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ISA CCST Level II study materials
ISA CCST Level II study resources

ISA CCST Level II practice questions

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Question 1Calibration, maintenance, repair and troubleshooting

A technician is verifying the calibration of a pressure transmitter with a 4–20 mA output. The transmitter is rated 0–100 psi. What is the expected output current at 25 psi?

  1. 20 mA
  2. 12 mA
  3. 8 mA Correct answer.
  4. 4 mA

Explanation

The 4–20 mA signal is linear with the measured variable. At 25 psi (25% of span), the current is 4 mA + 0.25 × 16 mA = 8 mA.

Question 2Calibration, maintenance, repair and troubleshooting

When performing a five-point calibration check on a transmitter, which sequence helps identify hysteresis?

  1. Apply only the zero and span inputs
  2. Apply inputs in random order
  3. Apply inputs in increasing order only
  4. Apply inputs in increasing order, then decreasing order Correct answer.

Explanation

Hysteresis is the difference in output when the same input is approached from opposite directions. Checking both upscale and downscale values reveals this difference.

Question 3Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a 4–20 mA loop that reads 0 mA at the control room. The transmitter is powered locally and the signal is isolated. What is the most likely cause?

  1. The loop wiring is open Correct answer.
  2. The process variable is at zero
  3. The transmitter is calibrated incorrectly
  4. The receiver has a high input impedance

Explanation

A 0 mA reading in a powered loop usually indicates no current flow, often from an open circuit. Calibration errors or a zero process variable would still produce at least 4 mA in a healthy loop.

Question 4Calibration, maintenance, repair and troubleshooting

What is the primary purpose of a calibration record for an instrument in a process plant?

  1. To record the instrument's purchase price
  2. To document traceability and as-found/as-left conditions Correct answer.
  3. To replace the need for periodic calibration
  4. To satisfy the manufacturer's warranty

Explanation

Calibration records provide traceability to standards and capture the as-found and as-left conditions. This supports quality systems and maintenance planning.

Question 5Calibration, maintenance, repair and troubleshooting

A technician is using a digital multimeter to measure the current in a 4–20 mA loop. How should the meter be connected?

  1. Across the power supply terminals
  2. In parallel with the transmitter
  3. Between the signal line and ground
  4. In series with the loop Correct answer.

Explanation

Current measurement requires the meter to be part of the circuit so the loop current flows through it. This means breaking the loop and connecting the meter in series.

Question 6Calibration, maintenance, repair and troubleshooting

Which of the following is a common symptom of a grounded thermocouple in a process measurement loop?

  1. The reading is exactly 0 mV
  2. The reading is always at maximum
  3. The reading drifts or is erratic Correct answer.
  4. The reading is stable but offset by a fixed amount

Explanation

A grounded thermocouple creates an unintended electrical path that can introduce noise or drift. The result is often an erratic or drifting reading rather than a fixed offset.

Question 7Calibration, maintenance, repair and troubleshooting

When replacing a pressure gauge on a steam line, what is the correct first step?

  1. Verify the gauge range matches the process
  2. Loosen the gauge fitting slowly
  3. Close the isolation valve and relieve pressure Correct answer.
  4. Apply thread sealant to the new gauge

Explanation

Safety procedures require isolating and depressurizing the line before breaking any connection. Only then should the gauge be removed.

Question 8Calibration, maintenance, repair and troubleshooting

What does a calibration error of 2% of span indicate about an instrument with a 0–200 °F range?

  1. The output is off by 20 °F
  2. The output is off by 0.2 °F
  3. The output is off by 2 °F
  4. The output is off by 4 °F Correct answer.

Explanation

Error as a percentage of span is calculated as (error / span) × 100. Here, 2% of 200 °F equals 4 °F.

Question 9Calibration, maintenance, repair and troubleshooting

A technician is calibrating a smart transmitter using a HART communicator. The transmitter is in a loop with a 250-ohm resistor. What is the purpose of the resistor?

