Essentia / Devices / Thermometer

Device Lab 64

Thermometer

A stainless-sheathed negative-temperature-coefficient bead on a lead, placed in a closed axillary pocket, reporting the temperature the bead has reached.

Also called: Clinical Thermometer. Arabic: مقياس الحرارة. Device Lab 64 of 69 in BMEssentia Medical City, 2 configurations.

Overview: the configurations

How it works: the main parts

What each part does, from the Thermometer lessons in the 3D Device Lab.

Instrument stand, articulated arm and cradle

A weighted disc 520 millimetres across on five rubber pads, an aluminium column just over a metre tall, and a two-segment arm on ball joints with a fitting at the far end. On one configuration that fitting is an open tray the instrument lies in.

Single-use barrier over the sensing face

A thin polyethylene sleeve about 62 millimetres long with a moulded collar at the open end, pulled on over the sensing face before every use and taken off after it. The same consumable serves both configurations, and on both it is the only thing between the instrument and a succession of different people.

Stainless sensing tip and the mass it has to warm

5 millimetres across and 8 millimetres long with a hemispherical end, at the patient end of a flexible lead. It looks like nothing at all and it is the numerator of everything difficult about this configuration.

Negative-temperature-coefficient bead and its resistance law

A sintered metal-oxide bead a little over a millimetre across with two fine leads out of it, potted into the closed end of the tip. Its resistance falls steeply as it warms, and that steepness is the only reason a cheap converter can resolve a hundredth of a kelvin.

Sheath between the tip and the housing, which is the drain

The continuation of the same stainless tube, 30 millimetres of it inside the closed pocket and 60 millimetres standing out in room air, with a witness band where one becomes the other. It is the reason this configuration reads low even after it has finished settling.

Strain relief boot where the lead leaves the housing

A tapered rubber boot about 22 millimetres long with four moulded ribs, where the lead comes out of the nose of the case. It is the most boring component on the instrument and it is where these probes die.

Flexible lead and its conductors

2 millimetre jacketed cable from the sheath to the boot, with two clips holding it where it would otherwise catch. It routes up and clear of the body rather than straight across it, which is a choice with a reason.

Bench board: the approach, and the error at the moment of reading

A 440 by 330 millimetre board on its own post beside the couch, drawing the exponential approach against time with a mark where somebody actually reads and another where the instrument decides it has finished. Across the top it says that no instrument shows you this, and it means it.

Explore it in the Device Lab

• The instrument that has to become the thing it measures: Set the contact configuration on the bench and read the number at five seconds, at ten, at fifteen, at thirty and at sixty. Then read the time constant off the board and check that the sequence is the exponential it claims to be.
• The probe as a thermal path to somewhere colder: Leave the contact configuration to settle completely, so nothing anywhere is still changing, and then look at what it reports. 767 kelvin below the site. There is no transient left to blame and no fault anywhere.
• A radiance divided by an assumption: Set the non-contact configuration at its standoff, so the geometry is exactly right, and then move only the true emissivity of the surface. 98 because there is no control for it.
• A field of view that grows until it is averaging the room: Take the non-contact configuration off its standoff and move it away from the site while watching the reported value and the spot diameter together. Nothing about the instrument changes.
• The term that is in neither instrument: Leave both instruments alone and move only the room. Then move only the tissue layer. Neither of those is a control on anything and both of them move the answer more than anything you can adjust.

Common faults and what to check

Most reported device problems (FDA MAUDE)

Raw counts of adverse event reports for this device type (FDA product code FLL), all years. Not adjusted for the number of units in use, so they show what gets reported, not failure rates. Report text is never copied.

Planned maintenance checks

From the BMEssentia procedure library: every 12 months, about 10 minutes, electrical class II, applied part type BF.

Test instruments: Calibrator or blackbody reference supplied by the manufacturer; Reference thermometer.

Standards engineers test against

Recent FDA recalls

From the FDA recall database (openFDA), newest first, imported 2026-10-22. 19 recalls on record for this device type. Recall text is the FDA's public text; each recall links to the official record.

Learn it, see it in 3D, ask about it

• Ask Essentia about the Thermometer: answers from named sources, with the device open in its 3D Device Lab beside the answer.
• The Thermometer on the BMEssentia Platform: the Device Library course, 13 sections from physics to maintenance.
• BMEssentia Medical City: Device Lab 64, the Thermometer fully assembled in 3D, with lab tasks and the simulations.

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