Basic setup of AS1 seismic sensor

Wipe the knife edge clean and spread one drop of oil along it.

Adjust the “sideways level” with the two screws near the mast.

Adjust the “lengthwise level” with the screw near the coil.

Adjust the level of the boom by adding or removing washers and by sliding the level bubble along the boom.

Double check that the damping washer is centered within the oil dish.

Center the magnet over the coil so that there is space on both sides. This is critical.

The knife edge may have to be offset to one side of the mast to center the magnet over the coil.

With a round file, make a grove in the base of the cover for the coil wires.

If you wish to calibrate the system, make a 5/16“-diameter hole in the top of the cover, near the hinge end.

If you wish to calibrate the system, make a white patch on the boom and then draw a line across it 10 cm from the mast.

For free-period check, lift the boom and slide an empty dish under the damping washer. Lower boom and adjust weight on boom.

Undamped oscillations. Helicorder gain = 5. Sixty lines per hour.

Undamped oscillations. One line per hour.

Undamped oscillations continue for more than three minutes.

Washer Calibration. Tie thread to washer and place it near the boom magnet.

Pulling the washer away sudenly creates this calibration pulse: down, up, and then return to zero.

Weight in place on boom, ready for lift-test calibration.


To check for electronic noise, place a weight on the boom.

The noise level is just a few counts when the magnet is not allowed to move.

For inductance calibration, lift boom and place one loop of 32 gauge wire around coil.

The loop of wire is attached to an RCA jack.

A pulse is generated when a AAA cell (1.4 V measured) is attached and then removed from the single loop of wire.