Interview Questions.

Question 1. What Are The Various Plc System In Simatic S7 Range ?

Answer :

Siemens has broadly three PLC degrees ie Siemens S7 2 hundred , three hundred and 400

Question 2. What Are The Software Used With Siemens ?

Answer :

For S7 two hundred PLC programming : Microwin
For S7 three hundred and 400 machine : Simantic S7 supervisor
The SCADA software utilized by Siemens is Win CC.
Earlier Siemens use to deliver COROS LS/B
Programmable Logic Controller (PLC) Interview Questions
Question 3. Components Of Siemens S7 three hundred Series Plc System ?

Answer :

CPUs (312 IFM, 313, 314, IFM, 314, 315, 315-2DP, 316-2DP, 318
Signal Modules (SM), Digital I/O (SM321/322/323), Analog I/O (SM331/332/334)
Function modules (FM) ex Positioning modules, Closed Loop
Communication Processor ex CP 342-five DP for Profibus
Interface module – For interconnecting individual racks (IM 360/ 361, IM365 S / R)
Question four. Explain The System Bits Available In S7-200 Plc Special Memory Area ?

Answer :

Special Memory Byte zero (SM0.Zero – SM0.7) affords eight bits that are updated by means of the S7-2 hundred CPU on the stop of every scan cycle. Your software can study the fame of these bits after which make decisions primarily based on a chunk’s fee.

Always_On : SM0.0 This bit is constantly ON.

First_Scan_On : SM0.1 This bit is ON for the first experiment cycle handiest. One use is to name an initialization subroutine.

Retentive_Lost : SM0.2 This bit is became ON for one scan cycle if retentive statistics changed into misplaced. This bit can be used as either an errors memory bit or as a mechanism to invoke a unique startup series.

RUN_Power_Up : SM0.Three This bit is became ON for one experiment cycle while RUN mode is entered from a electricity-up situation. This bit may be used to offer machine heat-up time before beginning an operation.

Clock_60s : SM0.4 This bit affords a clock pulse that is OFF for 30 seconds and ON for 30 seconds, for a cycle time of 1-minute. It offers an clean-to-use delay or a 1-minute clock pulse.

Clock_1s :  SM0.5 This bit presents a clock pulse that is OFF for zero.Five seconds and then ON for 0.Five seconds for a cycle time of one second. It presents an clean-to-use postpone or a 1-second clock pulse.

Clock_Scan : SM0.6 This bit is a experiment cycle clock that is ON for one test after which OFF for the next test. This bit may be used as a test counter input.

Mode_Switch : SM0.7 This bit indicates the cutting-edge position of the Mode switch (OFF=TERM function and ON=RUN function). You can use this bit to permit Freeport mode most effective while the transfer is inside the RUN position. Normal communication with the PC/programming tool may be re-enabled by using switching to the TERM role.

Question five. Explain The Time Stamp Available In S7-two hundred Plc ?

Answer :

This caution message indicates that the timestamps for the project do now not in shape the timestamps for the program within the PLC. This might also imply that the packages are unique, in which case it'd be risky to preserve the contemporary operation. However, the packages can be functionally equal and still have specific timestamps.

PLC/Microcontrollers/Microprocessors Interview Questions
Question 6. What Are The Time Stamps Available In S7-200 Plc ?

Answer :

Each program incorporates two wonderful timestamps; the “Created” timestamp and the “Last Modified” timestamp. The created timestamp is set while the assignment is created through the New Project option. The Created timestamp isn't always laid low with any user edits or application compilation.

The Last Modified timestamp is used to suggest whilst the person closing modified the program. There are many situations that motive the Last Modified timestamp to be set, it includes Edit of instructions or operands inside the program, Adding, deleting, or enhancing a Local or Global Symbol, Adding or deleting a POU, Compiling the program block and Downloading this system block (this mechanically compiles this system block and therefore sets the ultimate changed timestamp).

Question 7. How To Check Whether The Project And Program In The Plc Is Same ?

Answer :

STEP 7-Micro/WIN 32 affords the “Compare” option, to assist you to decide whether or not the applications are identical or distinct.

