KTY81-110 | GUILCOR SENSORS

KTY81-110
Temperature sensors

Reliable PTC sensor for temperature monitoring in electronic circuits and industrial control, covering −55 °C to +150 °C.

Maximum precision
+/- 2,0°K

Minimum temperature
-55°C

Maximum temperature
+150°C

Minimum dimensions
1,8 x 2 x 4

Response time
Fast

Self-heating
Low

Price
Low

Drift
Low

What is a KTY81-110 sensor ?

The KTY81-110 is a PTC (Positive Temperature Coefficient) silicon-doped sensor, whose resistance increases almost linearly with temperature.

Its nominal resistance is 1000 Ω at 25 °C, and its response is stable across the range of −55 °C to +150 °C.

Compact, robust, and low-cost, it is widely used for thermal monitoring of electric motors, power transistors, and lithium-ion batteries.

Operating principle

The KTY81-110 exploits the electrical properties of doped silicon, where conductivity decreases as temperature increases.

Unlike platinum or nickel RTDs, the change in resistance is more significant (≈ 8 Ω/°C around 25 °C), allowing for accurate measurement without complex amplification.

The empirical equation used to model its curve is:

R(T) = R25 x [1 + A(T - 25) + B(T - 25)²]

with :

R25 = 1000 Ω
A = 7,874 × 10⁻³
B = 1,874 × 10⁻⁵

(Valid from -55°C to +150°C)

Technical specifications

Parameter	Typical Value
Nominal resistance at 25 °C	1000 Ω
Temperature coefficient (at 25 °C)	≈ 8 Ω/°C
Recommended maximum tension	5 V
Typical measurement current	1 mA
Operating temperature	−55 °C → +150 °C
Typical measuring current	−65 °C → +170 °C
Case material	Hermetic axial glass
Typical response time	1 to 2 s in the air

Wiring configuration

Type	Description	Precision
2-wire	Simple assembly, sufficient for short measurements.	✅ Standard
3-wire	Reduces the influence of cables.	🏆 Industrial
Integrated (stuck)	Often soldered on transistor, module, or heatsink.	💡 Thermoprotection

Self-heating

The KTY81-110 generates very little heat (≈ 0.5 °C/mW in air and 0.1 °C/mW in oil).

Its low power dissipation ensures accurate measurement, even in confined environments.

Application areas

⚙️ Thermal surveillance of electric motors and windings

🔋 Battery and charger protection

💻 Sensors integrated into power modules (MOSFET, IGBT)

🚗 Temperature measurement in automotive embedded systems

🧠 Thermal regulation for precision electronics

Should I choose a KTY81-110 sensor ?

Strengths points

⚡ Very high thermal sensitivity
→ With a coefficient of approximately 8 Ω/°C, the KTY81-110 provides a high output signal that can be easily utilized without amplification.
🧱 Rugged and airtight enclosure
→ Its sealed glass design makes it resistant to moisture, thermal shocks, and vibrations, making it ideal for industrial and automotive environments.
💡 Nearly linear curve
→ Its linearity simplifies temperature calculations: it can be used directly in a voltage divider with very little error (< ±1% across the entire range).

Weaknesses points

🌡️ Limited measurement range
→ The sensor is only usable up to +150 °C, which is insufficient for high-temperature systems (> 200 °C).
🔋 Sensitive to excessive polarization
→ A voltage that is too high (> 5 V) or a current that is too strong (> 2 mA) can impair its accuracy or cause permanent drift.
🔧 Less standardized than the RTDs
→ The response curves differ slightly between manufacturers (NXP, Infineon, etc.), making brand substitution delicate.

Useful information

Here is some useful information regarding the KTY81-110 sensors.

Tolerances and precision classes

The KTY81 sensors are available in several classes according to the tolerance at 25 °C and the maximum deviation over the temperature range:

Class	Tolerance at 25 °C	Max. gap on the range	Typical beach	Remarks
A (enhanced precision)	±0,5 % (±5 Ω)	±1 °C	−40 °C → +125 °C	Individually sorted, calibrated version
B (standard)	±1 % (±10 Ω)	±2 °C	−55 °C → +150 °C	Typical curve KTY81-110
C (extent)	±2 % (±20 Ω)	±4 °C	−55 °C → +150 °C	Wide tolerance for economic applications

🔹 Note: The majority of industrial versions (KTY81-110, 120, 150, etc.) are delivered in class B, which is sufficient for most thermal regulations and protections.

Application example – Simplified equation

The simplified quadratic equation allows for calculating resistance as a function of temperature:

R(T) = R25 x [1 + A(T - 25) + B(T - 25)²]

with :

R25 = 1000 Ω
A = 7,874 × 10⁻³
B = 1,874 × 10⁻⁵

🔹 Example 1: calculation of resistance at 100 °C

R(100) = 1000 × [1 + 7,874×10⁻³(100-25) + 1,874×10⁻⁵(100-25)²]

R(100) = 1000 × [1 + 1,874590 × 75 + 1,874×10⁻⁵ × 5625]

R(100) = 1000 × [1 + 0,59055 + 0,105] = 1000 × 1,69555 = 1695,6 Ω

✅ Result: at 100 °C, the resistance of the KTY81-110 is approximately 1696 Ω.

🔹 Example 2: calculating the temperature from a measured resistance

We measure R=1350ΩR = 1350 ΩR=1350Ω.

What is the temperature?

We rearrange the formula:

T = 25 + [-A + √(A² - 4B(1 - R/R₂₅))] / (2B)

T = 25 + -7,874×10⁻³ + √((7,874×10⁻³)² - 4×1,874×10⁻⁵×(1-1,35)) / (2×1,874×10⁻⁵)

T ≈ 55°C

✅ Result: the corresponding temperature is approximately 55 °C.

🔹 Practical notes

The KTY81-110 curve is nearly linear between −40 °C and +125 °C.
Below −55 °C or above +150 °C, the drift becomes significant.
The equation is sufficient for an 8-bit microcontroller without complex floating-point calculations.

Integration diagram in an electronic system

The KTY81-110 is generally connected as a voltage divider: its variable resistance forms, with a fixed resistance, a divider powered by direct current.

🔹 Typical components

Component	Function
KTY81-110 (PTC silicon)	Sensitive element
Reference resistance (Rref)	Determine the output range
Power Supply: 5 V DC	Source stable
Integrated ADC (10–12 bits)	Convert the voltage to digital
Microcontroller (Arduino, STM32, ESP32)	Calculate T from Vout
RC Filtering (1 kΩ / 100 nF)	Reduces noise and transient spikes