plc interview basics test questions:
I. Judgment questions: (1 point per question, out of 20 points.) :
1. The CLR key on the handheld programmer CQM1-PRO01 of Omron's CPM1A-40CDR-type PLC is used to clear the entered program. (B)
A. Right B. Wrong
2. Programmable controllers are easy to learn and understand and easy to use, but poor immunity to interference limits their application. (B)
A, Right B, Wrong
3. TCMP instructions and BCMP instructions have the same function. (B)
A, Right B, Wrong
4. In the same program, both TIM000 can be used for timing and CNT000 can be used for counting, and there is no conflict between the two. (B)
A, Right B, Wrong
5. Parallel path branching and merging in a functional chart is shown by a single horizontal line. (B)
A, Right B, Wrong
6. The programming language of PLC is module-oriented. (B)
A, Right B, Wrong
7, inverter regulation methods in the analog panel speed control and analog knob speed control two ways are very suitable for PLC control inverter speed regulation. (B)
A, Right B, Wrong
8, Omron's CPM1A is an integral small PLC.(A)
A, Right B, Wrong
9, The lowest bit of the ST channel is lost after the execution of the shift register instruction SFT. (B)
A, Right B, Wrong
10, PLC runs the program with a lag in its input and output. (A)
A, Right B, Wrong
11, Sequential control in the selective structure and parallel structure, as well as the beginning and end of the two parts of the composition. (A)
A, right B, wrong
12, the programming language of each PLC manufacturer is common. (B)
A, Right B, Wrong
13, PLC input relays can only be driven by the program. (B)
A, Right B, Wrong
14, The number of I/O points of a PLC is the number of input and output terminals on the PLC. (B)
A, Right B, Wrong
15, T to T+15 words in TCMP instruction can be not in the same data area. (B)
A, Right B, Wrong
16, The operand of KEEP instruction can be a special function relay. (B)
A, Right B, Wrong
17, The use of low-speed timers is limited in timing time at a time, while the use of high-speed timers is not subject to such limitations. (B)
A, Right B, Wrong
18, Proximity sensors are different from contact sensors in that they are affected by the surrounding temperature, and surrounding objects. (A)
A, Right B, Wrong
19, The number of I/O points of a large PLC is generally more than 1024 points. (B)
A, Right B, Wrong
20, MOV instruction and @MOV instruction have the same function, but the execution conditions are different. (A)
A, right B, wrong
21, B22, B23, B24, C25, A26, A27, A28, C29, C30, A
31, C32, A33, B34, B35, B36, A37, A38, B39, B40, A
41, B42, B43, C44, C45, B46, A47, B48, C49, B50, C
II. Multiple Choice Questions: (21 to 50 questions. Please put the appropriate words into the underlined places. 1.0 points per blank. Full 30 points):
21, the following is not a timing control instructions (B).
A, JMPB, LDC, ENDD, JPE
22, step instructions are programmed in serial mode, the execution type does not include (B).
A, sequential B, single line C, parallel
23, LD is a (B) instruction.
A, Output B, Read C, Logical and D, Logical or
24, The OUT instruction is a drive instruction for the coil, which cannot be used for (C).
A, Output relay B, Auxiliary relay C, Input relay D, Holding relay
25, The control voltage in industry is generally (A) volts.
A, 24VB, 36VC, 220V
26, CPM1A model in the ordinary timer timing range is (A).
A, 0-999.9sB, 0-99.9sC, 0-9999.9sD, 6553.5s
27, 1 word contains (A) bits.
A, 16B, 8C, 4D, 1
28, The setting value of parameter SV of timer TIM cannot be (C).
A, HRB, IRC, SR
29, The counter in CPM1A model has a counting range of (C).
A, 0--255B, 0--999C, 0--9999D, 0--65535
30, STC is (A) instruction.
A, Set in Borrow Flag InstructionB, Set Borrow Flag InstructionC, Set in Borrow Flag Instruction
31, PLC copies the contents of (C) register to the output line terminals during the output scanning phase.
A, Input image B, Internal memory C, Output image
32, The ladder mnemonic for incremental instructions is (A).
A, INCB, ADDC, DEC
33, If the operand of KEEP is HR, the state of this bit during a power interrupt (B).
