AutoQuiz: Standard Wiring Color for Type K Thermocouple

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?

   

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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.

 

 

 

 

 

 
 

 

AutoQuiz: What Is the Liquid Flow Condition Where Falling Static Pressure Causes Formation of Vapor Bubbles?

AutoQuiz: What Is the Liquid Flow Condition Where Falling Static Pressure Causes Formation of Vapor Bubbles?

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.

What is the term used for phenomenon in liquid flow where falling static pressure causes the formation of vapor bubbles that subsequently collapse back into the all-liquid state as the fluid static pressure is recovered?

a) cavitation
b) pressure piling
c) saturation
d) vortex shedding
e) none of the above

   

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Answer B is not correct. Pressure Piling is a condition that results from the ignition of pre-compressed gases in compartments or subdivisions other than those in which ignition was initiated.

Answer C is not correct. Saturation is a device characteristic exhibited when a further change in an input causes no further change in the output.

Answer D is not correct. Vortex Shedding is the phenomenon that occurs when fluid flows past an obstruction. The shear layer near the obstruction has a high velocity gradient, which makes it inherently unstable. At some point downstream of the immediate vicinity of the obstruction, the shear layer breaks down into well-defined vortices.

The correct answer is A, Cavitation. Cavitation is a two-stage phenomenon of liquid flow. The first stage is the formation of vapor bubbles within the liquid system because of the fluid’s static pressure falling below the fluid vapor pressure  The second stage is the collapse or implosion of these cavities back into an all-liquid state as the fluid decelerates and static pressure is recovered.

Reference: The Automation, Systems, and Instrumentation Dictionary, Fourth Edition, ISA.

Tuning Strategies and the Fragility of Fractional-Order PID Controllers

Tuning Strategies and the Fragility of Fractional-Order PID Controllers

This post is an excerpt from the journal ISA Transactions. All ISA Transactions articles are free to ISA members, or can be purchased from Elsevier Press.

 

Abstract: This paper analyzes the fragility issue of fractional-order proportional-integral-derivative controllers applied to integer first-order plus-dead-time processes. In particular, the effects of the variations of the controller parameters on the achieved control system robustness and performance are investigated. Results show that this kind of controller is more fragile with respect to the standard proportional-integral-derivative controllers and therefore significant attention should be paid by the user in their tuning.

A properly designed control system must provide an effective trade-off between performance and robustness. One of the main reasons to investigate the fragility of fractional-orde PID controllers is to enable an engineer or technician to use alternative strategies for tuning the controller.

 

Free Bonus! To read the full version of this ISA Transactions article, click here.

 

Join ISA and get free access to all ISA Transactions articles as well as a wealth of other technical content, plus discounts on events, webinars, training & education courses, and professional certification.

Click here to join … learn, advance, succeed!

 

2006-2018 Elsevier Science Ltd. All rights reserved.

AutoQuiz: What are the Advantages and Disadvantages of RTDs?

AutoQuiz: What are the Advantages and Disadvantages of RTDs?

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.

RTDs (resistance temperature detectors) are used to measure temperature in a process stream because they have many distinct advantages over thermocouples, including higher resolution of measurement, are more stable, are more repeatable, and give a more linear measurement response. However, RTDs have some distinct disadvantages as compared to thermocouples. All of the following are disadvantages of RTDs as compared to thermocouples, except:

a) require a temperature transmitter to function
b) must have equal length and same type and gauge of lead wires
c) are not self-powered
d) are more expensive than thermocouples
e) none of the above

   

Click Here to Reveal the Answer
Answer B is not the correct choice; equal length and same type and gauge of lead wires is a distinct disadvantage of using RTDs, especially if the lead wires must be extended to the temperature measurement point. RTDs are resistance devices whose measurement can be influenced by variations in lead length and thickness (gauge). Thermocouples do not have this limitation (they are voltage devices).

Answer C is not the correct choice. RTDs are not self-powered (thermocouples generate their own mV signal based on the sample temperature as compared to the reference temperature). An RTD requires a power source, usually a 24VDC supply.

Answer D is not the correct choice. RTDs are much more expensive than thermocouples. The materials from which RTDs are manufactured (platinum and rhodium, among others) are more expensive than copper, iron, or tungsten, common thermocouple materials. Also, RTDs are more expensive to manufacture (e.g., RTD leads are often wound around an insulating core). Common RTD assemblies (3-wire) are typically 2-3 times the cost of comparable thermocouple assemblies measuring the same temperature range.

The correct answer is A, require a temperature transmitter to function. This is not a disadvantage of an RTD, since its function does not require a temperature transmitter to be installed. RTDs do require a power source and a measurement junction, but this can be done with any Wheatstone bridge circuit.

Reference: Maintenance of Instruments and Systems, 2nd Edition, Goettsche, L.D. (Editor), ISA Press.

Image Credit: coastalwiki.org

AutoQuiz: How to Interpret Relay Logic for a Pump Control Switch

AutoQuiz: How to Interpret Relay Logic for a Pump Control Switch

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.

Given the process shown in the post graphic, with the relay logic shown, which of the following statements is true?

a) when the pump control switch is in auto, and the pump is stopped, a low pressure in the pressure tank will start the pump
b) when the pump control switch is in auto, and the pump is running, a low pressure in the pressure tank will stop the pump
c) when the pump control switch is in auto, and the pump is running, a low level in the pressure tank will stop the pump
d) when the pump control switch is in auto, and the pump is running, a low level in the storage tank will stop the pump
e) none of the above

   

Click Here to Reveal the Answer

 

The pressure tank low pressure switch PSL103 is not in the motor control circuit, so a high pressure or low pressure does not have an impact on the pump status. The pressure storage tank low level switch LSL102 is involved in starting the pump, but does not stop the pump since the motor seal-in circuit is in parallel.

The correct answer is D. The storage tank low level switch LSL103 or the pressure tank high level switch LSH101 can stop the pump.

Want to learn more? Check out these ISA reference sources:

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

Programmable Controllers, 4th Edition, by Thomas A. Hughes, ISA Press.

 

 

 

 

 

 

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