Eriez METALARM 3500 series Manual

Metalarm™Series 3500 Metal Detectors
Installation, Operation
and Maintenance
Instructions
ERIEZ MAGNETICS HEADQUARTERS: 2200 ASBURY ROAD, ERIE, PA 16506–1402 U.S.A.
WORLD AUTHORITY IN SEPARATION TECHNOLOGIES
MM-246A
METALARM™
SERIES 3500
METAL
DETECTORS

2
Introduction
Careful attention to the following requirements will assure the most
efficient and dependable performance of this equipment.
If there are any questions or comments about the manual, please call
Eriez at 814/835-6000 for metal detection assistance.
©2011 ERIEZ MAGNETICS ALL RIGHTS RESERVED
CAUTION
Safety labels must be affixed to this product. Should
the safety label(s) be damaged, dislodged or removed,
contact Eriez for replacement.
CAUTION
Metal Detectors emit electromagnetic fields. Contact
the American Conference of Governmental Industrial
Hygienists, Cincinnati, Ohio, U.S.A. (www.acgih.org)
for additional information.
CAUTION
If you use a medical implant or similar device, you
must never approach the equipment because your
device may malfunction in the electromagnetic field,
with consequences up to and including death.

Metalarm™Series 3500 Metal Detectors
3
Table of Contents
METALARM™3500 AND 3500CE METAL DETECTOR SYSTEM
DESCRIPTION........................................................5
INSTALLATION .......................................................6
Control Unit Mounting.........................................6
Search coil Mounting..........................................6
Flat Coil (Model TR) ...........................................6
Idler Conveyors (Models TR & BR)
TR10 Tpe Search Coil .......................................7
Idler Conveyors
Bridge Coil (Model BR).......................................8
Vibrator or Belt Conveyors (Model VC)
Vibratory Trough Coil (Model VC) ....................10
Plate Coil (Model PL) .......................................11
Installation Recommendations .........................11
for Connecting RFI Filters to
High Frequency Inverters
Bag Dropper.....................................................12
ELECTRICAL CONNECTIONS.............................14
Power Supply ..................................................14
Control Relay Contacts ...................................15
Fuse .................................................................15
Sensor Coil Connections .................................15
OPERATING INSTRUCTIONS............................. 18
Indicator Lights ............................................... 19
Sensitivity Adjustment .................................... 19
Signal Level Indicator ..................................... 19
REPAIRS AND ADJUSTMENTS ..................... 20
Electronic Board Mounted Switches................ 20
Wiring to the Conveyor Motor Starter.............. 21
Auxiliary Relay ............................................... 22
Auxiliary Relay Wiring ..................................... 23
TROUBLESHOOTING ......................................... 23
Suggestions for Troubleshooting
Environmental Interference............................. 23
Movement of Metal ......................................... 23
Intermittent Loops of metal
surrounding the Sensor................................... 24
Excessive line voltage fluctuations ................. 24
Proximity of severe
RF radiation sources....................................... 25
PARTS LIST ......................................................... 26

4
Important Information
From Eriez
This information is provided to assemblers and
electricians due to the importance of proper methods
for wiring of controls. These methods are revised
and updated from time to time as Eriez perceives
necessary. This information covers distances from
various categories of cables and Eriez Metal Detector
wiring standards. The cable categories are:
1. AC Power cables
2. DC Distribution (thermocouple, power supplies)
3. Signal and Logic
3a. Analog (low level)
3b. Digital logic
Category 1 cables are to be routed along frame
members and panels. Avoid open space hanging.
Category 2 cables are routed as 1 but separate from 1.
Category 3 cables are routed separately from 1 and 2.
Category 3b are to be spaced 2.5 cm (1") from
Category 1 for each meter of run.
Category 3a cables are to be spaced 25 cm (10") from
category 1 for each meter of run.
Use separate machine entry holes for categories 1, 2
and 3 cables.
When Eriez Metal Detectors are being installed in
plants using VFC drives, the following precautions
are recommended:
1. Route VFC wiring and Eriez Metal Detector wiring
into separate metallic conduits.
2. Separate power sources should be used for VFC
drives and Eriez Metal Detectors.
3. The use of a Harmonic Neutralized Constant
Voltage Transformer for the Eriez Metal Detector
power is recommended. Use separate conduits
for in and out wiring.
4. Twist AC common circuit run wires together to
minimize electromagnetic field interference.
5. Follow cable category separations as
detailed above.

