Documentation Index
Fetch the complete documentation index at: https://docs.firstresonance.io/llms.txt
Use this file to discover all available pages before exploring further.
Overview
A reference designator is a positional identifier that pins a build requirement to a specific location in the assembly. Examples:R7— resistor at position 7 on a PCBU3— IC in socket U3Q1,Q2,Q3— three transistors at three distinct positionsJ1,J2— two connectors at distinct ports
When to use reference designators
Use them when:- The assembly has discrete positions that need to be tracked (PCBs, harnesses, panels with marked slots).
- A failure or recall might need to identify which exact position has the problem (“the resistor at R7 is wrong”).
- Your manufacturing routing requires position-specific inspection (each designator inspected separately).
- The requirement is a bulk count (
12 of FAST-M4with no positional distinction). ION treats this as a quantity-only build requirement. - The position is incidental — operators can install in any open slot without affecting fit, form, or function.
Configuring reference designators
On the build requirement in the mBOM editor:- Open the build requirement.
- Expand the Reference Designators section.
- Add one designator per position (e.g.
R1,R2, …,R12). - The total quantity automatically equals the number of designators (you can’t have 12 designators with quantity 8).
R7, but within one build requirement R7 appears once.
How operators install with reference designators
At run time:- The build requirement renders with one row per designator instead of a single quantity counter.
- For each designator, the operator selects (or scans) the part inventory to install at that position.
- ION records the (designator, installed part inventory) pair on the aBOM.
- The build requirement is satisfied when every designator has an installation.
Substitutes + reference designators
Substitutes (configured alternates) work alongside reference designators. For each designator, the operator can install the primary OR any approved substitute — independently per position. SoR1 could be the primary while R3 is a substitute, and that’s fine.
The aBOM records exactly which part went into which position. If you later ask “what’s at R3 on serial #ASM-00012?”, you get a precise answer.
Designator naming conventions
ION doesn’t enforce a designator format — it’s free text. But your downstream traceability is more useful if designators are consistent. Common patterns:| Asset class | Convention |
|---|---|
| Resistors | R1, R2, … |
| Capacitors | C1, C2, … |
| Integrated circuits | U1, U2, … |
| Connectors | J1, J2, … |
| Transistors / FETs | Q1, Q2, … |
| Diodes | D1, D2, … |
| Mechanical fasteners (when positional) | S1, S2, … or M3-1, M3-2, … |
Reference designators on substitutes
When a build requirement allows substitutes AND has reference designators, the substitute applies to every position the requirement covers. You don’t configure substitutes per-designator — that level of granularity is intentionally not supported. IfR3 and R7 need different alternates, they should be different build requirements.
Tips
- Include reference designators when there’s a chance you’ll need positional traceability. Adding them later requires re-installing every affected unit — it’s not cheap.
- Match the engineering source of truth. If your PCB layout calls a position
U3, the build requirement should call itU3. Renaming for “clarity” introduces drift. - Don’t use reference designators for sequential count tracking. If you need “fastener 1, then fastener 2, then fastener 3” because of torque pattern, that’s a procedure-step concern, not a designator.