DCS(allotted manage gadget) Interview Questions
Question eight. What Are Fatal Errors In Siemens S7 2 hundred Plc ?

Answer :

Fatal errors cause the PLC to stop the execution of your software. Depending on the severity of the mistake, a deadly blunders can render the PLC incapable of acting all or any features.

Question nine. What Happens To Plc When It Goes To Fatal Error ?

Answer :

The PLC plays the following duties while a fatal blunders is detected.
Changes to STOP mode
Turns on each the System Fault LED and the Stop LED
Turns off the outputs
The PLC stays on this condition till the deadly error is corrected.
Process Control and Instrumentation Interview Questions
Question 10. What Are Non – Fatal Errors Available In Siemens Plcs?

Answer :

Compile and run-time errors are non-fatal errors. Non-fatal mistakes can degrade a few element of the overall performance of your PLC, however do now not render the PLC incapable of executing the person software or updating the I/O.
Run-time mistakes are non-fatal errors detected in RUN mode, and meditated in unique reminiscence (SM) bits that your software can monitor and examine. At startup, the PLC reads the I/O configuration and stores this information in the SM reminiscence. During everyday operation, the I/O popularity is periodically up to date and saved within the SM reminiscence. If the PLC detects a distinction in the I/O configuration, it units the configuration-modified bit of the module-blunders byte; the I/O module will not be updated till this bit is reset. For the PLC to reset this bit, the module I/O should once more suit the I/O configuration stored inside the machine facts memory.
Run-time programming mistakes are non-fatal mistakes situations created via you or your application whilst the program is being carried out. An instance of this is an indirect-deal with pointer, which become valid when this system compiled, changed by way of application execution to factor to an out-of-range deal with. Use the PLC > Information… command to decide what form of blunders has happened.
You can accurate run-time programming errors best by means of editing the consumer program. The run-time programming errors are cleared at the subsequent transition from STOP to RUN mode.
Compile errors (or application-bring together mistakes) are detected at down load as the PLC compiles the program. If there's a collect errors, the compile halts, and the previous application (which is understood to be legitimate since it previously compiled) is retrieved. All of these steps occur even as the PLC is in STOP mode. Compile mistakes can be displayed using the PLC > Information… command.
Question eleven. How To Writing And Forcing Outputs In S7-200 Plc Stop Mode ?

Answer :

To enable Write and Force capabilities at the same time as in STOP mode, select the Debug > Write-Force

Outputs in STOP menu command.

The S7-2 hundred PLCs aid writing and forcing outputs (both analog and virtual) even as the PLC is in STOP mode. As a safety precaution, you should specially request this capability to be enabled in STEP 7-Micro/WIN 32. The menu option Debug>Write-Force Outputs in STOP enables you to Write or Force outputs at the same time as the PLC is in STOP mode.

Warning If the S7-two hundred PLC is attached to device whilst you write or pressure an output, those modifications may be transmitted to the equipment. This should result in unanticipated pastime within the equipment, that can also motive demise or serious harm to employees, and/ or harm to gadget.

Each time STEP 7-Micro/WIN 32 is opened, the menu alternative defaults to unchecked, and you are averted from writing or forcing outputs while the PLC is in STOP mode. Checking the menu option permits writing and forcing for the current modifying consultation with the modern-day venture. When a unique assignment is opened, the menu option returns to its default country and you are averted from either writing or forcing output addresses even as the PLC is in STOP mode.

Scada Interview Questions
Question 12. How To Write The Stl Program In S7-200 Plc ?

Answer :

The instance application under suggests formatting inside the STL editor in line with the recommendations given in How to Enter a Statement in STL. You might need to installation your program in addition, with the aid of having the network feedback supply a preferred review of the characteristic of the network and the assertion feedback identify the feature of the declaration. Note that the sample is written with symbolic addresses.

If you would love to peer this application (in both STL or LAD) in STEP 7-Micro/WIN 32, pick out File>Open, browse to the STEP 7-MicroWINSamplesEnglish directory, highlight the sample software and click on the Open button.

Sample Program for a Paint Mixer:

NETWORK 1      //Fill the tank with ingredient 1 and display tank degree.