A, clear 0 B, remain unchanged C, set 1 D, reset
34, OMRON programmable controller in the channel that is (B).
A, byte B, word C, bit D, double word
35, CPM1A model in (B) is always ON relay.
A, 25502B, 25313C, 25407D, 25503
36, XFER is (A) instruction.
A, block transfer B, data exchange C, multi-channel setup
37, OMRON series PLC, relay 25502, provides a square wave signal with a period of (A)s.
A, 1B, .1C, .5
38, The first PLC was developed by which of the following companies? (B)
A, GE B, DEC C, ABB D, OMRON
39, step instructions, the execution of each step must first be preceded by the control bit of (B).
A, STEPB, SNXTC, SET
40, When the digital tube is connected with *** cathode, the binary representation is (A) when 0 is displayed.
A, OO111111BB, OO1O1111BC, 1O1111O1BD, null
41, PLC's output interface, can only drive AC loads are: (B)
A, transistor output interface B, bidirectional thyristor output interface
C, relay output interface D, Darlington tube Output interface
42, sequential function diagrams in the use of (B) to indicate the direction in which the state proceeds.
A, double horizontal line B, directed line segment C, double line frame D, single line frame
43, IR indicates (C).
A, Input relay B, Output relay C, Internal relay D, Link relay
44, The following concept (C) is not a sequential function diagram concept.
A, Work step B, Transition condition C, Jump instruction D, Current step
45, TR denotes (B).
A, input relay B, staging relay C, internal relay D, link relay
46, CNT is (A) counter.
A, decremental B, incremental C, plus or minus D, null
47, The ladder mnemonic for the real number square instruction is (B).
A, MULB, ROOTC, DIVD, null
48, PLC capacity does not include (C) aspects.
A, the number of I/O points B, the user storage capacity C, the number of internal relays D,
49, two contacts in parallel circuit is called (B).
A, series circuit block B, parallel circuit block C, logic block with D, logic block or
50, which of the following is not a common classification of PLC? (C)
A, I/O points B, structural form C, PLC volume D, function
Plc Engineer Interview Experience Sharing:
Anhui Juyi Automation Equipment Co Ltd - PLC Engineer
Interview Time: 2017 Interview Position: PLC Engineer Sharing Time: 2017-06
Interview experience:
I first put my resume online, and HR called to ask about previous work and why I left. Then about a time to the company interview. Formal interview, the first PLC engineer and personnel manager **** with the interview, PLC engineers are mainly asked some technical questions, such as which brands will be used for industrial control products, for specific products and then ask a specific question. Personnel manager is to ask why leave, can adapt to long-term business travel. The last is a separate interview with a minister, mainly to talk about some of the company's specific work, and then ask whether it can be adapted. Finally, the personnel manager notified home to wait for news. Two days later notification, the company after discussion agreed that I can be admitted. An average of 270 days a year traveling, try to let the workers go home to rest 3 to 5 days a month. Basic salary 5.5k, travel meal allowance 100 per day, weekend overtime 200 per day, accommodation reimbursement by invoice. The year-end bonus is one month's salary.
Interviewer questions:
Can you adapt to long-term business travel. Why did you leave from the previous company. What PLCs will be used, what touch screens will be used, and what communications will be used.
Anhui Juyi Automation Equipment Co Ltd - PLC Engineer
Interview Time: 2017 Interview Position: PLC Engineer Share Time: 2017-06
Interview Experience:
I first put my resume online, and HR called me to ask about my previous work and why I left. Then about a time to the company interview. Formal interview, the first PLC engineer and personnel manager *** with the interview, PLC engineers are mainly asked some technical questions, such as which brands will be used for industrial control products, for specific products and then ask a specific question. Personnel manager is to ask why leave, can adapt to long-term business travel. The last is a separate interview with a minister, mainly to talk about some of the company's specific work, and then ask whether it can be adapted. Finally, the personnel manager notified home to wait for news. Two days later notification, the company after discussion agreed that I can be admitted. An average of 270 days a year traveling, try to let the workers go home to rest 3 to 5 days a month. Basic salary 5.5k, travel meal allowance 100 per day, weekend overtime 200 per day, accommodation reimbursement by invoice. The year-end bonus is one month's salary.