Metalarm™Series 3500 Metal Detectors
5
The Metalarm™3500 and 3500-CE Metal Detector
consists of a control unit, one or more sensor coils
dependent upon the application, and optional
accessories such as the sack dropper.
Description
FIGURE 1
Control unit dimensions

6
CONTROL UNIT MOUNTING
The Metalarm 3500 control unit is supplied with four
mounting brackets for wall mounting. The dimensions
are shown in Figure 1.
Ideally the control unit should be mounted within 10-15'
(3-5 m) of the sensor coil unit and no more than
66' (20 m).
The control unit must be mounted in a location with
low amounts of vibration, if the area exhibits a high
level of vibration, independent mounting of the control
enclosure must be implemented. Shock mounts for the
control enclosure may be another consideration, based
on the severity of the installation.
The Metalarm 3500 control unit will normally be
mounted by means of four 5/16 inch or M8 bolts
utilizing the four mounting holes.
Adequate clearance must be allowed below the control
unit enclosure to allow for cable entry and exit.
NOTE: Do not replace the HDPE mounting bars, as
these are provided to electrically isolate the control
unit from the metal conveyor framework. Similarly no
metal work should be in contact with the metal control
unit case after mounting on the conveyor.
Failure to comply with the above mounting procedures
will invalidate the ‘CE’ certificate covering the
EMC regulations.
SEARCH COIL MOUNTING
The following instructions give details of how to install
the various types of standard search coils supplied as
part of the Metalarm Metal Detector.
The search coil should be assembled using the
instructions supplied with the search coil.
UNDERBELT COIL (MODEL TR) ‑
IDLER CONVEYORS
Locate a suitable position in the conveyor mid way
between two idlers where:
• There will not be a return idler or cross piece
beneath the search coil.
• There is not a joint in the conveyor frame.
Installation • Metal, when detected, can easily be removed from
the conveyor belt.
• There is no moving metal in the vicinity.
• Any metal base plate present can be removed or
replaced by non-metallic material.
• Any metal covers over the belt can be removed or
replaced by non-metallic material.
Place the search coil on the conveyor frame at the
chosen position. There should be at least a 1' (25mm)
gap between the underside of the conveyor belt and
the top of the search coil. If not cut out notches in the
bottom of the search coil at all four corners so as to
lower the search coil within the conveyor frame.
User supplied stainless steel “L” brackets are
suggested for securing the search coil assembly to the
conveyor. Brackets should be fitted to the coil, in the
area marked for such purposes, as shown on the coil
assembly drawing. (See Figure 2)
The search coil should then be bolted to the conveyor
frame with the coil electrical connection on the
opposite side of the conveyor frame to any heavy-duty
cables or wiring.
A recommended idler spacing of 48"- 60" should apply
to the infeed and outfeed idlers adjacent to the search
coil. An idler isolation kit is recommended and may
be purchased from the factory. The idler isolation kit
provides suitable materials to electrically insulate the
idlers from the conveyor frame. Insulating the idlers
directly adjacent to each side of the search coil will help
to alleviate any possible false tripping. Electrical loops
can be created from the metal detectors field in relation
to the surrounding metal. The idlers on each side of
the search coil should be checked to see that all nuts
and bolts have been securely tightened.
The cable connecting the search coil to the control
unit should then be attached to the connector on the
underside of the search coil and to the control unit. The
cable should be secured and protected from damage.

Metalarm™Series 3500 Metal Detectors
7
The search coil coax cable must not cross directly
under the search coil, as this may cause false tripping
to occur. The cable should be replaced should any
nicks in its outer cover occur.
If standard metal conduit must be used to protect the
search coil, separate conduits must be used for each
cable; receiver and transmitter. If a clip detector is
required, the cable may be run in the same conduit as
the receiver or transmitter coil.
TR10 TYPE SEARCH COIL ‑ IDLER CONVEYORS
Locate a suitable position in the conveyor mid way
between two idler sets where:
• There will not be a return idler or cross piece
beneath the search coil.
• There is not a joint in the conveyor frame.
• Metal when detected can easily be removed from
the conveyor belt.
• There is no moving metal in the vicinity.
• Any metal base plate present can be removed or
replaced by non metallic material.
• Any metal overbelt covers can be removed
or replaced.
Place the search coil on the conveyor frame at the
chosen position. There should be at least a 1" (25mm)
gap between the underneath of the conveyor belt and
the top of the search coil. If not cut out notches in the
bottom of the search coil at all four corners so as to
lower the search coil within the conveyor frame.
FIGURE 2
Coil assembly

