Sierra FLAT-TRAKTM 780S - Manual (Page 9)

Series 780S Instruction Manual Chapter 1 Introduction
IM-78S-B 1-3
The Series 780S Flow Sensing Principle
Sierra’s unique Steel-Trak ™ sensor probe is responsible for the un-
surpassed accuracy, ruggedness and reliability of Sierra industrial
flow meters. The immersible Steel-Trak sensor consists of two
sensing elements–a velocity sensor and a temperature sensor that
automatically corrects for changes in gas temperature.
When power is applied to the flow meter, the transducer electronics
heats the velocity sensor to a constant temperature differential above
the gas temperature and measures the cooling effect of the gas flow.
The electrical power required to maintain a constant temperature dif-
ferential is directly proportional to the gas mass flow rate.
Both sensors are reference-grade platinum resistance temperature
detectors (RTDs). The platinum RTD wire is wound on a rugged ce-
ramic mandrel for strength and stability. Steel-Trak sensors are clad
in a rugged, sealed 316 stainless steel encasement.
Figure 1-1. Series 780S Flow Sensing Principle