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Professional Development
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Professional Development
Siemens Level 1 PLC #1
39 questions
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- 1. Multiple Choice
The basic function of a PLC is to ...
... amplify various weak signal sources
... control the speed of motors
... accept inputs, make logical decisions, and send outputs.
... control a high voltage output with a low voltage input.
... convert nonelectrical quantities into electrical voltage.
- 2. Multiple Choice
The basic difference between a PLC and a relay control system is that
… different types of input devices are used.
… different types of output devices are used.
… different input and output voltage levels are used.
… one uses analog signals and the other uses digital signals.
… one uses relay control logic and the other uses programmed instructions.
- 3. Multiple Choice
Field devices refer to ...
... input devices only.
... output devices only.
... load devices only.
... power devices only.
... all kind of sensors and actuators that are physically wired to PLC input/output modules.
- 4. Multiple Choice
The symbol shown below in the ladder diagram ...
... can be thought of as a contact that is usually closed.
... can be thought of as a contact that is usually opened.
... represents a capacitor.
... is always a logic 0.
... is always a logic 1.
- 5. Multiple Choice
The symbol shown below in a ladder diagram represents a(n) ...
... set of usually open contacts.
... imaginary coil that, when energized, will activate a digital output contact.
... a capacitor.
... is always a logic 0.
... is always a logic 1.
- 6. Multiple Choice
Determine the number of possible combinations of a six digit binary number.
6 combinations
16 combinations
32 combinations
64 combinations
128 combinations
- 7. Multiple Choice
A device used to convert a binary number to a 7-segment display format is
... a decoder
... a comparator
... a multiplexer
... a de-multiplexer
... an analog to digital converter
- 8. Multiple Choice
The largest decimal number that can be represented with eleven binary bits is …
... 255.
... 511.
... 1023.
... 2047.
... 4095.
- 9. Multiple Choice
The binary number 1010 0111 1100 0101 can be written in hexadecimal as …
A7D5
A7C5
B7C3
B7E3
C7C5
- 10. Multiple Choice
The conversion of the floating point binary number 1011 1101.0110 to decimal is ...
187.62
189.375
189.625
190.375
191.375
- 11. Multiple Choice
The conversion of the decimal number 156 to 8421 BCD is…
0000 1001 1100
0001 0101 0110
0001 0000 1100
0000 0101 0110
0110 0101 0001
- 12. Multiple Choice
If a given memory unit consists of 2,400 bytes the memory capacity would be rated:
2,400 bits
4,800 bits
9,600 bits
19,200 bits
38,400 bits
- 13. Multiple Choice
Which of the following statements about a NAND gate are correct? Two answers are correct.
If all inputs are 1, the output will be 1.
If all inputs are 0, the output will be 0.
If all inputs are 0, the output will be 1.
If one or more inputs are 0, the output will be 1.
NAND gates can have maximum 4 inputs.
- 14. Multiple Choice
If you want to know when one or both matching bits in two different words are logic ’1’ you would use the ...
... AND instruction
... OR instruction.
... NOT instruction.
... XOR instruction.
... NAND instruction.
- 15. Multiple Choice
A system contains two identical circuits operating in parallel as shown below. As long as both are operating properly, the outputs of both circuits are always the same. If one of the circuits fails, the outputs will be at opposite levels. To indicate the failure, the outputs of the circuits are connected to the inputs of …
…a NOR gate.
…an OR gate
…an XOR gate.
…an XNOR gate.
…a NAND gate.
- 16. Multiple Choice
The status bit of switches and pushbuttons connected to a PLC input module are stored in the …
… process image input file.
… process image output file.
… user program.
… in the ROM.
… none of the above.
- 17. Multiple Choice
Which of the following input combinations will definitely result in an output?
A AND B AND C
A AND NOT B AND NOT C
NOT C AND D
C AND NOT D
C AND D
- 18. Multiple Choice
The Boolean equation for the logic represented in the ladder diagram shown below can be expressed as …
Y = (A) + (CD) + (BC)
Y = (A) + (B) + (CD)
Y = (A) + (CD) + (BC
Y = A(BCD)
Y = (AB) + (CD)
- 19. Multiple Choice
Branch instructions are used to create:
series paths.
parallel paths.
a series of energized output conditions.
parallel connection of networks.
none of the above.
- 20. Multiple Choice
By which system does the CPU communicate with input and output modules located on the same rack?
Interface module – IM
RS – 232 Interface
Multiple Point Interface – MPI
PROFIBUS DP
Backplane Bus
- 21. Multiple Choice
The Central Processing Unit (CPU) ...
... accepts inputs, makes decisions provided by the program, and sets outputs.
... accepts outputs, makes the decision provided by the program, and sets inputs.
... serves only to store the program in memory.
... understands only ladder logic.
... reads all inputs and outputs and makes decisions provided by the program.
- 22. Multiple Choice
The PLC program is uploaded from the programming device into the PLC. Into which specific CPU-Memory of the PLC is the program loaded?
Block stack
Load memory
System memory
Process - image input table
Work memory
- 23. Multiple Choice
Which of the following counter is available in STEP 7?
Up/Up counter
Up/Down counter
Retentive Down counter
Reset counter
Incremental counter
- 24. Multiple Choice
In programs that are written in ladder logic, all outputs are represented by ...
... contact symbols.
... coil symbols.
... schematic load device symbols.
... either a or b, depends on the output interface module.
... negative contact symbols when relays are connected to outputs.