  1. To protect the transmitter from overvoltage
  2. To limit loop current
  3. To convert current to voltage for the communicator Correct answer.
  4. To provide a HART communication signal path

Explanation

HART communication superimposes a frequency signal on the 4–20 mA loop. The resistor develops a voltage that the communicator can read, enabling digital communication.

Question 10Calibration, maintenance, repair and troubleshooting

During a calibration check, a technician finds that a transmitter's output at 50% input is 11.8 mA instead of 12.0 mA. What type of error does this indicate?

  1. Hysteresis
  2. Span error
  3. Zero shift
  4. Linearity error Correct answer.

Explanation

A deviation at midscale while zero and span are correct indicates a linearity error. The output does not follow a straight line between the endpoints.

Question 11Calibration, maintenance, repair and troubleshooting

A technician needs to verify the calibration of a resistance temperature detector (RTD). Which simulated input is appropriate for a 100-ohm platinum RTD at 0 °C?

  1. 0 ohms
  2. 10 ohms
  3. 138.5 ohms
  4. 100 ohms Correct answer.

Explanation

A 100-ohm platinum RTD has a nominal resistance of 100 ohms at 0 °C. This is the standard base value for the sensor.

Question 12Calibration, maintenance, repair and troubleshooting

What is the recommended practice when tightening the bonnet bolts on a differential pressure transmitter after diaphragm replacement?

  1. Tighten one bolt fully, then the others
  2. Tighten until the diaphragm leaks
  3. Tighten in a star pattern to the specified torque Correct answer.
  4. Tighten by hand only

Explanation

A star or cross pattern distributes clamping force evenly and prevents diaphragm distortion. Always follow the manufacturer's torque specification.

Question 13Calibration, maintenance, repair and troubleshooting

A technician observes that a control valve responds slowly to a step change in signal. Which maintenance action is most likely to correct the problem?

  1. Increasing the air supply pressure
  2. Recalibrating the positioner
  3. Replacing the valve stem packing Correct answer.
  4. Changing the valve trim

Explanation

Slow response often results from excessive friction in the packing. Replacing or adjusting the packing can restore proper movement.

Question 14Calibration, maintenance, repair and troubleshooting

When using a loop calibrator to source a 4–20 mA signal into a transmitter, what must be verified first?

  1. The transmitter is in manual mode
  2. The calibrator battery is fully charged
  3. The calibrator is set to source mode and the loop is isolated Correct answer.
  4. The loop resistor is removed

Explanation

Sourcing current requires the calibrator to be in source mode and the loop isolated to prevent conflicts with other power sources. This ensures a controlled test signal.

Question 15Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a pH analyzer that reads a constant value regardless of process changes. What is a likely cause?

  1. The glass electrode is coated
  2. The analyzer is in hold mode Correct answer.
  3. The temperature compensation is disabled
  4. The reference electrode is dry

Explanation

A constant reading that does not respond to process changes often indicates the analyzer is in hold or simulate mode. Checking the mode is a first troubleshooting step.

Question 16Calibration, maintenance, repair and troubleshooting

What is the purpose of a calibration seal on an instrument?

  1. To indicate the instrument's age
  2. To prevent unauthorized adjustment Correct answer.
  3. To provide electrical grounding
  4. To improve measurement accuracy

Explanation

Calibration seals are tamper-evident devices that discourage or reveal unauthorized changes. They help maintain the integrity of a calibration.

Question 17Calibration, maintenance, repair and troubleshooting

A technician is replacing a thermocouple in a process. Which action helps prevent incorrect polarity connections?

  1. Soldering the connections
  2. Using any available copper wire
  3. Matching the wire color code to the thermocouple type Correct answer.
  4. Twisting the wires together

Explanation

Thermocouple wires use standardized color codes by type. Matching the color code ensures correct polarity and avoids measurement errors.

Question 18Calibration, maintenance, repair and troubleshooting

A technician is performing preventive maintenance on a pressure transmitter. Which task is typically included?

