Sillistor | GUILCOR SENSORS

Sillistor
Temperature sensors

Precision PTC sensor for industrial and laboratory use, providing stable resistance over a wide temperature range.

Maximum precision
+/- 2,0°K

Minimum temperature
-55°C

Maximum temperature
+200°C

Minimum dimensions
1,6 x 2 x 4

Response time
Fast

Self-heating
Low

Price
Medium

Drift
Low

What is a Sillistor sensor ?

The Silistor is a high-linearity silicon-doped PTC sensor designed for continuous temperature measurement, unlike "threshold" type PTCs (such as PTC130).

Its resistance increases gradually and proportionally with temperature, making it ideal for measurement and regulation applications rather than simple thermal cutoff.

This is a historical technology developed by Siemens, now taken over by Vishay, EPCOS, and NXP.

Operating principle

The Silistor relies on the electrical properties of doped silicon: as the temperature increases, the mobility of charge carriers decreases, resulting in a nearly linear increase in resistance.

The typical relationship is given by:

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

with :

R25 = 2000 Ω
A = 7,9 × 10⁻³
B = 1,9 × 10⁻⁵

This equation remains valid from −55 °C to +200 °C with a precision < ±2 K.

Technical specifications

Parameter	Typical Value
Nominal resistance at 25 °C	2000 Ω
Temperature coefficient (at 25 °C)	≈ 15 Ω/°C
Typical measurement current	1 mA
Maximum tension	5 V
Response time	1 s
Material	Doped silicon (linear PTC)
Linearity	Excellent (−40 → +150 °F)

Wiring configuration

Type	Description	Precision
2-wire	Simple setup for direct measurement.	✅ Standard
3-wire	Resistance compensation of cables.	🏆 Industrial
Integrated SMD	Directly soldered on PCB.	💡 Embedded electronics

Self-heating

With a measurement current ≤ 1 mA, the power dissipated remains < 2 mW → self-heating less than 0.1 °C, ensuring high measurement stability.

Application areas

⚙️ Industrial instrumentation and embedded sensors

💻 Thermal monitoring of electronic circuits

🔋 Thermal regulation of batteries and power modules

🚗 Automotive applications (air conditioning, injection, ECU)

🧠 Precision measurement and control systems

Should I choose a Sillistor sensor ?

Strengths points

🔥 Exceptional linearity
→ The R/T curve of the Silistor is almost perfectly linear between -40 °C and +150 °C, ideal for continuous measurements without complex conversion.
🧠 Low long-term drift
→ Thanks to doped silicon, the annual drift is less than 0.1%, ensuring remarkable stability over several years of use.
⚙️ Easy integration into electronic systems
→ Its nominal resistance (2 kΩ) and low consumption allow for a direct connection to a microcontroller or an ADC, without amplification.

Weaknesses points

🌡️ Temperature range limited to +200 °C
→ Beyond that, the R/T curve loses its linearity, making it unsuitable for extreme environments.
💰 Cost higher than a standard PTC
→ The silicon doping process and sorting in production make the Silistor slightly more expensive than conventional thermistors.
🔋 Sensitive to excessive polarization
→ A voltage higher than 5 V or too much current can cause self-heating and distort the measurement.

Useful information

Here is some useful information regarding Sillistor sensors.

Tolerances and precision classes

The Silistors are classified according to their resistance tolerance at 25 °C and their maximum deviation over the temperature range. Their exceptional stability allows for a precision superior to that of most classic ceramic PTCs.

Class	Tolerance at 25 °C	Max. gap on the range	Operating range	Remarks
A (high precision)	±0,5 % (±10 Ω)	±1 K	−40 °C → +150 °C	Unit selection and calibration
B (standard)	±1 % (±20 Ω)	±2 K	−55 °C → +200 °C	Most common version
C (extent)	±2 % (±40 Ω)	±4 K	−55 °C → +200 °C	Economic Applications

🔹 Remarks:

Class A Silistors are used in critical measurement and regulation instruments.
Class B versions are sufficient for the majority of industrial applications.
Long-term stability is better than ±0.1%/year over the range of −40 to +150 °C.

Application example – Simplified equation

The Silistor is a linear PTC whose resistance varies almost proportionally to temperature.

The following quadratic relationship provides good accuracy over the entire useful range:

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

with :

R25 = 2000 Ω
A = 7,9 × 10⁻³
B = 1,9 × 10⁻⁵

🔹 Example 1: calculation of resistance at 100 °C

R(100) = 2000 × [1 + 7,9×10⁻³ × (100-25) + 1,9×10⁻⁵ × (100-25)²]

R(100) = 2000 × [1 + 0,5925 + 0,107] = 2000 × 1,6995 = 3399 Ω

✅ Result: at 100 °C, the resistance of the Silistor is approximately 3.4 kΩ.

🔹 Example 2: calculating the temperature from a measured resistance

We measure R=2800Ω.

What is the corresponding temperature?

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

T = 25 + -7,9×10⁻³ + √((7,9×10⁻³)² - 4×1,9×10⁻⁵×(1-1,4)) / (2×1,9×10⁻⁵)

T ≈ 65°C

✅ Result: the corresponding temperature is approximately 65 K above zero Celsius (≈ 65 °C).

🔹 Practical Remarks

Linearity simplifies calculations with a simple linear approximation between −40 °C and +125 °C.
The high signal-to-noise ratio of the Silistor allows for direct wiring to the microcontroller's ADC input.
The equations can be integrated into a lookup table (R/T table) for low-power embedded applications.

Integration diagram in an electronic system

The Silistor is a linear sensor designed to be read directly by a voltage divider or an ADC input without amplification.

It can also be integrated onto a PCB in SMD format, making it a preferred component in compact applications.

🔹 Typical components

Component	Function
Silistor (PTC linear silicon)	Sensitive element
Rref ≈ 2 kΩ	Reference resistance for the bridge
Power Supply (3.3 or 5 V)	Source stable
ADC (10–16 bits)	Analog-to-digital converter
Microcontroller (ESP32, STM32, Arduino)	Calculation or correspondence table T = f(R)
RC Filtering (1 kΩ / 100 nF)	Measurement noise reduction