Interviewer questions:
Can you adapt to long-term business travel. Why did you leave from the previous company. What PLCs will be used, what touch screens will be used, what communications will be used.
plc interview basic quiz questions:
I. Overview
A safety PLC uses a special design to be able to achieve two important goals:
1. The system will not fail (with redundant operation), even if the component's failures are unavoidable;
2. Failures are predictable, and in the event of a failure, the system enters a safe mode.
When designing a safety PLC, there are many factors to take into account and a lot of special design is required. For example: a safety PLC more emphasis on internal diagnostics, combined with hardware and software, allows the device at any time to detect the discomfort of their own working conditions; a safety PLC has the software, to use a series of special techniques that can ensure the reliability of the software; a safety PLC with redundancy, even if a part of the failure, but also be able to maintain the system operation; a safety PLC also has an additional security mechanism. Not allowed to read and write internal data through the digital communication interface.
The difference between a safety PLC and a conventional PLC is that a safety PLC needs to be certified by a third-party professional organization to meet demanding international standards for safety and reliability. A thorough, systematic approach to designing and testing safety PLCs is required, with TUV experts in Germany and FM experts in the US providing third-party, independent validation and verification of the safety PLC design and testing process
Specialized electronics, detailed diagnostic software analysis, and an integrity design that tests for all possible failures ensures that safety PLCs have the ability to measure 99% or more of potentially hazardous failures of internal components. A Failure Mode, Effects, and Diagnostic Analysis (FMEDA) methodology has guided the design, which indicates how each component causes the system to fail and tells you how the system should detect this failure. tUV's engineers perform the failure testing themselves as a part of their certification process.
Rigorous international standard software is used for safety PLCs. these standards require special techniques to avoid complexity. Further analysis and testing meticulously examines the task interactions of the operating system. This testing includes real-time interactions such as multitasking (when in use) and interrupts. A special type of diagnostics is also required, called "program flow control" and "data validation". Program flow checking ensures that basic functions are executed in the correct order, and data validation allows all critical data to be stored redundantly in memory and tested for validity before use. During software development, a safe PLC requires additional software testing techniques. In order to verify data integrity checks, a series of "software failure injection" tests must be performed, i.e., the program is deliberately corrupted to check that the PLC's response operates in the expected safe manner. Software is designed and tested with detailed documentation so that third-party inspectors can understand how the PLC works, and most software development does not use this standardized process, which explains why there are so many bugs in so many pieces of crapware that go undetected.
Examples
Below is an example of a safety PLC from Schneider Electric to illustrate more specifically the difference between a safety PLC and a regular PLC.
2.1 Differences between the CPUs of a Safety PLC and a Conventional PLC
A Conventional PLC has one or more internal CPUs, which or their roles are: to execute the user's program, to perform I/O scanning, and to diagnose the system. However, the user's program is usually processed once, and the function of multiple CPUs is to share the realization of the program's `logical operations, arithmetic operations, communication functions, etc., that is, collaborative processing.
While the safety PLC has at least two or more CPUs, the function of the two CPUs is: respectively, the same user program each executed once, and then put the two results together for comparison, if the results of the comparison is consistent, the output of this result, and if it is inconsistent, select the safe result output. As you can see, this is the biggest difference between a safe PLC and a regular PLC: redundancy + comparison.
2.2 The structure of the CPU inside a safety PLC
A safety PLC contains 2 processors, each in its own memory area, executing their own safety logic, and then comparing it to the other's result at the end of each cycle. Each processor has its own independent shutdown channel, so that if a difference in the results is detected, or if there is a failure component, it is able to achieve a system shutdown and cut to a safe state. This dual-processing structure is known as an internal two-choice structure.
