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)