(7, 8) Magnetic Devices + ___

How does a solenoid actuator work?

Magnetic armature/plunger/slug against spring pressure, when coil energised plunger lifts then drops to original position when de-energised

What is the duty cycle of a solenoid and what happens when exceeded?

Ratio of on-time to off-time. Exceeding this may overheat or shorten life of solenoid

What causes noisy solenoid actuator, what can happen if left untreated?

Reduced voltage or dirt on armature, can reduce solenoid life

Difference between solenoid valve and solenoid actuator? What substances do solenoid valves control?

Valve directly controls liquid/gas flow, actuator produces motion to actuate valve

7.1.5

do when i get home

What is 3/2 way solenoid?

Solenoid has 2 positions, and 2 inlets with 1 outlet. Works like SPDT switch

How do relays differ from solenoids?

Relays move electrical contacts, solenoids move actuator or valve

7.2.2

DO AT HOME

Why is dropout voltage of relay/contactor always lower than pickup?

Air gap before pick-up, higher voltage required to overcome reluctance. Drop-out has no air gap, lower voltage required.

What is a “no volt” relay?

De-energises when voltage lost. Protects various electrical machines by disabling start-up or closure of contacts

Main difference between relay and contactor?

Contactor is heavy-duty relay

How does Hall Effect Sensor work?

Fixed DC current put into Hall Effect Sensor, electrons shift to one side of element when magnetic field applied. Creates Hall Voltage within device proportional to strength of magnetic field

Difference between two common sensing configs for Hall Effect Sensors?

Head On Detection: Detects magnetic field directly in front of sensor moving towards it

Sideways Detection: Detects magnetic field passing from one side of sensor to other

What are the advantages n disadvantages of Hall Effect Sensors when used as proximity sensors?

High reliability and fast response time, but object being sensed must produce magnetic field

What is Magnetostriction effect?

When materials change shape when subjected to magnetic field on microscopic level. Used in anti-shoplifting devices, is also the noise made by transformers

How does Hearing Loop System work?

Electromagnetic induction, audio system supplies current to loop producing magnetic field. Field detected by listener’s coil, converted to audio signal

How does vehicle detection work? (lights above spots, traffic detection etc.)

Induction loops placed under road pavement, when vehicle stops above inductance of loop is changed (vehicle becomes iron core)