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 is supposed to accomplish both tasks (motor control plus siren alert):

Unfortunately, there is a problem somewhere in this circuit. Instead of activating the siren before starting the motor, there is silence. The motor’s start is still delayed by the correct amount of time, but the siren never makes a sound. Identify some possible causes of this problem. Also, identify portions of the circuit you know to be functioning properly.

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):

However, this circuit is poorly designed. Although it works just fine under normal conditions, it may not do what it should in the event of an overload heater trip (if the normally-closed ÖL” contact opens). Explain what is wrong with this circuit.

Suppose you needed to build a circuit that pulsed a lamp on and off (once) when a pushbutton is pressed and held. In other words, you wanted the lamp to do this:

Draw a ladder logic diagram for a circuit that would fulfill this function, using at least one time-delay relay.