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A rotary resistive card reports where a contact travels along an arc, but its output is governed by more than the printed curve. Pivot location, shaft runout, carrier stiffness, wiper reach, angular stops, card seating and receiver loading determine which printed coordinate is actually sampled. The integration record must connect a mechanical zero to the artwork origin through measurable datums. It must also reserve radial coverage for the complete contact footprint at tolerance extremes. This guide develops that chain while keeping actuator safety, bearing design, sealing and final calibration with the system integrator.
System boundary
The boundary includes the printed rotary resistor card, its substrate locators, housing seat, pivot or shaft, contact carrier, mechanical stops, terminals, harness and receiving electronics. ChipSimple may review drawing-defined card geometry and passive electrical targets. The customer owns the pivot, bearings, actuator, enclosure, calibration, diagnostics and complete-system qualification.
System integration decisions
- Define one physical angular zero that survives assembly and calibration.
- Budget radial error separately from tangential angle error.
- Prove contact coverage at every stop, thermal state and tolerance corner.
- Specify the receiver so electrical loading cannot silently reshape the transfer curve.
Establish an angular reference that can be rebuilt
Choose a tangible event for zero: a keyed shaft face against a defined stop, a fixture pin relationship, or another controlled mechanical feature. State rotation direction, units and wrap convention. Then link that event to housing datums, substrate locators and the printed artwork origin. A software offset is useful for calibration, but it cannot repair an undocumented mechanical transformation. Record whether the assembly approaches zero clockwise or counterclockwise because clearance and friction can seat the mechanism differently. Inspection drawings and calibration instructions should use the same positive direction and reference state.
Separate radial reach from angular registration
Radial error determines whether the full wiper footprint remains on its intended contact lane. Angular error determines which transfer value is sampled. Treating both as one position tolerance hides different failure modes. Radial contributors include pivot location, shaft runout, substrate translation, printed arc radius, carrier reach and contact-footprint width. Angular contributors include stop location, key clocking, housing rotation, artwork rotation and backlash take-up. Calculate both axes at the same temperature and assembly state, then inspect their interaction at the arc endpoints where geometric margin is often smallest.
Calculate minimum radial contact coverage
A conservative screening calculation subtracts adverse radial contributors from the nominal overlap between footprint and conductive lane.
C_min = C_nom - |e_pivot| - e_runout - e_card - e_print - e_tilt
- C_nom is nominal radial overlap of the complete contact footprint with its allowed lane.
- e_pivot is pivot-to-card radial displacement.
- e_runout is the radial component of shaft runout at the contact.
- e_card and e_print are card-location and printed-radius deviations.
- e_tilt is the reach change caused by carrier angular tilt.
Terms are evaluated in the same radial direction at a defined angular position. Statistical cancellation is not assumed, and contact deformation is assessed separately.
Use a numerical example to expose inadequate margin
Suppose nominal overlap is 0.90 mm. An illustrative allocation contains 0.18 mm pivot displacement, 0.12 mm runout, 0.10 mm card seating variation, 0.08 mm printed-radius displacement and 0.16 mm reach change from carrier tilt. The residual coverage is 0.26 mm. If the agreed minimum complete-footprint coverage were 0.30 mm, this stack would miss the target before wear or vibration is considered. These values explain the accounting method only; drawing values and acceptance limits must come from the actual assembly owners. Increasing nominal reach may not be safe if it raises edge loading or force, so geometry and contact mechanics must be reviewed together.
Map mechanical angle to printed arc coordinate
The active coordinate should be defined at the pivot center used by the installed mechanism, not inferred from an image of the artwork. For each calibration point, record commanded angle, independently measured shaft angle, approach direction, wiper-center coordinate and direct electrical result. Include both endpoints and any intentional nonlinear segments. If the print origin differs from the housing origin, document the rigid transform and its measurement method. A small translational pivot error can create an angle-dependent tangential shift, so a single midpoint alignment does not prove the full sweep.
Keep passive transfer and receiver loading distinct
For a potentiometric arrangement, finite input impedance draws current from the wiper node and can bend an otherwise acceptable unloaded ratio. Harness resistance in the supply or return introduces additional angle-dependent error when track current changes. Define excitation magnitude and tolerance, receiver impedance, leakage, filtering, sample timing and diagnostic pulls. Compare four records where practical: end-to-end resistance, unloaded wiper resistance, loaded node voltage and digitized controller value. This progression localizes disagreement without assigning an electronic effect to the printed card.
Control the interface in one angular allocation table
A release table should distinguish values provided by the card drawing from values supplied by the mechanism and electronics teams.
| Item | Required definition | Evidence or owner |
|---|---|---|
| Angular zero | Physical event, direction and permitted offset | Mechanism drawing and calibration owner |
| Radial reach | Nominal radius, footprint and tolerance stack | Contact-system analysis |
| Active sweep | Stops, overtravel and qualified electrical interval | System integrator |
| Card geometry | Arc coordinates, datums and terminal locations | Reviewed card drawing |
| Readout circuit | Excitation, loads, harness and conversion law | Electronics schematic and test owner |
Observe runout, reversal and stop rebound dynamically
A static gauge can miss a once-per-revolution loss of coverage or a brief stop rebound. Rotate through the specified speed range while acquiring independent shaft angle, raw electrical output and supply. Repeat in both directions and after dwell at each endpoint. Look for periodic error tied to shaft phase, discontinuity tied to one artwork location and hysteresis tied to reversal. Those signatures help separate pivot runout, local surface condition and backlash, but teardown or dimensional evidence is still required before declaring cause. Controller filtering should be logged, not used to erase the raw event.
Recheck geometry under thermal and mechanical loading
Housing expansion can translate a card relative to a metal pivot; a spring carrier can change reach as temperature alters preload. Vibration may reverse clearances repeatedly. Contamination can alter friction and make approach direction more influential. Select thermal states from the actual application, allow stabilization, and measure the relative geometry or output without inventing a universal range. If the assembly is sealed, include pressure and condensation states defined by the integrator. Card material behavior is only one contributor, and a successful component inspection does not qualify the enclosure.
Validate the installed coordinate chain
Begin with card inspection to agreed substrate datums. Continue with card seating and pivot position in representative housings. Measure wiper footprint and normal force at selected sweep positions, then run slow bidirectional electrical sweeps before dynamic trials. Test tolerance-representative assemblies rather than one nominal unit. Record raw channels, independent angular reference, supply and temperature with synchronized time. The integrator establishes acceptance for accuracy, monotonicity, dropout, diagnostics and durability. ChipSimple review remains bounded to the drawing-defined card and does not certify actuator safety or final sensor performance.
Reopen review when any coordinate link changes
Changes to the pivot, bearing, shaft, carrier, spring, wiper, stop, housing locator, adhesive, substrate outline, artwork origin, contact lane, terminal assignment, harness or receiver can alter the result. Maintain a configuration list with drawing revisions and calibration software version. A card that is electrically unchanged may require new system evidence after a housing or wiper substitution. Conversely, a new printed arc cannot be accepted merely because the old mechanism passed. The change gate asks which radial, angular, contact and readout assumptions remain valid and assigns additional validation accordingly.
Provide the complete rotary coordinate chain
A useful card review starts with the installed geometry and receiver, not only a resistance target.
- Card outline, substrate datums, artwork origin, arc geometry and terminal definition.
- Pivot coordinates, shaft runout, bearing clearances, stops and rotation direction.
- Wiper reach, footprint, normal force, carrier compliance and sweep speed.
- Excitation, harness, receiver impedance, conversion law and fault thresholds.
- Temperature, vibration, contamination states and customer validation plan.
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