BCSO/SAR currently has 2 metal detectors:
Metal Detector Parts
Search Coil – contains a coil of wire (wrapped around the circular head at the end of the handle) known as the transmitter coil. When electricity flows through the coil, a magnetic field is created all around it.
Control Housing – contains electronics for display and audio as well as power supply
Metal Detector Basics
- Begin with the search head just above the ground. It shouldn’t touch the ground, but should be low enough for the signal to penetrate as deep as possible into the soil.
- Place the detector around two feet ahead.
- As you walk forward, slowly sweep the detector in a semi-circle. The detector should swing around a foot either side of you. Phrase to remember is “low and slow”
- Once you hear a beep from your detector, stop moving then switch from a wide swing to moving in small circles. This lets you determine where the object is with higher accuracy. You may also want to increase the detector’s sensitivity while you find the exact location
We are usually called to assist in cases involving crime scene items. With a metal detector the most common items assigned to look for a weapon or shell casings.
BCSO crime scene personnel will have most likely searched the central areas or “hot spots”. SAR is normally asked to search fringe/secondary areas of interest and should be worked usually applying a grid technique. Large areas are best broken down into sections in order to insure proper coverage.
Swing the searchcoil back and forth in front of you in a straight line with a sweep speed of about 3 to 5 feet per second while walking forward at a rate of about 1/2 to 1 foot per second. Maintain your searchcoil at a constant height of about 1 to 2 inches above the ground. When a target is detected it will be audibly and visually indicated by the detector.
Simply draw an imaginary “X” on the ground with the searchcoil where maximum sound occurs. You’ll notice that the searchcoil must be moving and that you cannot maintain detection sound with the searchcoil held completely still above the target.
CSI 250 – When you have detected a target, place the coil on the ground to the side of the target’s suspected location, then press and hold the Pinpoint pushbutton. Move the coil left and right, then front to back; the maximum sound will be heard when the target is directly beneath the center of the searchcoil. Also, when electronically pinpointing, the Upper Scale on the LCD Screen indicates signal strength. When the greatest number of LCD segments (increasing left to right on the scale) is shown, the center of the searchcoil is directly over the target with the depth of the target shown on the depth scale.
Discrimination (CSI 250)
When your CSI 250 is turned ON for the first time, it will begin operating in the ALL-METAL mode. This means that you will be searching using no discrimination adjustments. Many investigators may never require any discrimination adjustments. However, you can make adjustments by using the ELIM and DISCRIM pushbuttons for specific requirements.
Sensitivity (CSI 250)
The CSI 250 has 8 sensitivity settings for achieving maximum depth. However, you many not always be able to operate at full sensitivity. Electromagnetic interference, irregular ground mineralization and other environmental conditions may sometimes require that you operate at reduced detection sensitivity.
Additional Reference …
How a Search Coil Works:
Video on use of metal detector for evidence: