The Hach Sigma 980 Flow Meter is available with one of the following depth/velocity measurement technologies: Ultrasonic Sensor Velocity Sensor Area Velocity/Submerged Sensor

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The Hach Sigma 980 Flow Meter is an ultrasonic level detection meter with rugged, NEMA 4X, IP66 construction. The 980 Flow Meter case has several unigue features, all designed to simplify installation, operation, and maintenance. All controls are located within easy reach on the front panel behind a clear, protective front cover.

The 980 Flow Meter has eight wiring holes located along the bottom of the case. The one 1.38in and the seven 0.875in conduit holes provide easy access for all power, sensor, control, and communications wiring.

Connections to the 980 Flow Meter are made in the wiring panel behind the front cover. The interface connector ports are located on the bottom of the instrument. The 980 Flow Meter comes standard with a quick-connect RS232 serial communications port.

In addition, the flow meter can connect to a wide variety of optional peripheral devices:

4-20mA Current Loop Up to three 4-20mA Inputs Up to four 4.5vdc Inputs Mechanical Totalizer

Rain Gauge Sampler pH Sensor Modem

You can also control samplers, pumps, or other equipment based on flow or selected parameter(s) exceeding high/low set points.

The Hach Sigma 980 Flow Meter's low profile probe design and 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 The large LCD graphics display lets you quickly see the information you need, on site, without the inconvenience of outdated paper charts; you'll no longer need to replace pens, paper or service mechanical recorders.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 the Sigma 980 flow meter series. The implementation of the MODBUS protocol will allow your MMI, SCADA or DCS system to directly communicate with the 980 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 980 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 980 automatically corrects the effects of temperature on level measurement.
• Patented Drawdown Correction feature to correct the effects of velocity on accurate level measurement.
• NEMA 4X, IP66 construction.
• 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.

Optional Internal Modem with automated data retrieval, paging and reporting

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.

This testing resulted in US patent # US5691914:
Fluid flow measurement correcting system, and methods of constructing and utilizing the same.

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.