Operates for up to one year between battery changes and provide accurate, reliable data for proactive collection system management.

With the Hach Sigma 940 glow meter, remote monitoring becomes a way of life. Its rugged design, low-profile probes and long battery life significantly reduce site visits, and with scheduled data retrieval and alarms - based on level, velocity or flow - you can manage the sewer system right from your office. Choose up to two area velocity sensors, or one area velocity and one level backup. Whether it's redundancy in a single pipe or level and velocity in separate pipes, you'll profit from new performance levels in a single meter. The 940 is the safest investment for your sewer and your budget.

Industry standard MODBUS ASCII protocol has been incorporated into the 940 flow meter. The implementation of the MODBUS protocol will allow your MMI, SCADA or DCS system to directly communicate with the 940 flowmeter without the use (or additional cost) of a PLC. Now you can have real-time, read-only access to all available data channels in the 940 flow meter.

• CSA-NRTL/C, CE & DEMKO certified for operation in Class I, Division I, Groups C & D hazardous locations.
• Integrates with Vision and InSight software for easy presentation-quality reports.
• 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 940 automatically corrects the effects of temperature on level measurement.
• Patented Drawdown Correction feature to correct the effects of velocity on accurate level measurement.
• Low Power Draw, with a long, one-year battery life (with modem).
• NEMA 6P sealed to withstand submergence and prolonged surcharge conditions.
• Sampler Pacing capabilities, to document the extent of overflow problems.
• Multiple Sensors for redundancy, averaging and multiple pipe monitoring.
• FCC & Industry Canada approved external modem with Scheduling so that the data is waiting at your office.
• Telephone and Pager Alarms for quick notification of system changes.

Ideal for:

• Long Term Flow Studies in Hazardous or Potentially Hazardous Areas
• Sanitary Sewer Evaluation Studies
• CSO Studies and Monitoring

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.

Sigma 940 Intrinsically Safe Area Velocity Flow Meter Specifications

• Dimensions: 8.625" dia. x 23.625" L (21.9 cm dia. x 60 cm L).
• Weight: 17.52 lbs. (7.95 kg) with batteries.
• Enclosure Material: PVC.
• Enclosure Rating: NEMA 6P (IP67).
• Certification: CSA-NRTL/C, CE & DEMKO certified -Class 1, Div. 1, Groups C & D Intrinsically Safe.
• 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 (12V) Custom lithium battery pack.
• Battery Life: 365 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: Optically isolated 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, in non hazardous area.
• 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 - 297 days of 2 level readings, 2 velocity readings at a 15-minute recording interval. Data Types - Level, and velocity. Storage Mode - Wrap or slate.
• Output Conditions: Set point on level, velocity, flow, or flow rate of change.
• Sampler Output: 6-12 VDC pulse, 100 mA max. at 500 ms duration with approved interface.
• Communications: Serial connection via optically isolated interface to IBM compatible computer with Sigma data analysis software.
• Modem: FCC & Industry Canada approved external modem with fiber optic interface. 14400, V.32 bis,V.42, MNP2-4 error correction. V.42 bis, MNP5 data compression. MNP10EC Cellular Protocol.
• Local Terminal - RS232 at 19,200 baud.

• 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. O
• Operating Temperature Range: 32 to 160°F (0 to 71°C).
• Compensated Temperature Range: 32 to 86°F (0 to 30°C).
• Temperature Error: .018-11.5 ft. ±.004 ft./°F (.005 m - 3.5 m ± .0022 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. 100' (30.5 m) maximum.
• Dimensions (combination sensor): .8" H x 1.5" W x 5" L (2 cm x 3.8 cm x 12.7 cm).

• Dimensions: .44 in. H x 1.5 in. W x 2.7 in. L (1.12 cm x 3.81 cm x 6.86 cm).
• Nose Angle: 20 deg from horizontal.
• Cable Length: 25' (7.6 m) Standard, 100' (30.5 m) maximum; cable diameter - .225 in (.57 cm).
• Materials: Sensor - polymer; cable -urethane; sensor mounting hardware - stainless steel.

• Accuracy: At 72°F (22°C) still air, 40- 70% relative humidity from .125 to 15 ft. - ±.01 ft. (.038 to 4.57 m ± .003 m).
• Range: Minimum distance from sensor to liquid 0 in. (0 cm). Maximum distance from sensor to liquid 7 ft. (2.13 m). Span: .125 - 7 ft. (.038 - 2.13 m).
• Ambient Operating Temperature: 0 to 140°F (-18 to 60°C).
• Temperature Error: ±.0001 ft./°F (±.00005 m/°C) (maximum error within compensated temperature range - per degree of change).
• Resolution: .0075 in (.019 cm).
• Material: Stainless steel housing with PVC acoustic window. C
• able: 4 conductor.
• Cable Length: 25' (7.6 m) standard.
• Crystal Specification: 75 KHz, 7° beam angle.
• Dimensions: 1.5" dia. x 12" L (3.81 x 30 cm).