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Low Flow Indicating Paddlewheel Flow Meter

Micro-flow meter


Item# FTB321

In stock

Lead Time (If not in stock): 3 weeks
Micro-flow meter FTB321 FTB321
  • NEMA 4X (IP56) Enclosure
  • 6-Digit LCD
  • Displays both Rate and Total
  • Non-Volatile Programming and Total

FTB321 Model Options

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Edit these specs to order a different model. Not all combinations are valid. Options compatible with previous selections will be in bold.

*Highlighted options are not compatible. Please select a different combination.

Flow Range
Output Signal
Supply Power
Process Connection Size
Max Process Temperature
Max Operating Pressure
Wetted Materials
Process Connection Type

The FTB300 Series of digital paddle wheels are an economical choice for low flow rate applications. They use Infra-red light beam technology. Available connections include 1/8 FNPT, 1/4 FNPT and 3/8" OD tube fittings. Six available flow ranges as low as 30ml/min to 7000 ml/min. No display models have a 5 Vdc current sinking pulse output. Units with displays have a 6-digit LCD, with up to 4 decimal positions that display both flow rate and total. All units include an open collector alarm output.

User selectable scale factors include: flow units, gallons, liters, ounces, and milliliters. Time units include: minutes, hours, days. Users can also program custom units. Programming values and total are stored in the non-volitile memory. The total reset function can also be disabled. Standard units have a clear PVC viewing lens, PVDF chemical resistant lens are available as an option. The enclosure is a weather resistant Valox PBT and rated NEMA 4X (IP56).

Max Working Pressure:
    PVC Lens: 9 bar (130 psig) at 21°C (70°F)
    PVDF Lens ("-PVDF" Option): 150 psig (10 bar) @ 21°C (70°F)
Max Fluid Temperature:
    PVC Lens, FNPT Connectors: 54°C (130°F) at 0 PSI
    PVDF Lens ("-PVDF" Option), Tubing Connectors: 93°C (200°F) at 0 PSI
Full Scale Accuracy: ±6%
Input Power Requirement: 9 to 28 Vdc
Sensor Type: Infrared light beam
Alarm Output: Open collector 30 Vdc max
Enclosure: NEMA 4X (IP56)
Approximate Shipping Wt: 0.45 kg (1 lb) Materials of Construction
Body, Paddle, Axle Material: PVDF Connector Material
FNPT Connections: PVC
Tubing Connectors: PVDF Viewing Lens Material Option
    Clear See Through: PVC
    Opaque Chemical Resistant: PVDF (optional)
O-Ring Seals: FKM (EPDM optional)
Compression Seal to Pump: PVC Sensor Only
    Models: 5 Vdc digital square wave (2-wire)
    Output: 3-wire shielded cable, 1.8 m (6')

Model with Display Model without Display Range
1/8 FNPT 1/4 FNPT 3/8" OD Tube 1/8 FNPT 1/4 FNPT 3/8" OD Tube lpm gph
FTB311D FTB321D FTB331D FTB311 FTB321 FTB331 0.03 to 0.3 0.48 to 4.7
FTB312D FTB322D FTB332D FTB312 FTB322 FTB332 0.1 to 1 1.6 to 15.8
FTB313D FTB323D FTB333D FTB313 FTB323 FTB333 0.2 to 2 3.2 to 31.7
FTB314D FTB324D FTB334D FTB314 FTB324 FTB334 0.3 to 3 4.8 to 48
FTB315D FTB325D FTB335D FTB315 FTB325 FTB335 0.5 to 5 7.9 to 79
FTB316D FTB326D FTB336D FTB316 FTB326 FTB336 0.7 to 7 11.1 to 111
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Rated 5 out of 5 by from Great little flow meter We purchased this flow meter for a test project and we really loved the ease of use and accuracy. Would definitely recommend this product to others.
Date published: 2015-11-24
Rated 5 out of 5 by from Right Tool for the Job. Bought this, received fast, fairly priced, and the perfect tool for my needs.
Date published: 2016-04-29
Rated 1 out of 5 by from Fittings don't fit The fittings that came with the flow meter did not actually fit. And they only sent one. We have been in contact with Omega for several weeks now trying to fix the issue and it has not been resolved.
Date published: 2021-03-11
Rated 4 out of 5 by from Great product Good and precise flow meter, in addition, should have a hard reset switch, in case of the error
Date published: 2016-10-10
Rated 5 out of 5 by from Great product and easy to order Ordering was very easy and I received confirmation of the order quickly
Date published: 2023-05-03
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Is the pulse output need to have power on the + side before the resistor or that wire is the return + signal? Can we put that 5V signal on a relay or we are better of with the alarm system

Asked by: bobby10
Thank you for your inquiry about the flow meter. Yes, it requires power from 5 to 30 VDC.
Answered by: Application Engineer JC
Date published: 2023-02-28

What are the dimensions of the FTB311 Micro-Meter

Asked by: EngieTechie
Thank you for your question. A file has been sent to your email with dimensions for this part..
Answered by: application engineer je
Date published: 2019-07-01

Is it applicable for air flow?

Asked by: Paulwg
Thank you for your inquiry! Unfortunately, these units will not work properly with air flow. They will only work with clean liquids
Answered by: Application Engineer JM
Date published: 2022-01-26

Do you have a larger unit that can measure ~ 1-10 gal/min?

Asked by: MolecularExpress
Thank you for your inquiry about a flow meter. Please compose an email and send to and can provide options that best fits your application.
Answered by: JC ENGR
Date published: 2020-07-25

For the 300-3000mL/min model, for the square signal output, What is the signal frequency? (How many signals/L)

Asked by: ZachariahA
Thank you for your inquiry, the K-factor for that flow range is 6,646 pulses per Liters.
Answered by: Application Engineer JC
Date published: 2022-07-22

If using a FTB323D flow meter with a PG-25 (25% propylene glycol) water mixture, is there a need to do any extra calibration to ensure the meter is recording accurately for the fluid type?

Asked by: ChadB
Thank you for your inquiry about the low flow meter. Please note that the liquid must clear, not opague and works best with clear liquids based on the infrared sensor to measure the flow.
Answered by: Application Engineer JC
Date published: 2022-02-15

What are the dimesions of this meter?

Asked by: Ozzie
Please contact the Flow engineering department with this request and they will send you the details. Please send to
Answered by: AS Engineer
Date published: 2019-10-18

When this meter totals the volume does it account for reverse flow by subtracting from the volume total so that a tank level can be estimated from flow in and out?

Asked by: Engineer13
No matter which direction the paddlewheel spins the meter will accumulate a positive total.
Answered by: ASE HPO
Date published: 2019-12-19
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