Flow measurement accuracy requires flexible technology, tailored to your site conditions. That's why Hach gives you four ways to measure flow: bubbler, ultrasonic, submerged sensor, and area velocity.

For applications requiring more than flow, the 950 optionally monitors rainfall, pH, temperature, ORP, dissolved oxygen and/or conductivity. Also, you can control samplers, pumps, or other equipment based on flow or selected parameter(s) exceeding high/low set points.

Hach's Sigma low profile probe design and unique zero-deadband level sensor combine to capture higher levels and lower flows than any other area velocity flow meter on the market. The large LCD graphics display lets you quickly see the information you need, on site, without the inconvenience of outdated paper charts; you'll no longer need to replace pens, paper or service mechanical recorders.

Industry standard MODBUS ASCII protocol has been incorporated into Hach's Sigma 950 flow meter series. The implementation of the MODBUS protocol will allow your MMI, SCADA or DCS system to directly communicate with the 950 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 950 flow meter.

• 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 950 automatically corrects the effects of temperature on level measurement.
• Patented Drawdown Correction feature to correct the effects of velocity on accurate level measurement.
• NEMA 6P sealed to withstand submergence and prolonged surcharge conditions.
• Sampler Pacing capabilities, ideal for CSO and Storm Water.
• Rainfall Logging feature records and characterizes rain events, a true innovation in water monitoring.
• Complete solution for water quality monitoring; one meter does the work of several pieces of equipment.
• 150-Day Battery Life to lessen site visits and lower costs.
• Optional Internal Cellular Capable Modem with automated data retrieval, paging and reporting
• Optional cellular-compatible modem, 14,000 baud

Ideal for:

• Long Term Flow Studies
• Sanitary Sewer Evaluation Studies
• CSO Studies and Monitoring
• NPDES Stormwater Compliance

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."

Hach's Sigma 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 950 Flow Meter Specifications:

• Dimensions: 13.5" H x 10.0" W x 9.5" D (34.3 cm x 25.4 cm x 24.1 cm).
• Weight: 15 lbs. (6.8 kg) including power source.
• Enclosure Material: ABS, UV resistant, stable from -40º to 176ºF (-40ºC to 80ºC).
• Enclosure Rating: NEMA 4X,6 with front cover open or closed.
• Operating Temperature Range: +14º to 150ºF (-10ºC to 65.5ºC).
• Storage Temperature Range: -40º to 176ºF (-40ºC to 80ºC).
• Power Draw: <10 mA average at 12 volts DC.
• Power Sources: 12 VDC supplied from 6 amp-hr. gel or 4 amp-hr. Ni-Cad battery, or 115 VAC, 230 VAC or 100 VAC power supply/battery charger.
• Power Draw: <10 mA average at 12 volts DC.
• Graphics Display: Back lit LCD, auto-off when not in use. 8 line x 40 character in ASCII mode, 60 dot x 240 dot in graphics mode. Dimensions 1.5" H x 5" W (3.8 cm x 12.7 cm); displays level vs. time, flow vs. time. Optionally, may display rainfall, pH, ORP, temperature, DO, conductivity vs. time, sampler events and alarm events.
• Keypad: 21 position sealed membrane switch with blinking green LED to indicate power on; 4 "soft keys", functions defined by display.
• Totalizers: 8-digit resettable and 8-digit non-resettable LCD software totalizer.
• Time Based Accuracy: +1 second per day.
• Units of Measurement:
  • Flow - GPS, GPM, GPH, LPS, LPM, LPH, MGD, AFD, CFS, CFM, CFH, CFD, CMS, CMM, CMH, CMD.
    
