OFS 2000 – Optical Flow Sensing Explained

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Optical Scientific, Inc. was founded in 1985 to explore the results of Dr. Ting-I Wang’s original research using scintillometry to analyse the movement of air through a beam of light. For several years OSI engaged in design and development of a successful product line of weather sensing instruments: Light-Emitting-Diode Weather Indicators (LEDWI), Optical Rain Gauges (ORG) and Optical Weather Indicators (OWI –Present Weather and Visibility) –all still serving and leading the market today.

During this period OSI (as it does still) engaged in constant test and refinement of the original software algorithms, culminating in the introduction of the Long-baseline Optical Anemometer (LOA) in 1995.This ground-breaking instrument proved capable of measuring air movement through a light beam up to a distance of 10km. It was soon being used for scientific testing purposes at Argonne and Sandia National Laboratories. Commercial versions were used in the aluminum industry to monitor smelter emissions.

With the success of LOA it was decided to widen the scope by reducing the size and range to fit industrial applications. Again, all the discoveries and refinements that had gone before were adapted into this new sensor –the OFS 2000. In 1999,the OFS 2000 Optical Flow Sensor was introduced to the world market where it soon proved to be the sensor of choice for industrial customers concerned with Continuous Emissions Monitoring Systems (CEMS) to help reduce greenhouse gas emissions.

How It Works:

OSI’s patented Optical Flow Sensor (OFS) makes drift-free optical scintillation measurements across the entire distance between the transmitter and receiver and calculates an accurate average flow reading. It is the only flow sensor that gives a true non-contacting complete cross-stack flow measurement. OFS uses EPA Method 14 approved optical scintillation technology. The accuracy of the OFS has been proven both in NIST’s wind tunnel and in every real-world installation.

Optical Detection

OSI’s patented optical scintillation measurement algorithm uses advanced Digital Signal Processing (DSP) to measure the movement of turbulence found in a gaseous flow stream, providing highly accurate, path-averaged measurements. OFS takes 4000 data points every 0.3 seconds and measures instantaneous average velocity

No Calibration Required

Simply put: by its very nature OFS scintillation measurement does not drift. This means the all-digital / DSP-based OFS 2000 systems require no calibration –ever. OFS technology uses a proprietary patented algorithm developed by OSI and certified by NIST (National Institute of Standards and Technology) and is supported with over 20 million hours of observation data. Automatic calibration check and continuous self-test diagnostics are built-in for user security.Drift >3% from norm will cause a fault alarm. Since 1999 there have been no instances of calibration fault in any OFS system.

Standard Volumetric Flow

OFS is primarily a velocity sensor. However, all OFS models are equipped with two 4-20 mA inputs to accept readings from add-on smart temperature and pressure sensors, enabling OFS to report standard volumetric flow. Older models can be easily retrofitted in the field or at our facility.

OFS 2000 Scintillometric Measurement Features Unique Advantages:

Non-Intrusive

No direct contact with flow media. Measurement is immune to the effects of temperature, gas density, moisture content, particulate count, or pressure. If OFS 2000 can detect the turbulence-induced light fluctuations with even a fraction of the light, it can accurately measure the flow velocity. It is, in this sense, a “pure” measurement.

Full-Path Averaging

OFS 2000 provides a dynamic velocity measurement of the passage of gas or air through a light beam averaged directly across the entire volume. Scintillation through the entire path is detected, analyzed, calculated, and reported -a much more representative measurement than single point or slanted path.

Measures Volumetric Flow

Along with superior accuracy, OFS 2000 can also be configured with the ability to accept smart temperature and pressure sensor current loop data to calculate and report volumetric flow or mass flow in addition to velocity.

Measurement Not Affected By

• Distance •Pressure • Temperature • Gas Density • Moisture • Opacity

Measurement Not Dependent On

• Differential pressure • Design DP • Beta ratio • Temperature • Gas composition • Humidity • Speed of sound

OFS 2000 System Features:

Flexible Installation

OFS can install in tight spaces with minimum space requirements of 2 upstream / 1 downstream diameters. No re-piping needed. Installation is to standard ANSI pattern 4” pipe flange. OFS can be installed on live process pipes using hot tap procedure and gate valves for isolation. No shutdown needed.

Flexible Communication

All systems are equipped with 4-20mA Current Loop, RS-232/485, ModBus RTUdata outputs, and can be configured with Serial port, Limited Distance Modem, and Fiber Optic Interface for any type of WAN or LAN.

No Moving Parts

OFS 2000 is essentially maintenance-free, save for window cleaning. OFS internal monitoring alerts the user if window cleaning is required. (Typically only semi-annually (if then) on the dirtiest stack and duct applications.)

Assures Compliance

All OFS 2000 sensors meet or exceed requirements set by the Environmental Protection Agency, and California’s South Coast Air Quality Management District.

EPA Method 14
EPA MACT RSR 40 CFR 63.670
EPA 40 CFR part 60 & 75
EPA 40 CFR part 60 sub part J & Ja
SCAQMD rule 1118

From the beginning, OSI has followed a policy of constant research, innovation, and improvement. Since OFS 2000 was introduced OSI has responded to customer needs with models to support a variety of industrial applications. The most recent release is the OFS 2000R, designed for steam-assisted refinery flare stacks. Further refinements are constantly in process.

For further information: contact your local representative/re-seller; contact us by phone; or simply send us an email:Optical Scientific, Inc.2 Metropolitan Court Suite 6 Gaithersburg, MD 20878 USA

Tel: +01 301 963 3630 Fax: +01 301 948 4674
E-mail: infoawe@opticalscientific.com
Website: https://opticalscientific.com

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Optical Scientific Inc.

Optical Scientific, Inc. was founded in 1985. We are a research, development, engineering and manufacturing firm located in the I-270 high technology corridor outside of Washington, DC. We design and build the most advanced optical instruments in the world for measuring precipitation, air flow, turbulence, and visibility. For over thirty years we have been engaged in a constant research and development program to ensure our position as world leader. Our sensors and systems serve airports, highways, railroads, sea-borne vessels, smelters, power plants, refineries, and hundreds of other commercial and industrial sites around the world.