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Hand-Held Metal Locator

Ideal for finding steel frames and studs, steel bracing and nails in plaster walls, this Metal Locator can also show the length of the tang in knife handles, screwdrivers and other tools. As well, it can discriminate between ferrous and non-ferrous metals.

By John Clarke

Specifications

Detection range:...up to 25mm from the
underside of the case

Current drain: <20mA with LED fully lit

If you want to hang pictures, shelving or mirrors on a plaster wall in a steel-framed building it is useful to find where the metal studs are.

Click for larger image
Fig.1: the block diagram has the same functionality as the circuit below.

You may wish to secure your screws to the stud or alternatively, you may wish to avoid the stud and attach directly to the plaster wall using suitable fasteners. There are also other hidden items within the wall that should be located before drilling, such as metal bracing straps, screws and nails.

With the Metal Locator you can find the metal stud positions as well as any steel bracing, screw heads and nails. That is, provided the metal is no deeper than 25mm inside the wall. For small nails in wooden studs, the Metal Locator can detect them provided that the heads are within 10mm of the wall surface. Naturally, this device does not locate the timber studs themselves, nor can it find steel frames in walls that have a cladding thicker than 25mm (a very unusual wall, especially inside!). Nor can it detect power cables inside walls.

The Metal Locator can also distinguish between ferrous and non-ferrous metals. Ferrous metals include mild steel, stainless steel (both magnetic and non-magnetic), wrought iron, high tensile steel, galvanised iron, tin plated steel (steel cans or tinplate), passivated steels and cast iron. Non-ferrous metals include copper, brass, zinc, aluminium, gold, silver, lead and tin.

In the presence of ferrous metals, the LED on the Metal Locator dims. Conversely, the LED brightens in the presence of non-ferrous metal. For ferrous metals, the sensitivity knob is adjusted so that the LED is reasonably bright in the absence of the metal. The LED then dims in the presence of ferrous metal. To detect non-ferrous metals, the sensitivity is adjusted so that the LED is dim in the absence of the metal. The LED will then brighten in the presence of the non-ferrous metal. Greater sensitivity can be had with the LED just glowing in the absence of metal for detection of either metal type.

The Metal Locator is housed in a compact plastic case that includes a 9V battery compartment. On the lid are the on/off switch, sensitivity control and the indicating LED.

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