8
Installation (cont.) BRIDGE TYPE (MODEL BR) SEARCH COIL ‑
IDLER CONVEYORS
Locate a suitable position in the conveyor mid way
between two idler sets where:
• There will not be a return idler or cross piece
beneath the search coil.
• There is not a joint in the conveyor frame
• Metal, when detected, can easily be removed from
the conveyor belt
• There is no moving metal in the vicinity
• Any metal base plate present can be removed or
replaced by non-metallic material.
• Any metal overbelt covers can be removed or
replaced by non metallic material
Place the search coil on the conveyor frame at the
chosen position. There should be at least a 1" (25mm)
gap between the underside of the conveyor belt and
the top of the search coil. If not cut out notches in the
bottom of the search coil at all four corners so as to
lower the search coil within the conveyor frame.
FIGURE 3
Brackets (not supplied) to hold the search coil to the
conveyor frame should be fitted to the coil on the side
supports shown in Figure 3.
The search coil should then be bolted to the
conveyor frame.
Fit top search coil section and bolt down.
The pair of idlers adjacent to either side of the search
coil should be checked to see that all nuts and bolts
have been tightened down firmly. Preferably the idler
frames should also be spot welded once at each of the
four corners to the conveyor frame.
This type of coil configuration is designed for transmit/
receive mode operation only and both coils are
connected directly to the control unit. See Electrical
Connection: Sensor Coil Connections and Figure 3.
Remember to make sure the cables are tied to the
conveyor frame to prevent them from being damaged.

Metalarm™Series 3500 Metal Detectors
9
FIGURE 4
User supplied stainless steel “L” brackets are
suggested for securing the search coil assembly to
the conveyor. Brackets should be fitted to the coil. The
area for this purpose is shown on the coil assembly
drawing. (See Figure 4)
The search coil should then be bolted to the conveyor
frame so that the coil socket is on the opposite side of
the conveyor frame from any heavy-duty cables
or wiring.
Fit the top search coil section and bolt it in place.
A recommended idler spacing of 48"- 60" should apply
to the infeed and outfeed idlers adjacent to the search
coil. An idler isolation kit is recommended and may
be purchased from the factory. The idler isolation kit
provides suitable materials to electrically insulate the
idlers from the conveyor frame. Insulating the idlers
directly adjacent to each side of the search coil will help
to alleviate any possible false tripping. Electrical loops
can be created from the metal detectors field in relation
to the surrounding metal. The idlers, either side of the
search coil, should be checked to see that all nuts and
bolts are tight.
In the case of series connection, connect the lower
coil using the short length of cable provided to the
unmarked socket on the top coil. The cable to connect
the search coil to the control unit should be connected
to the socket marked ‘CU’ on the top search coil. In
the case of transmit/receive mode operation, both coils
are connected directly to the control unit.
In both cases make sure the cables are secured to the
conveyor frame and protected to prevent them
being damaged.
The search coil coax cable must not cross directly
under the search coil, as this may cause false tripping
to occur. The cable should be replaced should any
nicks in its outer cover occur.
If standard metal conduit must be used be used to
protect the coil cable(s), separate conduits must be
used for each cable; receiver and transmitter. If a clip
detector is required, the cable may be run in the same
conduit as the receiver or transmitter coil.

