System Engineer

The functions of PLC are as follows:

1) Sequential Control: PLC processes binary signal input into output that is used for the purposes of sequential technical processing, here PLC keeps all steps in the sequential process in the right order.

2) Plant Monitoring: PLC continuously monitors the status of a system and takes the necessary actions in connection with the process being controlled or displaying the message to the operator.

3) Shutdown System: The working principle of a PLC is to receive a process input signal that is controlled and then process the input signal in accordance with the program stored in memory and then produce an output signal to control the actuator or other equipment

There are three basic organizational elements associated with ladder logic:

1) RUNG: Ladder logic instructions are written on a function. During the scan program, the processor scans from left to right, one by one ladder from top to bottom.

2) INSTRUCTION: Ladder logic Instruction is divided into 2 parts;
2.1) Input instructions:
2.2) Displayed on the left side of the ladder Check, comparison, or specific conditions
2.3) Output instructions:
2.4) Shown on the right side Do something action.

3) BRANCHES: Branches are used in ladder logic to create different paths that directly read the state of inputs and outputs.

Inputs:

1) DC Inputs: DC input modules allow to connect either PNP (sourcing) or NPN (sinking) transistor type devices to them.

2) AC Inputs: There is no polarized AC voltage. The AC voltage is most frequently shifted via a limit switch or other form of switch.


Outputs:

1) Relay Outputs: One of the most common types of outputs available is the relay output. Existence of relays as outputs makes it easier to connect with external devices.

2) Transistor Outputs: Transistor type outputs can only switch a DC current. The PLC applies a small current to the transistor base and the transistor output “closes”.

3) Triac Output: Triac output can be used to control AC loads only. Triac output is faster in operation and has longer life than relay output.

Advantage : cost, size, significant capability, multiple hardware options, controls S & G drives via profinet or profibus or analog/digital - whichever you like.

Disadvantage : limited I/O bandwidth, local I/O max of 8 modules, can't use a lot of the existing work done for s7-300/400 in STL, processing speed - but getting even a large project to run under 10 ms scan time is common.

This warning message indicates that the timestamps for the project do not match the timestamps for the program in the PLC. This may indicate that the programs are different, in which case it would be dangerous to continue the current operation. However, the programs may be functionally identical and still have different timestamps.

It is a command used to jump if no carry occurs after an arithmetic operation. It is called as jump if no carry (conditional jump instruction). Here the carry flag bit in PSW register is used to make decision. The processor looks at the carry flag to see if it is raised or not.
If carry flag is 0, CPU fetches instructions from the address of the label.

1) External interrupt 0 (IE0) has highest priority among interrupts.
2) Timer interrupt 0 (TF0)
3) External interrupt 1 (IE1)
4) Timer interrupt 1 (TF1) has lowest priority among other interrupts.
5) Serial port Interrupt
6) Reset.

It is generally a program that initializes OS during startup i.e., first code that is executed whenever computer system startups. OS is loaded through a bootstrapping process or program commonly known as booting. Overall OS only depends on the bootstrap program to perform and work correctly. It is fully stored in boot blocks at a fixed location on the disk. It also locates the kernel and loads it into the main memory after which the program starts its execution.

Demand paging is a method that loads pages into memory on demand. This method is mostly used in virtual memory. In this, a page is only brought into memory when a location on that particular page is referenced during execution. The following steps are generally followed:

1) Attempt to access the page.
2) If the page is valid (in memory) then continue processing instructions as normal.
3) If a page is invalid then a page-fault trap occurs.
4) Check if the memory reference is a valid reference to a location on secondary memory. If not, the process is terminated (illegal memory access). Otherwise, we have to page in the required page.
5) Schedule disk operation to read the desired page into main memory.
6) Restart the instruction that was interrupted by the operating system trap.

These are file management commands. These are used for:

chmod - It changes the permission set of a file
chown - It changes the ownership of the file.
chgrp - It changes the group of the file.

Example :
$ chmod g+w test
It changes permission for a user group to write.

$ chown adas1923 testfile
It changes the owner of testfile to adas1923.

$ chgrp moderators testfile
It changes a group of testfile to moderators.

1) ls -> Lists files in current directory
2) cd -> Change directory to tempdir
3) mkdir -> Make a directory called graphics
4) rmdir -> Remove directory (must be empty)
5) cp -> Copy file into directory

Few types of VPN are:

1) Access VPN: Access VPN is used to provide connectivity to remote mobile users and telecommuters. It serves as an alternative to dial-up connections or ISDN (Integrated Services Digital Network) connections. It is a low-cost solution and provides a wide range of connectivity.

2) Site-to-Site VPN: A Site-to-Site or Router-to-Router VPN is commonly used in large companies having branches in different locations to connect the network of one office to another in different locations. There are 2 sub-categories as mentioned below:

3) Intranet VPN: Intranet VPN is useful for connecting remote offices in different geographical locations using shared infrastructure (internet connectivity and servers) with the same accessibility policies as a private WAN (wide area network).

4) Extranet VPN: Extranet VPN uses shared infrastructure over an intranet, suppliers, customers, partners, and other entities and connects them using dedicated connections.

Open System Interconnections (OSI) is a network architecture model based on the ISO standards. It is called the OSI model as it deals with connecting the systems that are open for communication with other systems.

The OSI model has seven layers. The principles used to arrive at the seven layers can be summarized briefly as below:

1) Create a new layer if a different abstraction is needed.
2) Each layer should have a well-defined function.
3) The function of each layer is chosen based on internationally standardized protocols.

TCP : TCP or TCP/IP is the Transmission Control Protocol/Internet Protocol. It is a set of rules that decides how a computer connects to the Internet and how to transmit the data over the network. It creates a virtual network when more than one computer is connected to the network and uses the three ways handshake model to establish the connection which makes it more reliable.



UDP : UDP is the User Datagram Protocol and is based on Datagrams. Mainly, it is used for multicasting and broadcasting. Its functionality is almost the same as TCP/IP Protocol except for the three ways of handshaking and error checking. It uses a simple transmission without any hand-shaking which makes it less reliable.

If you get this question, it's an opportunity to choose the most compelling information to share that is not obvious from
your resume.

Example :

Strength -> I believe that my greatest strength is the ability to solve problems quickly and efficiently, which makes me
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Abillity to Handle Pressure -> I enjoy working under pressure because I believe it helps me grow and become more
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Tip : Emphasize why you were inspired to apply for the job. You can also explain that you are willing to invest a great
deal of energy if hired.

These are generally very open ended questions and are asked to test how quick wit a candidate is. So there is
nothing to worry about if you have a good command over your communication skills and you are able to propagate
your thoughts well to the interviewer