The new flow sensor uses screen-printed thick-film thermistors and resistive heaters protected by a thin layer of Parylene-C to convert heat transfer to fluid flow velocity using King's law. The thick film substrate is connected to a small electronics board, which includes a TI MSP 430 microprocessor. The electronics manage power to the resistive heaters, and measure differential output across a four-wire bridge formed by four of the screen-printed thermistors. They also detect alarm conditions such as dry-line and reverse flow. Dry line is measured using a temperature rate-of-rise algorithm. Reverse flow is detected using a secondary resistive heater positioned in immediate proximity to a temperature measuring thermistor. When the flow direction is opposite to that of the normal forward direction, an abnormal temperature rise is detected, and alarm condition is posted.
The sensor can be installed in a number of applications which require high accuracy and reliability. The sensor utilizes NO moving parts, making it suitable for environments where debris and contamination may be present. Each sensor is indvividually calibrated between 0.125 and 2.500 m/sec in a temperature range of 0C to +65C. The sensor is packaged in a robust glass-filled polymer housing which insures repeatable orientation with respect to fluid flow direction. It also insures repeatable insertion depth into the flowing fluid stream. Flow conditioners serve to provide uniform flow velocity profile around the sensing chip, and protect the chip during installation. Several output options are available, including analog (0-10V) and digital (Modbus) formats. Alam signals include dry-line, low flow, reverse flow, out-of range temperature, and out-of-range flow. Several patents have been awarded, and product is expected to launch this year.