Discussion in 'Weapons, Technology & Equipment' started by dbf, Jan 28, 2012.
See attached for details
German mine detector development on the whole followed the same lines as British development proceeding from the mechanical prod type of searching probe to the use of electrical devices of varying complexity so far as circuit details were concerned. The mechanical construction of these electrical devices remained sensibly the same, obviously because of the physical requirements which demanded an easily carried pack containing the bulk of the equipment and power supplies, and a searching head for the remote detection of the buried objects. For this reason a variety of devices, generally named after German towns, were used, each of which utilised similar carrying packs and spares case. The search coils themselves showed a greater variety in structure.
The electrical detectors, while differing in details of circuit design, all operated fundamentally on the same principle - the variation of a fixed coupling between two coils caused by the presence of a mass of metal. One of the coils was part of an oscillating circuit in which oscillations were maintained. The second coil forming the link to an audio amplifier, was placed at right angles to the first coil thus arranging for the minimum coupling between the two. Various adjustments were provided in the form of a shortened turn or moveable plate so that the equipment could be adjusted to give a suitable tone in the earphones.
The subsequent movement of the search head into the vicinity of metal objects distorted the magnetic fields of the two coils, thereby increasing the coupling between them, resulting in a change in the intensity of sound in the earphones.
The better detectors which the Allies had available, associated with economic considerations, caused the Germans to produce wooden mines, and, for purposes of detecting them after they had laid them the Germans included with them a quantity of TARNSAND which, among other things, contained some Pitchblende residues. The position of the mine was therefore detected by the ionising effect on a gas occasioned by the radio active elements in the Pitchblende. This principle as used in the Stuttgart detectors which were the last type to be produced by the Germans.
The various equipments are discussed as far as possible in developmental sequence.
This was one of the earliest types of German Mine detector and was essentially the same as the British "Mine Probe".
The rod was made of two lengths of light metal tubing weighing about 1 lb, one of which the "the vibrating tube" carried a hardened steel point some 9 1/2 ins. long. The second tube formed an extension piece to be added to the rod for use in an upright position, the connection being effected by means of a Bayonet joint.
The road was inserted into the ground and when a buried object was encountered a skilled operator could tell from the sound emitted the nature of the object contacted. From wood a dull note was emitted and the point stuck into the object, while from metal objects it rebounded giving a high note. If a pebble was struck the rod rebounded sharply and emitted a high shrill note.
The earliest report on this type of detector originated in the M.E. in Sept/Dec 41 and gave a brief description and circuit diagram.
The equipment comprised a search coil mounted on a long pole at the upper end of which was fitted a case containing the oscillators, amplifier and batteries.
The search head was a circular ring 11 3/8 inches in diameter, 1 inch high and 1 1/8 inch thick, cut from solid bakelite, suitably channeled to take the coil windings and sealed by bakelite and cement.
At the rear of the base was a hinge joint composed of two flanges on the base, and a small bakelite block attached to the lower end of the pole, the three sections being secured together by a bakelite bolt with nuts at each side. The arrangement was not very satisfactory as the leads were liable to damage by frequent movements of the hinge.
The lower part of the pole was made of bakelite (11 1/2 inches) while the upper part was aluminium, the total length being 82 1/2 inches. The oscillator case was attached to the pole by means of a collar-shaped casting, into which the end of the pole fitted. The conductors, two copper wires, which traversed the pole, held in position by suitably spaced bakelite discs, passed into the oscillator case and terminated in a screw head and ring assembly. The oscillator case was made of sheet aluminium (10 1/2" x 8" x 4"), so contracted that easy access to battery and valve compartments was possible.
Method of Operation
The equipment worked on the heterodyne principle, and thus included two oscillatory circuits, one coil located in the search head, and the second in the main oscillator case. The two circuits operated in conjunction with the octode mixer valve and the mixed signal was fed via a transformer to the headphones.
The search coil circuit was provided with a variable condenser as external adjustments while the second oscillator could be coarsely tuned by means of a variable core in the inductance. The frequency of operation was 50 - 70 kcs, and adjustments were made so that a low note was heard in the headphones, following which, the movement of the coil into the vicinity of a mine or metal object caused a noticeable change of pitch.
It is to be noted that the valve filament circuit was completed through the headphones plug.
The equipment was provided already assembled, and it was only necessary to set the search coil at the required angle, adjust the carrying strap and plug the headphones into the jack on the oscillator case, for the equipment to be ready for use. The equipment in operation weighed some 15 lbs.
With the search head lifted clear of the ground and metal, the knob on the front of the oscillator case was turned until a note was heard, and adjustment was continued until no sound was audible; movement of the knob was continued in a counter-clockwise direction until a low pitched note was produced. The search coil was now lowered to within 2" of the ground and swung slowly from side to side keeping the clearance as constant as possible. The presence of large metallic objects was indicated by a distant rise in the pitch of the beat note.
The sensitivity of this detector was not as good as other heterodyne detectors. It satisfactorily indicated the presence of large metal objects but gave relatively poor indication of small pieces of metal.
There was a tendency to instability which necessitated constant readjustment of the tuning knob.
The following mines gave indications at the distance noted below, in determining these ranges the control was set to the high frequency side (counter-clockwise) of zero beat. The effect of normal ground was negligible.
Teller mine - 12 ins.
Riegel mine - 10 ins.
British Mk. V mine - 10 ins.
S-mine - 8 ins.
A200 Potmine - 5 1/2 ins.
Holz mine - nil
Schumine - nil
ZZ42 Igniter - 1/2 in.
Ferrous rock (pavé) - about 6 ins.
See attached for details
Colour attachment from IWM:
Catalogue number: FEQ 873
Display status IWM London
Materials: metal & wood
FULL NAME: Mine Detector, Wien 41
SIMPLE NAME: mine detector : German
Separate names with a comma.