Metalarm
™
Series 3500 Metal Detectors
19
INDICATOR LIGHTS
SET ZERO
When the Metalarm is operating and correctly set,
the green light of these three lights is the only one
illuminated. If a piece of metal passing across the
Sense coil is large enough it will cause the green light
to go out and the right hand red light to illuminate
while the metal is within the detect range of the
Sense coil.
DETECT
This red light illuminates whenever metal is within the
detect range of the Metalarm.
COIL FAULT
This red light illuminates if the sensor is either open
circuit, not connected or short circuited.
This light also causes the Detect light to illuminate to
prevent operation of the Metalarm until the coil fault
is rectified.
Normally, the Metalarm control unit should not require
any major re-adjustments after performing the
adjustments during installation. After switching the
control unit on, the green ‘Set Zero’ light should
illuminate immediately without the need to turn the
‘Set Zero’ control. Proper operation may be verified by
depressing the ‘Test’ button, which is mounted on the
electronic circuit board beneath the front panel.
Certain extremely large objects may produce an
overload signal causing the unit to indicate continuously
even after the object has passed clear of the sensor
coil. Depress the ‘Reset’ button to cancel the indication.
NOTE:
Although the control unit will adequately zero
out stationary masses of background metal, it will
respond to moving metal near the sensor coil. When
mounting the sensor coil, consideration should not be
limited to only large objects such as forklift trucks, but
should be extended to smaller objects such as
maintenance workers carrying metal tools and
equipment in the vicinity.
Although the metal detector system is suppressed
against both airborne and power supply interference,
some false alarms may nevertheless
occur occasionally.
Such triggering is usually due to transient effects,
which are both infrequent and unpredictable.
Metallic framework encircling the search coil can act
as a “shorted turn”. It may be necessary to insert
insulating sections to prevent comparatively small
masses of metal generating very large
background signals.
SENSITIVITY ADJUSTMENT
The ‘sensitivity’ controls permit adjustment of the
circuit gain for detecting or rejecting the desired size
of metal objects. Rotate the ‘sensitivity’ control
clockwise to increase the Metalarm sensitivity or
counter-clockwise to decrease the sensitivity.
A coarse sensitivity adjustment (VR2) may be
performed by means of the sensitivity adjustment
control on the control unit printed circuit board. (See
Figure 13.) Extreme care must be used in performing
the coarse sensitivity adjustment. Consult the factory
prior to making any coarse sensitivity adjustments.
Refer to page 22 for coarse sensitivity
adjustment details.
The sensitivity of the control unit may be reduced by
rotating the coarse sensitivity adjustment control
(VR2) in the clockwise direction. Rotate this control
one section at a time, checking each time to determine
whether the gain has been reduced sufficiently.
After each coarse sensitivity adjustment, it may be
necessary to re-zero the internal lights using the ‘Set
Zero’ control and depress the reset button on the
enclosure door.
SIGNAL LEVEL INDICATOR
This consists of a row of ten lamps, which light in
sequence from left to right, as the detected signal
level increases when metal approaches the sensor.
The Metalarm will produce an alarm when the signal
level reaches the right hand lamp marked T.P. (Trip
point) This lamp is permanently illuminated. Normally
none or perhaps the first 1 or 2 lamps may be
flickering ON and OFF.
CAUTION
Take particular care with the mains supply
connected, parts of the printed circuit board will
be carrying high voltages. Therefore DO NOT touch
anything other than the coarse sensitivity control.
