HMR2300

www.honeywell.com

9

DEVICE ID

The Device ID command (*ddID=nn) will change the HMR2300 ID number. A Write Enable (*ddWE) command is required

before the device ID can be changed. This is required for RS-485 operation when more than one HMR2300 is on a

network. A Device ID = 99 is universal and will simultaneously talk to all units on a network.

BAUD RATE COMMAND

The Baud Rate command (*dd!BR=F or S) will change the HMR2300 baud rate to either fast (19,200 baud) or slow (9600

baud). A Write Enable (*ddWE) command is required before the baud rate can be changed. The last response after this

command has been accepted will be either BAUD=9600 or BAUD=19,200. This will indicate to the user to change to the

identified new baud rate before communications can resume.

ZERO READING COMMAND

The Zero Reading command (*ddZN) will take a magnetic reading and store it in the HMR2300’s microcontroller. This

value will be subtracted from subsequent readings as an offset. The zero reading will be terminated with another

command input(*ddZF) or a power down condition. This feature is useful for setting a reference attitude or nulling the

earth

’s field before anomaly detection.

SET/RESET AND AVERAGE COMMANDS

The set-reset function generates a current/magnetic field pulse to each sensor to realign the permalloy thin film

magnetization. This yields the maximum output sensitivity for magnetic sensing. This pulse is generated inside the

HMR2300 and consumes less than 1mA typically. The Set/Reset Mode command (*ddTN or *ddT) activates an internal

switching circuit that flips the current in a “Set” and “Reset” condition. This cancels out any temperature drift effects and

ensures the sensors are operating in their most sensitive region.

Fluctuations in the magnetic readings can be reduced by using the Average Readings commands (*ddVN or *ddV). These

commands provide a low pass filter effect on the output readings that reduces noise due to Set/Reset switching and other

environmental magnetic effects. The two figures below show the average readings effect for step and impulse responses.

Switching the set-reset state is not required to sense magnetic fields. A single Set (or Reset) pulse will maximize the

output sensitivity and it will stay that way for months or years. To turn off the internal switching, enter the command *ddTF

or *ddT. In this state the sensors are either in a Set or Reset mode. If the HMR2300 is exposed to a large magnetic field

(>10 gauss), then another set pulse is required to maximize output sensitivity.

In the Set mode, the direction of the sensitive axis’ are shown on the enclosure label and the board dimensions figure. In

the Reset mode, the sensitive field directions are opposite to those shown. By typing *dd], the user can manually activate

a Set or Reset pulse. The S/R pulse commands can be used the continuous read mode to flip between a Set and Reset

state. Note that the first three readings immediately after these commands will be invalid due to the uncertainty of the

current pulse to the sensor sample time.

DEFAULT AND RESTORE COMMANDS

The Defaut Settings command (*ddD) will force the HMR2300 to all the default parameters. This will not be a permanent

change unless a Store Parameter command (*ddSP) is issued after the Write Enable command. The Restore Settings

command (*ddRST) will force the HMR2300 to all the stored parameters in the EEPROM.