//Maintain Pump Status if Start Switch Opens.

LD    Start_1             //Load cost of Start_1 I0.0.

O      Pump_1          //Or with Pump_1 Q0.Zero fee. A Stop_1 //And with Stop_1 I0.2.

AN   High_Level   //And Not with High_Level I0.Four.

=       Pump_1       //Assign result to Pump_1 Q0.0.

NETWORK 2      //Fill the tank with paint factor 2 and monitor tank.

//level. Maintain Pump Status if Start Switch Opens.

LD    Start_2             //Load fee of Start_2 I0.1.

O      Pump_2         //Or with Pump_2 Q0.1 value. A Stop_2 //And with Stop_2 I0.3.

AN   High_Level  //And Not with High_Level I0.Four.

=      Pump_2      //Assign result to Pump_2 Q0.1.

NETWORK three //Set memory bit if High Level is reached.

LD   High_Level                       //Load fee of High_Level I0.Four.

S      High_Lev_Reached, 1  //Set High_Lev_Reached M0.1 to at least one (on).

NETWORK 4 //Start Timer if High Level is reached.

LD    High_Lev_Reached   //Load value of High_Level_Reached M0.1.

TON  Mix_Timer, +100     //Timer 37, Preset = a hundred (@zero.1 s).

NETWORK five //Turn on Mixer Motor.

LDN   Mix_Timer                   //Load Not price of Mix_Timer T37.

A         High_Lev_Reached //And with High_Lev_Reached M0.1.

=         Mixer_Motor          //Assign end result to Mixer_Motor Q0.2.

=         Steam_Valve        //Assign end result to Steam_Valve Q0.3.

NETWORK 6 //Drain mixing tank.

LD   Mix_Timer              //Load fee of Mix_Timer T37.

AN   Low_Level           //And Not with Low_Level I0.5.

=      Drain_Valve      //Assign end result to Drain_Valve Q0.Four.

=       Drian_Pump  //Assign result to Drain_Pump Q0.Five.

NETWORK 7 //Count every cycle.

LD        Low_Level    //Load value of Low_Level I0.Five.

A          Mix_Timer //And value of Mix_Timer T37.

LD       Reset         //Load cost of Reset I0.7.

CTU    Cycle_Counter, +12     //Counter 30, Preset = 12.

NETWORK eight //Reset memory bit if Low Level reached and Timer //timed out.

LD   Low_Level        //Load price of Low_Level I0.Five.

A     Mix_Timer      //And price of Mix_Timer T37.

R      High_Lev_Reached, 1   //Reset value of High_Lev_Reached M0.1 to 0.

Programmable Logic Controller (PLC) Interview Questions
Question thirteen. What Is The Protocol Used In The In S7-200 Plc And How Many Station Can Be Possible In The S7-two hundred Network?

Answer :

A. Protocol used inside the in S7-2 hundred PLC is PPI Protocol

B. 32 station Can Be Possible within the S7-200 Network

S7 300 PLC Questions

Question 14. What Is Absolute And Symbolic Addressing In S7_300 Plc?

Answer :

In a STEP 7 application you work with addresses such as I/O indicators, bit reminiscence, counters, timers, facts blocks, and characteristic blocks. You can get right of entry to these addresses on your application definitely, but your applications could be plenty simpler to examine in case you use symbols for the addresses (for example, Motor_A_On, or other identifiers according to the code system used inside your business enterprise or enterprise). An address for your person application can then be accessed thru this symbol.

Absolute Addresses

An absolute address comprises an cope with identifier and a memory vicinity (for instance, Q four.0, I 1.1, M 2.0,FB21).

Symbolic Addresses

You can make your application less complicated to study and simplify troubleshooting in case you assign symbolic names to absolutely the addresses.

STEP 7 can translate the symbolic names into the specified absolute addresses routinely. If you'll opt to get right of entry to ARRAYs, STRUCTs, statistics blocks, local statistics, common sense blocks, and user-described records kinds the use of symbolic names, you need to first assign symbolic names to absolutely the addresses earlier than you can deal with the facts symbolically.

