6.4 Switches in Electrically Controlled Systems

Compare and contrast switches and sensors/transducers.

Discuss observed properties of closed and open switches with respect to resistance and current.

Define the terms pole and throw.

Draw the schematic symbol for the following switches: SPST, SPDT, SPTT-CO, DPST, DPDT, 3PST

Define the term electrical isolation.

Define the term actuation and differentiate between manually and mechanically/automatically actuated switches.

Define making and breaking.

Differentiate between the deactivated state and activated state of a switch.

Identify in which state switches are illustrated in schematics.

Differentiate between the deenergized state and energized state of a load.

Differentiate between NC and NO switches in their deactivated and activated states. Identify resistance and current carrying ability in both states.

Describe advantages of a double break switch over a single break switch.

Define a mechanical interlock.

Differentiate between momentary and maintained contact switches.

Draw the schematic symbol for a maintained contact ESTOP button.

Draw the schematic symbol for a momentary contact break-make pushbutton package consisting of a mechanically interlocked set of NC and NO contacts.

Identify the purpose of an auxiliary contact block.

Draw the schematic symbol for a maintained contact 3 position selector switch with two associated contacts A and B. Assume contact A is closed in position 1, both contacts are open in position 2, contact B is closed in position 3. Draw the target table/contact chart illustrating this functionality.

Draw the schematic symbol for a drum or cam switch used to reverse the rotational direction of an industrial 3 phase AC motor. Draw the target table/contact chart illustrating this functionality.

Draw the ladder logic representation of a limit switch consisting of a mechanically interlocked pair of NC and NO contacts. Draw the hydraulic schematic representation of a limit switch.

Describe the concept of switches being held in their activated state using both the gravity and arrow convention. Draw examples of each. Identify the preferred method.

Draw the schematic symbol for a temperature switch consisting of a mechanically interlocked pair of NC and NO contacts.

Draw the ladder logic representation of a pressure switch consisting of a mechanically interlocked pair of NC and NO contacts. Draw the hydraulic schematic representation of a pressure switch.

Differentiate between the set and reset value of a pressure switch. Identify why this is a desirable trait.

Draw the ladder logic representation of a float switch consisting of a mechanically interlocked pair of NC and NO contacts.

Draw the ladder logic representation of a rotational speed (plugging/anti-plugging) switch consisting of a mechanically interlocked pair of NC and NO contacts.

Differentiate between electromechanical and solid state switches, give examples of each.

Draw the ladder logic representation of a proximity switch consisting of a SPDT transfer contact. Draw the hydraulic schematic representation of a proximity switch.

Identify the advantages and disadvantages of proximity switches compared to limit switches.

Differentiate between inductive and capacitive proximity switches.

Define the terms operating point, release point, and hysteresis with respect to a proximity switch.

Draw the ladder logic representation of a photoelectric switch consisting of a SPDT transfer contact. Draw the hydraulic schematic representation of a photoelectric switch.

Differentiate between through beam scanners, retroreflective scanners, and diffuse scanners. Identify when a polarized retroreflective scanner would be used.