STH-3 vs STH-3A vs STH-5: Complete KHT Heat Seal Tester Model Comparison

STH-3 (Manual): Single-point, manual control, no printed records — the ASTM F88 workhorse at the lowest price. STH-5 (Digital Gradient): 5-point gradient, digital display, manual records — the R&D and film qualification tool most labs should start with. STH-3A (Touchscreen): automatic sealing pressure, built-in printer, ±0.5°C accuracy — the production and pharma/battery standard.

The STH-3 is the right choice when: (1) your testing involves verifying a single, known production parameter — not discovering what that parameter should be; (2) your test volume is low (fewer than 20 cycles/day); (3) manually written records are acceptable; (4) budget is the primary constraint. For pharmaceutical QA labs running ISO 11607 incoming material inspection at a fixed validated temperature, the STH-3 is often perfectly adequate.

The STH-5 is recommended for: (1) any lab performing film qualification, SIT determination, or seal window mapping; (2) labs qualifying incoming material batches where lot-to-lot variation is expected; (3) R&D teams developing new packaging formats; (4) packaging labs that need to generate seal curve data for regulatory submissions or customer qualifications. The 5-point gradient capability typically represents 70–80% time savings per seal curve compared to sequential single-point testing.

The STH-3A is designed for: (1) pharmaceutical production labs that need a printed record of every test; (2) battery cell lines requiring consistent, automatically applied sealing pressure; (3) facilities with multiple operators where manual pressure adjustment causes variation; (4) labs that need the tightest temperature accuracy in the STH line (±0.5°C). The touchscreen interface reduces operator-induced variation by eliminating manual dial settings.

R&D / Film qualification lab → STH-5. Small QC lab, known parameters → STH-3. Pharmaceutical production, FDA-regulated → STH-3A. Battery manufacturer, production line → STH-5 or STH-3A. Food factory, SIT mapping → STH-5. Contract lab, multiple clients → STH-5 or STH-3A (depends on gradient vs. printed-record needs).