Sensor Design Key Advantage In Thermal Mass Flow Meter Performance

Immersible thermal sensors are finding growing acceptance in the gas flow measurement field. By using two Platinum Resistance Temperature Detectors (PRTDs) immersed in a stream of flowing gas, modern thermal flow meters can directly measure mass flow, without the need for temperature or pressure compensation. Thermal meters offer very high turndown, accu¬racy and repeatability at an economical price. However, all ther¬mal sensors are not created equal. Recent optimization of sensor design has led to a marked increase in the performance of ther¬mal mass flowmeters in the field. To understand just what role sensor design plays in thermal flow meter performance, it is necessary to understand the basics of how immersible thermal sensors work. An immersible sensor typically consists of a heated element (called the velocity sensor) and a passive element (called the tem¬perature sensor). Both are precision PRTDs. In operation, the velocity sensor is heated to a temperature Tv.