Instrumentation Vocab Flashcards
The science of automated measurement and control.
Instrumentation:
The physical system we are attempting to control or measure. Examples: water filtration system, molten metal casting system, steam boiler, oil refinery unit, power generation unit.
Process:
The specific quantity we are measuring in a process. Examples: pressure, level, temperature, flow, electrical conductivity, pH, position, speed, vibration.
Process Variable (PV):
The value at which we desire the process variable to be maintained at. In other words, the “target” value for the process variable.
Setpoint (SP):
A device directly sensing the process variable and translating that sensed quantity into an analog representation (electrical voltage, current, resistance; mechanical force, motion, etc.).
Primary Sensing Element (PSE):
A device converting one standardized instrumentation signal into another standardized instrumentation signal, and/or performing some sort of processing on that signal.
Transducer:
A device translating the signal produced by a primary sensing element (PSE) into a standardized instrumentation signal, which may then be conveyed to an indicating device, a controlling device, or both.
Transmitter:
The values of process measurement deemed to be 0% and 100% of a transmitter’s calibrated range.
Lower- and Upper-range values (LRV and URV):
The alternative descriptions to LRV and URV for the 0% and 100% points of an instrument’s calibrated range. “Zero” refers to the beginning-point of an instrument’s range (equivalent to LRV), while “span” refers to the width of its range (URV − LRV).
Zero and Span:
A device receiving a process variable signal from a primary sensing element or transmitter, comparing that signal to the desired value for that process variable, and calculating an appropriate output signal value to be sent to a final control element.
Controller:
A device receiving the signal output by a controller to directly influence the process. Examples: variable-speed electric motor, control valve, electric heater.
Final Control Element (FCE):
The quantity in a process we adjust or otherwise manipulate in order to influence the process variable (PV). Also used to describe the output signal generated by a controller.
Manipulated Variable (MV):
When the controller generates an output signal based on the relationship of process variable (PV) to the setpoint (SP).
Automatic mode:
When the controller’s decision-making ability is bypassed to let a human operator directly determine the output signal sent to the final control element.
Manual mode:
Instrumentation Documents
The proper form of diagram to represent the “big picture” of a process.
Process flow diagram (PFD):
Shows the layout of all relevant process vessels, pipes, and machinery, but with instruments superimposed on the diagram showing what gets measured and what gets controlled.
Process and instrument diagrams (P&IDs):
Show the interconnections of individual instruments, including all the wire numbers, terminal numbers, cable types, instrument calibration ranges, etc.
Loop diagrams (“loop sheets”):
Diagrams used to document the strategy of a control system. In these diagrams, emphasis is placed on the algorithms used to control a process, as opposed to piping, wiring, or instrument connections.
Functional diagrams:
Instrumentation, Systems, and Automation society. Instrument Connections
ISA:
A hollow structure designed to provide an enclosed pathway for fluids to flow.
Pipe:
A ring of metal, usually welded to the end of a pipe, with holes drilled in it parallel to the pipe centerline to accept several bolts
American National Standards Institute.
A pipe “flange”:
ANSI:
The technique of alternating the torque sequence between four quadrants of the flange, ensuring the flanges are evenly compressed together as all bolts are gradually tightened.
Cross-torquing:
Special wrenches that exist for the purpose of measuring applied torque during the tightening process.
Torque wrenches:
A blank metal plate comprised of a regular blind plate attached to an equal diameter ring by a short tab, the outline of which resembles a pair of spectacles.
Spectacle blind:
