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Main points of this past exam are: Memory Unit, Input Interface, Output Interface, Processing Unit, Sequence, Implemented, Monostable Directional
Typology: Exams
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Answer Four Questions Examiner: Dr. M. J. O’Mahony
Describe the relationship between and the function of the above four basic components. (25 Marks)
(i) How many groups are required are required if a cascade system is used? (5 Marks)
(ii) Draw a SiemensS7 ladder diagram for the above sequence. Use a counter to simplify the solution. Assume that all internal PLC relays have to be latched. (20 Marks)
Use the attached pneumatic circuit (FigQ2) as a aid to numbering the solenoids and limit switches.
The following nomenclature is to be used: A, B, C:Double acting pneumatic cylinders A+, etc:The extend stroke of cylinder A A+p: The pilot signal to cause the A+ stroke of cylinder A A-p: The pilot signal which initiates the return stroke of cylinder A A (^) d : The logic complement of A-p, used to reset single solenoid valves by disabling the latch function.
V,W: Internal PLC relays which can be set on or off V (^) p : Signal which sets relay V _ V (^) p : Signal which resets relay V V (^) d : The logical complement of Vp which disables relay V by disabling the latch.
Use the symbol table given in Table Q2.
Figure Q.
Name Address Comment
a0 I0.0 A retract limit switch a1 I0.1 A extend limit switch b0 I0.2 B retract limit switch b1 I0.3 B extend limit switch c0 I0.4 C retract limit switch c1 I0.5 C extend limit switch S1 I0.6 Main start switch a_sol Q0.0 A Solenoid b_sol Q0.1 B Solenoid c_sol Q0.12 C Solenoid COUNTER C60^ COUNTER W M1.0 MEMORY BIT W
