Plant Operator Selection System Test Plant Operator Selection System Technical Manual Interpretation 5 — Questions and Answers
Question 1: A manual shows a logic diagram with two inputs (A and B) connected by an AND gate leading to output C. Input A is 'High Pressure Switch Active' and Input B is 'High Temperature Switch Active.' When will Output C activate?
- When either high pressure OR high temperature is detected
- Only when both high pressure AND high temperature are simultaneously detected (Correct answer)
- When neither condition is detected
- When high pressure is detected but high temperature is not
Correct answer: Only when both high pressure AND high temperature are simultaneously detected
An AND gate produces a true output only when all inputs are simultaneously true; Output C activates only when both the pressure and temperature switches are active at the same time.
Question 2: A material safety data sheet (MSDS/SDS) lists a chemical's flash point as 73°F. The plant ambient temperature on a summer day reaches 85°F. What does this indicate about handling the chemical?
- The chemical is safe to handle since the flash point has been exceeded without incident
- The chemical's vapors can ignite since ambient temperature exceeds the flash point (Correct answer)
- The flash point is irrelevant unless the chemical is directly heated
- The chemical requires cooling only below 32°F
Correct answer: The chemical's vapors can ignite since ambient temperature exceeds the flash point
When ambient temperature exceeds the flash point, the chemical produces sufficient vapor to ignite if an ignition source is present, requiring ignition source control.
Question 3: A procedure contains a two-column table. Column 1 lists 'IF condition' and Column 2 lists 'THEN action.' One row reads: IF 'pump discharge pressure < 20 PSI for more than 30 seconds' THEN 'shut down pump and notify supervisor.' Current discharge pressure is 18 PSI for 45 seconds. What action is required?
- Continue monitoring; 18 PSI is close enough to 20 PSI
- Shut down the pump and notify the supervisor immediately (Correct answer)
- Wait for pressure to recover before taking any action
- Notify the supervisor but keep the pump running
Correct answer: Shut down the pump and notify the supervisor immediately
Both conditions of the IF clause are met (pressure < 20 PSI and duration > 30 seconds), so the THEN action (shut down pump and notify supervisor) is required.
Question 4: A technical drawing uses the symbol '≈' next to a dimension. In the context of a manufacturing tolerance table, what does this symbol most likely indicate?
- The dimension is exact and must be met precisely
- The dimension is approximate and a tolerance range applies (Correct answer)
- The dimension applies only at elevated temperatures
- The dimension has been revised from a previous version
Correct answer: The dimension is approximate and a tolerance range applies
The '≈' symbol means 'approximately,' indicating the value is nominal and subject to tolerances specified elsewhere in the document.
Question 5: A startup checklist has 25 items. Items 1-10 are marked 'Pre-Startup,' items 11-20 are marked 'Startup,' and items 21-25 are marked 'Post-Startup Verification.' An operator completes all Pre-Startup items and begins item 15. Which phase is being executed?
- Pre-Startup phase
- Startup phase (Correct answer)
- Post-Startup Verification phase
- The phases cannot be determined from item numbers alone
Correct answer: Startup phase
Item 15 falls within the range 11-20 labeled 'Startup,' so the operator is in the Startup phase of the checklist.
Question 6: An equipment specification states: 'Maximum allowable working pressure (MAWP): 250 PSIG at 400°F; at 500°F, derate to 200 PSIG.' The vessel currently operates at 230 PSIG and 490°F. Is operation within safe limits?
- Yes, because 230 PSIG is below the 250 PSIG MAWP
- No, because at 490°F the derated MAWP of 200 PSIG applies and 230 PSIG exceeds it (Correct answer)
- Yes, because 490°F is below the 500°F threshold
- No, because all derating applies immediately above 400°F
Correct answer: No, because at 490°F the derated MAWP of 200 PSIG applies and 230 PSIG exceeds it
The derating to 200 PSIG applies at 500°F; at 490°F the limit is between 200 and 250 PSIG, and since 490°F is very near 500°F, interpolation shows the limit is approximately 205 PSIG—230 PSIG exceeds safe operation near this threshold and the conservative reading requires compliance with the 200 PSIG derated limit.
Question 7: A manual states that a sensor has a 'range' of 0-500 PSIG and an 'accuracy' of ±1% of full scale. A reading shows 250 PSIG. What is the actual pressure range that this reading could represent?
- 249 to 251 PSIG
- 247.5 to 252.5 PSIG
- 245 to 255 PSIG (Correct answer)
- 200 to 300 PSIG
Correct answer: 245 to 255 PSIG
1% of full scale (500 PSIG) = ±5 PSIG; the actual pressure could be anywhere from 245 to 255 PSIG.
Plant Operator Selection System Test Plant Operator Selection System Technical Manual Interpretation 5
A manual shows a logic diagram with two inputs (A and B) connected by an AND gate leading to output C.
Input A is 'High Pressure Switch Active' and Input B is 'High Temperature Switch Active.' When will Output C activate?