99 PLC SCADA Interview Questions and Answers 5

99 PLC SCADA Interview Questions and Answers 5

PLC SCADA Interview Questions and Answers

81.What are the software Used with AB?

For Pico soft for Pico PLC
RS Logix 500 for Micrologix and
SLC PLCs programming
RS Logix 5000 for Control Logix
PLCs programming

SCADA – RS View earlier Control View

82.What is use of RS Linx software?


RS Linx software is used to perform following tasks.
ØConfigure communication drivers
ØView configured drivers and active nodes
ØEnable communication tasks such as uploading,
downloading, going online, updating firmware and sending messages.

83.What is use of RS Logix Software?

RS Logix is a PLC programming software. It contains all the instructions needed for PLC programming. We can develop the program, down load/upload the program, work on line/ off line and force the I/Os using the software.  RS Logix 500 is used for Micrologix and SLCs RS Logix 5000 is used for Control Logix PLCs

84.What file gets created in PC for RS Logix PLC program?

The extension of the file will be.rss. So if you create an application with “Reliance” name the file created will be “Reliance.rss”. By default it will be stored in “c:Program FilesRockwell Software/RS Logix 500 Eng location.

85.How to creating linkage between PLCs and PLC programming software?

The RS Linx software is used for linking the PLC and software  Either you can manually configuration the communication settings or By using Auto Configure facility the software will detect the communication settings automatically.

86.Hardware configuration (PLC and I/Os)

ØManual configuration
ØAuto detect

87.What is the meaning of Upload and Download?

Upload means transferring the program data from PLC to PC Download means transferring the program data from PC to PLC

88.What are the various communication interfaces supported by AB?

The commonly used communication protocol in AB includes DH+, DH485, ETH, Modbus, Device Net and Control Net.

89.Give information about DH, Control Net, DeviceNet and Ethernet protocol.

Data Highway : The proprietary data network used by Allen Bradley PLCs to communicate information to and from other PLCs on the network
or to and from host computers attached to the network. 
ControlNet : A real-time, control-layer network providing high-speed transport of both time-critical IO data and messaging data, including upload/ download of programming and configuration data and peer-to-peer messaging, on a single physical media link.
FC Functions : It is a logic block without memory. An FC is always executed by calling in another block. FC is used either for returning a function value to a calling function or executing a technological function. Temporary variable belonging to FC are saved in local stack and this data is
lost when the FC has been executed.
Function Blocks (FBs) : A function block is block with a memory. A FB contains a program that is always executed when a different logic block calls the FB. FB make it much easier to program frequently occurring complex functions.


90.What is latency in communication?


The delay time between the end of one communication and the start of another. During this time, the processes associated with the communication are hung up and cannot continue. The latency to be minimum.

91.How the communication protocols are distinguished?

The protocols are distinguished with following specifications

Ø No. of nodes supported, total network length,
speed of communication.

92.Comparison between various Protocols used with AB

Device Net
Control Net
Baud rate max
230.4 kbits/s
19.2 kbit/s
500 kbit/s
5 Mbit/s
No. of max. nodes
Network Length
3.048 Km
1.2 km
0.487 Km
30 km

Programmable Logic Controller- Siemens

93.What are the various PLC system in SIMATIC range?

Siemens has broadly 3 PLC ranges ie Siemens S7 200, 300 and 400

94.What are the software used with Siemens?

For S7 200 PLC programming Micro win
For S7 300 and 400 system: Simantic S7 manager
The SCADA software used by Siemens is Win CC. Earlier Siemans use to supply COROS LS /B

95.Components of Siemens S7 300 Series PLC system?

CPUs (312 IFM, 313,314,IFM,314,315,2DP,316-2DP,318 Single Modules (SM), Digital I/O
(SM321/322/323), Analog I/O (SM 331/332/334)
Function modules (FM) ex Positioning Modules, Closed Loop Communication Processor ex CP 342-5 DP for Profibus
Interface module- For interconnecting individual racks (IM 360/361, IM 365 S/R)

96.What are the Communication Protocol used in Siemens?

Multi- Point Interface (MPI):
Data Transfer-187,5 kbits to 15
Mbit/ s
Distance-50 m without RS 485 repeater /10 Km
with repeater
Number of nodes- up to 32


Data Transfer-12 Mbit/s,
Distance-23 Km with fibre optic cable
Number of nodes – up to 125

97.What are the blocks used in Siemens?

Simantic S7 manger uses DB, OB, FC, PB, and FB
Obs: Determine the structure of the user program
Data Black: These are the blocks used by logic blocks in
CPU program for storing the data. DB’s does not contain any instructions and it
take up space in the user memory. The user program and access a data block with
bit, byte, word or double word operations. Global data block: These contain
information that can be accessed by all the logic block in the user program.
Instance data block: These DBs
are always assigned to a particular FB.
UN : (enable) Specifies whether
or not the timer instruction is enabled
DN : (Done) Specifies whether or
not the accumulated value of the timer equals to the preset value of the timer.
Programming instruction (Advance)
MCR, Compute, PID, STI,
Sequencer, Register, RTC

98.      What are SFCs and SFBs?

SFBs and SFCs are integrated in
the S7 CPU and allow you access to some important system functions.

99.      What is Statement List?

Statement List (STL) is a textual programming language that can be used to create the code section of logic blocks. Its syntax for statements is similar to assembler language and consists of instructions followed by addresses on which the instructions act.


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