Stopping a start is not a starting stop!

Stopping a start is not a starting stop! This presentation is partially animated. Only use the control panel at the bottom of screen to review what you have already seen. When using your mouse, make sure you click only when it is within the blue frame that surrounds each slide.

Pre-presentation Self Assessment Activity Your comfort level with your responses to the following 2 question assessment tool should indicate if the presentation that follows will increase you knowledge base on the topic outlined by the questions in this tool.

PB 1 LB 1 MR 1 M1 5 volts CR 1 PB 1 clear Q 7474 Q set PB 2 5 volts Pre-presentation Self Assessment Activity 1) Examine the following circuit ladder diagram. • What is the circuit’s significant flaw with respect to the operation of the active high motor circuit associated with relay contacts MR1? b) Draw a new ladder diagram circuit and include elements that will solve this circuit design flaw. 2) What logic value is on Q after (a) PB1 has been pressed? (b) PB2 has been pressed?

Stop element and Memory component

+ Seal-in review PB 1 NO LB 1 0 voltage Cartoon of circuit CR 1 MR 1 NO 0 NO current Ladder diagram of circuit PB 1 LB 1 MR 1 M1 CR 1

+ Note: a) The magnetic field closes the CR1 contacts and closes the MR1 contacts. b) The ladder diagram is never drawn such that a set of normally open contacts is shown closed. It is your minds eye that sees them closed. Seal-in review PB 1 NO LB 1 0 voltage Cartoon of circuit CR 1 MR 1 NO 0 NO current Ladder diagram of circuit PB 1 LB 1 MR 1 M1 CR 1

+ Seal-in review PB 1 NO LB 1 0 voltage Cartoon of circuit CR 1 MR 1 NO 0 NO current Ladder diagram of circuit PB 1 LB 1 MR 1 M1 CR 1

+ Seal-in review PB 1 NO LB 1 0 voltage Cartoon of circuit CR 1 MR 1 NO 0 NO current Ladder diagram of circuit PB 1 LB 1 MR 1 M1 CR 1 Note: a) The ladder diagram is never drawn such that a set of normally open contacts is shown closed. It is your minds eye that sees them closed. b) The magnetic field closed the CR1 and MR1 contacts when the button was first engaged. Now the field remains no matter the current position of the button.

+ Seal-in review PB 1 NO LB 1 0 voltage Cartoon of circuit CR 1 MR 1 NO 0 NO current Motor associated with relay contacts MR1 is on and remains on no matter the status of the push button. Ladder diagram of circuit PB 1 LB 1 MR 1 M1 CR 1 How do you include the motor stop idea into this seal-in ladder diagram?

Start + NO 0 LB 1 0 voltage CR 1 MR 1 NO NO current Stop for Seal-in circuit Insert the correct type of Stop push button in the correct place in the circuit. How do you include the motor stop idea into this seal-in ladder diagram? Cartoon of circuit This is the correct place. What is the correct type?

Stop Stop NO NC Start + NO 0 LB 1 0 voltage CR 1 MR 1 NO NO current Stop for Seal-in circuit Insert the correct type of Stop push button in the correct place in the circuit. How do you include the motor stop idea into this seal-in ladder diagram? Cartoon of circuit Make your selection by clicking on one of these two buttons.

Cartoon of circuit You must Make a push button selection. Click to go back to your options Start + NO 0 LB 1 0 voltage CR 1 MR 1 NO NO current Stop for Seal-in circuit Insert the correct type of Stop push button in the correct place in the circuit. How do you include the motor stop idea into this seal-in ladder diagram?

