Fox Thermal flow meters use a constant temperature differential (ΔT)technology to measure air and gases' mass flow rate. The thermal mass flow sensor consists of two Resistance Temperature Detectors (RTDs). The sensor elements are constructed of a reference-grade platinum wire around ceramic mandrels inserted into a stainless steel or Hastelloy tubes.
The reference RTD measures the gas temperature. The heated element is kept at a constant temperature, and the instrument electronics measure the gas flow's cooling effect. The electrical power required to maintain a constant temperature differential is directly proportional to the process gas's mass flow rate. The microprocessor then linearizes this data to deliver a 4-20mA output signal.
PowerPro™ Sensor Technology
Used in Fox Thermal Models FT2A and FT3, the Fox Thermal PowerPro™ Sensor operates at a higher power level than other competitive thermal technologies, providing better response time and wider turndown. Compared to a typical Differential Pressure(DP) type flowmeter (see inset), thePowerPro™ sensor offers better low flow or low-end sensitivity. The PowerPro™ sensor also provides exceptional accuracy at high velocities - up to 60,000 SFPM air.
The Fox Thermal DDC-Sensor™ is a new state-of-the-art sensor technology used in the FT1, FT4A, and FT4X flow meters. The DDC-Sensor™ is a Direct DigitallyControlled sensor that is interfaced directly with the microprocessor for more accuracy, speed, and programmability. Like thePowerPro™ Sensor, the DDC-Sensor™accurately responds to changes in process variables (gas flow rate, pressure, and temperature), which are used by the microprocessor to determine mass flow rate, totalized flow, and temperature.
In addition to measuring flow, the DDC-Sensor™ provides a technology platform for calculating accurate gas correlations. The correlation algorithms allow the meter to be calibrated on a single gas in the factory while giving the user the ability to select other gases in the theGas-SelectX™ gas selection menus. These technologies provide an accurate, multigas-capable thermal mass flow measurement from the leader in accuracy and innovation in thermal mass flow measurement technology.