Test method — ANSI/ESD S4.1 in one paragraph
Place the part of interest on a grounded conductive plate. Set a 5-pound (2.27 kg) cylindrical electrode on the part's top surface, at least 4 inches from any edge.
Apply 10 V (for resistance < 10⁶ Ω) or 100 V (for 10⁶–10¹² Ω). Read the surface resistance after 15 seconds dwell.
Compare to the spec range: conductive 10⁴–10⁶ Ω/sq, dissipative 10⁶–10⁹ Ω/sq. Run at controlled 23±2°C, 12±3% RH for the worst-case humidity test.
Equipment you actually need
(1) A surface-resistance meter with switchable 10/100 V output and a digital readout to 10¹² Ω (typical: Trek 152-1, ProStat PRS-801, Desco 19780).
(2) Two 5-lb cylindrical electrodes per the spec.
(3) A grounded conductive mat.
(4) An environment chamber if you need to qualify at low-humidity worst case.
Total equipment cost: $2,000-4,500 for a basic kit; rent for $300/month if you only run incoming QA monthly.
Acceptance limits and sampling
For a typical incoming QA on dissipative containers: 10 samples per lot, all measured, all must read 10⁶ to 10⁹ Ω.
For conductive items, 10⁴ to 10⁶ Ω.
One reading out of range = reject the lot and request a CofA from the supplier. Most supplier disputes here are about humidity — both sides should test at the same RH and document it on the report.
Common failure modes
(1) Topical anti-static washing off — repeated handling on incoming bins makes the surface resistance drift upward over months. Spec permanent / non-migratory grades to avoid.
(2) Humidity drift — same part will read 10¹⁰ Ω at 12% RH and 10⁷ Ω at 50% RH. Always log both.
(3) Edge effects — readings within 4 inches of the part edge are unreliable; the standard mandates the 4-inch buffer.