Friends this the most awaited post I am writing for all the fresher in the field of Automation and those are looking for job and preparing for interviews. It is difficult to find the PLC SCADA DCS Interview Questions and Answers
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So here we go.
Question: Give some applications of DCS
Answer:
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
Answer:
a. ASEA BROWN BOWERI – ABB
b. TATA HONEYWEL
c. FOXBORO – INVENSYS
d. YOKOGOWA BLUE STAR – YBL
e. ALLEN BRADLEY
f. GE FANUC
g. FISHER ROSEMOUNT
h. TOSHIBA
Question: What are the factors to be considered in selecting a DCS?
Answer:
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
Answer:
“Highway 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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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
Answer:
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?
Answer:
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?
Answer:
Baud 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 interface.
Answer:
Advantages of RS232 a) Up to 50 m between Microlink hardware and computer b) Over 250 channels per Microlink 3000
Disadvantages 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?
Answer:
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?
Answer:
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 established.
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?
Answer:
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.
