Certified Automation Professionals (CAP) Questions

Certified Automation Professionals (CAP) Questions

This post covers the Certified Automation Professionals (CAP) Questions and answers which are useful for the exam preparation.


A set of new, 4-20mA gage pressure transmitters has been wired to an analog input card in an existing PLC system, and you are tasked with scaling the raw input values in the PLC logic. This analog card has the following characteristics:

  • Unsigned, 14-bit analog data format
  • Eight (8) channels, 0-20mA inputs
  • Single-ended inputs
  • No channel diagnostics
  • Data stored internally in integer “counts,” from 0 up to the maximum 14-bit value

After reviewing these specifications, you determine the correct equation to program into the PLC to determine the current process values from the new transmitters is (where Engineering Units Value at 20 mA = EU100% and Engineering Units Value at 4 mA = 0 psig):

a. Analog Value in Eng Units=[EU100%-(Raw Counts-3277)] ÷ 4096

b. Analog Value in Eng Units=[(Raw Counts-819) × EU100%] ÷ 6048

c. Analog Value in Eng Units=[(Raw Counts-3277) × EU100%] ÷ 13106

d . Analog Value in Eng Units=[(Raw Counts+1637) ÷ EU100%] × 16384

CAP answer

The correct answer is C . To scale the analog input, calculate the “% of the raw counts range” that is represented by the analog input, and multiply by the EU100% range, since the EU0% value is 0.

For a 14-bit input with no sign bit or diagnostics bit, the maximum number of counts is (2^14 - 1), or 16383. Since the analog input card raw counts are for a 0-20mA signal, we need to determine the number of raw counts that represents a 4-20mA signal. 4mA is 20% of the 0-20mA range, so the raw counts that correspond to a 4-20mA signal: (20% x 16383) = 3277 counts at 4mA and 16383 counts at 20mA. Therefore, the span of raw counts is (16383 - 3277) = 13106 counts.

Therefore, the percent of range of the current analog value is = (Raw Counts - 3277) / 13017. Multiplying by EU100% gives us the scaled analog input value.

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition , ISA, 2006.



CAP question

Which one of the following flow sensors naturally generates a pulsed output as a representation of the flow rate:

A. orifice plate with differential pressure transmitter

B. thermal mass flowmeter

C. turbine meter

D. magnetic flowmeter

CAP answer

The correct answer is C , “turbine meter.” Turbine meters almost universally use a magnetic pickup to determine the number of rotations of the spinning turbine element. Each time a magnetized blade passes the pickup sensor, a pulse is generated. The volumetric flow rate can be determined by counting the number of pulses in a unit of time.

Answers A, B, and D are not correct; each of these flowmeter types generally produces an electrical signal, with a magnitude that is proportional to flow rate. Each of these flowmeter types could be outfitted with a transmitter capable of transmitting pulses, but only the turbine meter from the choices above naturally generates pulses (with frequency proportional to flow rate).

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge , Second Edition, ISA, 2006.


CAP question

If a hacker intercepts and changes set point data traveling over an industrial network, which basic security property is affected?

A. integrity
B. functionality
C. availability
D. defensibility

CAP answer

The correct answer is A, integrity. Data integrity implies that the data received is the same (value, format, quality) as the data sent. If a hacker is successful in changing set point data as that data travels over the network, the hacker has compromised integrity of the data, since it is no longer the same when received as when sent.

Answer B is incorrect, because functionality is not a basic security property.

Answer C is incorrect, because the problem statement did not address the availability of data. It appears that only the value of the set point (data integrity) was affected.

Answer D is incorrect, because defensibility is not a basic security property, but rather a measure of the vulnerability of a system.

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition , ISA, 2006.

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CAP question

The fastest “electronic” method to bring a DC motor to a full stop is to use:

A. regenerative braking

B. mechanical braking

C. ramp to stop

D. coast to stop

CAP answer

The correct answer is A. In regenerative braking, all of the motor’s energy is fed directly back into the AC power line. This is accomplished through the use of “reverse-connected” SCRs, which allow the drive to conduct current in the opposite direction and oppose the rotation of the motor, bringing it to a quick stop.

