Glossary · Process instrumentation and analytical measurement
Instrument index
Also known as: Instrument list, Instrument register
German: Messstellenverzeichnis
In process plant engineering, an instrument index is the controlled list of all measuring points, control loops and instruments of a plant, identified by tag number, with key data such as service, location, measuring range, signal type and references to data sheets and loop diagrams.
- Process instrumentation
- Process industry
- Technical documentation
In one sentence
An instrument index lists all measuring points and instruments of a plant by tag number, with key data and links to related documents.
Example
Before a shutdown, the maintenance team filters the instrument index for all transmitters with calibration due and plans the work by area.
How it applies
- Engineering: The instrument index is built from the P&IDs and grows through basic and detail engineering. Tag numbering follows the plant's conventions, often based on IEC 62424 or ISA-5.1 letter codes.
- Commissioning: It serves as the checklist for loop checks and as the link between field devices, control system tags and documentation.
- Operation and maintenance: Changes to instruments, ranges or services must update the index, or it quickly stops reflecting the plant.
- Documentation: Treat the index as a Controlled document and, ideally, as a Source of truth from which data sheets, loop diagrams and control system configurations are derived. Technical writers should use its tag numbers and names in manuals.
Instrument index vs. instrument data sheet
The index gives an overview of all instruments. The data sheet specifies one instrument in detail.