Free PE-CS Practice Questions

Question 1

An orifice flow installation is calibrated for 0-250 m³/h at 0-25 kPa differential pressure, with constant fluid density. During commissioning, an applied differential pressure of 10.24 kPa produces 14.24 mA and a transmitter display of 160 m³/h, but the distributed control system (DCS) displays 200 m³/h. Both displays read correctly at zero and full scale. What explains the discrepancy?

Accepted Answer

Square-root extraction is occurring twice; make the DCS input linear.

Answer

The differential-pressure span is too large; reduce the transmitter's upper range value.

Answer

The transmitter has no square-root extraction; enable its flow conversion.

Answer

The analog input has a zero error; apply a new input zero trim.

Question 2

Steam-header pressure disturbances reach a heat exchanger faster than its outlet-temperature controller can respond. A well-tuned steam-flow loop is much faster than the temperature loop, and both use the same steam valve. Product outlet temperature must remain the controlled variable. Select the appropriate cascade connection.

Accepted Answer

Let the temperature controller set the flow controller's setpoint; let the flow controller position the valve.

Answer

Let the flow controller set the temperature controller's setpoint; let the temperature controller position the valve.

Answer

Add the temperature-controller and flow-controller outputs; send their sum directly to the steam valve.

Answer

Replace temperature feedback with header-pressure feedforward; set the valve from header pressure alone.

Question 3

A hot-liquid control valve discharges a persistent liquid-vapor mixture. At the operating temperature, the liquid's vapor pressure is 3.0 bar absolute; inlet pressure is 8.0 bar absolute and downstream pressure is maintained at 1.8 bar absolute. Inspection finds erosion extending into the downstream pipe. The process pressures and temperature cannot be changed. Which proposal addresses the governing mechanism?

Accepted Answer

Treat the service as flashing and select erosion-resistant geometry with adequate two-phase outlet capacity.

Answer

Install multistage anti-cavitation trim to eliminate vapor formation while retaining the existing outlet pressure.

Answer

Use a higher-pressure-recovery valve to raise vena-contracta pressure above the liquid's vapor pressure.

Answer

Use hardened trim with single-phase liquid sizing; the phase change affects wear but not required outlet capacity.

Question 4

A two-wire transmitter must operate throughout its 4-20 mA measurement range and deliver its configured 22 mA high-fault signal. The supply is nominally 24 VDC but can fall to 22.5 VDC. The transmitter requires at least 12.0 V at its terminals. A series interface drops 2.0 V, and the passive receiving input has a 250 Ω resistance. There are no other loads. Which is the largest listed total cable resistance, including both conductors, that satisfies the complete output requirement?

Accepted Answer

120 Ω

Answer

90 Ω

Answer

150 Ω

Answer

200 Ω

Question 5

A layer of protection analysis evaluates vessel rupture initiated by a pressure transmitter failing low, at 0.08 events per year. An independent relief system is credited with a probability of failure on demand of 0.10. A proposed alarm/operator layer uses that same failed transmitter and claims a probability of failure on demand of 0.10. The tolerable rupture frequency is 4 × 10⁻⁵ per year, with no additional conditional factors. A new low-demand safety instrumented function (SIF) will be independent of the initiating failure and the relief system. What is its largest permissible average probability of failure on demand (PFDavg), and which safety integrity level (SIL) probability band contains that value?

Accepted Answer

0.005 - SIL 2 probability band

Answer

0.0005 - SIL 3 probability band

Answer

0.05 - SIL 1 probability band

Answer

0.5 - below the SIL 1 risk-reduction range

Question 6

A closed-vessel level transmitter has its high-pressure side connected to the bottom tap and its low-pressure side connected to the vapor space through a filled wet leg. After maintenance, the indicated level is higher than the sight-glass level. Process density and actual level are unchanged, and the transmitter passes an applied-pressure calibration. Which maintenance change would produce this direction of error?

Accepted Answer

Returning the low-side wet leg to service before it has been completely refilled.

Answer

Refilling the low-side wet leg with a denser liquid than the calibration assumes.

Answer

Raising the low-side reference pot while keeping the wet leg completely filled.

Answer

Increasing the configured process density while retaining the original wet-leg correction.

Question 7

A pressure override temporarily limits steam-valve opening through a low-signal selector. While the temperature controller is not selected, its requested output continues to rise. When the pressure constraint clears, the valve stays wide open even after temperature exceeds setpoint; it closes only after a prolonged recovery. Valve-position feedback confirms that the actuator follows the selected command. Which control modification targets this behavior?

Accepted Answer

Feed the selected valve command back to the temperature controller for integral tracking.

Answer

Shorten the temperature controller's integral time to remove the accumulated error more rapidly.

Answer

Widen the temperature controller's output limits so its requested output does not saturate.

Answer

Increase derivative filtering to suppress the delayed temperature response after the override clears.

Question 8

Select the valve trim that can regulate at both operating points below. The service is water with specific gravity 1.0; flow is turbulent and unchoked, and piping correction factors are unity.

Low load: 12 US gpm, with 36 psi across the valve.
Peak load: 72 US gpm, with 9 psi across the valve.

Each listed Cv range is the manufacturer's usable range over the permitted travel band. All trims meet the pressure, temperature, and material requirements.

Accepted Answer

Trim C: usable Cv range 1.5-30

Answer

Trim A: usable Cv range 1.0-16

Answer

Trim B: usable Cv range 3.0-40

Answer

Trim D: usable Cv range 0.5-20

Question 9

An intrinsically safe transmitter and its proposed barrier are each certified for the required hazardous location, but their certificates require an entity-parameter compatibility check. The transmitter's maximum permitted input voltage Ui is 28 V; the barrier's certified maximum output voltage Uo is 30 V. Normal operation is at 24 V, and the commissioning current-loop test passes. All other entity and installation checks are satisfactory. What disposition is justified?

Accepted Answer

Replace the barrier with a compatible lower-Uo unit and reverify the circuit.

Answer

Accept the combination because its measured operating voltage remains below the transmitter's 28 V limit.

Answer

Retain the barrier and lower the normal supply voltage; no further entity review is necessary.

Answer

Retain the combination and place the field junction box in an explosion-proof enclosure instead.

Question 10

During an authorized online test, an exothermic reactor's high-high-temperature trip input is bypassed and connected to a simulator. The test permit requires independent temperature monitoring and an available manual shutdown. The independent measurement now exceeds the trip setpoint and continues rising. The safety requirements specification calls for isolating reactant feed while maintaining cooling; the manual shutdown performs those actions and is unaffected by the test bypass. Restoring the automatic input would take several minutes. Which action takes priority?

Accepted Answer

Initiate the available manual shutdown immediately, isolating reactant feed while maintaining cooling.

Answer

Restore the automatic trip input before taking shutdown action, preserving the normal protection sequence.

Answer

Trip all reactor pumps, including the cooling pumps, to maximize immediate isolation of the equipment.

Answer

Increase cooling and continue the test while watching for the temperature trend to reverse.

Free PE-CS Practice Questions

Domain 1: Measurement

Question 1

Question 2

Domain 2: Control Systems

Question 3

Question 4

Domain 3: Final Control Elements

Question 5

Question 6

Domain 4: Signals, Transmission, and Networking

Question 7

Question 8

Domain 5: Safety Instrumented Systems

Question 9

Question 10

That's 10 of 1,030