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One cycle is not a physical dose. A full slow sweep, a short high-frequency dither and repeated reversal at one coordinate can have different contact distance, frictional heating, debris movement and local track exposure even when each is counted once. This guide converts service motion into a binned duty vector and a reviewable laboratory sequence. It does not promise life or define a universal accelerated test. Contact material, load, environment and failure criteria remain project-specific.
Key design decisions
- Describe service with motion bins containing count, stroke, speed, load, dwell, reversal and environment.
- Preserve localized dither and end-stop events instead of averaging them into full sweeps.
- Validate that any accelerated sequence retains the observed wear mechanism before using its cycle ratio.
Define what a counted cycle contains
State the start coordinate, end coordinate, return path and counting rule. A cycle may mean one traverse, an out-and-back pair, a start-stop event or one operating mission. Without that definition, two test reports containing the same number cannot be compared. Record the contact's actual path on the resistor and collectors, including any overtravel. If the mechanism pauses or unloads between strokes, preserve that state because debris redistribution and contact recovery can differ from continuous motion.
Separate full-range sweeps, partial sweeps and micro-motion. A fuel or position sender may spend most of its time in one narrow band, with occasional complete excursions. The local region can therefore accumulate many more reversals than the total-travel count suggests. Use service data when available; otherwise document the engineering assumptions and treat the sequence as provisional. Do not convert an estimated mission profile into a field-life claim.
Create a motion-bin duty vector
Represent service as D={n_k, s_k, v_k, a_k, F_k, t_d,k, q_k, E_k}. For bin k, n is repetitions, s is stroke, v is speed, a is acceleration or reversal severity, F is contact load, t_d is dwell, q describes direction or sequence, and E identifies environment. Add electrical state when current through the contact may influence the interface. Each coordinate needs units and a source. A bin is useful only if it groups events with similar wear-driving conditions.
Do not average opposing effects away. An average speed of 10 mm/s cannot represent alternating 1 and 100 mm/s events if frictional heating or contact dynamics changes across that range. Likewise, average stroke conceals whether one small region receives all reversals. Preserve a position histogram or transition matrix alongside the bins. Environmental states such as dry, condensing, dusty or media-exposed must be separately qualified rather than combined into one generic harsh label.
Calculate distance without calling it damage
Total sliding distance is L = sum(n_k s_k) when s_k already represents the distance counted per event. If a reported cycle is out-and-back and s_k is one-way stroke, use L = sum(2 n_k s_k). The convention must be explicit. Distance is a useful exposure coordinate but not a complete damage model because load, speed, reversal, materials and environment can alter the mechanism. Use it to check arithmetic and compare sequences, not to claim equivalence by itself.
For illustration, 8,000 out-and-back cycles over a 24 mm one-way stroke contribute 384,000 mm, while 120,000 out-and-back dither cycles over 0.7 mm contribute 168,000 mm. The dither has less total distance but far more reversals concentrated locally. A test containing only 552 m of uniform full sweeps would reproduce the summed distance yet erase that concentration. This calculation uses invented example inputs solely to demonstrate bookkeeping; project values must come from the application.
| Coordinate | Why it matters | Evidence needed |
|---|---|---|
| Position and stroke | Locates repeated exposure and end transitions | Travel trace or bounded assumption |
| Speed and reversal | Affects dynamics and local disturbance | Time-resolved motion record |
| Load and electrical state | Defines contact-interface condition | Mechanism and circuit inputs |
| Environment and dwell | Controls films, debris and recovery | Mission-state definition |
Translate service bins into a laboratory sequence
A laboratory sequence should retain important order effects. Environmental exposure before motion may produce a different interface than exposure after a cleaning sweep. Long dwell followed by breakaway can challenge adhesion or surface films differently from steady reciprocation. Assemble blocks that reproduce start, operating, stop and storage states in a justified order. Include representative transitions between high-use regions and full travel. Randomization can help separate fixture position from sequence, but it must not destroy a physically meaningful order.