  1. Replacing the transmitter electronics
  2. Changing the loop power supply
  3. Recalibrating the DCS graphics
  4. Inspecting and cleaning the impulse lines Correct answer.

Explanation

Preventive maintenance for pressure transmitters includes checking impulse lines for blockages or leaks. This helps ensure reliable measurement.

Question 19Calibration, maintenance, repair and troubleshooting

A technician is testing a 4–20 mA loop with a multimeter and reads 24 VDC across the transmitter terminals. The transmitter is supposed to output 12 mA. What does this indicate?

  1. The transmitter is calibrated incorrectly
  2. The transmitter is working correctly
  3. The multimeter is in the wrong mode Correct answer.
  4. The loop is open

Explanation

Measuring 24 VDC across the transmitter terminals suggests the meter is set to voltage, not current. A current measurement would require the meter in series and would read milliamps.

Question 20Calibration, maintenance, repair and troubleshooting

What is the effect of a leak in the impulse line of a differential pressure transmitter?

  1. The transmitter reads a lower differential pressure
  2. The transmitter output increases linearly
  3. The transmitter reading becomes unstable or zero Correct answer.
  4. The transmitter reads a higher differential pressure

Explanation

A leak in an impulse line causes loss of pressure or air ingress, leading to unstable or zero differential pressure. The reading may fluctuate or drop to zero.

Question 21Calibration, maintenance, repair and troubleshooting

A technician is calibrating a temperature transmitter with a 0–500 °F range and a 4–20 mA output. The transmitter is found to have a zero error of +2 °F and no span error. What is the as-found output at 250 °F?

  1. 12.13 mA
  2. 12.06 mA Correct answer.
  3. 12.00 mA
  4. 11.94 mA

Explanation

A zero error shifts the entire curve. At 250 °F, the ideal current is 12 mA. A +2 °F error adds 2/500 × 16 mA = 0.064 mA, resulting in 12.064 mA, approximately 12.06 mA.

Question 22Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a control loop where the measured variable oscillates continuously. The controller output also oscillates. What is the most likely cause?

  1. The controller tuning is too aggressive Correct answer.
  2. The final control element is stuck
  3. The controller is in manual mode
  4. The transmitter is calibrated incorrectly

Explanation

Continuous oscillation in both measurement and output often indicates excessive controller gain or too little integral time. Reducing the tuning aggressiveness can stabilize the loop.

Question 23Calibration, maintenance, repair and troubleshooting

A technician is using a deadweight tester to calibrate a pressure gauge. The tester's piston area is 0.1 in². What mass is required to generate 100 psi? (Assume g = 32.2 ft/s²)

  1. 10 lb Correct answer.
  2. 1000 lb
  3. 1 lb
  4. 100 lb

Explanation

Pressure equals force divided by area. Force = 100 psi × 0.1 in² = 10 lb. The required mass is therefore 10 lb.

Question 24Calibration, maintenance, repair and troubleshooting

A technician is calibrating a vortex flowmeter. The meter is installed with insufficient straight pipe upstream. What effect is most likely?

  1. The meter will be immune to installation effects
  2. The meter will have a reduced accuracy due to swirl Correct answer.
  3. The meter will output a constant 20 mA
  4. The meter will read zero

Explanation

Vortex flowmeters require sufficient straight run to develop a stable flow profile. Insufficient upstream length introduces swirl and distorts the vortex shedding, reducing accuracy.

Question 25Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a 4–20 mA loop that intermittently drops to 0 mA. The problem occurs only when a nearby motor starts. What is the most likely cause?

  1. The loop power supply is failing
  2. The loop resistor is too large
  3. Electrical noise is causing a ground loop or interference Correct answer.
  4. The transmitter is failing

Explanation

Intermittent failures correlated with motor starts suggest electrical noise or a ground loop. Motor starting creates transients that can interfere with the signal.

Question 26Calibration, maintenance, repair and troubleshooting

A technician is preparing to calibrate a pressure transmitter that is installed in a process line. Which action should be taken before applying any test pressure?