  • Totalized Flow - gal., ft.3, acre-ft., lit., m3.
• Primary Devices:
  • Flumes: Parshall, Palmer Bowlus, Leopold-Lagco, H, HL, HS, Trapezoidal.
  • Weirs: V-notch (15 - 120º) Contracted/Non-contracted rectangular, Thelmar, compound Cipolletti.
  • Manning Equation: Round, U and Rectangular Trapezoidal Channels.
  • Flow Nozzles: Kennison, Parabolic, California Pipe.
  • Head vs. Flow: Custom programmable curve of up to 99 points.
• Datalogging:
  • Dynamic memory allocation allows using memory on any channel or channels;
  • Memory Mode: Slate or Wrap-around storage mode may be selected.
  • Daily statistics available for up to 32 days.
• Sampler Output: 12-17 VDC pulse, 100 mA max at 500 ms duration.
• Communications:
  • RS232 - up to 19,200 baud
  • Modem (optional) - up to 14,400 baud
  • Cellular Communications - 14,400
  • Remote Programming
  • Pager Alarms

• Level Measurement
  • Accuracy: (linearity and hysteresis at 72ºF, 22ºC)
  • From .01 to 11.75 ft. - +/-0.011 ft. (+/-0.003m).
  • Range: .01 to 11.75 ft. (.003 - 3.6 m)
  • Ambient Operating Temperature Range: 0º to 145ºF (-18º to 63ºC)
  • Compensated Temperature Range: 32º to 138ºF (0º to 59ºC)
  • Temperature Error: +/-.0003 ft/ºF (maximum error within compensated temperature range per degree of change)
• Air Intakes: Bubble source and reference port desiccant protected. Fittings provided for remote intakes.
• Filters: 10 micron on bubble source intake.
• Line Purge: Bubble line is high pressure purged at programmed intervals, or in manual mode on demand.
• Line Size: 1/8" (.32 cm) ID standard.
• Line Lengths: 500' (150 m) maximum.

• Level Measurement Accuracy: (at 72ºF, 22ºC, still air, 40 - 70% relative humidity) from 1 to 10 ft. +/- .01 ft. )(+/-.003 m).
• Range:
  • Minimum distance from sensor to liquid 9 in. (23 cm).
  • Maximum distance from sensor to liquid 11 ft. (3.3 m).
• Span: 0-10.4 ft. (0-3 m).
• Ambient Operating Temperature Range: 0º to 140ºF (-18º to 60ºC)
• Temperature Error: +.000047 ft/Fº (maximum error within compensated temperature range - per degree of change)
• Resolution: .0011 ft.
• Material: PVC housing with Buna-N acoustic window.
• Cable: 4 conductor with integral stainless steel support cable.
• Cable Length: 25' (7.6 m) standard.
• Crystal Specification:
  • 40 KHz, 12º beam angle - 7º beam angle with horn:
  • 75 KHz, 14º beam angle - 7º beam angle with horn.
• Dimensions (transducer only):
  • 40 KHz, 3.75" H x 2.75" D (9.5 cm x 7 cm).
  • 75 KHz, 5.0" H x 2.25" D (12.7 cm x 5.7 cm).
• Weight: 1.5 lbs.

• Level Measurement Accuracy: (non-linearity and hysteresis)
• Transducer Type: Differential piezo resistive with balanced bridge.
• Transducer Orientation: Inverted
• Maximum Range:
  • P/N 2963 - 2.5 psi .04 - 5.75 ft. (.01 m - 1.75 m)
  • P/N 2343 - 5.0 psi .04 - 11.75 ft. (.01 m - 3.58 m)
  • P/N 2333 - 10.0 psi .04 - 23 ft. (.01 m - 7.0 m)
• Accuracy: ±1% Full Scale
• Maximum Allowable Level: 6x over pressure.
• Operating Temperature Range: 32º to 160ºF (0-71ºC)
• Compensated Temperature Range: 32º to 96ºF (0-36ºC)
• Air Intake: Atmospheric pressure reference is desiccant protected.
• Material: 316 stainless steel body with titanium diaphragm.
• Cable: 4 conductor polyurethane sensor cable with air vent.
• Cable Length: 25' (7.6 m) standard. 250' (76 m) maximum.
• Dimensions (sensor only): 1" H x 6.75" L (2.54 cm x 17.2 cm).
• Probe Frontal Area: 0.875 sq. in.
• Weight: 1.5 lbs.