plc interview basics questions
Multiple Choice Questions
1, programmable controllers generally use the programming language (A, B, C, D)
(A) ladder diagram (B) statement table (C) function chart programming (D) high-level Programming language
2, programmable controller memory (A, B)
(A) system program memory (B) user program memory (C) backup memory (D) read and write memory
3, PLC machine in the cyclic scanning work in each scanning cycle of the work stage is (A, C, D)
(A) Input Sampling Phase (B) (C) program monitoring phase (D) program execution phase (D) output refresh phase
4, the components of the state transfer is (A, B, C, E)
(A) the initial step (B) intermediate work step (C) termination of the work step (D) directed linkage (E) transitions and transition conditions
5, the basic structure of the state transfer diagram has (B, D, E)
p> (A) statement table (B) single flow (C) step ladder diagram (D) selective and parallel process (E) jump and loop process
6, the use of stepping instructions in the PLC sequential control into what advantages (A, B)
(A) the method is simple, regularity (B) to improve the efficiency of programming work, easy to modify the program (C) the program can not be modified (D) ) functional, specialized instructions
Short Answer Questions
1. What are the characteristics of LC?
A: PLC has the following characteristics: ① high reliability, anti-interference ability; ② complete support, perfect function, strong applicability; ③ easy to learn and easy to use, welcomed by engineers and technicians; ④ system design, construction workload is small, easy maintenance, easy to transform; ⑤ small size, light weight, low energy consumption.
2. What are the differences between LC machine and relay control system?
A: PLC machine is actually a computer, it is the logical relationship between the various components is expressed through the program, change the logical relationship as long as the change program, and relay control system on a variety of electrical components, with wires according to a certain law to connect them, wiring expresses the logic of the relationship between the various components to change the relationship can only change the wiring. PLC machine is a serial mode; relay control system is a parallel mode; relay control system is a parallel mode. PLC machine is a serial mode of operation; relay control system is a parallel mode of operation.
3, programmable controller hardware and its structure?
A: PLC uses a typical computer structure, including CPU, RAM, ROM, input and output interface circuits, power supply units and programmers and peripherals.
4, ladder programming in several ways?
Answer:
1, according to the logic instruction ladder program;
2, according to the step instruction ladder program.
5. Working principle of programmable controller. (P460/Short Answer 1)
A: The programmable controller uses a cyclic scanning mode of operation with centralized sampling and centralized output. Its working process can be divided into five stages: internal processing, communication operation, input processing, program execution and output processing.
7, briefly explain the composition of the basic structure of the ladder diagram of the programmable controller.
A: Mitsubishi FX system example of the basic structure of the ladder diagram programmable controller by the left and right bus, all kinds of contact symbols, all kinds of coil symbols, text symbols, and indicate the energy flow of the line, node composition.
8, briefly explain the meaning of nodes and ladder rungs?
Answer: node is the logical relationship between the contact representation; ladder is to indicate a logical relationship between the refresh or output.
9, briefly describe the programming skills of programmable controllers.
A: Programming skills and no certain rules to follow, can only be accumulated in the process of programming, first of all, should be able to skillfully use the machine components and common basic links, such as timing links, oscillating links, frequency division links, etc., in the programming process, there is a parallel series circuit, the circuit should be placed in the forefront of the most contacts; there are a number of parallel circuits in series, the circuit should be placed in the leftmost contact, so that it can make the programmable controller. In the programming process, if there is a series circuit connected in parallel, the circuit with the most contacts should be put in the front; if there are several parallel circuits connected in series, the circuit with the most contacts should be put in the leftmost side, which can make the program concise and understandable with less statements. Encountered in the process of programming non-programmable circuits must be rearranged in order to correctly apply the PLC instructions for programming.
10, RST instruction in the actual use of what should be noted?
A: RST instruction is generally used in conjunction with the SET instruction, the same component, SET, RST instruction can be used several times, and does not limit the use of the order, but the last executor of the validity of the RST instruction can also be used for the accumulation of timers, counters, data registers, addressable registers, such as reset, the current value of the zero.
11, under what circumstances allow dual-coil output?
A: The same program can have the same output coil in two segments that will never be executed at the same time. In a step instruction program, double coils that are not "active" at the same time are allowed; double coil outputs are also allowed in subroutine call programs.
12, PLC programming is divided into what steps? (P460 / short answer 5)
A: Programming should be a detailed understanding of the process requirements of the controlled object, clear PLC to complete the task should have the function of determining the overall structure of the program, draw the control system's work cycle diagram or state flow charts in order to clarify or select the program structure, listed in the I / O table and the selection of components within the machine schedule, you can use the ladder diagram or instruction table method to complete the program design. The program design can be completed using the ladder diagram or instruction list method, and input to the PLC machine for debugging and modification.
