Review and summary

REVIEW AND SUMMARY

• The electrical control devices are widely used to improve the overall control flexibility of fluid power systems.

• Types: The most commonly used electrical control devices are:

1. Push-button switches,

2. Limit switches,

3. Pressure switches,

4. Temperature switches,

5. Solenoids,

6. Relays, and

7. Timers.

• The push-button switches are mainly used for starting and stopping of the machinery. They also provide manual operation when an emergency arises.

• The limit switches are used to identify the extreme limits of the cylinder actuation.

• The pressure switches are used to sense a change in pressure automatically, and opens or closes an electrical switch when a predetermined pressure is reached.

• The temperature switches are used to sense a change in temperature automatically, and opens or closes an electrical switch when a predetermined temperature is reached.

• A solenoid is an electromagnetic mechanical transducer that converts an electrical signal into a mechanical output force.

• An indicator lamp is used to indicate the state of a specific circuit component.

• Relays are commonly used to open to close the contacts and thereby energize or de- energize solenoids.

• Timers are time delay switches used to control the time duration of a working cycle. 

• A ladder diagram is a representation of hardware connections between switches, relays, solenoids, etc., which constitute the basic components of an electrical control system.

• At the end of the chapter, the various electrohydraulic circuits have been analyzed with the help of ladder diagrams.

KEY TERMS ONE SHOULD REMEMBER

Electrical Control devices

Push-button switches

SPST-NO

SPST-NC

Pressure switches

PS-NO

PS-NC

Temperature switches

TS-NO

Time-delay relays 

Ladder diagram

Legs

Rungs

DPST-NO/NC

DPDT-NO/NC

Momentary switches

Limit switches

LS-NO

LS-NC

TS-NC

Solenoids

Indicator lamp

Relays

Timers

Electrohydraulic circuits

Dual-cylinder sequencing circuit 

Regenerate circuit