• Dimensions: 13.5" H x 10.0" W x 9.5" D (34.3 cm x 25.4 cm x 24.1 cm).
• Weight: 15 lbs. (6.8 kg) including power source.
• Enclosure Material: ABS, UV resistant, stable from -40º to 176ºF (-40ºC to 80ºC).
• Enclosure Rating: NEMA 4X,6 with front door open or closed.
• Operating Temperature Range: +14º to 150ºF (-10ºC to 65.5ºC).
• Storage Temperature Range: -40º to 176ºF (-40ºC to 80ºC).
• Power Sources: 12 VDC supplied from 6 amp-hr. gel or 4 amp-hr. Ni-Cad battery, or 115 VAC, 230 VAC or 100 VAC power supply/battery charger.
• Power Draw: 5.9 mA at 12 VDC.
• Graphics Display:
  • Back lit LCD.
  • Auto-off when not in use.
  • 8 line x 40 character in ASCII mode, 60 dot x 240 dot in graphics mode.
  • Dimensions 1.5" H x 5" W (3.8 cm x 12.7 cm).
• Keypad: 21 position sealed membrane switch with blinking green LED to indicate power on.
• Totalizers:
  • 8-digit resettable
  • 8-digit non-resettable LCD software totalizer
  • 6-digit non-resettable mechanical totalizer optional.
• Monitoring Intervals: 1, 2, 3, 5, 15, 30 or 60-minute intervals.
• 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, CMS, CMM, CMH, CMD.
  • Totalized Flow - gal., ft.3, acre-ft., lit., m3.
• Data Storage:
  • Capacity - Up to 512k bytes: 402 days of level, velocity and rainfall readings at 15 minute intervals plus 300 events.
  • Partitions - No partitioning required, dynamic memory allocation up to 12 channels.
  • Data Types - Level, velocity, flow rate, rainfall, samples, pH, D.O., Conductivity, ORP.
  • Storage Modes - Slate or wrap.
• Output Conditions: Set point on level, velocity, rainfall, and time OR combination of any two - level, velocity, flow rate, rainfall and time; values may be above or below set point, inside or outside range or based on rate of change.
• Sampler Output: 12 - 17 VDC pulse, 100 mA max at 500 ms duration.
• Communications: Serial connection to IBM compatible computer with Hach's Sigma Data Analysis Software.
• Velocity Measurement:
  • Method: Doppler ultrasonic.
  • Transducer Type: Twin 1 MHz piezoelectric Crystals.
  • Typical minimum depth for Submerged Depth/Velocity Sensor: .8 in. (2 cm).
  • Typical minimum depth for Velocity Only Sensor: .4 in. (1 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 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. 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).

• Level Measurment (linearity and hysteresis at 72F, 22C) from .01 to 11.75 ft. - .011 ft. (.033 m).
  • Range: .01 to 11.75 ft. (.003 - 3.6 m).
  • Ambient Operating Temperature Range: 0 - 145F (-18 - 63C).
  • Compensated Temperature
  • Range: 32 - 138F (0 - 59C).
  • Temperature Error: ±.0003 ft./deg F (maximum error within compensated temperature range per degree of change).
  • Air Intakes: Bubble source and reference port desiccant protected. Fittings provided for remote intakes.
  • Filters: 10 micron on bubble source intake.
  • Line Purge: Bubble line is high pressure purged at programmed intervals, or in manual mode on demand.
  • Line Size: 1/8" (.32 cm) standard.
  • Bubbler Line Lengths: 500 ft. (150 m) maximum.
  • Cable Length: Standard Range Probe - 25 ft (7.6m).
  • Custom Cable Lengths to 200 ft (61m).
  • Cable Diameter: 0.4in (1cm).
  • Dimensions: 3.7"L x 0.8"H x 1.5" W (9.7cm x 2cm x 3.8cm).

• Velocity Sensor:
  • 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: Standard range probe - 25' (7.6 m); custom cable lengths to 250' (76 m); cable diameter - .225 in (.57 cm).
  • Materials: Sensor - polymer; cable - urethane; sensor mounting hardware - stainless steel.
• Ultrasonic Level Sensor (In-Pipe):
  • 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 form sensor to liquid 0 in. (0 cm). Maximum distance from sensor to liquid 15 ft. (4.57 m).
  • Span: .125 - 15 ft. (.038 - 4.57 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 Buna-N acoustic window.
  • Cable: 4 conductor.
  • Cable Length: 25' (7.6 m) standard, 1000' (305 m) using RS485 two wire remote sensor option.
  • Crystal Specification: 75 KHz, 14° beam angle.

