This blog is wrote about PLC AND TURBINE SYSTEM QUESTION and focuses on instrument engineers, supervisor and technicians of petrchemical industry, plants and fertilizers companies.
- WHAT IS A PLC? WHAT ARE ITS DISTINCT ADVANTAGES OVER CONVENTIONAL CIRCUITS?
ANS: A PLC STANDS FOR PROGRAMMABLE LOGIC CONTROLLER. ALL TYPE OF LOGIC FUNCTIONS CAN BE PERFORMED BY IT. SUCH AS SEQUENTIAL START UP OF SYSTEMS, FAIL SAFE RUNNING PLANT AND SEQUENTIAL SHUTDOWNS. THE CONVENTIONAL CIRCUITS USING RELAY DIGITISED GATES AND DIFFICULT TO CHANGE OR BYPASS AND BULKY. WHILE PLC IS SMALLER AND CHANGES CAN BE MADE BY PROGRAMMING WITHOUT CHANGING HARDWARE, MEANT FOR INDUSTRIAL TMOSPHERE, CAN BE INSTALLED IN PLANT CONVENIENT, NO MOVING OR MECHANICAL PARTS SO, CHANCES OF FAILURE IS MINIMISED.
- WHAT ARE DIFFERENT TYPES OF I/O IN TYPICAL PLC SYSTEM USED FOR SAFETY SHUTDOWN SYSTEM IN OIL INDUSTRIES?
ANS: INPUTS
- RELAY AND SWITCHES CONTACTS. WITHOUT VOLTAGE (DRY CONTACT)
- RELAY AND SWITCHES CONTACTS WITH 120 V AC OR 24 V DC.
- LOGIC LEVELS FROM TRANSISTORISED CIRCUITS CAN ALSO BE INPUTS.
OUTPUTS
- LOW VOLTAGE CONTACT FOR OTHER INTERLOCK FUNCTION
- HEAVY RATED CONTACTS FOR SOV OR OTHER DEVICES
- THYRISTER OUTPUTS.
- DEFINE THE FOLLOWING TERMS USED IN DIGITAL SYSTEMS.
ANS: A) CPU – CENTRAL PROCESSION UNIT. THE HEART OF COMPUTER. B) ALU – ARITHMETIC LOGIC UNIT. PERFORMS ALL MATHEMATICAL FUNCTIONS. C) EPROM – ERASABLE PROGRAMMABLE READ ONLY MEMORY D) RAM – RANDOM ACCESS MEMORY E) FLOPPY DISK – FLEXIBLE MAGNETIC DISK FOR DATA/ PROGRAM STORAGE F) MODEM – MODULATOR / DEMODULATOR FOR COMMUNICATION OVER LONG DISTANCE G) RS 232 – MOST COMMONLY USED SERIAL INTERFACE FOR PERIPHERALS. H) HIWAY – MAIN CABLE FOR COLLECTION AND DISTRIBUTION OF DATA AT HIGH FREQ TO ALL THE DCS SUBSYSTEMS. I) WATCH DOG TIMER – TIMER TO KEEP OVER MICROPROCESSOR CYCLE OPERATION. J) PARITY – DIGITAL SIGNALS ARE CODED TO HAVE A DEFINE PATTERN (EVEN/ODD/OTHER) FAILING WHICH. K) A/D CONVERTER – ANALOGUE TO DIGITAL CONVERTER. 1 TO 5V. 0 TO 12 BITS OF DIGITAL SIGNAL BY A/D CONVERTER.