PLC SCADA DCS Interview Questions and Answers 3

PLC SCADA DCS Interview Questions and Answers 3

PLC Interview
Questions and Answers

SCADA Interview
Questions and Answers

DCS Interview
Questions and Answers

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freasher in the field of Automation and those are looking for job and preparing
for interviews. It is difficult to find the PLC interview questions and answers
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Question:Give some applications of DCS
 a. Thermal Power Plant
b. Oil and gas (extraction, production and storage)
c. Energy generation (and waste incineration)
d. Water and the environment (production and purification)
e. Chemical industry
f. Paper and cement.
Question: Mention some of the DCS manufacturers
Question:What are the factors to be considered in selecting a DCS?
a. Lifecycle Services
b. Data Model
c. Configuration Management
d. Alarm System
e. Documentation
f. Fault Tolerant Capabilities
g. Networking & Connectivity
h. Regulatory and Batch Control
i. ISA95 Standard Support
j. Supervisory Applications
k. ERP Integration
l. Complete Replacement
m. Services Capability and Quality
Question:What is HART
addressable remote transducer”, Uses the same 4-20mA wiring, Super imposes the
digital signal on the top of the analog one
Question:List the features of HART protocol or List the important
performance parameters of HART protocol or List any four, salient feature of
HART protocol or What is the purpose of the HART protocol?
a. 35-40 data items Standard in every HART device
b. Standard commands provide easy access
c. Increases control system integrity
d. HART is Safe, Secure, and Available
e. Saves Time and Money
f. Improves Plant Operation and Product Quality
g. Protects Asset Investments
h. Fully inter operable and reliable
Question:What is Fieldbus?
The Fieldbus
Foundation gives the following definition: “Fieldbus is a digital, two-way, multidrop
communication link among intelligent measurement and control devices.” Fieldbus
is gradually replacing 4 to 20 mA standard instrumentation signals used to
transfer measurement and control data between control room and plant floor. It
is one of several local area networks dedicated for industrial automation.
Question:What is DDL in Fieldbus?
A Device
Description (DD) provides an extended description of each object in the Virtual
Field Device (VFD), and includes information needed for a control system or
host to understand the meaning of data in the VFD.
Question:What is interoperability on Foundation Fieldbus?
Conventional hybrid
communications can transmit digital signals, but information exchange between
devices of different manufacturers is difficult because each device uses its
manufacturer’s protocol. In Fieldbus communication, international
standardization of the protocol ensures the Interoperability between FF devices
including FF interface card in host system. FF devices allow digital data to be
exchanged between devices from different manufacturers. Therefore, the freedom
to configure the process control system increases since there is no need to
choose one device manufacturer.
Question:Compare HART and Profibus
A Profibus solution
permits full use of the advantages of digital communication such as improved
resolution, remote diagnostics and set-up/configuration. Profibus technology
adds extra intelligence and simplifies maintenance. FINT offer owners and users
of Modbus technology and infrastructure the change off upgrading their systems
to Profibus technology. Fint delivers complete hardware and software
documentation, manufacturing drawings, training, certification consulting,
large scale manufacturing of electronic modules and customer service and support.
Fint has the know-how, and it customizes to your specific requirements ensuring
your success in the marketplace.
Question:What is bit Rate?
Bit rate is a
measure of the number of data bits (that’s 0’s and 1’s) transmitted in one
second. A figure of 2400 bits per second means 2400 zeros or ones can be transmitted in one second, hence the
abbreviation ‘bps’.
Question:What is baud Rate?
rate by definition
means the number of times a signal in a communications channel changes state.
For example, a 2400 baud rate means that the channel can change states up to
2400 times per second. When I say ‘change state’ I mean that it can change from
0 to 1 up to 2400 times per second. If you think about this, it’s pretty much
similar to the bit rate, which in the above example was 2400 bps. Whether you
can transmit 2400 zeros or ones in one second (bit rate), or change the state
of a digital signal up to 2400 times per second (baud rate), it the same thing.
So we can conclude that in the above example, the bit rate is the same as the
baud rate. Hence, 1 bit rate = 1 baud rate for this example
Question:List the advantages and disadvantages of RS-232
 Advantages of RS232
a) Up to 50 m between Microlink hardware and computer
b) Over 250 channels per Microlink 3000
a) Slow, runs at up to 38 400 baud over short distances; lower speeds
as the distance increases owing to capacitance effects
b) Maximum logging speed with Streamer software = 700 samples per
second, with Windmill software = 35 samples per second
c) Only one device can be connected to an RS232 cable
d) Computers now rarely have serial ports and a USB-serial (for
example) adaptor may be needed.
Question:What is RS-232?
The RS-232
interface is the Electronic Industries Association (EIA) standard for the
interchange of serial binary data between two devices. It was initially
developed by the EIA to standardize the connection of computers with telephone
line modems. The standard allows as many as 20 signals to be defined, but gives
complete freedom to the user. Three wires are sufficient: send data, receive
data, and signal ground. The remaining lines can be hardwired on or off
permanently. The signal transmission is bipolar, requiring two voltages, from 5
to 25 volts, of opposite polarity.
Question:What is the categories of signals used in RS232?
Signal functions in
the EIA232 standard can be subdivided into six categories. These categories are
summarized below, after which each signal described.
a) Signal ground and shield.
b) Primary communications channel. This is used for data
interchange, and includes flow control signals. c) Secondary communications
channel. When implemented, this is used for control of the remote modem,
requests for retransmission when errors occur, and governance over the setup of
the primary channel.
d) Modem status and control signals. These signals indicate modem
status and provide intermediate checkpoints as the telephone voice channel is
e) Transmitter and receiver timing signals. If a synchronous
protocol is used, these signals provide timing information for the transmitter
and receiver, which may operate at different baud rates.
f) Channel test signals. Before data is exchanged, the channel may
be tested for its integrity, and the baud rate automatically adjusted to the maximum
rate that the channel can support.
Question:Name the Secondary Communications Channel of RS232?
 a) Pin 14 – Secondary
Transmitted Data (STxD)
b) Pin 16 – Secondary Received Data (SRxD)
c) Pin 19 – Secondary Request to Send (SRTS)
d) Pin 13 – Secondary Clear to Send (SCTS) These signals are
equivalent to the corresponding signals in the primary communications channel.
The baud rate, however, is typically much slower in the secondary channel for
increased reliability.

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