Hedland”sMR flow transmitter recently received a U.S. patent for a design thatconserves power by activating only portions of the AnisotropicMagnetoresistive (AMR) array electronics in a systematic way. One of the greatest hurdles to overcome when integrating themagnetic sensor technologies into an industrial sensor is they arepower hungry. Most are powered and transmit information on thesame two wires. Unique to the MR Transmitter is that it does notpower all of the MR sensors at once. The microprocessor selectsand reads the output voltage of seven AMR sensors, one at a time, untilthe entire array of sensors have been read. This voltage isrouted through a multiplexing circuit and then into an instrumentationamplifier. The signal is amplified, passed through a low-passfilter, and then input to the A/D converter built into themicroprocessor. Based on the readings, the microprocessordetermines the absolute position of the magnet inside the flowmeterand calculates the flowrate based upon user selectable setup scalingparameters. The flowrate is then displayed on the LCDdisplay. The unit can also calculate and display the totalaccumulated flow. Analog outputs of four to 20 mA current loop, zero to five Vdc and zero to 10 Vdc are provided. Theseoutputs are calibrated to output an analog current or voltagecorresponding to the measured flowrate. The transmitter also has the ability to enter up to10 linearization points to compensate for the nonlinearity of the flowmeter.
