HMR2300

Honeywell's three-axis smart digital magnetometer (HMR) detects the strength and direction of a magnetic field and communicates the x, y, and z component directly to a computer. Three independent bridges are oriented to sense the x, y, and z axis of a magnetic field. The bridge outputs are then converted to a 16-bit digital value using an internal delta-sigma A/D converter. A command set is provided (see Table 1) to configure the data sample rate, output format, averaging and zero offset. An on-board EEPROM stores any configuration changes for next time power-up. Other commands perform utility functions like baud rate, device ID and serial number. Also included in the HMR2300 magnetometer is a digital filter with 50/60 Hz rejection to reduce ambient magnetic interference.

About the HMR2300, a unique switching technique is applied to the permalloy bridge to eliminate the effects of past magnetic history. This technique cancels out the bridge offset as well as any offset introduced by the electronics. The x, y, and z digitized data is sent out as a series of bytes, either after an ID match is received from the control processor, or as a continuous data stream. The data is serially output at either 9,600 or 19,200 baud, using the RS-232 or RS-485 standard, for serial input to most personal computers. The RS-485 standard allows connection of up to 32 devices on a single wire pair up to 4,000 feet in length. An HMR address can be stored in the on-board EEPROM to assign one of thirty-two unique ID codes to allow direct line access. An internal microcontroller handles the magnetic sensing, digital filtering, and all output communications eliminating the need for external trims and adjustments. Standard RS-485 or RS-232 drivers provide compliant electrical signalling.

About the HMR2300, Honeywell's magnetoresistive magnetometers provide an excellent means of measuring both linear and angular position and displacement. Low cost, high sensitivity, fast response, small size, and reliability are advantages over mechanical or other magnetometer alternatives. With an extremely low magnetic field sensitivity and a user configurable command set, these sensors solve a variety of problems in custom applications. The HMR2300 is available either as a circuit board with an optional 9-pin connector or in an aluminum enclosure with a 9-pin connector. Possible applications include compassing, remote vehicle monitoring, process control, laboratory instrumentation, anomaly detection, traffic and vehicle detection, and retail security systems.