ISA CAP flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Live zero in 4–20 mA
- A 4–20 mA loop uses 4 mA for 0% of span and 20 mA for 100%, providing a live zero so a broken wire reads below zero and is distinguishable from a valid minimum signal.
- Square root extraction DP flow
- Differential pressure across an orifice varies with the square of flow, so a DP flow transmitter or the control system applies square-root extraction to linearize the signal before control, totalizing, or recording.
- Pt100 RTD resistance
- A Pt100 RTD measures 100 ohms at 0 °C and changes about 0.385 ohms per °C; it is more linear and stable than a thermocouple but has a slower response.
- Thermocouple Seebeck effect
- A thermocouple produces a small voltage proportional to the temperature difference between its measuring and reference junctions, so cold-junction compensation is required to compute the actual process temperature.
- PID integral removes steady-state offset
- The integral or reset term accumulates error over time and drives steady-state offset to zero, but excessive integral action causes oscillation and integrator windup after output saturation.
- Cascade control inner loop speed
- The outer controller output becomes the inner controller's setpoint; the inner loop should respond roughly three to five times faster than the outer loop for cascade control to improve disturbance rejection.
- Fail-closed control valve
- A fail-closed valve uses spring or stored energy to shut on loss of air or power, and is selected when closing is the safe action for the process.
- Equal-percentage valve characteristic
- An equal-percentage inherent characteristic increases flow by the same percentage for each equal increment of stem travel, suiting processes with wide load changes and large varying pressure drop.
- SIL 2 PFDavg range
- In low-demand mode, SIL 2 requires an average probability of failure on demand between 10⁻³ and 10⁻², equivalent to a risk reduction factor of 100 to 1000.
- IEC 61511 safety lifecycle
- IEC 61511 defines the process-sector safety lifecycle, covering hazard and risk assessment, safety requirements specification, design, installation, commissioning, operation, modification, and decommissioning of safety instrumented systems.
- 2oo3 voting architecture
- Two-out-of-three voting trips when at least two of three channels agree, giving high safety availability while tolerating one failed channel without a spurious trip.
- Common cause beta factor
- The beta factor models the fraction of failures shared by redundant channels through common causes such as identical devices, shared utilities, or common environment, and it limits the reliability redundancy can achieve.
- LOPA independent protection layers
- Layer of protection analysis assigns risk reduction factors to independent protection layers to determine whether existing safeguards are sufficient or an additional safety instrumented function is needed.
- SIF versus SIS
- A safety instrumented function is one defined protective action with a target SIL; the safety instrumented system is the complete set of sensors, logic solver, and final elements executing one or more SIFs.
- Proof test interval
- The proof test interval is the scheduled time between complete functional tests that reveal dangerous undetected failures; lengthening the interval raises the average probability of failure on demand.
- Safety requirements specification
- The safety requirements specification documents each safety instrumented function's trip points, process safety time, target SIL, required response, and proof test requirements, forming the basis for design and verification.
- FAT and SAT
- Factory acceptance testing verifies hardware and software against specifications at the vendor's works, while site acceptance testing confirms correct installation, wiring, and integration with plant systems after delivery.
- Earned value CPI and SPI
- Cost performance index is earned value divided by actual cost, and schedule performance index is earned value divided by planned value; values below one indicate overrun or slippage.
- P&ID and instrument index
- Piping and instrumentation diagrams show process equipment and instrument bubbles, while the instrument index is the master database listing every tag with its service, range, and specification.
- ISA-5.1 instrument symbols
- ISA-5.1 standardizes instrument tag letters and symbol conventions, for example FT for flow transmitter and FIC for flow indicating controller, as used on P&IDs and loop drawings.
- Cause and effect matrix
- A cause and effect matrix maps each trip cause or input to its resulting outputs and valve actions, documenting interlock logic for programming, testing, and management of change.
- Front-end loading FEL
- Front-end loading phases progressively define project scope, design basis, and estimate accuracy before detailed engineering; FEL-3 typically supports a funding-grade estimate and final investment decision.
- Management of change
- Management of change is a formal process that evaluates, approves, documents, and communicates modifications to equipment, software, or procedures before implementation so that new risk is identified and controlled.
- Loop check commissioning
- A loop check verifies the complete signal path from the field instrument through wiring and I/O card to the control system display, confirming calibration, correct tag, and proper control action.
- OPC UA
- OPC Unified Architecture is a platform-independent, secure client-server and publish-subscribe standard for exchanging plant data between control systems, historians, MES, and enterprise applications, replacing older OPC DA.
- Purdue model levels
- The Purdue enterprise reference model places process control at levels zero to two, operations and MES at level three, and enterprise IT at levels four and five, with a DMZ between OT and IT.
- IEC 62443 zones and conduits
- IEC 62443 partitions an industrial automation system into security zones with target security levels, connected only through controlled conduits such as firewalls and data diodes, enforcing defense in depth.
- Modbus master-slave protocol
- Modbus is a master-slave protocol where the master polls slaves by register address; Modbus RTU runs over serial links and Modbus TCP over Ethernet, with no built-in authentication or encryption.
- HART digital signal
- HART superimposes a frequency-shift-keyed digital signal on the 4–20 mA loop, enabling device configuration, diagnostics, and multivariable readings without disturbing the analog control value.
- Foundation Fieldbus H1
- Foundation Fieldbus H1 is a 31.25 kbit/s digital bus that powers and communicates with multiple devices on one segment and allows control functions to be distributed into field instruments.
- NTP versus PTP
- Network Time Protocol synchronizes clocks to millisecond accuracy for general networks, while Precision Time Protocol (IEEE 1588) reaches sub-microsecond accuracy needed for sequence-of-events recording and synchronized control.
- WirelessHART mesh network
- WirelessHART (IEC 62591) is a self-healing 2.4 GHz mesh network using time-synchronized channel hopping, giving reliable low-power measurement for process monitoring in plant environments.