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AutoQuiz: How to Read a Gauge Pressure Transmitter

AutoQuiz is edited by Joel Don, ISA’s community manager.

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

A gauge pressure transmitter that measures the pressure in a 150 # high pressure steam header is mounted 6 feet below the center line of the header. The tap for the impulse line connects to the top of the header and rises 2 feet above the header center line, extends horizontally for 3 feet, and then drops down to the transmitter. In order to read the pressure in the steam header correctly, the transmitter output must be:

a) calibrated for suppressed zero, the suppression equal to 8 feet of liquid head pressure
b) calibrated for suppressed zero, the suppression equal to 6 feet of liquid head pressure
c) calibrated for elevated zero, the elevation equal to 8 feet of liquid pressure
d) calibrated for true zero
e) none of the above

At zero gauge pressure in the steam line, you are essentially suppressing (pushing) the transmitter output back down to zero after the system reaches equilibrium with the 8 feet of impulse line full of liquid. The transmitter will read that impulse line liquid head pressure plus any pressure exerted on top of the liquid. 6 feet of liquid head suppression is incorrect as the impulse arrangement will cause 8 feet of liquid head to accumulate.  Elevated zero is incorrect as that adjustment is used to adjust for negative pressure offsets resulting from the transmitter being mounted above the zero reference point (high pressure tap point) and where a liquid in the impulse line or a capillary system would exert a negative pressure.

The correct answer is A, calibrated for suppressed zero with the suppression equal to the 8 feet of liquid height that is in the impulse line.

Reference: Thomas A. Hughes; Measurement and Control Basics, 5th Edition, ISA Press.

AutoQuiz: Failures of Complex Systems in SIS Design and SIL Selection

AutoQuiz is edited by Joel Don, ISA’s social media community manager.

Today’s automation industry quiz question comes from the ISA Certified Automation Professional certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional’s skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.

In safety instrumented system design and safety integrity level selection, what is the most common top-down approach for describing the failures of complex systems?

a) Fault Tree Analysis
b) HAZOP Analysis
c) Root-Cause Analysis
d) Markov Analysis
e) none of the above

A fault tree analysis begins with the “top event,” which is the result of a number of basic events that contribute to, or initiate, the system failure.  The logic of a fault tree is displayed by the symbols that represent the basic events and gates that logically relate those events.

The correct answer is A, Fault Tree Analysis.

Reference: Edward M. Marszal, P.E., C.F.S.E and Dr. Eric W. Scharpf, MIPENZ; Safety Integrity Level Selection: Systematic Methods Including Layer of Protection Analysis, ISA Press.

AutoQuiz: Loop Tuning Terminology for Change in Amplitude

AutoQuiz is edited by Joel Don, ISA’s community manager.

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

What common loop tuning terminology is used to describe the change in amplitude of the control loop oscillations shown in the post graphic?

a) 4:1 Decay Ratio
b) Quarter Wave Decay
c) ¼ ZN Diffraction
d) 4/1 Gain Response
e) none of the above

The common method of judging tuning is known as the “quarter wave decay” method.  It has been shown if a loop is tuned so the oscillation decays with each wave being one quarter of the previous wave, it produces satisfactory, if not optimum, set point response and disturbance rejection.

The correct answer is B, Quarter Wave Decay.

Reference: Harley M. Jeffery; Loop Checking: A Technician’s Guide, ISA Press.

AutoQuiz: Industrial Applications for Nonincendive-Rated Field Wiring

AutoQuiz is edited by Joel Don, ISA’s social media community manager.

Today’s automation industry quiz question comes from the ISA Certified Automation Professional certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional’s skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.

Nonincendive-rated field wiring is allowed to be used in which of the following combinations of hazardous area classifications?

a) Class 1, Division 2 and Class 1, Zone 0
b) Class 1, Division 1; Class 1, Division 2; Class 1, Zone 1 and Class 1, Zone 2
c) Class 1, Division 2; Class 1, Zone 1 and Class 1, Zone 2
d) Class 1, Division 2; Class 1, Zone 2 and Non-hazardous
e) none of the above

Nonincendive is allowed in Class 1, Division 2; Class 1, Zone 2, and Non-hazardous rated areas. Use in higher hazard areas, such as Division 1, Zone 1, or Zone 0 areas, is not allowed.

Reference: NFPA 70, National Electrical Code 2005 or 2008.

AutoQuiz: Standard Wiring Color for Type K Thermocouple

AutoQuiz is edited by Joel Don, ISA’s community manager.

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

In the diagram in the post image, which (A, B, C or D) is the standard wiring color for a Type K thermocouple in the U.S. and Canada?

A illustrates the very common Type J, Iron/Constantan thermocouple.

B illustrates the less common Type E, Chromel/Constantan thermocouple.

D illustrates the less common Type T, Copper/Constantan thermocouple.

The correct answer is C, which illustrates the very common Type K, Chromel/Alumel thermocouple.

References:

Control Systems Engineering Exam Reference Manual: A Practical Study Guide, by Bryon Lewis, ISA Press.

Measurement and Control Basics, 5th Edition, by Thomas A. Hughes, ISA Press.