  1. Disconnect the transmitter from the loop power supply
  2. Isolate the transmitter from the process and vent trapped pressure Correct answer.
  3. Increase the process pressure to the upper range value
  4. Loosen the process connection to verify it is tight

Explanation

Before calibration, the transmitter must be isolated from process pressure and any trapped pressure vented so that the applied test pressure is the only pressure seen by the sensor. Failure to isolate can expose the technician to process fluid and can make the calibration invalid because process pressure adds to the test pressure.

Question 27Calibration, maintenance, repair and troubleshooting

When performing a five-point calibration check on a 4–20 mA transmitter, which input sequence is standard practice?

  1. Apply 0%, 50%, 100%, 50%, and 0% to check both upscale and downscale Correct answer.
  2. Apply 100%, 75%, 50%, 25%, and 0% in decreasing order only
  3. Apply 50% only, since the zero and span are assumed correct
  4. Apply 0%, 25%, 50%, 75%, and 100% of span in increasing order only

Explanation

A five-point check typically includes both increasing and decreasing inputs so that hysteresis and deadband can be detected. Checking only one direction can miss differences between upscale and downscale response. The 0–50–100–50–0 sequence provides both directions with a manageable number of points.

Question 28Calibration, maintenance, repair and troubleshooting

A technician is checking a 4–20 mA transmitter with a 0–100 psig range. The transmitter outputs 12.0 mA at 50 psig. What does this indicate?

  1. The transmitter output is saturated
  2. The transmitter has a zero shift of 50 psig
  3. The transmitter has a span error of 50%
  4. The transmitter is calibrated correctly at midscale Correct answer.

Explanation

For a linear 4–20 mA transmitter with a 0–100 psig range, 50 psig is 50% of span and should produce 12.0 mA. The reading matches the expected output, so no calibration error is indicated at that point. A full five-point check would still be needed to confirm the entire range.

Question 29Calibration, maintenance, repair and troubleshooting

A technician is repairing a 4–20 mA loop and needs to measure the current through the transmitter without breaking the circuit. Which instrument setup is appropriate?

  1. A multimeter set to resistance connected in series with the loop
  2. A multimeter set to DC milliamps connected in parallel with the transmitter
  3. A multimeter set to DC volts connected across the transmitter terminals
  4. A clamp-on current meter set to DC milliamps around one loop conductor Correct answer.

Explanation

A clamp-on DC current meter placed around a single loop conductor measures current without opening the circuit. This is useful for troubleshooting live 4–20 mA loops because the process can remain running. The meter must be capable of DC current measurement and must clamp only one conductor.

Question 30Calibration, maintenance, repair and troubleshooting

What is the primary purpose of a calibration certificate for a process instrument?

  1. To replace the need for periodic calibration of the instrument
  2. To certify that the instrument is approved for use in hazardous areas
  3. To document the as-found and as-left conditions and traceability of the calibration Correct answer.
  4. To guarantee that the instrument will never drift out of tolerance

Explanation

A calibration certificate records the as-found and as-left readings, the standards used, and their traceability so that the calibration can be audited. It provides evidence of the instrument's condition at the time of calibration. It does not guarantee future performance or replace a calibration schedule.

Question 31Calibration, maintenance, repair and troubleshooting

A technician is inspecting a control valve that has been in service. Which condition most directly indicates that the packing needs attention?

  1. The valve stem has a slight discoloration from heat
  2. The valve positioner has a small deadband
  3. Process fluid weeping from the packing gland area Correct answer.
  4. The actuator air supply is regulated to 20 psig

Explanation

Visible leakage at the packing gland indicates that the packing has worn or lost compression and should be adjusted or replaced. Packing leakage is a common maintenance finding on control valves and can become a safety or environmental issue. Discoloration, air supply pressure, and positioner deadband are not direct indicators of packing condition.

Question 32Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting an RTD temperature loop that reads a fixed low temperature. The RTD leads are connected to the transmitter with a two-wire configuration. Which condition is most likely?

