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Process Control and Instrumentation Flashcards

7 cards from real SACA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Process Control and Instrumentation flashcards as text

  1. A thermocouple installation requires a reference junction compensation because:

    Answer: The EMF output depends on the temperature difference between measuring and reference junctions

    A thermocouple generates a voltage proportional to the temperature difference between its hot (measuring) and cold (reference) junctions, so the reference temperature must be known and compensated.

  2. Which process variable is typically controlled using a split-range valve configuration?

    Answer: Pressure that requires both heating and cooling

    Split-range control divides the controller output signal between two valves (e.g., one for heating, one for cooling) so a single controller manages both process directions.

  3. What does the term 'rangeability' mean when describing a control valve?

    Answer: Ratio of maximum to minimum controllable flow

    Rangeability is the ratio of the maximum to minimum flow rates over which the valve maintains its specified flow characteristic, indicating how wide a flow range it can control.

  4. An RTD with alpha (α) = 0.00385 Ω/Ω/°C is measured. What does this alpha value represent?

    Answer: Temperature coefficient of resistance per degree Celsius

    Alpha (α) is the temperature coefficient of resistance, indicating how much the RTD resistance changes per ohm per degree Celsius; 0.00385 is the IEC standard for platinum RTDs.

  5. In a Fieldbus (Foundation Fieldbus H1) network, what is the role of the Link Active Scheduler (LAS)?

    Answer: Manages deterministic communication scheduling on the bus segment

    The LAS is the bus master that controls the deterministic token-passing schedule, ensuring all devices communicate in an orderly, time-synchronized manner on an H1 segment.

  6. A process has a first-order transfer function with a time constant of 60 seconds. Approximately how long will it take for the process output to reach 63.2% of its final value after a step change?

    Answer: 60 seconds

    For a first-order process, the output reaches 63.2% of its total change in exactly one time constant (τ), which is 60 seconds in this case.

  7. Which type of pressure measurement is referenced to absolute zero pressure (perfect vacuum)?

    Answer: Absolute pressure

    Absolute pressure is measured relative to a perfect vacuum (zero pressure reference), so it equals gauge pressure plus local atmospheric pressure.