{
  "slug": "touchdown-sensor",
  "term": "Touchdown sensor (TDS)",
  "aliases": [
    "TDS",
    "embedded contact sensor"
  ],
  "definition": "An HDD touchdown sensor is a temperature-sensitive element used to observe thermal changes near the head-disk interface during clearance and contact studies.",
  "note": "Ma et al. describe a thin-film resistance sensor whose response includes both pre-contact cooling changes and contact-related heating [touchdown]. Their experiment recorded its AC component; the spacing signal and sensor signal were not acquired simultaneously in the stage comparison. A sensor variation alone is not proof of contact, a calibrated absolute gap or a catastrophic head crash.",
  "status": "shipping",
  "related": [
    "head-disk-interface",
    "thermal-flying-height-control"
  ],
  "citations": [
    {
      "id": "touchdown",
      "title": "Ma, Xue, Peng and Bogy: Study of Head Disk Interface Characterization using Touchdown Sensor and Electro-Magnetic Signal in Hard Disk Drives, CML report 15013, sections I-III",
      "url": "https://cml.berkeley.edu/wp-content/uploads/blue-reports/15013.pdf",
      "accessed": "2026-10-15"
    },
    {
      "id": "analysis",
      "title": "Hesela: HDD mechanical faults, evidence and diagnostic limits",
      "url": "https://hesela.com/analyses/hdd-mechanical-failure-points/",
      "accessed": "2026-10-15"
    }
  ],
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-15"
}