metal pipe detector

Water and gas pipes, as well as elec- trical conduit, embedded in walls are not easy to trace, although this is essential when work is to be carried out to the wall. This handy little unit will be a godsend at such times. The principle of the detector is based on the property of metals of absorbing magnetic energy when they are brought into a magnetic field. Transistor T1in figure 1 is a simple LC oscillator, of which the sensor, L1, forms a part. The oscillator frequency is around 15 kHz. When energy is withdrawn from the magnetic field around L1by a metal object, the alter- nating voltage across the LC circuit will diminish. By rectifying that voltage in IC,, and applying the resul- tant direct voltage to a differential amplifier, IC2, which compares it with a voltage preset with P3, an on/off indication is obtained. When L1is brought in the vicinity of metal, D4 goes out. The sensitivity of the detec- tor is set with P1and P3. The unit is powered by a 9 V battery ( P P3). To ca...