13, programmable controller selection.
A: The basic principle of selection of programmable controllers is to meet the requirements of the control function under the premise of ensuring that the system is reliable, safe, economical and easy to use and maintain, the main consideration should be the CPU capacity, the number of I / O points, the response speed, the command function of a few performance indicators to meet the needs.
14, the purchase of PLC machine should consider what factors?
A: PLC machine should be based on the characteristics of the process, control requirements and the number and type of signals needed to purchase the scene, generally should consider the following aspects: PLC functions, input and output points, the requirements of the PLC response time, program memory capacity estimates, system reliability and programmer and peripheral equipment.
15, the installation and maintenance of programmable controllers and application considerations.
A: the installation and maintenance of programmable controllers and applications should pay attention to the following matters: in the installation should pay attention to the setup of safe lines, suitable for programmable controllers, the operating environment and the correct wiring; maintenance should pay attention to the inspection before and after the operation of the inspection, once found abnormal, should be correctly dealt with; should also pay attention to the service life of the lithium battery, when the "BATT. When the "BATT.V" LED lights up, the battery should be replaced immediately according to the correct procedure to prevent the loss of the program after the failure of the lithium battery.
16, what are the requirements for PLC grounding?
A: PLC should have a special grounding line, the cross-sectional area of the grounding line should not be less than 2mm2, grounding resistance of less than 100Ω, prohibited and other equipment in series grounding, and try to get close to the PLC.
17, PLC machine routine maintenance work mainly includes what aspects?
A: should include the following aspects: ① daily cleaning and inspection, ② regular inspection and maintenance, ③ programming software usage and application, ④ lithium battery replacement. 18, briefly describe the programming procedure of the portable programmer. A: ① operation preparation, ② original program clear, ③ program input, ④ program read out check, ⑤ program insertion and modification, ⑥ program monitoring and testing.
19, what factors should be considered to estimate the programmable controller memory?
A: The memory capacity required for the user program can be estimated in advance. For the switching control system, the number of words of memory required for the user program is equal to the total number of input/output signals multiplied by 8; for the analog input/output system, each analog signal requires about 100 words of storage.
20, programmable controller has what internal resources? (P460/Short Answer Question 2)
A: PLC machine internal are non-contact electronic circuits, in order to facilitate programming, according to their functional equivalents for the various types of electrical components, there are input relays, intermediate relays, timers, counters, output relays, and a number of other special relays and so on.
21, PLC output components of which types? What is the main difference between them?
A: PLC's output components are relays, transistors, bi-directional thyristors of three types, their main difference is that the speed is different, the output capacity is not the same, the nature of the power supply used is different.
22, why PLC contacts can be used countless times? (P460/Short Answer 3)
A: PLC programming elements are just similar to the components of the relay, is actually a storage unit, the state of a component changes, just means that the component's storage unit system to set 1 or 0, because the components are nothing more than a storage unit that can be accessed countless times, so the PLC's programming elements of the contacts, can be used countless times.
23, what is the instruction? What is the program? What are the types of programming languages?
Answer: Instructions are the computer to complete a basic operation of each control information required, the program is a computer to complete a complete task of a series of instructions. PLC programming language: ladder programming language, instruction statement table programming language, function block diagram programming language, high-level language.
24, briefly explain the PLC ladder diagram "energy flow" concept.
A: PLC ladder diagrams evolved from relay circuit diagrams, using symbols similar to relay circuit diagrams, PLC ladder diagrams and relay circuits are very similar to the structure of the bus instead of the power line, the concept of energy flow (energy flow) instead of the concept of current in the relay circuit.
25, briefly describe the main components of the FX2 series PLC and their numbering.
A: Input relay X0 ~ X177, output relay Y0 ~ Y177, auxiliary relay M0 ~ M499, special auxiliary relay M8000 ~ M8255, timer T0 ~ T255, counter C0 ~ C199, etc. 26, PLC machine internal equivalent components? A: PLC machine has many internal devices with different functions, in fact, these devices are composed of electronic circuits and memory. In order to separate them from the usual hard devices, called soft devices or equivalent components, there are X, Y, T, C, M, S, D, V / Z and other equivalent components