprietary dual time-base time  
expansion algorithm, advanced DSP and digital  
cross-correlation. The cost effective and versatile  
FDT-80 flowmeter comes complete with all accessories 
necessary for measuring piping systems from  
50 to 2540 mm (2 to 100").
FDT-80 Series has a flow measuring range that  
exceeds 4000:1. This feature allows the instrument to 
measure normal process flow rates as well as flows 
resulting from leaks in piping and valves.
User configurable rate and totalizer units include: feet, 
gallons, ft 
liters, m3, million-liters and kg. Non-invasive clamp-on 
transducers are simple and cost efficient to install.  
Since the transducers do not contact the liquid, fouling 
and maintenance are eliminated. 
Automatic Reynolds Number compensation assures 
accurate measurements through the laminar, transition 
and turbulent system flow regions. An integral 24 hour 
rechargeable battery allows extended operation when 
AC power is not available. Both AC and cigarette socket 
style power adaptors (battery chargers) are included. 
Compartmentalized and padded carrying case keeps 
the FDT-80 meter and all of its accessories organized 
and protected.
3
, million-gal, barrels, acre-feet, lbs, meters, 
E-5

FDT-81 shown smaller 
than actual size.
SPECIFICATIONS
Transmitter
Power Requirements: Internal 12V 
lead-acid gel cell battery provides 24 hrs 
of continuous operation @ 20°C (68°F) 
Charging: Wall mount power converter, 
115 or 230 Vac 50/60 Hz ±15% @  
5 VA maximum; 12 to15 Vdc @ 
2.5 VA maximum 
Velocity: -12 to +12 MPS  
(-40 to +40 FPS) 
Outputs: All output modules are  
optically isolated from earth and system 
grounds. A maximum of two modules 
may be installed 
Analog Output: 4 to 20 mA, 800Ω  
maximum; 12-bit resolution; passive  
or active 
Other Options: Pulse output MOSFET, 
dual form C relays, heat flow and high 
temperature, and small pipe sensors 
(consult Engineering for details) 
Display: 128 x 64 pixel graphics LCD, 
LED back lit. Two user selectable font 
sizes: 8.9 or 5.0 mm (0.35 or 0.2")  
8-digit rate, 8-digit totalizer (resettable) 
Units: Feet, gallons, ft 
acre-feet, lbs., meters, liters, m 
mil-liters, kg (with Heatflow option: 
BTUs, calories, watts tons) [rate time: 
sec, min, hr, day]; Totalizer (NET, FWD, 
REV or BATCH): gallons, ft 
acre-feet, lbs., liters, m 
flow option: BTUs, calories,  
watts tons) (user configured)
3
, mil-gal, barrels, 
3
3
, 
3
, barrels, 
, kg (with Heat-
Ambient Conditions: -40 to 85°C  
(-40 to 185°F), 0 to 95% relative  
humidity, non-condensing 
Enclosure: NEMA 4X (IP-66) while 
open, NEMA 6 (IP68) while closed,  
ABS with SS hardware 
Electronic Enclosure: 14.8 lbs  
(6.7 kg), 356 W x 154 H x 268 mm D 
(14 x 6.06 x 10.56") 
Accuracy Flow Rate: ±1.0% of reading 
at rates > 1 FPS 
Sensitivity Flow: 0.0003 MPS  
(0.001 FPS)
Repeatability: ±0.3% of reading 
Response Time Flow: 
0.3 to 30 seconds, user configured,  
to 100% of value, step change in flow. 
Security keypad lockout, 4-digit user 
selected access code
Approvals: Ordinary area 
Cable: 6.1 m (20') 
Pipe Sizes: 50 to 2540 mm (2 to 100") 
Pipe Temperature: -40 to 121°C 
(-40 to 250°F); NEMA 6 (IP68) housing 
Material Standard Sensor: CPVC, 
®
 and Nylon
Ultem
 To Order Visit omega.com/fdt-81 for Pricing and Details
 Model No.  Description
 FDT-81  Transit-time flowmeter
Accessories 
 Model No.  Description
 FDT-81-STD  Replacement standard sensor 
 FDT-GREASE  Coupling grease for fdt-30/80 Series
Comes complete with AC and automobile power adaptors, carrying case, coupling grease, 
standard sensors, straps, cables, mounting track, NIST certificate, and operator’s manual.
High temp and small pipe models are available, consult Flow Engineering for details. 
Ordering Example: FDT-81, complete transit time ultrasonic flowmeter kit, and FDT-GREASE, 
coupling grease.
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