- Omega Sensor User's Guide

pg. 5 of 29

proven design minimizes zero drift while maintaining fast response and

linear outputs with virtually no maintenance.

Flow is measured using a miniature turbine wheel similar in size to a U.S.

dime (16 mm diameter, 0.75 mm thick). The micro-turbine wheel is

supported on a very small sapphire shaft that is held in position by two

sapphire bearings.

As flow passes through the sensor, a precision machined nozzle directs the

gas onto the very small teeth of the micro-turbine wheel. This causes the

wheel to spin at a speed proportional to the volumetric flow rate.

The micro-turbine wheel has alternating white and black sections evenly

spaced on one side of the wheel. An infrared light beam is directed onto

the wheel. As the wheel rotates the infrared beam is reflected off each

white section. The reflected beam is detected by a phototransistor that

converts the reflections into electrical pulses. As the wheel spins faster the

pulse rate increases. Processing circuitry provides analog and/or pulse

output that are linearly proportional to the volumetric flow rate

When the wheel stops (under zero flow conditions), no pulses are

generated. Consequently, zero drift is not possible and zero adjustments

are never required.

Every unit is supplied with a calibration certificate detailing the results

obtained during calibration. Units are calibrated using AIR as the reference

media. Flowing gases with different physical characteristics may effect the

calibration.

Installation

Caution: Do not exceed the pressure, temperature or

power operating ranges detailed in the SPECIFICATIONS

section of this manual. Omega Engineering shall not be

liable for any damage or injury caused by incorrect

operation of their products.