4-2) Analog Circuit Devices Flashcards
What is a toggle switch?
A two position switch that toggle between open and closed. The toggle classes of switches have throws and poles.
What is a pole?
“Pole” indicates the number of circuits that one switch can control for one operation of the switch.
If one switch can control one circuit for one operation, it is a single-pole switch. If it can control two or three circuits for one operation, it is a double-pole or a triple-pole switch.
What is a throw?
“Throw” indicates the number of contact points.
What is a single pole multi-throw (SPMT) switch?
A type of switch that only allows one channel to be connected to the output at a time. These types of switches can have any number of channels available. Often can appear as a dial or rotary switch.
What is a momentary on switch? How is it configured? Where might you find one in an aircraft?
A switch that only makes electrical contact when pressed. The switch is spring loaded off so that when the button is released the circuit is open again. The Push To Talk (PTT) button on an audio panel is an example of this.
How is a double pole double throw constructed and what is its function?
DPDT is basically two SPDTs together on the same switch. It is a dual ON-ON kind of switch derived from the characteristics of SPDT. A DPDT switch usually has two (ON-ON) or three (ON-OFF-ON) positions.
The pair of SPDT switches operates together with four circuits with two independent circuit systems. The circuits can be switched on at the same time. In this situation, both appliances in the same circuits will be powered when the switch is on. Meanwhile, in a DPDT’s four circuits, only two circuits can be energized at the same time. The DPDT uses polarity reversal that allows it to handle two energized circuits at once.
The advantage of DPDT is that it can be used in different applications. With a DPDT switch, one can turn on an appliance and, at the same time turn off another appliance with only one flick.
What is the purpose of a relay or solenoid?
Relays/solenoids are used extensively for remote control and automatic switching.
What is a relay and what is it used for?
A relay is a device that uses a magnetic field to draw an armature to it. Relays can be small or very large. Most are used to switch circuits remotely from cockpit switches to functions in other parts of the aircraft.
What is a solenoid?
A solenoid is a device that uses a magnetic field to draw a plunger into it. Solenoids are more ruggedly constructed and therefore used for more heavy duty operations such as a starter.
What is the armature on a relay and how does it work?
The armature is the only moving part of a relay. On one end is the contacts and the other is a spring. The armature is either made of ferrous metal or has a ferrous metal plate attached. This is so that when the magnetic field is generated it is drawn to the coil.
What is a coil on a relay and how does it work?
The coil is an electromagnet. When DC voltage is applied, a magnetic field is created magnetizing the core that in turn attracts the armature. The voltage that operates the coil can (and often is) a different voltage type and amplitude than the voltage that runs through the contacts.
What is the core on a relay and what does it do? How does a relay core differ from a solenoid core?
The core is a contact surface applied to the top of the coil that is magnetized by the coil. The core has a matching surface to the armature. In a relay, the core does not move, in a solenoid, the core is moveable and is drawn to the coil.
What does the spring in a relay do and how does it work?
The spring is used to return the relay to its de-energized condition. This depends on whether the relay is a normally open or normally closed relay. The spring holds the armature away from the coil and core makes or breaks contacts. If the spring breaks, the relay will not open when the coil is de-energized.
What are relay contacts and what do they do?
The contacts are electrical points that conduct electricity when the relay is actuated. There will be at least two contacts–one that is attached to the yolk and a moveable set that is attached to the armature. Contacts needs to be matched to the required load. Using a relay not rated for the circuit load can damage the relay, burning the contacts.
What are the two circuits contained in a relay?
Primary and secondary
What does a relay’s primary consist of?
The primary circuit consists of the coil, a power supply for the coil, and a control or switch the activate the magnetic field of the coil. The armature pulls towards the coil that actuates the contacts.
What does a relay’s secondary consist of?
The secondary circuit is the contacts, armature and the load. Current will flow through the secondary as long as the coil’s magnetic field is energized. When the current is removed from the primary circuit, the spring will return the armature back to its normally open condition and current will stop in the secondary circuit.
Relay Troubleshooting
No power to the primary circuit
- Verify power to relay
- Verify the function of the switch
- Check continuity through the coil
Relay Troubleshooting
No power to the secondary circuit
- Verify power to the secondary
- Check if armature is broken
- Make sure contacts are clean and not broken
Relay Troubleshooting
Relay will not de-energize when power is removed from the primary circuit
- Make sure spring is not broken
- Ensure that core does not have too much residual magnetism
What does a solenoid do and what are its characteristics?
A solenoid is a type of relay that is designed to draw the core into a hollow coil. The characteristics of a solenoid are that it has a moveable plunger as part of the armature. It is generally rugged in design.
Can a solenoid primary and secondary share the same power supply?
Yes, they can. If the primary and secondary circuits use the same power supply, they may use different gauge wire if the working load requirements are different.
