Time-Delay Electromechanical Relays

An electric motor is used to power a large conveyor belt. Before the motor actually starts, a warning siren activates to alert workers of the conveyor’s forthcoming action. The following relay circuit accomplishes both tasks (motor control plus siren alert):

Study this ladder logic diagram, then explain how the system works.

Large electric motors are often equipped with some form of soft-start control, which applies power gradually instead of all at once (as in “across the line” starting). Here is an example of a simple “soft start” control system:

Analyze this ladder logic diagram, and explain how it starts up the electric motor more gently than an “across-the-line” starter would.

The following ladder logic diagram is for a reversing motor control circuit:

Study this diagram, then explain how motor reversal is accomplished. Also, identify the function of each “M” contact in the control circuit, especially those normally-closed contacts in series with the motor starter coils.

Now consider the following modification made to the reversing motor control circuit (motor and power contacts not shown here):

What extra functionality do the time-delay relays contribute to this motor control circuit?