10
MODEL VC “U” SECTION BELT CONVEYORS OR
VIBRATOR CONVEYORS ‑ SEARCH COILS
Locate a suitable position in the conveyor where there
is going to be no metal within approximately 20"
(500mm) of the underside of the search coil when it
is mounted onto the conveyor. There should be no
moving metal in close proximity to the search coil.
In the case of vibratory conveyor the coil is usually
located midway between two of the vertical supports.
Cross braces under the search coil should be cut and
moved. To install a trough coil, it is necessary to cut
out a length of the base and part of the side walls of
the conveyor. (See Figure 5).
The exact dimensions of the required cut out will be
shown on the search coil assembly drawings supplied
with the search coil.
Draw a line 1" (25mm) from the edge of the cut out.
Along this line drill 5/16" dia (M8) holes at 4" (100mm)
spacing or longer depending upon the weight and
width of the search coil. Countersink the holes from
the inside of the conveyor.
Locate the search coil into the cut out and clamp it in
position. Using the holes in the conveyor as a guide,
drill through side and base of the search coil.
Bolt the search coil into position using countersunk
5/16" (M8) bolts x 1-1/2" (40mm) long and shakeproof
lock washers.
The cable from the search coil to the control unit
should be connected into the underside of the search
coil. The cable should be secured and protected
from damage.
The search coil coax cable must not cross directly
under the search coil, as this may cause false tripping
to occur. The cable should be replaced should any
nicks in its outer cover occur.
If standard metal conduit must be used to protect the
coil cable(s), separate conduits must be used for each
cable; receiver and transmitter. If a clip detector is
required, the cable may be run in the same conduit as
the receiver or transmitter
Installation (cont.)
FIGURE 5

Metalarm™Series 3500 Metal Detectors
11
MODEL PL PLATE COIL
Plate coils can either be mounted under a previously
prepared metal free section such as wood or fiberglass
or if the plate coil is a SF or SFC type item directly
mounted onto the base of a metal-sided conveyor.
In the latter case if the base of the conveyor is metal,
a section of it must be removed for the length of the
coil plus 1/8" (3mm). The search coil can be drilled into
or through in any of the crossed areas shown on the
drawing supplied with the search coil.
The PL search coil should be mounted such that the
conveyor belt passes above the plain surface of the
coil with the resin side facing down.
INSTALLATION RECOMMENDATIONS FOR
CONNECTING RFI FILTERS TO HIGH FREQUENCY
INVERTER DRIVES
Because of the complex circuit design used in these
filters a Ground Leakage Current of 8 to 80MA may
be observed. It is possible that nuisance tripping of
extremely sensitive type of ground fault circuit breaker
may occur so this figure should be considered when
choosing such a device. It is important to provide
well-defined paths for the high frequency currents
involved. The best results are achieved when both
filter and inverter are mounted securely on the same
conducting, grounded backplate and not on rails etc.
FIGURE 6

12
SUPPLY CABLE
The supply cable should be a stranded conductor
and not a solid conductor type to achieve proper
connection inside the terminal block. Cable lengths
inside the wiring cabinet should be kept to a minimum
i.e. cable entry to filter and filter to inverter. This will
reduce the effect of radiated emissions back into the
input cables. (See Figure 7).
MOTOR CABLE
Since the cable between the inverter and motor is a
major source of radiated and conducted interference,
it should be a shielded type and as short as possible
with the shield and safety ground wire connected
directly to the bonded ground post at one end and to
the motor ground at the other. Never connect only one
end of the shield to ground, as this can be detrimental.
(Pig tail effect). It is strongly recommended that the
conducting cores (not the ground or shield) are
threaded through, or, if possible, wound around an
output cable filter choke as shown. (See Figure 8).
GROUNDING
The point here is to clearly define the paths through
which high frequency earth currents flow, and thereby
minimize their harmful effect on other nearby,
sensitive devices.
All grounding leads, including the filter ground, inverter
ground and shielded cable grounds, should be as
short as possible and securely fastened to the bonded
backboard ground post. Poor connections and loops
of cable will act as aerials and pick up stray
radiated emissions.
SEPARATION
Keep the separation of the input and output cables
as great as possible to prevent feedback. Input and
motor output cables should never be run together in
the same trunk or conduit. (See Figure 9).
CONTROL CABLES
The control cables to the inverter or any other
equipment in the vicinity are obviously highly
susceptible to radiated emissions in the same way
and should never be run with the motor output cables.
MULTIPLE INVERTERS
Where more than one inverter is used, for effective
suppression, it is preferable that a separate filter
should be used for each inverter. (See Figure 10).
BAG DROPPER INTRODUCTION
The bag dropper is used to indicate the location of
tramp metal on the conveyor after the belt has stopped.
The bag dropper consists of a bag dropper control unit
and a bag.
Installation (cont.)
FIGURE 7
FIGURE 8

