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Relays, Solenoids, Actuators

There are a group of electro-magnetic devices that operate in a similar manner to an electric motor, except that their moving parts do not rotate continuously; they have limited range of motion or travel.

Traditional electro-magnetic devices contain a wire-wound coil of insulated fine copper wire on a yoke, or core, of iron or steel. When electricity is passed through the wire windings, called the field coil, they generate a magnetic field, which is concentrated in the steel portion and amplified by it.

This force field can be made to do work. In a motor, the wire-wound iron core that rotates continuously around an axle or spindle within the field coil, is called the "armature". Rotation continues as long as the field coil is energized, that is, as long as electricity flows through the wires.

In a solenoid the core or armature is usually a solid steel rod, pointed at one end that makes a sliding fit in a thin plastic or cardboard tube, and travels a short distance to a stop, when energized. Some times are spring-loaded, and the rod compresses the coil spring around it when pulled into the coil. When the power is cut, the spring pushes outward and returns the rod to its original position, almost completely outside of the coil.

In some solenoids, the moving arm rotates through a partial circle, and then rotates back to the resting position when the power is cut, instead of producing the linear motion of most solenoids.

An actuator is a type of more powerful solenoid, often designed and capable of doing work in both directions (the forward stroke and the return stroke). Power in the field coil forces the arm to move. It usually has a longer travel distance-- or “throw” --than the rod in a solenoid. An example is the electronic door lock in a car door. Operating the switch on the door panel one way, causes the actuator to lock the door; operating the switch the other way, causes the actuator arm to unlock the lock’s latching mechanism in the door.

A relay is a type of magnetic switch. The field coil does not have a moving rod like the actuator and solenoid. It has a fixed iron or steel rod within the coil.

When the coil is energized, the magnetic force emerges from the end of the rod and pulls a spring-loaded, hinged steel plate down ward. This plate has an electrical switch contact on it with a wire running from it back to a second power source (although in some applications it may be powered from the same power supply that send s electricity to the field coil windings).

This moving contact is the “common” contact strip in the switch. It is pulled a very short distance (perhaps 1mm, or 1/16th of an inch), in one direction when the coil is energized. At the end of its travel, it touches a fixed contact with another wire attached to it. When the coils is de-energized (battery power runs down to the point where it can no longer produces sufficient magnetic force or pull to keep the common contact tightly against the fixed contact—or if it is completely cut) the common contact returns back to its original position, and touches against a second fixed contact with a third wire attached to it. Some relays have one movable contact and one fixed contact.

Some have two fixed contacts, and the relay is thus bi-directional in operation, operating two separate switches. Some relays have multiple or “ganged” contacts, all with wires attached to the. Thus one relay switch --through its multiple contacts --can control multiple devices to which it is wired.

Reed relays are a special type of relay where the switch portion is a glass-encapsulated double strip of steel (called a “reed”) with an air space between them. The capsule is surrounded by the field coil. Most reed relays are in the normally open contacts position. The small rectangular box or tubular housing contains the coil with the reed switch running through the center; it normally has either 4 wire contacts or leads--or 5 of them in bi-directional reed switch types.

These three magnetic devices are often used by bombers in circuitry designed as firing devices that may be radio controlled, as boobytraps designed to operate if coil power is cut, or as “battery decay” or “collapsing circuit” devices as battery power gradually drains away. They will also fire from a second power source through the switch contacts running to the detonator, if the battery powering the field coil is physically removed from the circuit. One cannot generally tell by looking at any of these three devices, particularly on x-ray, how they will function or what the energy strength within the field coil.

However, it is extremely important for a police or military bomb technician to understand the general function and be able to identify each of these devices on an x-ray image, surmise its function in a particular IED, and determine where the power is coming from to operate the field coil.

Securesearch, Inc. manufactures a number of training aids built around box relay switches, reed relay switches, solenoids and magnetic actuators. They are essential for training bomb technicians in the operation and hazards of these devices—particularly when field coil energy from battery power has become marginal—and subject to spontaneous detonation of the IED at the slightest touch or vibration.
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Relays, Solenoids, Actuators

INERT DOUBLE SWITCHING IED
Order Sku: ITA-136
Double-switching. Training module is equipped with four independent anti-lift switches wired through a relay and extremely sensitive. Relay acts as a battery decay arming switch.

