ISA CAP Technology & Tools 3 — Questions and Answers
Question 1: Which ISA standard governs the functional safety of Safety Instrumented Systems (SIS) in the process industry?
- ISA-5.1
- ISA-18.2
- ISA-84 (IEC 61511) (Correct answer)
- ISA-101
Correct answer: ISA-84 (IEC 61511)
ISA-84, which is equivalent to IEC 61511, establishes the requirements for the design, installation, and maintenance of Safety Instrumented Systems in the process industry.
Question 2: In process instrumentation, what does the term 'turndown ratio' describe?
- The ratio of maximum to minimum measurable flow for a given instrument accuracy (Correct answer)
- The ratio of output signal range to input signal range
- The percentage of full scale at which an instrument loses linearity
- The physical angle a control valve can rotate from fully open to fully closed
Correct answer: The ratio of maximum to minimum measurable flow for a given instrument accuracy
Turndown ratio (also called rangeability) is the ratio of the maximum to the minimum flow that an instrument can measure within its specified accuracy.
Question 3: What is the function of a SCADA Remote Terminal Unit (RTU) in a typical oil and gas pipeline system?
- Runs advanced model predictive control algorithms at the master station
- Collects field data and transmits it to the master station via a communication link (Correct answer)
- Provides operator display graphics for the control room HMI
- Manages cybersecurity certificates for OPC UA connections
Correct answer: Collects field data and transmits it to the master station via a communication link
An RTU acquires data from local field instruments and control equipment, then transmits it to the SCADA master station while executing commands received from the master.
Question 4: A thermocouple produces a voltage based on which physical phenomenon?
- Piezoresistive effect
- Seebeck effect (Correct answer)
- Hall effect
- Faraday induction
Correct answer: Seebeck effect
Thermocouples exploit the Seebeck effect, where a temperature difference between two dissimilar metal junctions generates a measurable electromotive force (EMF).
Question 5: In ISA-5.1 instrumentation symbology, what does a circle with a line through the middle (bisected circle) on a P&ID represent?
- A field-mounted instrument with local indication
- A shared display/shared control device located in the main control room (Correct answer)
- A computer function or software-based control element
- An instrument mounted in an auxiliary panel
Correct answer: A shared display/shared control device located in the main control room
ISA-5.1 uses a circle bisected by a horizontal line to represent a shared display/shared control instrument located in the primary instrument panel or main control room.
Question 6: Which Modbus function code is used to read the status of multiple discrete input coils?
- Function Code 01 (Correct answer)
- Function Code 03
- Function Code 04
- Function Code 06
Correct answer: Function Code 01
Modbus Function Code 01 (Read Coils) reads the ON/OFF status of discrete output coils, while FC 02 reads discrete input contacts.
Question 7: What is the primary purpose of a hazardous area classification exercise (per IEC 60079-10 / NEC 500) in an automation project?
- Determine the required SIL level for safety instrumented functions
- Define zones where ignitable atmospheres may be present to select appropriate equipment (Correct answer)
- Establish the redundancy architecture for the DCS control network
- Calculate the pressure relief valve set points for process vessels
Correct answer: Define zones where ignitable atmospheres may be present to select appropriate equipment
Hazardous area classification identifies locations where flammable gases, vapors, or dusts may occur, enabling the selection of appropriately rated (explosion-proof or intrinsically safe) electrical equipment.
ISA CAP Technology & Tools 3
Which ISA standard governs the functional safety of Safety Instrumented Systems (SIS) in the process industry?