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Simple Magnetic Gradiometer

• Gradiometers are basic magnetic anomaly detectors, commonly used for metal detection. The near sensor is the reference in which the far sensor is used to probe for metals. Differences show up in the meter.
• Position of the HMC1021S sensors must be well aligned in the rod axis.
• Voltage Supply (V+) can be from 3 to 12 volts, depending on quad op-amp supply range.
• Rmeter selected based on chosen meter movement. Typical values are from 500-ohms to 10k-ohms.
• Large temperature changes may require re-adjusting the offset trim pots.
• Magnetic fields larger than 20 gauss may require a set/reset circuit for each HMC1021S to restore performance.
• Multiple axis gradiometers may be built by replicating this circuit and using the HMC1022 or HMC1023 sensor arrays.