ISA CCST Level III flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Calibration versus adjustment

Calibration documents an instrument's deviation from a traceable standard without changing it; adjustment physically alters the instrument to reduce that deviation. A calibration certificate reports as-found and as-left data.

Span error formula

Percent span error equals (indicated value minus true value) divided by calibrated span, times 100. A 0.5 mA error on a 16 mA span equals 3.1% span error.

4-20 mA percentage

In a 4-20 mA loop, 4 mA is 0%, 12 mA is 50%, and 20 mA is 100% of span. Each 1 mA equals 6.25% of span.

HART multidrop current

HART multidrop mode fixes each transmitter's analog output near 4 mA and polls devices digitally by unique address. Only one device may be point-to-point with a live 4-20 mA signal.

Four-wire RTD advantage

A four-wire RTD connection uses separate current and voltage leads, canceling lead resistance. It provides the most accurate measurement, especially for low-resistance sensors or long cable runs.

Thermocouple cold junction compensation

Thermocouples measure the difference between hot and reference junctions, so the instrument must compensate for ambient terminal temperature. Without CJC, readings shift by the ambient temperature error.

NAMUR NE43 fault levels

NAMUR NE43 recommends signaling transmitter failure with output below 3.6 mA or above 21 mA. Normal operating range is 3.8 to 20.5 mA, leaving margin for fault detection.

Valve bench set

Bench set is the air pressure range that moves a spring-return actuator from closed to open without process force. It is set on the bench and verified during stroke testing.

Two-wire loop power check

With the transmitter disconnected, a 24 VDC loop supply should read about 24 V open-circuit. A low reading indicates a short, excessive load, or failed supply; infinite indicates an open.

Loop divide-and-conquer

Troubleshoot by splitting the loop at accessible points, such as the DCS terminal or junction box, and injecting a known mA signal to determine which side is faulty.

Proportional band definition

Proportional band is the error span, in percent of measurement range, that drives controller output through 100%. It equals 100 divided by proportional gain.

Integral action eliminates offset

Integral action accumulates error over time and moves output until error reaches zero. Too much integral gain causes overshoot and oscillation; integral windup occurs when output saturates.

Derivative action noise

Derivative acts on rate of change and anticipates future error, but it amplifies measurement noise. It is normally avoided on noisy flow loops and often applied only to temperature.

Ziegler-Nichols PID settings

From ultimate gain Ku and ultimate period Pu, Ziegler-Nichols PID gives Kc = 0.6 Ku, Ti = Pu/2, and Td = Pu/8, producing quarter-amplitude decay.

Cascade control rule

In cascade control the master controller's output becomes the slave's setpoint. The slave loop must be at least three to five times faster than the master loop for stable benefit.

Dead time and controllability

Dead time is transport delay between a controller output change and measured response. Large dead time relative to the process time constant makes a loop difficult to control with PID.

Bumpless transfer

Bumpless transfer prevents an output jump when switching between manual and automatic. The controller initializes its integral term so the computed output matches the current output.

Equal percentage valve characteristic

An equal-percentage valve changes flow by a constant percentage per unit of stem travel. It compensates for installed characteristics that otherwise become linear at high pressure drop.

Loop check purpose

A loop check verifies the complete path from field instrument through wiring, I/O, controller, and final element. It confirms tag, polarity, scaling, alarms, and valve stroke.

Cold versus hot loop check

A cold loop check uses simulated signals with process equipment de-energized. A hot loop check repeats verification with live process or energized equipment before handover.

PSSR requirement

A pre-startup safety review confirms construction matches design, procedures are ready, training is complete, and safety systems function before introducing hazardous chemicals under OSHA PSM.

Factory acceptance test

A factory acceptance test runs the control system at the vendor's facility against approved specifications. It verifies hardware, software, graphics, alarms, and I/O before shipment.

Punch list classification

Punch list items are categorized by severity: A items block start-up, B items must be fixed before acceptance, and C items are minor and can be closed later.

Cause and effect testing

Cause and effect testing injects each input condition and verifies every specified output action, including trips, alarms, and interlocks, against the approved cause and effect matrix.

Instrument air commissioning

Before instrument air is used, verify dew point, oil content, and pressure at the header. Blow down lines and confirm filter regulators and airsets are installed and set.

Cost performance index

CPI equals earned value divided by actual cost. A CPI below 1.0 means the project is over budget; above 1.0 means under budget for work performed.

Schedule performance index

SPI equals earned value divided by planned value. An SPI below 1.0 indicates the project is behind schedule; above 1.0 indicates ahead of schedule.

Management of change

MOC is a documented review of proposed changes to process, equipment, or procedures to assess safety, environmental, and operational impacts before implementation and update documentation.

LOTO six-step procedure

Lockout/tagout requires preparation, notification, shutdown, isolation, lock and tag application, release of stored energy, verification, and restoration. It protects workers from unexpected energization.

ISA-84 safety lifecycle

ISA-84 and IEC 61511 define a safety instrumented system lifecycle: hazard assessment, SIL determination, design, installation, validation, operation, maintenance, and decommissioning.

Calibration traceability

Traceability links an instrument's calibration to national or international standards through an unbroken chain of documented comparisons, each with stated uncertainty.

Span of control

Span of control is the number of subordinates reporting directly to one supervisor. It affects communication, supervision quality, and organizational layers.