Select specimens and positions to cover real geometry variation rather than running every unit on the same central track. Record contact and card identities, assembly condition and initial electrical map. Fixtures should reproduce alignment, contact orientation and load without adding uncontrolled side force. If the test mechanism differs from the product mechanism, demonstrate which motion and load coordinates are preserved. A motor revolution counter alone is insufficient evidence that the card experienced the commanded path.
Accelerate only within one retained mechanism
Higher speed, load, temperature or contaminant concentration can shorten a test, but each can also change the dominant wear mechanism. Acceleration is defensible only after comparing morphology, debris, electrical signatures and location of damage between service-representative and accelerated conditions. A ratio of cycle counts has no meaning when one condition causes abrasive track removal and another mainly produces intermittent films. Keep at least one reference condition close to the intended application.
If a project proposes an acceleration factor A = damage rate_test/damage rate_service, define the measured damage coordinate and uncertainty. Do not derive A merely from temperature or speed unless a qualified physical model and parameters exist. A test that reaches a criterion sooner is evidence about that condition; it is not automatically equivalent field life. Report failed mechanism-equivalence checks and retain separate empirical results instead of forcing them into one factor.
Observe electrical and physical progression
Measure more than final resistance. Useful observations can include output continuity versus position, contact-noise events under a stated bandwidth, hysteresis between directions, witness-path width, debris location and changes near collectors or reversals. Use the same coordinate system for electrical traces and images. Interim readouts reveal whether damage grows gradually, appears after an environmental transition or stays confined to one motion bin. They also prevent a final pass measurement from hiding temporary interruptions during motion.
Control the measurement circuit, sampling rate, filter, contact load and motion state. A static reading after motion cannot establish dynamic continuity. Conversely, a high-bandwidth spike count is difficult to interpret without threshold, duration and instrument limits. Physical marks show where interaction occurred but do not alone establish unacceptable electrical behavior. Link each observation to a project-defined function and preserve raw data or representative traces for review.
Use location and timing as failure signatures
Damage at reversal coordinates suggests concentrated micro-motion or breakaway effects. Uniform change along the entire track points toward distance-related interaction or a broad environmental influence. End-only marks implicate stops, collectors, overtravel or alignment. A sudden common shift on several specimens after one fixture adjustment suggests test setup rather than accumulated wear. Electrical interruptions without a corresponding permanent track mark may involve movable debris, surface film or contact dynamics. These patterns guide discriminating checks but should not be presented as proof of one root cause.
When a signature appears, compare a controlled variant: move the reversal location, change only the dwell, inspect a matched unpowered sample, or use an independent position reference. Keep all other relevant coordinates fixed. If several factors changed together, state that the mechanism remains confounded. A wear test is most useful when it identifies which service bin drives the signature, not simply when it produces a large count followed by a binary result.
Release the duty cycle with clear boundaries
The controlled test definition should include the cycle counting convention, bin table, sequence, path coordinates, speed profiles, load, electrical state, environment, dwell, specimen configuration, fixtures, measurement settings, interim readouts and acceptance owner. Identify which values come from field data, drawings, analysis or assumptions. Changes to mechanism, contact, card material, housing seal, software filtering or mission profile reopen the affected bins and equivalence argument.
For engineering review, send the motion trace or bounded mission profile, card and contact drawings, contact material and load, electrical circuit, travel and stop definitions, environment, expected life usage, known failure signatures and required functional limits. State whether the objective is comparative design screening, process verification or an application durability decision. A project-specific plan can then be proposed. No cycle count should be converted into a universal service-life claim without representative evidence and system approval.
Define a service-representative resistor-card wear cycle
Send motion, contact, electrical and environmental inputs so the laboratory sequence preserves the important service exposures.
- Motion traces or bounded counts by stroke region
- Speed, reversal, dwell and stop behavior
- Contact geometry, material, load and alignment
- Card artwork and material stack
- Electrical state, sampling and required failure criteria
- Temperature, humidity, media and contamination states
- Purpose of test and required evidence level
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