MiniMAG Magnetometer

We operate a stand-alone version of the ROV Jason magnetometer for use on deep-towed camera and other platforms of opportunity. This is a small fully digital 3-axis magnetoresistor magnetometer (Honeywell model HMR2300) with an optional separate data logger system. The sensor is approximately 8 inches long 3 inches diameter in a titanium pressure housing rated to 6000 meters depth. The sensor communicates via an RS232 protocol to a separate Persistor-based datalogger that stores data to a CF card. The logger also contains a battery and can operate the system for upwards of 24 hours.

How the sensor works
The magnetic sensing device is built upon the phenomenon of magneto-resistance. The sensing material changes its electrical resistance depending on the strength of the ambient magnetic field. The Honeywell sensors use a property called anisotropic magnetoresistance (AMR). In AMR sensors the electrical resistance varies according to the angle between the direction of electrical current and that of the magnetic field. Electical resistance has a maximum value when the current is in the same direction as the applied magnetic field. Magnetoresistive sensors are typically made of a nickel-iron (Permalloy) thin film deposited on a silicon wafer and patterned as a resistive strip.

Link to HMR Minimag Documents

We currently have three deep sea HMR2300 magnetometer sensors that we use on a variety of platforms. These are identical to the HMR sensor on ROV Jason, except that we use Impulse bulkhead connectors and cabling. Below are summary documents for these instruments:

For more information on the MiniMAG magnetometer, contact:

Dr. Maurice Tivey
mtivey@whoi.edu

Mini magnetometer: HMR2300. Photo Credit: Maurice Tivey, WHOI.

Mini magnetometer (right) and datalogger+battery (left) in pressure housings. Photo Credit: Maurice Tivey, WHOI.