Electrical Engineering Exam

ET 304 Name:____________________________ Exam 2- Spr20

1. Assuming all timers start with an accumulated value of 0, for which of the following would the DN bit be activated the moment after the timer is energized for 10 seconds and then de-energized for 20 seconds?

a.) ControlLogix TOF with preset of 8000

b.) ControlLogix RTO with preset of 8000

c.) ControlLogix TOF with preset of 80000

d.) ControlLogix TON with preset of 8000

2. Answer the questions about the ladder logic program shown below.

a.) If Switch_1 was turned on and 5 seconds later Switch_2 was turned on, what

would the following values be 12 seconds after Switch_2 was first turned on? i. Accumulated value of My_Timer?

ii. Accumulated value of My_Counter?

b.) How would your previous answer be different if the ONS instruction were removed?

3. State the instruction that is best suited to each of the following situations.

a.) __________ Instruction used to reset the accumulated value of a counter to zero.

b.) __________ An MCR instruction is placed at the beginning of a master control relay fenced zone and this instruction is placed at the end of the zone.

c.) __________ Instruction is used at the end of a subroutine to return a value to the routine that called it.

d.) __________ A JMP instruction causes the execution to jump to this instruction.

e.) __________ Instruction is used with a CTU instruction to create an up-down counter.

f.) __________ This is the only timer instruction that requires a reset instruction.

4. Answer the questions about the following instructions. a.) For the instruction shown, what would the accumulated value be if the rung had

continuity 6 different times? Afterwards, would the DN bit be on or off?

CTU Count Up Counter Counter My_Counter Preset 15 Accumulated 11

b.) For the instruction shown, what would the accumulated value be if the rung had continuity 6 different times? Afterwards, would the DN bit be on or off?

CTD Count Down Counter Counter My_Counter Preset 15 Accumulated 3

c.) For the instruction shown, what would the accumulated value be if the rung had continuity for 6 seconds? At the 6 seconds, would the DN bit be on or off?

TON Timer On Delay Counter My_Timer Preset 8000 Accumulated 0

a.) For the instruction shown, what would the accumulated value be if the rung had continuity for 6 seconds? At the 6 seconds, would the DN bit be on or off?

TOF Timer Off Delay Counter My_Timer Preset 8000 Accumulated 0

5. Consider the ladder logic program shown below. Assume Switch_1 is closed for 50

seconds before re-opening.

a.) How many seconds after Switch_1 first closes will Lamp_1 turn on?

b.) How many seconds will Lamp_1 stay on? c.) If the TON instruction were replaced with a TOF instruction, how many seconds

after Switch_1 first closes will Lamp_1 turn on?

d.) If the TON instruction were replaced with a TOF instruction, how many seconds will Lamp_1 stay on?

6. List 4 instructions that we have covered so far that are retentive.

7. Which of the following statements are true? (Circle the letter of each true statement)

a.) In a PLC5 or SLC500, a timer instruction must have a time base specified.

b.) The accumulated value of a counter in a CTD instruction can get no lower than zero,

c.) The scan time of a program has a significant effect on how many items per second can be counted with a standard counter instruction.

8. Answer the questions about the ladder diagram below. Unless stated otherwise,

assume all lamps and all switches are off prior to each step below.

a.) If all switches are off, what order with the rungs be evaluated?

b.) If only Switch_1 and Switch_5 are on, what order will the rungs be evaluated?

c.) If only Switch_5 is on, what order will the rungs be evaluated?

d.) If Switch_4 is turned on and then

Switch_3 is turned on and then Switch_1 is turned on, what lamps are on?

e.) If Switch_4 is turned on and then Switch_3 is turned on and then Switch_2 is turned on, what lamps are on?

f.) If Switch_4 is turned on and then Switch_5 is turned on and then Switch_6 is turned on and then Switch_7 is turned on, what lamps are on?

g.) If Switch_4 is turned on and then Switch_6 is turned on and then Switch_1 is turned

on and then Switch_7 is turned on, what lamps are on?

9. Consider a PLC system with the following inputs and outputs. Design a ladder diagram that does the following:

• A timer counts up to 1.5 seconds, resets itself, and then repeats

• Every time S1 is on and the timer makes it to 1.5 seconds, a counter increments its accumulated value.

• PL1 turns on any time that the count of the counter is 20 or higher.

• The counter should be reset whenever PL1 is first turned on (i.e. transitions from off to on)

• PL2 should blink on and off any time that S2 is on. The blink should be on for 0.5 seconds and off for 0.5 seconds.

• PL3 should turn on whenever S1 and S2 are both on and PL3 should remain on for 8 seconds after either S1 or S2 turn off.