Probe for detecting the presence of magnetic material in a ground hole

Apparatus, which is suitable for detecting the presence of magnetic material in a ground-hole, characterised:

• in that the apparatus includes a probe comprising a housing, a magnet, a movable mounting for the magnet, and a pair of electrical contacts;
• in that the housing surrounds and encloses the magnet;
• in that the movable mounting includes a means for holding the magnet in a first at-rest position, in which the magnet is, in substance, clear of any operative contact with the housing;
• in that the movable mounting includes a means for permitting the magnet to move towards the housing to a second position, in response to magnetic attraction between the magnet and steel located outside the housing;
• in that the arrangement is such that as the magnet moves between the first and second positions, the electrical contacts change between OFF and ON;
• in that the movable mounting includes a spring means for restoring the magnet to the said at-rest position upon removal of the probe from the said steel;
• in that the spring means comprises a springy stalk, one end of which is built-into the housing;
• in that the magnet is attached to a point on the springy stalk remote from the built-in end;
• in that the length of the springy stalk is disposed along the length of the probe;
• in that the apparatus includes a suspension means, by means of which the apparatus may be lowered down into the ground-hole, and raised therefrom;
• in that the apparatus includes a means for measuring the depth below the ground surface to which the probe has been lowered;
• in that the apparatus includes a means for indicating whether the electrical contacts are in the ON or OFF condition, and said indicating mean situated at the ground surface for indicating said condition;
• and in that the probe is sealed tight against entry of liquid into the probe, whereby the electrical contacts in the probe are isolated from water present within the ground-hole.