How digital thermometers are made
Inside a digital thermometer is a bead of sintered metal oxide whose electrical resistance changes with heat.
- stations
- 7
- things upstream
- 79
- raw sources
- 26
- steps from the ground
- 9
The short version
A digital thermometer measures temperature with a thermistor, a small bead of pressed and fired metal oxide whose electrical resistance changes with heat. The bead is coated in epoxy or glass, wired to a small chip and a battery, and sealed in a plastic body with a stainless tip. Each unit is calibrated against a reference before sale.
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Press the oxide powder
Powders of metal oxides are mixed and pressed into a bead, disk or cylinder. The blend decides how strongly resistance shifts as temperature climbs.
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Fire the bead
A kiln sinters the pressed shapes so the grains fuse into a hard ceramic. Fine adjustments in the firing control the resistance.
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Attach the leads
Metal contacts are added and thin wires are attached to the bead. These carry the signal out of the probe.
Goes in -
Encapsulate it
The bead is sealed in epoxy or glass so moisture can't change its behavior. A metal tip or plastic cap then covers the sensor.
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Wire up the electronics
The sensor connects to a small board with a chip that turns resistance into a temperature, then to a display and a small button cell.
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Mold the housing
Plastic halves are injection molded, then snapped and sealed around the board, with a window for the display.
Goes in -
Calibrate each unit
Thermometers are dipped in a bath held at known temperatures. Software stores the correction so every reading matches the reference.
Worth repeating
- The first thermistor effect was reported by Michael Faraday in 1833, when he saw that the resistance of silver sulfide fell as it warmed.
- Modern thermistors are typically pressed into a bead, disk or cylinder and then sealed in epoxy or glass.
Back to the ground
Follow every input upstream and digital thermometer starts as these 26 raw sources.
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Sources
Cite this page: "How digital thermometers are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/thermometer