  1. A short circuit across the RTD element Correct answer.
  2. An increase in the RTD element resistance
  3. A high-resistance connection in one lead
  4. An open circuit in one RTD lead

Explanation

A short across the RTD element produces a resistance near zero, which the transmitter interprets as the low end of the temperature range. An open circuit would typically drive the reading high or to an alarm condition. High lead resistance and increased element resistance would both read higher, not lower.

Question 33Calibration, maintenance, repair and troubleshooting

A technician is verifying the calibration of a pressure gauge with a deadweight tester. Which practice is required for an accurate result?

  1. Apply pressure rapidly to minimize the test time
  2. Read the gauge only at the maximum pressure
  3. Use any available weights as long as they fit the piston
  4. Level the tester and use the correct weights for the piston area Correct answer.

Explanation

A deadweight tester must be level so that the piston operates vertically and gravity acts along its axis. The weights must match the piston area and the local gravity to produce the intended pressure. Rapid pressure application and mismatched weights introduce errors, and a single-point check does not verify the gauge across its range.

Question 34Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a 4–20 mA loop in which the transmitter output reads 0 mA. The loop power supply is energized. Which step should be taken first?

  1. Replace the transmitter immediately
  2. Short the loop to force a current reading
  3. Increase the process variable to raise the output
  4. Check for an open circuit or loose termination in the loop wiring Correct answer.

Explanation

A 0 mA reading in an energized loop usually indicates an open circuit, a loose connection, or a failed power supply path. Checking wiring and terminations is a safe first step before replacing components. Replacing the transmitter or shorting the loop can cause additional problems and does not confirm the cause.

Question 35Calibration, maintenance, repair and troubleshooting

A technician is calibrating a differential pressure transmitter that measures flow across an orifice plate. The transmitter is found to have a 0.5 mA zero error at 0% input. What is the effect on the indicated flow at low flow rates?

  1. The indicated flow will be unaffected because flow is a square-root function
  2. The indicated flow will be correct but the span will be wrong
  3. The indicated flow will be higher than actual at low flow Correct answer.
  4. The indicated flow will be lower than actual at low flow

Explanation

A positive zero error adds a constant offset to the differential pressure signal, which is converted to flow by a square-root relationship. At low differential pressures, the offset is a larger fraction of the true signal, so the indicated flow is biased high. The error is most pronounced near the low end of the flow range.

Question 36Calibration, maintenance, repair and troubleshooting

A technician is repairing a thermocouple circuit and finds that the extension wire polarity is reversed at the transmitter terminals. What is the most likely effect on the temperature reading?

  1. The thermocouple will produce no voltage at all
  2. The indicated temperature will be lower than the actual temperature Correct answer.
  3. The indicated temperature will be higher than the actual temperature
  4. The transmitter will output 4 mA regardless of temperature

Explanation

Reversed thermocouple extension wire reverses the polarity of the small DC voltage produced by the thermocouple. The transmitter interprets the reversed voltage as a lower temperature, so the indication reads low. The magnitude of the error depends on the temperature difference between the measuring junction and the reference junction.

Question 37Calibration, maintenance, repair and troubleshooting

A technician is performing preventive maintenance on a pressure transmitter installed on a steam line. Which task is appropriate?

  1. Check and blow down the impulse line and verify the isolation valve operates freely Correct answer.
  2. Disconnect the grounding conductor to reduce electrical noise
  3. Increase the transmitter damping to the maximum setting
  4. Remove the transmitter from the line and store it in a dry location

Explanation

On a steam line, the impulse line can accumulate condensate and sediment, so blowing it down and verifying valve operation are standard preventive maintenance tasks. This helps ensure the transmitter sees the true process pressure. Removing the transmitter, maximizing damping, or disconnecting grounds are not routine maintenance actions.

Question 38Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a control loop where the controller output is steady but the measured variable oscillates. Which condition is most likely?

