IoTClass Inside the measurement
A closer look · 01

Temperature sensing

Look inside
a sensor.

NTC thermistor

A thermistor is a temperature-sensitive resistive body on two leads. In an NTC (negative temperature coefficient) thermistor, resistance falls as it warms. The response is curved: equal resistance changes do not mean equal temperature changes. For an IoT temperature reading, the thermistor and a fixed resistor form a voltage divider. The ADC measures its middle-node voltage; firmware infers resistance, then uses a nonlinear conversion such as the Beta equation to obtain temperature. A simple slope and offset cannot model that curve.

01

Recognize the element

Two leads. One resistive body.

An NTC thermistor: two leads, a changing resistanceA conceptual bead thermistor has a resistive body on two leads. Warming lowers its resistance. A divider supplies a measurable voltage and a conversion equation turns resistance into temperature. Not to scale.ConceptualResistive bodyTwo leadsWarming ↑Resistance ↓Divider + conversionTemperature readingNTC thermistor
The bead changes resistance; the circuit makes it readable. Follow the two leads into a divider, then convert the curved response into temperature.

Course-based conceptual drawing. The supplied comparison illustration contains no thermistor, so this drawing is a replacement rather than an extract.

02

Peel the teaching model

From case to sensing element

Choose a layer to see the measurement path. The enclosure and board layout are invented teaching choices, not a particular product.

The full text version below describes every layer. All measurement explanations are available without 3D.
Conceptual, not to scale
Case: outer coatingThe outer coating covers the thermistor body, with two leads extending below it.

Drag to rotate; pinch to zoom. With the view focused: arrow keys rotate, + / − zoom, 1–3 choose a layer, Home resets rotation and zoom. Step advances to the next layer; Reset returns to the case and default view. Layer buttons select a view directly. The page does not move on its own.

Layer 1 of 3 / Outside

Case: outer coating

The outer coating covers the thermistor body, with two leads extending below it.

Teaching view: The grey coating and blue dot mark the outside of the thermistor. Peel away the coating to see the body whose resistance falls as it warms.

The measurement to rememberAs a negative temperature coefficient (NTC) thermistor warms, its resistance falls along a curve rather than a straight line. [Cheap Nonlinear Thermistors]

Full text version · every layer

1 · Case: outer coating

The outer coating covers the thermistor body, with two leads extending below it.

Teaching view: The grey coating and blue dot mark the outside of the thermistor. Peel away the coating to see the body whose resistance falls as it warms.

2 · Readout: voltage divider

A fixed resistor and the thermistor form a voltage divider. [Practitioner: The Beta Equation, Worked]

The divider voltage is used to infer thermistor resistance. [Practitioner: The Beta Equation, Worked]

Teaching view: The two leads connect the thermistor to an external voltage divider. A fixed resistor completes the divider, turning the changing thermistor resistance into a voltage to measure.

3 · Element: temperature-sensitive resistor

A bead-style NTC thermistor is a resistive body on two leads. [Cheap Nonlinear Thermistors]

As an NTC thermistor warms, its resistance falls along a curve rather than a straight line. [Cheap Nonlinear Thermistors]

Teaching view: The tan body represents a temperature-sensitive semiconductor connected to two silver leads. As it warms, its resistance falls. The voltage divider turns this change into a voltage, which the readout uses to calculate temperature.

Explore the layers in order to follow the teaching model.

03

Listen

Package narration

Read transcript
Imagine Leo building a connected battery pack temperature monitor. He chooses a negative temperature coefficient thermistor, or N T C thermistor. As the pack warms, he expects its resistance to fall. The sensing body is a temperature sensitive resistor on two leads. It does not supply a digital temperature by itself. Leo connects it with a fixed resistor to form a voltage divider. An analog to digital converter measures the voltage at their meeting point. His firmware infers the thermistor's resistance, then uses the Beta equation to convert that curved response into temperature. Use the chapter's worked example. The reference is ten kilo ohms at twenty five degrees Celsius, with a Beta constant of three thousand nine hundred fifty kelvin. A measured resistance of four kilo ohms goes into that model and gives approximately forty seven point two degrees Celsius. The resistance has fallen while the calculated temperature has risen. Leo's misconception was that a simple slope and offset could convert the whole range. The response is curved, so that straight line shortcut does not model it. The takeaway is to follow the complete path from changing resistance, through divider voltage, to a temperature equation that fits the curve.

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