Metalarm™Series 3500 Metal Detectors
13
INSTALLATION
A frame should be constructed over the top of the
conveyor to mount the bag dropper control unit. If the
frame is constructed of metal, it must not be in the
search field of the sensor coil, so a distance of at least
5' (1.5 meters) down line from the sensor
is recommended.
Remove the bag dropper control unit by removing the
4 screws located in each of the four corners of the
top cover. Mount the control unit to the frame over the
conveyor by bolting through the existing holes. The
fixing centers are marked on the back. Make sure
the entry release hole and cable outlets are
directed downwards.
CONNECTION
The 3-wire power supply cable can be connected to
the Metalarm power supply at terminal block TB 1 on
the Metalarm circuit board.
The blue wire of the 2-wire cable is used to trigger the
bag dropper and it is connected through the Metalarm
relay contacts. The red wire is used to disable the
Metalarm and connects to terminal 3 on TB3.
Also a jumper on the QM2 is required from TB2-12 to
TB3-1. Refer also to the drawing on the following page.
ADJUSTMENT
Switch the power on to both the bag dropper and the
Metal Detector. It should not be possible to start the
conveyor. If the conveyor can start refer to section
entitled IMPORTANT NOTE on the next page.
Push the bag stem all the way into the aperture on the
underside of the control unit and press reset on the
Metalarm. The conveyor should now be able to run.
In the bag dropper, check that the green LED (D1 ) is
on and that the amber LED (D3) and the red LED (D2)
light up when metal is detected.
D3 (amber) shows the delay from detection to the drop.
This must be set up so that an object detected at the
search coil will be under the ‘bag dropper’ when the
bag drops (indicated by the red LED D2). Adjustment
is made by rotating RV2 (coarse) and RV1 (fine).
RV3 is for the adjustment of the solenoid ‘on time’ and
should not need any adjustment.
When satisfied that the operation of the bag dropper is
correct the lid of the control unit needs to be replaced
and tightly sealed against moisture.
FIGURE 9
FIGURE 10
Wire Dropper QM2
Red O/P TB3-3
Blue I/P TB2-11
Screen OV TB3-1

14
IMPORTANT NOTE
The bag dropper is set to run in Fail-Safe Mode and
therefore will prevent the operation of the Metalarm
when the bag is not present. This is indicated by the
“Detect” light being illuminated.
It is vital that the conveyor is wired to stop when metal
is detected, otherwise the bag stem may enter the
equipment being protected. Although aluminum alloy
has been used in its construction, it would still mean
replacement of a relatively expensive part.
For any further information, please do not hesitate to
contact ERIEZ customer service.
Installation (cont.) Electrical
Connections
The standard electrical connections are for power
supply connections and for sensor coil connections.
Other cables may be added as necessary for control
and monitoring functions.
Please note where armored cables are being used,
the armor must be cut back at the gland plate of the
control unit so that it does not touch the Metal Detector
Control Unit. The control unit must be
electrically isolated.
POWER SUPPLY
The mains connection is made via the green terminal
block (TB1) using ‘E’ for earth/ground connection,
either of the ‘L’ terminals for live positive connection
and either of the ‘N’ terminals for live
negative connection.
The spare ‘L’, ‘N’ and ‘E’ terminals can be used for
driving external controls or the bag dropper accessory.
FIGURE 11

Metalarm™Series 3500 Metal Detectors
15
FIGURE 12
The Voltage Selector Switch should be set to 240V
AC or 120V ac as required. This is located just above
the green terminal block (TB1).
CONTROL RELAY CONTACTS
Connection to the output contacts of the control relay
is made to terminal block (TB2) as indicated in Figure
11. Four sets of DPDT relay contacts are provided.
The contacts are rated for 5 amps resistive, for either
low voltage DC application or for a maximum of 250V
AC application.
Terminals 11 and 12 are used for a ‘fault’ indication.
FUSE
Note there is only one fuse on this Control Unit. It is
located on the front panel and is rated at 0.5A.
SENSOR COIL CONNECTIONS
The sensor coil connections are made to the right
hand 4 position terminal block (TB4). The inner
conductor is connected to terminals 2 or 4. The outer
shielding (ground) is connected to terminals 1 or 3 for
all coils respectively.
SINGLE SEARCH COIL (SEE FIGURE 12)
For all single search coils (i.e. a TR or PL), the unit is
connected to TB4, terminal 3 (for the ground/shield)
and terminal 4 (for the center conductor).