  1. The control valve is sticking and then slipping Correct answer.
  2. The loop power supply is too high
  3. The controller is in manual mode
  4. The transmitter is calibrated correctly

Explanation

A sticking valve can cause the measured variable to oscillate even when the controller output is steady, because the valve moves in jumps rather than smoothly. The controller may be trying to correct the resulting error, but the root cause is in the final control element. Controller mode and power supply voltage do not produce this pattern when the output is steady.

Question 39Calibration, maintenance, repair and troubleshooting

A technician is repairing a pH analyzer that reads a constant value regardless of process changes. The analyzer has been in service for several years. Which maintenance action is most appropriate to investigate the cause?

  1. Recalibrate the analyzer with the same buffer solutions
  2. Replace the analyzer's display board
  3. Increase the analyzer's output damping
  4. Inspect and clean the pH electrode and check the reference junction Correct answer.

Explanation

A pH electrode that is coated, fouled, or has a clogged reference junction can produce a fixed reading because the sensor no longer responds to changes in the process. Cleaning the electrode and checking the reference junction are appropriate first steps. Replacing boards, recalibrating with the same buffers, or adding damping does not address a fouled sensor.

Question 40Calibration, maintenance, repair and troubleshooting

A technician is calibrating a temperature transmitter with a 0–500 °F range and a 4–20 mA output. At an applied input of 250 °F, the transmitter outputs 12.2 mA. What is the approximate error in percent of span?

  1. 0.25%
  2. 12.5%
  3. 1.25% Correct answer.
  4. 2.5%

Explanation

The expected output at 50% of a 0–500 °F range is 12.0 mA. The actual output is 12.2 mA, a difference of 0.2 mA. Since the full span is 16 mA, the error is 0.2 ÷ 16 = 0.0125, or 1.25% of span.

Question 41Calibration, maintenance, repair and troubleshooting

A technician is using a HART communicator to configure a smart transmitter in a loop with a 250-ohm resistor. The communicator fails to communicate. Which condition is most likely?

  1. The loop resistance is too low for the HART signal to be detected Correct answer.
  2. The loop current is below 4 mA
  3. The transmitter is in multidrop mode with a fixed address
  4. The communicator is connected across the power supply

Explanation

HART communication requires a minimum loop resistance, typically around 230 to 250 ohms, to develop a detectable signal. If the loop resistance is below the required minimum, the communicator may not detect the HART signal. Checking the total loop resistance and the communicator connections is the appropriate first step.

Question 42Calibration, maintenance, repair and troubleshooting

A technician is repairing a control valve that does not fully close. The actuator receives the correct signal and the positioner is calibrated. Which condition is most likely?

  1. The valve stem packing is too loose
  2. The positioner has a small deadband
  3. The valve trim is worn or the seat is damaged Correct answer.
  4. The actuator air supply is too high

Explanation

If the actuator and positioner are functioning correctly, a valve that does not fully close usually has mechanical damage such as worn trim, a damaged seat, or debris between the plug and seat. These conditions prevent tight shutoff even when the stem reaches the closed position. Air supply, deadband, and packing tightness do not directly prevent full closure when the signal is correct.

Question 43Calibration, maintenance, repair and troubleshooting

A technician is calibrating a pressure transmitter and finds that the output is correct at 0% and 100% but deviates at midscale. Which condition is most likely?

  1. The transmitter has a zero shift
  2. The transmitter has a span error
  3. The transmitter has a damping setting that is too high
  4. The transmitter has a linearity error Correct answer.

Explanation

A linearity error appears as a deviation at intermediate points while the endpoints remain correct. Zero and span errors affect the endpoints or the slope of the output. Damping affects response time rather than steady-state accuracy.

Question 44Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a 4–20 mA loop that intermittently drops to 0 mA when a nearby motor starts. Which action is most appropriate?

  1. Check the loop grounding and shield termination Correct answer.
  2. Replace the transmitter with a different model
  3. Disconnect the shield at both ends
  4. Increase the loop power supply voltage

Explanation

Intermittent drops to 0 mA when a motor starts suggest electrical noise or a grounding problem. Checking the loop grounding and shield termination helps ensure that noise is drained properly. Disconnecting the shield at both ends can make the problem worse by removing the noise path.

