The Hach Sigma 910AV uses an advanced 1 MHz Doppler sensor, providing unparalleled accuracy and range of performance from low flows to surcharge conditions.

The Sigma 910AV measures average velocity directly without the need for time consuming flow profiling, significantly reducing the cost of installation and operation. With a compact 4 1/2 x 18" design, weighing less than 8 lbs (with battery), the 910AV is one of your best options for remote environments. This meter will log level and velocity data for more than 30 days without changing a battery, and its sealed design provides superior system protection against surcharge conditions.

• Advanced, ultrasonic one-MHz Doppler technology avoids signal dropouts and ensures high levels of accuracy in low-flow, full-pipe or reversed-flow conditions, without the need for onsite calibration.
• A higher level of accuracy, since the 910 automatically corrects the effects of temperature on level measurement.
• Patented Drawdown Correction feature to correct the effects of velocity on accurate level measurement.
• Easy Installation with a small, 4 1/2" diameter and no velocity calibration required.
• NEMA 6P sealed to withstand submergence and prolonged surcharge conditions.
• Low Profile, Non-Fouling Probe reduces your need for maintenance and is detachable/interchangeable for ultimate flexibility.

Ideal for:

• Short Term Flow Studies
• Sanitary Sewer Evaluation Studies

Sigma's Patented Drawdown Correction and the Bernoulli Principle

The Bernoulli* Principle states that as the velocity of a fluid increases, its pressure decreases. The Bernoulli Principle simply describes the relationship between the velocity of a fluid and its pressure.

If a measurement of the pressure of the moving fluid is taken at a point just forward of the front edge of the shape, and another measurement is taken at the apex, of the upper curved surface, one would notice that the pressure at the apex is lower than the pressure at the leading edge. It is this same principle that is responsible for the lift on an airplane wing. Level measurement using a submerged depth sensor is similarly affected by increases in fluid velocity.

1. As the velocity of water increases past the probe.
2. A drop in pressure (vacuum) is induced near the pressure sensor (level) port located at the sides of the probe.
3. This results in the lowering of the indicated level (or pressure) sensed at the port.
4. Sigma's patented "Drawdown Correction" software adjusts the level readings for this effect. Sigma's patented drawdown correction adjusts for these effects through software. The software correction algorithms are based on flow data collected during extensive laboratory and real life testing.

Abstract: "An apparatus for calculating fluid flow in a channel, comprising a probe member which detects fluid depth in the channel; a mechanism for measuring average fluid velocity in the channel; a mechanism for correcting the detected fluid depth based upon the measured average fluid velocity in order to account for drawdown; and a mechanism for calculating average flow rate based upon the average fluid velocity measurement and the corrected fluid depth value."

The Hach Sigma series flow meter models that utilize Drawdown Correction: 910, 911, 920, 930, 940, 950 & 970

Daniel Bernoulli (1700-1782)
Swiss mathematician, son of Johann Bernoulli, who showed that as the velocity of a fluid increases, the pressure decreases, a statement known as the Bernoulli Principle. He won the annual prize of the French Academy ten times for work on vibrating strings, ocean tides, and the Kinetic Theory of gases. His Kinetic Theory proposed that the properties of a gas could be explained by the motions of its particles. He was the first person to encounter the functions today known as Bessel Functions.

Model 910 Area Velocity Flow Meter Specifications

• Dimensions: 4.5" dia. x 17.625" L (11.4 cm dia. x 44.8 cm L).
• Weight: 7.8 lbs. (3.54 kg) with battery.
• Enclosure Material: PVC.
• Enclosure Rating: NEMA 6P (IP67).
• Operating Temperature Range: 0 to 140°F (-18 to 60°C).
• Storage Temperature Range: -40 to 140°F (-40 to 60°C).
• Power Source: One (6V) Alkaline lantern battery.
• Battery Life: 30 days typical with a 15-minute recording interval, 1 level and 1 velocity, data download once per week, at 50° F (10°C) (also affected by site conditions).
• User Interface: IBM compatible PC.
• Monitoring Intervals: 1, 2, 3, 5, 6, 10, 12, 15, 20, 30, 60 minutes.
• Program Memory: Non-volatile, programmable flash, can be updated via RS-232 port.
• Time Based Accuracy: ±1 second per day.
• Units of Measurement: Level - in., m, cm, ft. Flow - GPS, GPM, GPH, LPS, LPM, LPH, MGD, AFD, CFS, CFM, CFH, CFD, M3S, M3M, M3H, M3D.
• Totalized Flow - gal., ft.³, acre-ft., L, m³.
• Data Storage: Capacity - 90 days of 1 level reading and 1 velocity reading at a 15-minute recording interval.
• Data Types - Level and velocity.
• Storage Mode - Wrap or slate.
• Communications: Serial connection to IBM compatible computer with Sigma analysis software. Velocity Measurement Accuracy:
• Method: Doppler ultrasonic.
• Transducer Type: Twin 1 MHz piezoelectric crystals.
• Typical minimum depth for velocity: .8 in. (2 cm). Range: -5 to 20 fps (-1.52 to 6.10 m/s).
• Zero Stability: <.05 fps. (.015 m/s).
• Accuracy: ±2% of reading.
• Operating Temperature: 0 to 140°F (-18 to 60°C).

• Level Measurement (non-linearity and hysteresis): Standard - .018 to 11.5 ft. ±. 023 ft. (.005 m - 3.5 m ± .007 m). Extended - .018 to 34.6 ft ± .07 ft. (.005 - 10.5 m ± .021 m).
• Maximum Allowable Level: 3x over pressure.
• Operating Temperature Range: 32 to 160°F (0-71°C).
• Compensated Temperature Range: 32 to 86°F (0-30°C).
• Temperature Error: .018 - 34.6 ft. ±.012 ft./°F (.018-10.5 m ± .006 m/°C). .018 - 34.6 ft. ± .012 ft./°F (.018-10.5 m ± .006 m/°C) (maximum error within compensated temperature range - per degree of change).
• Velocity Induced Error on Depth (patent pending): 0 to 10 ft/sec. (0 to 3.05 m/s) = .085% of reading.
• Air Intake: Atmospheric pressure reference is desiccant protected.
• Material: Polymer body with stainless steel diaphragm.
• Cable: Urethane sensor cable with air vent. Cable Length: 25' (7.6 m) standard. 250' (76 m) maximum.
• Dimensions (combination sensor): .8" H x 1.5" W x 5" L (2 cm x 3.8 cm x 12.7 cm).