Stop Stop NO NC Stop + NC 0 Stop for Seal-in circuit Insert the correct type of Stop push button in the correct place in the circuit. How do you include the motor stop idea into this seal-in ladder diagram? Cartoon of circuit Great Selection! This is always the correct real push button type to pick for a STOP push button. Start NO LB 1 0 voltage CR 1 MR 1 NO NO current

Start Stop NO NC LB 1 0 voltage CR 1 MR 1 NO NO current + 0 LB 1 Stop for Seal-in circuit Cartoon of circuit Ladder diagram of circuit Stop PB Start PB MR 1 M1 CR 1

Start Stop NO NC LB 1 0 voltage CR 1 MR 1 NO NO current + 0 LB 1 Memory circuit Cartoon of circuit Ladder diagram of circuit Stop PB Start PB MR 1 M1 CR 1 This circuit has remembered that the start push button was pushed even though it has already been released.

Start Stop NO NC LB 1 0 voltage CR 1 MR 1 NO NO current + 0 LB 1 Memory circuit Cartoon of circuit Ladder diagram of circuit Stop PB Start PB MR 1 M1 CR 1 It took a separate action, in this case a different button had to be pushed, to forget current relay status and return the MR1 relay circuit back to its state before the Start P.B. was engaged.

LB 1 Memory circuit Stop PB Start PB MR 1 M1 Remember CR 1 Forget

PB 2 PB 1 LB 1 MR 1 M1 LB 1 CR 1 Memory circuit Stop PB Start PB MR 1 M1 Remember CR 1 Light remembers to stay on even when the button is not engaged. Forget

LB 1 Memory circuit Stop PB Start PB MR 1 M1 Remember CR 1 This situation is now forgotten. PB 2 Forget PB 1 LB 1 MR 1 M1 CR 1

MR 1 Memory circuit PB 2 PB 1 Remembers CR 1 The circuit remembers that PB 1 was pushed.

Memory circuit PB 2 PB 1 Forget Remembers MR 1 CR 1 The circuit remembers that PB 1 was pushed. The circuit has forgotten that PB 1 was pushed.

MR 1 Memory circuit PB 2 PB 1 Remembers CR 1

Memory circuit PB 2 PB 1 Forget Remembers MR 1 CR 1

A logic “0” at this input terminal will activate the “clear” concept. The variable assigned to output Q. This variable, x, is an output that can be at logic “1” or logic “0”. clear output terminals The variable assigned to output Q. This variable, x, always has the opposite value as x. x set A logic “0” at this input terminal will activate the “set” concept. Electronic memory circuit Partial pin assignment for the 7474 Flip-flop x Q 7474 Q

clear x set Electronic memory circuit 5 volts PB 1 1 x Q 7474 Q PB 2 1 5 volts

clear x set Electronic memory circuit 5 volts PB 1 0 0 x Q 7474 1 Q PB 2 1 5 volts

clear x set Electronic memory circuit 5 volts PB 1 The logic “0” remains even after PB 1 has been released. 1 0 x Q 7474 1 Q PB 2 1 5 volts

clear x set Electronic memory circuit 5 volts PB 1 The logic “1” remains even after PB 2 has been released. 1 1 x Q 7474 0 Q PB 2 0 5 volts

clear x set Electronic memory circuit 5 volts PB 1 The logic “0” remains even after PB 1 has been released. 1 0 1 x Q 7474 0 1 Q PB 2 0 5 volts

Post Presentation Self Assessment Activity 1) Examine the following circuit ladder diagram. PB 1 LB 1 MR 1 M1 CR 1 • What is the circuit’s significant flaw with respect to the operation of the active high motor circuit associated with relay contacts MR1? The button action did energize the circuit that is associated with (but not shown) MR1 however, there is no element in the circuit shown above that will interrupt the seal-in caused by CR 1 also being energized.

Post Presentation Self Assessment Activity b) Draw a new ladder diagram circuit and include elements that will solve this circuit design flaw. PB 1 LB 1 MR 1 M1 CR 1

5 volts PB 1 clear Q 7474 Q set PB 2 5 volts Post Presentation Self Assessment Activity b) Draw a new ladder diagram circuit and include elements that will solve this circuit design flaw. PB 1 PB 2 LB 1 MR 1 M1 CR 1 2) What logic value is on Q after (a) PB1 has been pressed? Logic 0 (b) PB2 has been pressed? Logic 1

Stopping a start is not a starting stop!