Thermal Flow Meters For Pure Gas Applications

Fox Thermal Flow Meter use a constant temperature differential (constant delta T) technology to measure mass flow rate of air and gases. The thermal mass flow sensor consists of two Resistance Temperature Detectors (RTD's). The sensor elements are constructed of a reference grade platinum wire wound around ceramic mandrels that are inserted into stainless steel or Hastellory tubes.

The Reference RTD measures the gas temperature. The instruments electronics heat the mass flow sensor, or heated element, to a constant temperature differential (constant delta T) above the gas temperature and measures the cooling effect of the gas flow. The electircal power required to maintain a constant temperature differential is directly proportional to the gas mass flow rate. The microprocessor then linearizes this signal to deliver a linear 4 to 29 mA signal.