SIGMA 940 IS

Open Channel
Flowmeters

SIGMA 940 Area Velocity Flow Meter, Intrinsically Safe

The Sigma 940 Intrinsically-Safe Flow Meter supports dual sensors, interfaces with samplers, has a long battery life, and offers increased data storage and optional modem capability.

The Sigma 940 Flow Meter is the safest investment for your sewer and your budget. With the 940, remote monitoring becomes a way of life. Its rugged design, low-profile probes and long battery life significantly reduce site visits. Choose up to two area velocity sensors, or one area velocity and one level backup. Whether you're experiencing redundancy in a single pipe or level and velocity in separate pipes, you'll profit from new performance levels in a single meter.

Industry standard MODBUS ASCII protocol has been incorporated into the Sigma 940 Flow Meter. The implementation of the MODBUS protocol will allow your MMI, SCADA or DCS system to directly communicate with the 940 Flow Meter 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 DEMKO listed and certified for operation in Class I, Division I, Groups C & D hazardous locations.
	Multiple sensors for redundancy, averaging and multiple pipe monitoring.
	Telephone and pager alarms for quick notification of system changes.
	Low power draw, with a long, one-year battery life.
	NEMA 6P sealed to withstand submergence and prolonged surcharge conditions.
	Sampler pacing capabilities, to document the extent of overflow problems.
	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 on-site calibration.
	A higher level of accuracy, since the 940 automatically corrects the effects of temperature on level measurement.
	Patented Drawdown Correction feature corrects the effects of velocity on accurate level measurement.

Ideal for:

	Long Term Flow Monitoring 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.

As the velocity of water increases past the probe.
A drop in pressure (vacuum) is induced near the pressure sensor (level) port located at the sides of the probe.
This results in the lowering of the indicated level (or pressure) sensed at the port.
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."

*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.

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