Answer B is incorrect, because mechanical braking is not an electric method for braking a DC motor. This is a mechanical method, which uses friction to stop the motor shaft once power has been removed.

Answer C, ramp to stop, is an electronic means of stopping a motor over a longer period of time. A high-wattage bank of resistors transforms the rotating energy into heat, thereby dissipating the voltage generated by the motor, slowly bringing the motor to a stop.

Answer D, coast to stop, is the slowest way to stop a motor, and is accomplished by simply removing the motor current and allowing inertia to bring the motor to a stop.

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition , ISA, 2006.

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CAP question

In the maintenance sequence, the technician often knows what the needed resources are before going to fix the device or equipment, as in a known transmitter failure.

The technician’s challenge is to restore the device to service as quickly as possible. Which definition below, according to the maintenance sequence, defines the quantity “restore time”?

A. repair time + time to close work order

B. repair time + testing time

C. time to troubleshoot/diagnose/isolate + travel time + repair time

D. repair time and restore time are the same quantity.

CAP answer

The correct answer is C, “time to troubleshoot/diagnose/isolate + travel time + repair time.” The restore time includes all activities required to diagnose and repair the device. This includes diagnosing the problem, isolating the device from the system, travelling to the device, and repairing the device. Repair time includes removing/repairing/replacing the device, aligning/adjusting/calibrating the device, and testing/restarting the device.

Answer A is not correct, as work order closure is not required to restore a device to service. Cleanup, work order closure, and return to shop are activities that occur after the restore time period.

Answer B is not correct, because testing time is included in the repair-time activities.

Answer D is not correct, because restore time requires additional activities to be completed beyond the repair-time activities, as described above.

Reference : Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition , ISA, 2006.


CAP Sample Questions

The following six questions were taken from the CAP® examination question item bank and serve as examples of the question type and question content found on the CAP® examination.

1. The method by which the tasks and hazards associated with a machine or process are analyzed is known as:

A. Risk assessment.
B. Machine assessment.
C. Risk reduction.
D. Risk abatement.

2. To test controller tuning or prototype new control strategies offline, the model should be a(an):

A. Tie-back (loopback) simulation.
B. Artificial neural network.
C. Dynamic process simulation.
D. Steady state process simulation.

3. The temperature measurement with the BEST repeatability and resolution is the:

A. Thermocouple.
B. Resistance temperature detector (RTD).
C. Dial thermometer.
D. Capillary system.

4. Which of the following is NOT a variable speed drive setup parameter?

A. Acceleration rate.
B. Motor winding type.
C. Output frequency.
D. Maximum speed.

5. A complete test plan for system integration testing MUST include:

A. Comments for the application programmer.
B. Multiple test cases for each mode of operation.
C. At least five test cases for each test.
D. Expected results for each test case.

6. Frequency of maintenance should be determined by:

A. Failure rates of components.
B. Availability of personnel and parts.
C. Management targets for efficiency and productivity.
D. Effectiveness of maintenance personnel.

Sample Questions Answer Key

Question Number Correct Answer Examination Content Outline
1 A Domain 1, Task 4
2 C Domain 2, Task 2
3 B Domain 3, Task 3
4 B Domain 4, Task 7
5 C Domain 5, Task 5
6 A Domain 6, Task 2

Which choice is NOT a major advantage of using cascade control?

a) Any disturbances that affect the slave variable are detected and compensated for by the slave controller before they have time to affect the primary control variable

b) The controllability of the outside loop is improved because the inside loop speeds up the response of the process dynamic elements between the control variable and slave variable.

c) Nonlinearities of the process in the inner loop are handled by that loop and removed from the more important outer loop.

d) It can further improve the performance of loops that are already very controllable.

e) None of the above


The correct answer is D . Cascade control does very little to improve upon control loops that were previously stable. Examples are liquid level and gas pressure control loops.