You can, for example, assign the symbolic name MOTOR_ON to the deal with Q four.Zero and then use MOTOR_ON as an address in a program declaration. Using symbolic addresses it's miles easier to understand to what extent the factors in the software fit the additives of your procedure control challenge.

Question 15. What Is Meaning By Instance Data Block In S7_300 Plc?

Answer :

An instance records block is assigned to every function block name that transfers parameters. The real parameters and the static information of the FB are stored in the example DB. The variables declared within the FB determine the structure of the example facts block. Instance manner a function block name. If, as an example, a characteristic block is called 5 instances within the S7 person software, there are five instances of this block.

Creating an Instance DB

Before you create an example records block, the corresponding FB need to already exist. You specify the number of the FB when you create the instance records block.

One Instance DB for Each Separate Instance

If you assign several example facts blocks to a feature block (FB) that controls a motor, you may use this FB to manipulate one of a kind cars.

The facts for each specific motor (for example, pace, runup time, overall working time) are saved in exclusive statistics blocks. The DB related to the FB when it's miles called determines which motor is controlled. With this method, simplest one function block is vital for numerous motors.

Plc Scada Interview Questions
Question 16. What Are System Function Are In S7_300 Plc?

Answer :

System Functions:

A machine characteristic is a preprogrammed function that is integrated at the S7 CPU. You can call the SFC on your program. SFCs are a part of the working machine and aren't loaded as a part of the program. Like FCs, SFCs are blocks ”with out memory.”

S7 CPUs provide SFCs for the following features:

Copying and block functions
Checking the program
Handling the clock and runtime meters
Transferring information units
Transferring events from a CPU to all other CPUs in multicomputing mode
Handling timeofday and timedelay interrupts
Handling synchronous mistakes, interrupts, and asynchronous mistakes
Information on static and dynamic gadget records, for instance, diagnostics
Process photo updating and bit subject processing
Addressing modules
Distributed I/O
Global statistics communique
Communication thru nonconfigured connections
Generating blockrelated messages
Question 17. Differences Between Instance Data Blocks And Shared Data Blocks?  

Answer :

A shared facts block isn't always assigned to a common sense block. It carries values required by means of the plant or machine and may be referred to as directly at any factor inside the application.
An instance facts block is a block this is assigned without delay to a logic block, including a feature block. The example statistics block includes the records that had been stored in a characteristic block in the variable assertion table.
Safety Instrumented System Engineer Interview Questions
Question 18. How To Exchanging/swapping Modules In The Configuration Table In S7-300?

Answer :

If you using HW Config to revise a station configuration and also you want to trade a module for one with a brand new order range for example,

continue as follows:

Use a drag-and-drop operation to drag the module from the Hardware Catalog window over the vintage module that is already placed.
Drop the new module. To the quantity possible, the new module assumes the parameters of the only that become already inserted.
This process is faster than changing modules by deleting the antique module after which inserting the brand new one and assigning parameters to it.

You can flip this function on or off in HW Config by the menu command Options > Settings (“Enable Module Swapping”)

PLC/Microcontrollers/Microprocessors Interview Questions
Question 19. What Is Meant By Complex Data Types?

Answer :

Complex information kinds define statistics businesses which might be large than 32 bits or records businesses along with other statistics types.

The following desk describes the complicated information kinds. You define structures and arrays either in the variable assertion of the logic block or in a data block.

Data Types :

DATE_AND_TIME

Defines an area with 64 bits (eight bytes). This records kind saves in binary coded decimal format: DT

STRING

Defines a collection with a maximum of 254 characters (information kind CHAR). The general region reserved for a character string is 256 bytes lengthy. This is the distance required to keep 254 characters and a header of 2 bytes. You can reduce the reminiscence required for a string by means of defining the number of characters on the way to be saved inside the character string (for example: string[9] ‘Siemens’).

ARRAY

Defines a multidimensional grouping of 1 facts type (either simple or complex). For example: ”ARRAY [1..2,1..3] OF INT” defines an array within the layout 2 x 3 along with integers. You get right of entry to the records saved in an array the use of the Index (”[2,2]”). You can outline up to a most of 6 dimensions in a single array. The index may be any integer (-32768 to 32767).