Question 45Calibration, maintenance, repair and troubleshooting

A technician is repairing a flow measurement loop that uses a magnetic flowmeter. The meter reads zero flow when the process is known to be flowing. Which condition is most likely?

  1. The flowmeter is installed in a vertical line
  2. The flowmeter is calibrated for the wrong fluid density
  3. The flowmeter has a high span setting
  4. The flowmeter is not completely full of liquid Correct answer.

Explanation

Magnetic flowmeters require a full pipe to measure accurately; if the pipe is partially empty, the electrodes may not be in contact with the liquid and the meter can read zero. Vertical installation is acceptable if flow is upward and the pipe remains full. Span and density settings affect the reading but do not typically cause a zero reading in a flowing line.

Question 46Calibration, maintenance, repair and troubleshooting

A technician is calibrating a pressure switch and finds that it trips at 48 psig on rising pressure and resets at 42 psig on falling pressure. What is the deadband?

  1. 48 psi
  2. 6 psi Correct answer.
  3. 42 psi
  4. 90 psi

Explanation

Deadband is the difference between the trip point and the reset point. Here the switch trips at 48 psig and resets at 42 psig, so the deadband is 6 psi. The trip and reset values themselves are not the deadband.

Question 47Calibration, maintenance, repair and troubleshooting

A technician is repairing a temperature control loop that uses a thermocouple. The indicated temperature is correct at ambient conditions but reads low when the process is hot. Which condition is most likely?

  1. The thermocouple is installed with the wrong immersion depth
  2. The thermocouple extension wire is reversed
  3. The transmitter has a zero shift
  4. The thermocouple is grounded to the sheath and creating a ground loop Correct answer.

Explanation

A thermocouple that is grounded to its sheath can create a ground loop that affects the reading, especially at higher temperatures where the voltage signal is larger. The problem may not appear at ambient conditions. Reversed extension wire would cause a low reading at all temperatures, and a zero shift would affect the reading uniformly.

Question 48Calibration, maintenance, repair and troubleshooting

A technician is calibrating a differential pressure transmitter with a 0–100 inH2O range. The transmitter is found to have a 2 inH2O zero error and a 4 inH2O span error. What is the approximate error at 50% of span?

  1. 8 inH2O
  2. 2 inH2O
  3. 4 inH2O Correct answer.
  4. 6 inH2O

Explanation

At 50% of span, the zero error contributes 2 inH2O and the span error contributes half of 4 inH2O, or 2 inH2O. The combined error is approximately 4 inH2O. The errors add because both shift the output in the same direction in this example.

Question 49Calibration, maintenance, repair and troubleshooting

A technician is troubleshooting a control valve that oscillates continuously. The controller output is changing in response to the measured variable. Which action is most appropriate to isolate the cause?

  1. Reduce the transmitter damping to zero
  2. Replace the valve positioner immediately
  3. Increase the controller gain to reduce the oscillation
  4. Place the controller in manual and observe whether the oscillation stops Correct answer.

Explanation

Placing the controller in manual removes the feedback path and helps determine whether the oscillation is caused by the controller tuning or by the valve and process. If the oscillation stops in manual, the controller tuning is likely involved. If it continues, the valve or process is the source.

Question 50Calibration, maintenance, repair and troubleshooting

A technician is repairing a 4–20 mA loop that has a transmitter, a controller, and a recorder connected in series. The recorder reads 8 mA while the controller reads 12 mA. Which condition is most likely?

  1. The recorder has a calibration error or a high-resistance input Correct answer.
  2. The loop power supply is failing
  3. The controller is configured for the wrong range
  4. The transmitter is producing an incorrect output

Explanation

In a series loop, all devices should see the same current. If the controller reads 12 mA and the recorder reads 8 mA, the recorder is likely mis calibrated or has an input impedance problem that affects its reading. The transmitter and power supply are less likely because the controller reads the expected value.