Ch11 Circuit Control Devices

Toggle switches

Manual-type switch featuring the use an angled lever having an internal spring-loaded mechanism to rapidly switch into its latched or closed position.

Rotary switches

Manual-type switch rotated to select an output. Wiper speed and blower motor speed are common examples.

Magnetic reed switch

Automatic type switch with contacts opened or closed by magnetic fields.

Pressure-sensitive switches

Automatic-type switches that are activate by gas or liquid pressure.

Smart switches

Automatic-type switches with self-diagnostic capabilities. These switches usually have at least a resister connected in parallel with switch contacts.

Fixed-type resistors are

Designed to conduct either heavy or light amounts of current.

Stepped resistors are

Made from two or more wire-wound resistors.

Resistors in commercial vehicles are typically

Fixed, stepped or variable.

Magnetic switch

A mangnetic relay-type switch designed to handle higher current flow than smaller ISO relays.

Smart switches can function

As digital inputs to electronic control systems.

It is important to check the linkage adjustment of a solenoid with

A solenoid with a pull-in and hold-in winding during service to ensure it doesn't drop out and to prevent premature burning out of pull-in windings.

Multiplex switch

A switch arrangement using two or more switches that can share a single wire for a switch pole and throw circuit, but transmit unique circuit control information from each wire.

Positive temperature coefficient (PTC) thermistor

A thermistor in which resistance increases as the temperature increases.

Potentiometer

A variable resistor with three connections - one at each end of a resistive path, and a third sliding contact that moves long the resistive pathway.

An intermittent-duty relay quickly burns out when it is used in a continuous-duty application. A continuous-duty relay

Chatters when used in place of an intermittent-duty relay.

Switches are the simplest circuit control device. Opening and closing switches ...

Completes or Breaks a circuit's electrical pathway.

A typical relay has a

Control circuit and a load circuit.

Solenoids are devices with a movable core that converts

Current flow into mechanical movement.

Relays use a small amount of current to switch a larger amount of current. As such, they

Eliminate voltage drop caused by long lengths of wire and eliminate the use of heavy conductors inside the cab.

Magnetic switches are available as

Intermittent-dusty or continuous-duty relays. The two types of mag-switches are not interchangeable.

ISO relays have standardized terminal

Location, numbering, and dimensions.

Momentary contract switches

Manual-type switch that may be toggled or pushed, but does not latch into position. Horn contact or starter button are examples of momentary contact switches.

Common variable resistors used as circuit control devices include

Rheostats and potentiometers.

Solenoids can be either pull-type or push-and-pull type. In pull-type solenoids, an electromagnet pulls a

Soft iron core into the coil. Push-pull-type solenoids use a permanent magnet, instead of an iron core, to produce bidirectional movement.

Magnetic switches are in function to relays, except that they

Switch even larger amounts of current and have different dimensions from relays.

Solid-state relays a perform the same function as electromagnetic relays, but can

Switch without noise and use less control circuit current.

Proximity switches

Switches designed to sense the approach of metal components.

Simple switches are categorized by

The number of input and output terminals they have and by their operation.

ISO mini and micro are

The two most Common types of relays used by commercial vehicles.

Electric circuits use control devices to

direct the flow of current. Controls can be electrical switches, resistors, or electromagnetic relays.