Optical Scientific Inc. (OSi)

- Model OFS 2000W - Emissions Air Flow Sensor



OSi's patented Optical Flow Sensor (OFS) makes drift-free measurements across the entire stack, duct or pipe diameter and calculates a true average flow reading. The OFS 2000-W model is equipped with Automatic Gain Control (AGC) to compensate for variations in opacity caused by particulate matter or moisture carried in the stack flow. The OFS uses our EPA Method 14 approved optical scintillation technology. The optical scintillation technique relies on advanced Digital Signal Processing (DSP) electronics to 'see' and measure the movement of turbulence found in a gaseous flow stream to provide highly accurate, path-averaged air velocity measurements. The accuracy of the OFS has been proven both in the NIST wind tunnel, and time after time in real-world applications.

  • Cross stack/duct/pipe line measurement for more accurate flow readings.
  • Measurement path 90° to stack; second platform not required – save $100K or more
  • Easily replaces existing ultrasonic sensors.
  • Non-interfering; nothing in flow path.
  • Easy installation and optical alignment.
  • Minimal upstream/downstream diameters; typically 2 & 1, not 20 & 10 like others.
  • Long-term reliability: no blowers or moving parts; operates unattended - 24 / 7 / 365.
  • Rugged ultra-low maintenance. Designed for harsh environments.
  • Automatic Gain Control (AGC) to compensate for opacity variation.
  • Built-in continuous self-test diagnostics.
  • Unaffected by media pressure, moisture.
  • No flow media high temperature limits.
  • Compliant with EPA 40CFR Parts 60 & 75.
  • Wide versatility, NIST-tested and unbeatable combination of advanced technology, high performance and proven reliability!

OFS-2000 Options:

  • Order Z-Purge Option for Class I Div I/II applications.
  • Standard Control Unit is rack mount; for wall mount, order 1910-301, NEMA4 Option.
  • For custom receiver cable length, order 1910-216-nnn where “nnn” is cable length in feet (max 300).

OFS-2000 Accessories:

  • 1910-431-nn Sight Glass w/ gaskets for media isolation (2 required, multiple models)
  • 1910-420 Cast Iron Gate Valves for high temperature applications (2 required)
  • 1910-804 Laptop DB9 serial communications cable


The OFS consists of DSP / multiprocessor - based control unit teamed with a set. of optical transmit and receive heads which are easily installed on opposite sides. of a stack, duct, vent or pipe. The OFS heads mount fully outside of the media. volume behind optical windows for easy access, more accurate measurements,. and greater durability. The transmit head sends a visible diverging light beam. directly across and perpendicular to the flow (existing angled-path port can be. used). Transmitter output is controlled using an AGC feedback signal from the. receiver to compensate for variations in flow opacity. The control unit processes. the scintillation detected by the receive head, displays the flow data locally and. transmits it to a PC, PLC, DAS or other data collection device that accepts a serial. data link and/or a 4-20 mA current loop. The control unit can be configured from. either the local keypad and display, or from a laptop or portable terminal.

Flow Performance

  • Measurement Technique: Optical Scintillation (OSi Patented)
  • Dynamic Range: 0.1 to 40 m/sec
  • Accuracy (absolute): +/- 0.1 m/sec basic -or- +/- 2% of reading, whichever is greater
  • Repeatability (relative): +/- 0.1 m/sec basic -or- +/- 1% of reading, whichever is greater
  • Long Term Drift: Less than 1% per year
  • Response Time: 3 to 600 seconds, user-selectable
  • Automatic Calibration Check: 2 or 3 point; user-selectable interval -or- on external command
  • Sensor Health Monitoring: Continuous self-test of voltages, performance, optics, etc.

Media / Environmental

  • Stack / Duct / Pipe Diameter: 0.2 to 12 meters standard -- consult factory for other ranges
  • Media Temperature / Pressure / Humidity: No effect on measurement
  • Media Transparency: Up to 95% opacity (OFS 2000-W is recommended for high opacity)
  • Ambient Temperature / Humidity: -40 to 60 C (-58 to 140 F) / 0 - 100% condensing

Physical Specifications

  • Light Source: Eye-safe 670 nm visible red LED, 5 deg. divergence angle
  • Sensor Heads (w/ 4” sch.40 flange extender): 9 x 9 x 13 inches, 13 lbs. – NEMA 4 weather resistant
  • Control Unit: Rack Mount Version (standard)  NEMA4 Wall Mount (optional)
    • 5 x 17 x 20 inches, 13 lbs. (for indoor use) -or-
    • 12 x 16 x 10 inches, 15 lbs. (for outdoor / factory floor use)
  • Purge Air for Heads: Normally not needed. 1 - 4 CFM max for demanding applications

Electrical Specification

  • User Interface:
    • RS-232 serial I/O and / or 4-20 mA optically isolated current loop;
    • Relay contacts for fault alarm and calibration check initialization.
  • Power for Transmit Head: Universal 100-240 VAC, 50/60 Hz, 12 VA (fused & surge protected)
  • Power for Control Unit: Universal 100-240 VAC, 50/60 Hz, 40 VA (fused & surge protected)
  • Cable between Control Unit & Receive Head: 15 foot standard; to 300 foot optional (shielded, 10 cond., 22 AWG)

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