SIGMA 950 Factory Installed Options

• Control/Logging: Field selectable to log pH-Temperature/ORP independent of flow or in conjunction with flow; also controls sample collection in response to value exceeding low/high set points.
• Recording Intervals: 1, 2, 3, 5, 6, 10, 12, 15, 30, and 60 minutes.
• Probe Pre-Amplifier/Junction Box: NEMA 4X with labeled terminal strip.
• pH/Temperature Sensor: Temperature compensated; impact resistant ABS plastic body; combination electrode with porous Teflon® junction.
• Measurement Range: 2 to 12 pH within specifications, 0 to 14 pH maximum range.
• Operating Temperature Range: 0 to 176ºF (-18ºC to 80ºC).
• Dimensions: 0.75" dia. x 6" long with .75" mpt cable end (1.9 cm x 15.2 cm long with1.9 cm mpt cable end).

• Measures and records ambient or sample stream temperature.
• Control/Logging: Field selectable to log temperature independent of flow or in conjunction with flow; also controls sample collection in response to value exceeding low/high set points.
• Recording Intervals: 1, 2, 3, 5, 6, 10, 12, 15, 20, 30, and 60 minutes.
• Sensor: Platinum RTD with 316 stainless steel body.
• Range: 32 to 212°F (0 to 100°C).
• Accuracy: ±1.8°F (±1°C).
• Operating Temperature Range: 0 to 176°F (0 to 80°C).
• Probe Dimensions: .125" dia. x 6" long, with .75" mpt cable end (0.317 cm x 15.24 cm long with1.9 cm mpt cable end).

• Control/Logging: Field selectable to log dissolved oxygen independent of flow or in conjunction with flow; also controls sample collection in response to value exceeding low/high set points.
• Recording Intervals: 1, 2, 3, 5, 6, 10, 12, 15, 20, 30, and 60 minutes.
• Measurement Method: Polargraphic.
• Sensor: Temperature compensated; impact resistant polypropylene body.
• Range: 0-20 mg/L.
• Resolution: .01 mg/L.
• Accuracy: +0.2 mg/L.
• Operating Temperature Range: 32 to 122°F (0 to 50°C).
• Dimensions: 0.65" dia. x 5" long with .75" mpt cable end (1.65 cm dia. x 12.7 cm long with 1.9 cm mpt cable end).

• Control/Logging: Field selectable to log conductivity independent of flow or in conjunction with flow, also controls sample collection in response to value exceeding low/high set points.
• Recording Intervals: 1, 2, 3, 5, 6, 10, 12, 15, 20, 30, and 60 minutes.
• Sensor: Temperature compensated; impact resistant polypropylene body.
• Range: 0-20 mS/cm.
• Resolution: 0.01 mS/cm or 0.01 µS/cm (user selected)
• Accuracy: ±1% of reading +0.05mS/cm.
• Operating Temperature Range: 32 to 122°F (0 to 50°C).
• Dimensions: 0.67" dia. x 5" long with .75" mpt cable end (1.70 cm dia. x 12.7 cm long with 1.9 cm mpt cable end).

• For use with Hach's Sigma Tipping Bucket Rain Gauge.
• External wastewater sampler can be initiated upon field selectable rate of rain.
• Flow meter records rainfall data.
• Each tip (contact closure) equal to .01 inches of rain.
• Metric conversion performed in software.

• Up to 7 additional data logging channels record data from external source(s).
• field assignable channel name(s) and units.
• Input Requirements: -4.5 to +4.5 VDC and/or 0-20 mA.

• Two integral field assignable outputs available.
• Optically isolated, up to 1000 ohm load per output.
• 0.1% FS error.

• 6 digit non-resettable mechanical totalizer.
• Enclosure: NEMA 4x panel / wall mount.
• Selectable units: gal, litr, ft3, m3, acre-ft.

• Up to 4 integral alarm relays.
• 10amp, Form C.
• User assignable to any internal or external data channel.

• 14400, V.32 bis, V.42, MNP2-4 error correction.
• V.42 bis, MNP5 data compression.
• MNP10EC Cellular Protocol.

• Increases standard memory from 18,000 to 116,000 data points.

• Provides power in the event of an A/C power failure.