99 PLC SCADA Interview Question and Answers 3

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99 PLC SCADA Interview Question and Answers


41.      What type of user
input in InTouch?
 User inputs include data
entry Discrete, Analog, String/ Message, Sliders and Pushbuttons.
type of animation can be given in InTouch?
Colour fill, % Fill Blinding, Size Control, Location, Orientation,
Visibility, Action, Hide Show window
43.      What are trends?
 Trends means graphical
representation of data.
“Real- time and “ Historical. You can configure both trend objects
to display graphical representations of multiple tag names over time. Real-
time trends allow you allow you to chart up to four pens ( data values). While
Historical trends allow to chart up to pens.
Real-time trends are dynamic. They are updated continuously during
runtime with whatever time span given in configuration. You can not scroll the
real- time trends to see previous data.
Historical trends provide you with a “ snapshot” of data from a
time and data in the past. They are not dynamic Unlike real- time trends
historical trends are only updated when they instructed to do so either through
the execution of a Quick- Script or an action by the operator, for example,
clicking a button, You can zoom in/ zoom out the trends. You can also access
the pervious data.

44.      What are Alarm and Events
in InTouch?
Alarms and Events are the notifications used to inform operator of
process activity. Alarms represent warnings of process conditions that could
cause problems, and require an operator response. A typical Alarms is triggered
when a process value exceeds a user defined limit. InTouch uses for types of
alarm LOLO LO HI and HIHI.
Events represent normal system status message, and do not require
an operator response. A typical event is triggered when a certain system
condition takes place, such as an operator logging into InTouch.
45.      Security management
Security provides the ability to control whether or not specific
operators are allowed to perform specific functions within an application.
Security is based on the concept of the operator “logging on” to the
application and entering a “User Name” and “Password.” (The application
developer sets up each operator with a “User Name,” a pre-assigned “Password”
and an “Access Level” via the Special/Security/Configure Users command wither
in WindowMaker or Windows Viewer).
When a new application is created, the default “User Name” is
“Administrator” with an access level of 1999 (which allows access to all
security commands).
46.      What is the use of
Scripts in InTouch?
Is a way of writing logic in InTouch. InTouch has its own
instructions and way of writing program.
Application                 :
Linked to the entire application.
Windows                    :
Linked to a specific window.
Key                              :
Linked to a specific key or key combination on the keyboard.
Condition                    :
Linked to a discrete tagname or expression.
Data Change   : Linked to a
tagname and/or tagname field only.
47.      What is driver?
A software which allows a computer to access the external devices
using com ports or communication cards.
48.      What is DDE?
Dynamic Data Exchange is the facility developed by Microsoft for
exchanging the data between various programs.
DDE has three important settings
Application / Server name, Topic Name and Item Name
49.      Communication with
software (Excel)
DDE settings for Excel
Ø  App. Name – Excel,
Ø  Topic Name – [book.xls]sheet1
Ø  Item Name – Cell Address ie
DDE settings for InTouch
Ø  App. Name – View
Ø  Topic Name – TAGNAME
Ø  Item Name – Name of tag

50.       How to monitor the
data from InTouch to Excel? ie One way communication from InTouch to Excel.
In Excel worksheet write a formula ie = View [TAGNAME A1
A1 is name of tag in InTouch
51) How to have two way communication between Excel and InTouch?

Programmable Logic Controller – General

51.      What is PLC?
PLC means Programmable Logic Controller. It is a class of
industrially hardened devices that provides hardware interface for input
sensors and output control element. The field I/p include element like limit
switches, sensors, push button and the final control elements like actuator,
solenoid/control valves, drives, hooters etc.
PLC Senses the input through I/p modules, Processes the logic
through CPU and memory and gives output through output module.
52.      Applications of PLC
PLC can be used in almost all industrial application solutions
right from small machine to large manufacturing plants. Even it caters
applications of redundant systems at critical process plants. 
53.      Role of PLC in
PLC plays most important role in automation. All the monitoring as
well as the control actions are taken by PLCs. PLC Senses the input through I/P
modules, Processes the logic through CPU and memory and gives output through
output module.
54.      Role of CPU ?
This component act as a brain of the system.
CPU consist of Arithmetic Logic Unit, Program memory, Process
image memory, Internal timers and counters, flags.
It receives information from I/P device, makes decisions depending
upon the information and logic written and sends information through the O/P
The CPU’s are distinguished with following features
Memory capacity, Instruction set supported, communication option,
time required to execute the control program.
55.      Role of Power supply
in PLC system?
Power supply provides system power requirement to processor, I/O and
communication modules. Typically the power supply has input voltage 120 V – 230
V AC or 24 V DC and back plane output current 2 A to 5 A at 5 V DC
56.      Role of Rack or
Chassis in PLC system?
A hardware assembly, which houses the processor, communication and
I/O modules. It does following functions.
Ø  Power distribution
Ø  Containment of I/O modules
Ø  Communication path between I/O
module and CPU
The chassis are available in different slots in various PLC
systems. Additional chassis can be connected using chassis interconnecting

57.      What is role of I/O
Electronic plug in units used for interfacing the i/p and o/p
device in the machine or process to be controlled.
I/P module receives data from i/p devices (Pushbutton, Switches,
Transmitters) and send it to processor. The O/P module receives data from
processor and send it to output device (Relay, Valves).
Digital/Discrete:- Sends and Receives On/Off signal
Analog:- Sends and receives variable input or output signals
58.      Role of EEPROM
memory module?
This module is inserted into
processor system for maintaining a copy of project (PLC program). This is
helpful in case of memory corruption or Extended power loss.
59.      Communication module
communication modules are used either for communication between
external hardware or software. The hardware can be PLCs (same or other make),
Controller, I/O module, smart transmitters. The software can be SCADA software,
MIS system or programming software.
60.      Difference Between
Fixed and Modular PLCs?
In non modular PLCs the processor will have inbuilt power supply
and I/Os in one unit.

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