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Sensor Installation

The DIY Gradiometer uses two FG-3+ fluxgate magnetometer sensors placed at different positions along the tube.

The upper sensor and lower sensor measure the magnetic field at two points. The system then calculates the difference between the two measurements to detect magnetic field gradients.

Correct sensor placement and orientation are essential for proper operation of the gradiometer.

Sensor Configuration​

Upper Sensor
│
│
│ (sensor separation)
│
Lower Sensor

The separation between sensors determines the sensitivity to magnetic gradients.

We recommend spacing sensors 0.5–2.0 m apart. Do not place FG-3+ sensors closer than 0.5 m.

Installing the Upper Sensor​

The upper sensor is mounted near the top of the tube.

  1. Insert the FG-3+ sensor into the upper sensor holder
  2. Push the sensor into the holder until it passes the retaining latch
  3. Connect the sensor using the short cable supplied with the kit
  4. Secure the cable with hot glue to prevent movement

Once installed, insert the sensor assembly into the tube approximately 10 cm below the top. Fix the sensor holder using hot glue so that the sensor remains stable during operation.

Installing the Lower Sensor​

The lower sensor is installed at the bottom of the gradiometer tube.

  1. Connect the lower FG-3+ sensor using the long sensor cable
  2. Route the cable through the tube
  3. Before inserting fully, lubricate the seal using liquid soap or hand cream — this makes it easier to insert and adjust the sensor position
  4. Insert the lower sensor assembly into the bottom of the tube
remarque

Leave the lower sensor adjustable at this stage — it will be precisely aligned during the calibration step.

Sensor Orientation​

attention

Both sensors must be oriented in the same direction (both facing the same way — upside down). If one sensor is reversed, the gradiometer will not measure the magnetic gradient correctly.

Cable Routing​

When installing the sensors:

  • ensure cables are not twisted
  • avoid sharp bends in the cables
  • secure cables to prevent movement during operation

Stable cable routing helps prevent electrical noise and mechanical strain on the sensors.

Verifying Sensor Installation​

Before continuing, verify the following:

  • both sensors are securely installed
  • sensors are oriented in the same direction
  • cables are connected to the MAG-BOARD
  • the upper sensor is fixed in position
  • the lower sensor remains adjustable

Once these checks are complete, the system is ready for calibration.

Next Step​

Calibration