- 25. Multiple Choice
The move instruction copies data from …
... an integer byte to a floating byte
... a floating byte to an integer byte.
... a destination byte to a source byte.
... a source byte to a destination byte.
... a double byte to a source byte.
- 26. Multiple Choice
The maximum number of networks allowed in a Step 7 program is ...
... 1.
... 8.
... 256.
... 1024.
... limited only by the memory size.
- 27. Multiple Choice
The maximum number of outputs allowed per network in a Step 7 program is ...
... 1.
... 4.
... 8.
... 16.
... limited only by the memory size.
- 28. Multiple Choice
In PLC operation, a scan is usually a sequential process of ...
... reading control logic, evaluating outputs, and updating inputs.
... writing control logic, evaluating outputs, and updating inputs.
... reading/writing the status of inputs and updating outputs.
... reading the status of inputs, evaluating control logic, and updating outputs.
... updating and evaluating inputs according to control logic and updating outputs.
- 29. Multiple Choice
Parallel connections of a ladder logic program are typically called …
... rungs.
... branchs.
... loops.
... inputs.
... outputs.
- 30. Multiple Choice
Given below is the truth table of a 3-input logic gate. Which logic gate represents the behavior between inputs and outputs according to the truth table?
NAND gate
AND gate
NOR gate
OR gate
XOR gate
- 31. Multiple Choice
What kind of signal varies continuously?
Analog signal
Variable signal
Digital signal
Discrete signal
Permanent signal
- 32. Multiple Choice
An 8-bit binary counter has to count balls going into a box from a conveyor belt. A sensor detects the passing of a ball. If it has counted one hundred balls, the binary value of the counter is …
... 0110 0010.
... 0110 1000
... 0110 0100.
... 0001 0100.
... 0000 0100.
- 33. Multiple Choice
The following digital system controls the number of work pieces going into a carton. The preset number of 86 is entered on the keypad and also appears on the 7-segment display. What is the specified content of register A and the data on 8-bit input B of the comparator when the carton is full?
Register A: 1000 0110 Comparator input B: 0101 0110
Register A: 1000 0110 Comparator input B: 0110 1000
Register A: 0110 1000 Comparator input B: 0101 0110
Register A: 1000 0110 Comparator input B: 1000 0110
Register A: 0101 0110 Comparator input B: 0101 0110
- 34. Multiple Choice
Two pushbuttons and a proximity switch of a PLC controlled mechatronic system are connected to PLC inputs and a contactor is connected to a PLC output. Which of the following statements according to Network 2 and the program extract shown below is correct?
The program does not work and K1 is never activated.
K1 is only activated when pushbutton PB1 is pressed and sensor B1 is not activated.
K1 is only activated when pushbuttons PB1 and PB2 are pressed and sensor B1 is not activated.
K1 is only activated when pushbutton PB2 is pressed and sensor B1 is activated.
K1 is either activated when pushbutton PB1 is pressed and sensor B1 is not activated or when pushbutton PB2 is pressed and sensor B1 is activated.
- 35. Multiple Choice
The connections of input and output devices to the PLC and the corresponding ladder logic program are shown below. Which of the following statements about the operation are correct? Two answers are correct.
If pushbutton S1 is pressed and pushbutton S2 is not pressed, solenoid 1M1 is de-energized.
If pushbutton S2 is pressed and pushbutton S1 is not pressed, solenoid 1M1 is de-energized.
If pushbutton S1 is pressed and pushbutton S2 is pressed, solenoid 1M1 is energized.
If pushbutton S1 is pressed or pushbutton S2 is pressed, solenoid 1M1 is energized.
If neither pushbutton is pressed, solenoid 1M1 is energized.
- 36. Multiple Choice
The connections of input and output devices to the PLC and the corresponding ladder logic program are shown below. Which of the following statements about the operation are correct? Two answers are correct.
If pushbutton S1 is pressed and pushbutton S2 is not pressed, solenoid 1M1 is energized.
If pushbutton S2 is pressed and pushbutton S1 is not pressed, solenoid 1M1 is energized.
If pushbutton S1 is pressed and pushbutton S2 is pressed, solenoid 1M1 is energized.
If pushbutton S1 is pressed or pushbutton S2 is pressed, solenoid 1M1 is energized.
If neither pushbutton is pressed, solenoid 1M1 is de-energized.
- 37. Multiple Choice
As shown below, the LED display connected to a PLC output module enables the machine operator to view the number of workpieces produced. Which of the following statements about the display are correct? Two answers are correct.
The LED display shows the decimal form of the binary coded decimal value (BCD).
To display the next higher number, in this case 39, only PLC output QX.0 must be changed to 1.
The binary value to display the number “39” is 1001 0011.
If all eight data lines are set to 1, the number “99” is displayed.
Each decimal digit is controlled by eight data lines.
- 38. Multiple Choice
The Boolean equation for the logic represented by the relay circuit diagram of the drilling machine
shown below can be expressed as:
M : K1 = PB1 + PB2 +B1
M : K1 = PB1 x PB2 x B1
M : K1 = (PB1 x PB2) + B1
M : K1 = (PB1 + PB2) x B1
M : K1 = (PB1 x B1) + PB2
- 39. Multiple Choice
At the operator panel you find out that the output of the PLC to execute the next step is set, but this step is not executed. Which action should you take to find the fault?
Verifying input signals of the PLC
Checking the signals between sensor and input module of the PLC
Checking the signals between output module and actuator
Switching of the control voltage
Measuring the supply voltage and output voltage at the sensor
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