Common instrument terminology
(1) Measurement point (single point)
Primary points refer to the points in a detection or control system that are in direct contact with the process medium. Examples include pressure taps in a pressure detection system and thermocouple/resistance temperature detector (RTD) mounting points in a temperature detection system. These primary points can be located on process piping or on process equipment.
(2) Primary component (source component)
This usually refers to instrument components installed at a primary point, such as pressure tapping sections in pressure detection systems and thermometer bosses in temperature measurement systems.
(3) Primary valve (pressure tapping valve)
This refers to valves installed on primary components, such as valves in pressure detection systems connected to pressure tapping sections, and valves connected to the positive and negative pressure chamber outlet pipes of orifice plates.
(4) Primary components (sensors)
This refers to components installed on-site and in contact with the process medium, such as thermocouples and resistance temperature detectors (RTDs).
(5) Primary instrument
A type of field instrument refers to an instrument installed in the field and in direct contact with the process medium, such as a Bourdon tube pressure gauge, a bimetallic thermometer, and a differential pressure transmitter.
(6) Single calibration (individual unit calibration)
This refers to the calibration of instruments before installation. According to the "Code for Construction and Acceptance of Industrial Automation Instrumentation Engineering" (GBJ-86), each instrument should, in principle, undergo calibration at least once. The focus of calibration is to check the instrument's indication error and variation, and to adjust the errors in proportional gain, integral time, derivative time, control point deviation, and balance. Only instruments that meet the design or product manual requirements after the first calibration can be installed to ensure the quality of the second calibration.
(7) Secondary instruments
Secondary instruments refer to a group of instruments whose input signals do not directly contact the process medium. The input signals of secondary instruments are typically standard signals converted by transmitters. There are generally three types of accepted standard signals: pneumatic signals (0.02–0.1 MPa); Type II electric unit combination instrument signals (0–10 mA DC); and Type III electric unit combination instrument signals (4–20 mA DC or 1–5 V).
(8) Field Instruments
This refers to all instruments installed in the field, including all primary instruments and secondary instruments installed in the field.
(9) Secondary calibration (secondary joint calibration, system calibration)
This refers to the inspection of the entire detection loop or automatic control system after the instrument's on-site installation is completed, the control room piping and wiring are finished and verified, and it is also a comprehensive verification before the instrument is put into formal use. The verification method typically involves adding a signal to the detection process...
Then carefully observe whether each instrument in the system is operating within the allowable error range. If it exceeds the allowable error range and the cause cannot be found, all instruments in the system must be readjusted.
(10) Instrument machining parts
It refers to all metal and plastic machined parts used for instrument installation, and occupies a special position in instrument installation.
(11) Flowchart with control points
A drawing that uses process monitoring and control system design symbols to describe the automation of a production process. It details the installation locations of instruments, is crucial for determining primary control points, comprehensively reflects the control scheme and level of automation, serves as the basis for control system design, and provides reference during construction, installation, and production operation.
