ISCO 4250 Area Velocity Flowmeter

4250 Area Velocity Flowmeter (DISCONTINUED)

  • Maintenance-Free Sheds debris and withstands corrosive flow stream chemicals, resists fouling by oil and grease. Does not require frequent cleanings
  • Multifunctional Ideal for sites where submerged, full pipe, surcharged or reverse flow may occur
  • Standard or Extended Ranges Available in standard 10ft or extended 30ft level measurement ranges
Product Options



The 4250 Flow Meter's sensor directly measures average velocity in a flow stream with patented Doppler technology. This system eliminates the profiling and calibration required by electromagnetic systems by continuously profiling the flow stream. A pressure transducer measures the depth of the liquid to determine the flow area and the 4250 then multiplies this by the average velocity of the flow to calculate flow rate. With area velocity flow measurement there is no need to estimate the slope and roughness of the channel

The shorter wavelength of 1MHz systems can cause them to give 'nearsighted' velocity measurement in a typical waste water application. Isco's exclusive 500 kHz Doppler that's used in the 4250 can penetrate further into deep flow streams. The 4250 can give greater accuracy where full pipe, submerged, reverse flow or surcharged conditions occur, and where weirs or flumes are not practical.

Standard Features

  • Setup using 160 character LCD screen with built-in keypad, or via a connection to a PC running Flowlink software.
  • Built-in flow conversions for most applications including data points, Manning formula, or equations if needed.
  • 10ft (standard) or 30ft (extended) level measurement range.
  • Accurate on-site printouts using built-in dot matrix printer.
  • Large internal memory can store 2 months of flow, parameter, rainfall and sample data taken at 15 minute intervals.
  • Inputs for water quality sonde and 674 Rain Gauge.
  • Sealed sensor that resists fouling by oil and grease. Streamlined shape shreds debris.
  • Provides interface for sampler activation and alarm outputs.

Manufactured by: Teledyne ISCO
Model: 4250 Area Velocity Flowmeter (DISCONTINUED)

Services offered for this product

  • Sales
  • Rental
  • Installation
  • Calibration
  • Maintenance


Accurate open channel flow measurement without a weir or flume
Pretreatment compliance
Stormwater runoff monitoring
Permit enforcement
Sewer flow monitoring
Combined sewer overflow studies
Inflow and infiltration studies
River and stream gauging


Size (H x W x D) 17.0 x 11.5 x 10.5 in. (43 x 29 x 26.7 cm) (without power source)
Weight 17.3 lbs (7.8 kg) (without power source)
Material High-impact molded polystyrene structural foam
Enclosure NEMA 4X (iP65)
Power 12 to 14V DC, 14 mA average at 12.5V DC
Typical Battery Life (printer set at 1 in/hr, 1 minute level reading interval, 5 minute velocity reading interval)
934 Nickel-Cadmium Battery 8 to 11 days
946 Lead-Acid Battery 12 to 16 days
948 Lead-Acid Battery 2½ to 3 months
Program Memory Non-volatile, programmable flash. Updateable without opening enclosure.
Display Backlit LCD, 2-line, 80-character (5.5 mm high x 3.2 mm wide)
Level-to-Area Conversions
Channel Shapes Round, U-shaped, rectangular, trapezoidal
Data Points Four sets of 50 level-area points
Level-to-Flow Rate Conversions
Weirs V-notch, rectangular, Cipolletti
Flumes Parshall, Palmer-Bowlus, Leopold-Lagco,Trapezoidal, H, HS, HL
Manning Formula Round, U-channel, rectangular, trapezoidal
Data Points Four sets of 50 level-flow rate points
Equation Two-term polynomial
LCD Total, forward, and reverse flow; 9 digits each, floating decimal point, resettable
Mechanical (optional) Total flow, 7 digits, non-resettable
Area Velocity Sensor (See separate specifications for low-profile sensor)
Size (LxWxH) 6.6 x 1.6 x 1.2 inches (16.8 x 4.1 x 3.0 cm)
Weight, incl. cable 2.1 lbs (0.96 kg) for standard probe with 25 foot cable; 3.9 lbs (1.8 kg) for extended range probe with 50 ft cable.
Ambient Operating Temperature Range 0° to 140°F (-18° to 60°C)
Compensated Temperature Range 32° to 140°F (0° to 60°C)
Materials Polybutadiene-based polyurethane, stainless steel; PVC and CPVC cable
Velocity Measurement
Method Doppler Ultrasonic, 500 kHz
Velocity Range -5 to +20 ft/s (-1.5 to 6.1 m/s)
Level Measurement
Method Submerged pressure transducer
Standard Range Probe Measurement range 0.05 to 10 ft (0.015 to 3.05 m); max level 20 ft (6.1 m)
Extended Range Probe Measurement range 0.05 to 30 ft (0.015 to 9.14 m); max level 40 ft (12.2 m)
Standard probe accuracy (Non-linearity, repeatability, and hysteresis at 25°C (77°F). Max error for indicated level range.
0.033 to 5.0 ft (0.01 to 1.52 m) ±0.008 ft/ft (±0.008 m/m)
>5.0 ft (>1.52 m) ±0.012 ft/ft (±0.012 m/m)
Extended Probe Accuracy (Non-linearity, repeatability, and hysteresis at 25°C (77 °F). Max error for indicated level range.
0.05 to 15 ft (0.015 to 4.57 m) ±0.03 ft (±0.009 m)
0.05 to 21 ft (0.015 to 6.4 m) ±0.09 ft (±0.027 m)
0.05 to 30 ft (0.015 to 9.14 m) ±0.3 ft (±0.09 m)



No, all of our flowmeters are competitively priced and rental is an ideal option for cutting costs to a fraction of a full priced new flowmeter.
No problem. The quick start guide is designed to make installing the flow meters a simple task. Everything you require for set up will be found in the peli-box supplied with the flowmeter.
Every flow meter is tested upon shipping and return as part of our ISO9001 procedure. Also, as part of this procedure, the flow meter is calibrated once a year. If a copy of the calibration certificate is needed let us know.
The flow meters typically provide an accuracy of ±1 to 2% of rate, so if you are measuring 100l/sec then the accuracy is between 98-102l/sec.
We are here to help. If the self-help and quick start guides do not help, then call one of our technical support engineers on +44 (0) 1527 882060. We have supplied and supported many clamp on rental installations throughout Europe.
First, contact us for a quote. If you are happy with the quote then send us a purchase order. Or alternatively call us with credit card details and fill out and send us a rental agreement form.
If the stock is permitting, and all paperwork is received by 12pm then flow meters can usually be available the next day.
The minimum hire period for flow meters is one week.
Once you have the meter you can rent it for as long as you need it. However, it would help if you can let us know that you wish to extend the rental period. Upon return the meter is off-hired and once checked and tested, an invoice will be issued to you. Also, if you extend your rental past a 4, 8 or 12 week rental threshold, then you are entitled to a discount.
You are only charged for the period of time for which you have the flowmeter. So, if a flowmeter is returned 3 days late you are only charged for 3 extra days, and each of these days is charged at one fifth of the weeks hire cost.
Normally, you will use your own courier but if you have any problems let us know and we can arrange a pick up the day after you notify us, but you will be charged for the carriage and this cost will be added to the invoice.
Without exception, all our flow meters are tested. If you need a 110v plug instead of the standard 230v plug let us know.
All of our standard transducers will do -40degC to +150degC, but this will depend on your application.
  • Liquid: below 50mm CFLP transducers are required, 50-1000mm CRS-402 transducers and 150-8000mm CRS-401 transducers. All the bits you need can be supplied, and delivered with the meter.
  • Gas: below 80mm CRS-402 is required, for 80-300mm the CRS-401/CRV-310 and for above 300mm the CRW-312 transducers are required.
  • High temperatures: For liquid we can measure +450degC for liquid and for gas/steam +250degC. But please consult RS Hydro.
Of course, we make a small surcharge for each set of transducers. Most applications only require one set, but on occasion some people may require two, for more diverse pipe sizes and applications.
An ultrasonic wall thickness gauge, that measures to within 0.05mm, is provided as standard with all flow meter rental packages.
The screendump facility on the integrated dataloggers on all our flow meters, allows you to photograph any screen and download it to your pc.
After the equipment has been shipped, it is the responsibility of the hirer. However, in our experience it is rare that any of our flow meters are damaged. Our flow meters are tough, as well as accurate, and reliable.
We have hired more ultrasonic clamp on flow meters than any other company in Europe. We are now one of the world's largest distributors of GE Panametrics flow meters. We always review your application before hire so no unwanted surprises are encountered. Every effort has been made to make your flow meter hire and enjoyable experience: quick start guides to help you set up with ease, online videos for further help, rugged packaging for extra durability anywhere, and real flow engineers available for online/telephone support.