16
Electrical
Connections (cont.)
BRIDGE (APERTURE) TYPE SEARCH COIL
IN SERIES CONFIGURATION (SEE FIGURE 13)
A Bridge type search coil will be supplied in a series
configuration for optimum sensitivity. The top and
bottom search coils will be connected together by
means of a 20" (.5 meter) or 40" (1 meter)
interconnecting cable.
FIGURE 13
There will then be one main cable,which connects the
search coil to the control unit. The cable is connected
to TB 4 terminal 3 (for the ground/shield) and terminal
4 (for the center conductor).

Metalarm™Series 3500 Metal Detectors
17
FIGURE 14
BRIDGE (APERTURE) TYPE SEARCH COIL
IN TRANSMIT/RECEIVE CONFIGURATION
(SEE FIGURE 14)
NOTE: When operating in a transmit/receive
configuration, Switch 4 should be moved to position 2.
A Bridge type search coil will be supplied in a
transmit/receive (TX/RX) configuration when either
a conductive material is being conveyed or when a
certain size piece of metal is to be detected and all
smaller pieces being ignored.
When in the TX/RX configuration, both the top and
bottom search coils are independently connected to
the control unit. The lower coil, which is the transmitter,
will be connected to TB4 terminal 3 (for the ground/
shield) and terminal 4 (for the center conductor). The
top coil, which is the receiver, will be connected to
TB4 terminal 1 (for the ground/shield) and terminal 2
(for the center conductor).

18
Operating
Instructions
FIGURE 15
Switch on the line power and the ‘ON’ lamp on the
case door illuminates. (See Figure 15).
The red ‘FAULT’ light will be on if the sensor coil is not
connected. When the sensor is properly connected
the light will extinguish.
NOTE: The illuminated fault light will also cause the
‘Detect’ lamp to be on.
Rotate the SET ZERO control fully clockwise. If the
right hand light illuminates, rotate the Set Zero control
counter-clockwise until this light extinguishes and the
green light illuminates.
This adjustment compensates for or “zeros out” any
near by metal in the sensor coil detection area. If this
light cannot be illuminated there may be too much
metal near the sensor coil. This can be confirmed by
positioning the sensor coil away from all surrounding
metal and repeating the test.
After these adjustments, the ‘Detect’ light and the
‘Reset’ light on the detector door may be illuminated.
Pressing the ‘Reset’ lamp button will extinguish
both lights.
The relay function is controlled by the ‘Relay’ control
switch. In the OFF position only the ‘Detect light and
door ‘Reset’ lamp operate when metal is present in
the sensing area.
In the ON position, the 4 pole DPDT relay, the ‘Detect’
light and the door ‘Reset’ light operate when metal is
present in the sensing area.
In the LATCH position, the relay and above indicators
operate but after the metal is removed, the relay and
the indicators remain on until either the door ‘Reset’
button is pressed or the ‘Relay’ control switch is
turned to the ON or OFF position.
The ‘Gain’ control is a sensitivity adjustment control to
adjust for the detection of the desired size of metal or
to allow for smaller pieces of metal to be ignored.

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.

20
If the Metalarm is suffering from ‘false alarms’ fairly
regularly, this indicator should be examined. It may
show more than the first one or two indicators
flickering indicating the presence of some interference
which is either mains or air-borne. Rotating VR7
clockwise may reduce the effects of this. The signal
level should now move to the left until only 1 or 2
indicators are on. Care should be taken to not rotate
this control further than necessary, since it reduces
the sensitivity of the unit. Refer to page 21 for further
adjustment details.
FIGURE 16
ELECTRONIC BOARD ‑ MOUNTED SWITCHES
For the position of the switches, which control
additional optional features, refer to Figure 16.
Repairs &
Adjustments
Note: Consult Eriez metal detector technical help
before adjusting any of the following settings. Before
changing any of the following adjustments, mark the
original position with a marker, where applicable.
SW1 ‑ Selection of voltage - 110V or 230V 50Hz
or 60Hz.
SW2 Brown ‑ Fail Safe Operation - With the switch
down the ‘Detect’ relay is immediately energized
when power is connected to the control unit rather
than when metal is detected. When metal is detected
or if the power to the unit fails the ‘Detect’ relay drops
out, creating a fail safe mode.
SW4 ‑ This separates the TX and RX coil connections
when switched ‘on’ and is used when separate
search coils are used for transmitting and receiving,
such as to create an even search field or where
magnetic ore is being processed.
SW5 ‑ Test button.