A sensitive magnetometer
- A sensitive magnetometer
- 1. Introduction.
- 2. Hardware description.
- 3. Software description.
- 5. Thermal drift.
- 6. Performance.
1. Introduction.
A magnetometer measures disturbances in the earth magnetic field.
It can be used to signal geomatic storms in progress following
the impact of a coronal ejection on the sun and so predict
possible auroral displays.
The hardware of this magnometer consist of two small printed circuit
boards, a powersupply board and an analog board.
It uses the Honeywell HMC1022 an extremely sensitive low field solid
state magnetic sensor.
fig 1. powersupply board fig 2. analog board
The ATmega328 is used as a microprocessor, but any microprocessor is suitable.
Because of the clever modular design and software a jeenode is used.
JeeNodes are compatible with the Arduino platform so there's a lot of
support available.The Jeenode has an ATmega328p and a RFM12B radio module
on board , so if needed it wil be possible to control/read the magnetometer
from a distance by radio. http://jeelabs.com/products/jeenode
fig 3. controller jeenode fig 4. magnetometer
2. Hardware description.
fig 6. POWERSUPPLY BOARD
1. power supply
A 5V voltage regulator is used to produce a constant regulated 5V output voltage.A 6V voltage
regulator is used to generate a strong set/reset puls for the flipping generator. The supply
voltage can be between 9 - 15 Volts . It's possible to operate from a 9 Volt batttery .
Current drawn from 9 volts is about 50 mA .(configuration 1)
2. flipping generator.
The flipping is generated by applying alternataly positive and negative short pulses to the
set/reset coil of the sensor .As a result the output is converted into a squarewave.
Offset can now be blocked by means of a capacitor. An IRF7105 is used to switch these pulses.
This flipping forces the sensor in a high sensitive mode and improves linearity and temperature
effects.
3. Vref + lock-in ref.
A 2.5 Vreference voltage (Vref) is used to supply the reference voltage for the instrumentation
amplifier , the second stage amplifier and to the 0-5V to 0-3.3V converter. A TL431A is used
to generate this reference voltage.
The lock-in signal is derived from the flipping puls and connected to a lock-in amplifier.
4. 3-buttons-menu.
The buttons are used to control the magnetometer manually.
5. out to analog board.
Connections to the analog board.