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DOORBELL COLLAPSING CIRCUIT IED
Order Sku: ITA-137
Doorbell collapsing circuit IED. This bomb model is set up to dupe the bomb technician into cutting wires which appear to serve a normal function. In fact, these wires have been fiendishly set up to collapse the magnetic field of a relay coil, if cut. The logical wires to cut could be the doorbell switch, detonator, or power supply wires. Cutting any of these wires would in fact detonate the bomb. X-Ray examination of the bomb model is essential to reveal concealed relay, wiring, and other components not obvious to the casual observer.

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MAGNETIC SEARCH COIL BOOBYTRAP
Order Sku: ITA-139
Magnetic search coil boobytrap, using modified metal detector.

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DISPLAY BOARD WITH A VARIETY OF ELECTRONIC PRINTED CIRCUIT BOARDS
Order Sku: ITA-185-ECB-DB
Display board with a variety of electronic printed circuit boards attached. Each P.C. board has a sensor attached for initiation by such means as temperature charge, light level change, vibration, sound level change, etc. all are wired and armed separately from each other.
Each board’s relay or SCR terminates in a detonator and whistle common to the complete range of circuit boards. Common power supply.

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DOUBLE CROSSOVER BATTERY DECAY COLLAPSING CIRCUIT
Order Sku: ITA-19
Double crossover battery decay collapsing circuit. Two independent and cross-linked circuits.

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MAGNETO-ELECTRIC SWITCHES
Order Sku: ITA-619
Magneto-electric switches: relays, reed switch, solenoid, servo.

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SINGLE RELAY BATTERY DECAY COLLAPSING UNIT
Order Sku: ITA-79
Single relay battery decay collapsing unit, cut out of, or shorted, in circuitry. Designed to collapse the magnetic field and fire the detonator as the batteries run down or are cut out of shorted in circuitry.

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DOUBLE RELAY-INITIATED IED
Order Sku: ITA-80
Double Relay-initiated IED. This model demonstrates the same principles as ITA-79, except that all components used in ITA-79 are doubled in ITA-80. However, they are used independently of each other, not double-crossed over, as in ITA-19 or ITA-81. Thus, one circuit does not depend on the other through interconnection.

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DOUBLE-RELAY, DOUBLE CROSSOVER COLLAPSING DELAY (BATTERY-DECAY) IED
Order Sku: ITA-81
Double-relay, double crossover collapsing delay (battery-decay) IED, with 2 C-4 military demolition blocks. Similar in design to ITA-19. All components are doubled from those used in single relay units, and are crosswired, so that tampering with components in circuit one triggers detonator / relay assembly in circuit two (and vice-versa).

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REED SWITCH INITIATED, ANTI-WITHDRAWAL IED
Order Sku: ITA-82
Reed switch initiated, anti-withdrawal IED. Model demonstrates operation of a magnetic reed switch, as used in door and window contacts, in intrusion alarm systems. Reed switch operates relay coil circuit, and when withdrawn from magnetic field, it causes the relay coil magnetism to fail, initiating the electric detonator. Designed to instruct bomb technicians in recognition of all components before they decide on render-safe procedure (RSP).

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SOLENOID SWITCH ACTIVATED BATTERY DECAY/COLLAPSING CIRCUIT IED
Order Sku: ITA-83
Solenoid switch activated battery decay/collapsing circuit IED. This model functions on same principle as magnetic relay switch, using a device constructed to meet other electro-mechanical requirements. A solenoid has a metal shaft moving forward or backward. Solenoid is mounted on board and wired to operate on the principle of battery run-down reducing the strength of its magnetic coil.

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DOORBELL RELAY-(SOLENOID)-INITIATED IED
Order Sku: ITA-84
Doorbell relay-(solenoid)-initiated IED. In this device, the detonator is not fired by current from the doorbell push button, but indirectly from the bell ringer coil.

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