STRUCT

Defines a grouping of any mixture of facts types. You can, for instance, outline an array of systems or a shape of systems and arrays.

UDT

Simplifies the structuring of large quantities of facts and coming into data sorts while growing facts blocks or asserting variables in the variable announcement. In STEP 7, you could combine complicated and basic statistics sorts to create your personal ”userdefined” statistics type. UDTs have their very own name and might consequently be used more than once.

FB, SFB

You determine the structure of the assigned example statistics block and allow the transfer of example statistics for several FB calls in one instance DB.

Structured information types are stored in accordance with phrase limits (WORD aligned).

Question 20. What Meant By User-defined Data Types (udt)?

Answer :

User-described records sorts are unique data structures you create your self that you could use in the complete S7 application when they were described.
User-described data sorts may be used like standard information sorts or complicated statistics sorts in the variable announcement of logic blocks (FC, FB, OB) or as a information kind for variables in a facts block (DB). You then have the benefit which you only want to outline a unique facts structure as soon as if you want to use it as usually as you desire and assign it any variety of variables.
User-defined records kinds may be used as a template for developing facts blocks with the equal data structure, which means you create the shape as soon as and then create the specified facts blocks by way of absolutely assigning the person-described facts kind (Example: Recipes: The shape of the facts block is usually the identical, simplest the amounts used are exclusive.)
User-described facts kinds are created within the SIMATIC Manager or the incremental editor just like other blocks.
Industrial Automation Engineer Interview Questions
Question 21. What You Mean By Memory Compressing? (ram) When It Can Be?

Answer :

After deleting and reloading blocks, gaps can arise in the person memory (load and paintings memory) and reduce the usable reminiscence region. With the compress feature, the present blocks are rearranged within the consumer reminiscence with out gaps, and a continuous free memory is created.
Always Try to Compress the Memory in STOP Mode
Only if you compress the memory in “STOP” mode are all of the gaps closed up. In the RUNP mode (mode selector putting), the blocks presently being processed can't be shifted on account that they are open. The compress characteristic does no longer work in the RUN mode (mode selector setting) (write safety!).
Question 22. What Are The Communication Protocol Used In Siemens 300 ?

Answer :

Multi-Point Interface ( MPI ) :

Data Transfer – 187.Five kbits to 15 Mbit/s,

Distance – 50 m with out RS 485 repeater / 10 Km with repeater

Number of nodes – up to 32

Profibus :

Data Transfer – 12 Mbit/s,

Distance – 23 Km with fibre optic cable

Number of nodes – as much as one hundred twenty five

Question 23. What Are The Blocks Used In Siemens ?

Answer :

Simantic S7 supervisor uses DB, OB, FC, PB and FB

OBs : Determine the structure of the consumer program

Data Block : These are the blocks used by common sense blocks in CPU program for storing the statistics. DB’s doesnot incorporate any instructions and it take up area within the person reminiscence. The consumer application can get entry to a statistics block with bit, byte, word or double phrase operations.

Global records block : These consists of statistics that may be accessed with the aid of all the common sense block in the person application.

Instance data block : These DBs are constantly assigned to a particular FB.

FC Functions : It is a logic block with out reminiscence. An FC is continually finished through calling in every other block. FC is used both for returning a function price to a calling function or executing a technological function. Temporary variable belonging to FC are stored in neighborhood stack and this data is misplaced when the FC has been completed.

Function Blocks (FBs) : A feature block is block with a reminiscence. A FB carries a application that is constantly carried out when a distinct logic block calls the FB. FB make it plenty less difficult to software often going on complicated capabilities.

HPLC Interview Questions
Question 24. What Are Sfcs And Sfbs ?

Answer :

SFBs and SFCs are incorporated within the S7 CPU and permit you get right of entry to to some crucial system capabilities.

DCS(disbursed manage gadget) Interview Questions
Question 25. What Is Statement List?

Answer :

Statement List (STL) is a textual programming language that may be used to create the code phase of logic blocks. Its syntax for statements is similar to assembler language and includes commands followed through addresses on which the commands acts.