TFPT | GUILCOR SENSORS

TFPT
Temperature sensors

High-performance PTC sensor tailored for electronics, HVAC, and automation systems with dependable temperature detection.

Maximum precision
+/- 2,0°K

Minimum temperature
-55°C

Maximum temperature
+250°C

Minimum dimensions
1,8 x 2 x 4

Response time
Fast

Self-heating
Low

Price
Medium

Drift
Low

What is a TFPT sensor ?

The TFDT is a linear silicon PTC sensor (Temperature Fast Detect Thermistor), specifically designed to provide fast, stable, and linear temperature measurement in industrial and embedded environments.

It is a direct evolution of the Silistor, optimized for better linearity, low hysteresis, and rapid dynamic response.

This sensor is particularly used in motor control systems, battery thermal management, power electronics, and automation.

Operating principle

The TFDT uses a thin layer of doped silicon deposited on an insulating substrate.

Its resistance increases almost linearly with temperature according to the law:

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

with :

R25 = 1000 Ω
A = 8,1 × 10⁻³
B = 1,6 × 10⁻⁵

This equation remains valid over the range of -55 °C to +250 °C with an error of less than ±2 K.

Technical specifications

Parameter	Typical Value
Nominal resistance at 25 °C	1000 Ω
Temperature coefficient (at 25 °C)	≈ 8 Ω/°C
Typical measurement current	1 mA
Recommended maximum tension	5 V
Response time	1 to 2 s
Linearity	Excellent
Typical drift	< 0,1 %/year
Case	High-temperature glass or ceramic

Wiring configuration

Type	Description	Precision
2-wire	Standard assembly, low cost.	✅ Classic
3-wire	Compensate for the line resistance.	🏆 Industrial
Integrated SMD	Directly soldered onto the circuit board.	💡 Embedded applications

Self-heating

With a measurement current ≤ 1 mA, the power dissipated is approximately 1 mW, resulting in a temperature rise of less than 0.1 °C, which ensures excellent reproducibility.

Application areas

⚙️ Thermal surveillance of electric motors and IGBTs

🔋 Temperature management in batteries and BMS

💻 Thermal regulation in power modules and converters

🧠 Precision sensors for embedded systems

🚗 Thermal control of automotive electronic systems

Should I choose a TFPT sensor ?

Strengths points

⚡ Ultra-fast response
→ The TFDT offers a response time on the order of one second, ideal for systems requiring instantaneous thermal reaction (IGBT protection, fast charging circuits, etc.).
📈 Improved linearity and precision
→ Its R/T curve is more regular than that of the Silistors, with an error of less than ±2 K over the range of −40 °C to +200 °C.
🧠 Perfect for embedded environments
→Its low power consumption and direct compatibility with the analog inputs of microcontrollers allow for simple integration without additional electronics.

Weaknesses points

🌡️ Limited to +250 °C
→ Although efficient, it remains unsuitable for extreme applications (> +250 °C) where the KTY84-130 or a platinum RTD would be safer.
💰 Price slightly higher than classic PTCs
→ Its fabrication on doped substrate and its precise factory calibration make it more expensive than standard ceramic thermistors or Silistors.
🔋 Sensitive to surges
→ A current greater than 1 mA can generate measurable self-heating, especially in a closed environment.

Useful information

Here is some useful information regarding TFDT sensors.

Tolerances and precision classes

The TFDT (Temperature Fast Detect Thermistors) sensors are classified according to their resistance tolerance at 25 °C and their maximum deviation over the range of −55 °C to +250 °C.

Their stability is comparable to the best silicon sensors (KTY and Silistor), but with a faster response.

Class	Tolerance at 25 °C	Max. gap on the range	Operating range	Remarks
A (high precision)	±0,5 % (±5 Ω)	±1 K	−40 °C → +200 °C	Individual tri and factory calibration
B (standard)	±1 % (±10 Ω)	±2 K	−55 °C → +250 °C	Most common version
C (extent)	±2 % (±20 Ω)	±4 K	−55 °C → +250 °C	Economic variant, non-critical use

🔹 Remarks:

Class B is the most common for TFDT sensors used in thermal management systems.
Even the economical versions maintain long-term stability of less than 0.1%/year.
No recalibration is necessary after installation if the measurement current remains ≤ 1 mA.

Application example – Simplified equation

The TFDT follows a linearized quadratic law, stable across its entire useful range

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

with :

R25 = 1000 Ω
A = 8,1 × 10⁻³
B = 1,6 × 10⁻⁵

🔹 Example 1: calculation of resistance at 150 °C

R(150) = 1000 × [1 + 8,1×10⁻³ × (150-25) + 1,6×10⁻⁵ × (150-25)²]

R(150) = 1000 × [1 + 1,0125 + 0,26] = 1000 × 2,2725 = 2272,5 Ω

✅ Result: at 150 °C, the resistance of the TFDT is approximately 2273 Ω.

🔹 Example 2: calculating the temperature from a measured resistance

We measure R=1350ΩR = 1350 ΩR=1350Ω.

What is the corresponding temperature?

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

T = 25 + -8,1×10⁻³ + √((8,1×10⁻³)² - 4×1,6×10⁻⁵×(1-1,35)) / (2×1,6×10⁻⁵)

T ≈ 63°C

✅ Result: the corresponding temperature is approximately 63 °C.

🔹 Practical Remarks

The quadratic equation is sufficient for embedded calculations on 8 or 16-bit microcontrollers.
The TFDT is faster than KTY sensors, ideal for dynamic systems (liquid cooling, motors).
Linearity allows for the direct use of simple voltage dividers.

Integration diagram in an electronic system

The TFDT easily integrates into a divider bridge powered at 3.3 V or 5 V, with direct reading on an ADC input.

Its stable behavior and moderate nominal resistance allow for reliable measurement without amplification.

🔹 Typical components

Component	Function
TFDT (linear silicon PTC)	Sensitive element
Rref ≈ 1 kΩ	Reference resistance of the bridge
Power supply 3.3–5 V	Source stable
ADC (12–16 bits)	Analog-to-digital conversion
Microcontroller (ESP32, STM32, Arduino)	Calculation T = f(R)
RC Filtering (1 kΩ / 100 nF)	Playback noise reduction

🔹 Functional diagram (ASCII)

+5 V │ [Rref] │ ├───→ Vout → ADC / µC │ [TFDT] │ GND

🔹 Operating Principle

1️⃣ The TFDT forms a voltage divider with Rref, where the output voltage depends on the temperature.

2️⃣ When the temperature increases → the resistance of the TFDT increases → Vout increases.

3️⃣ The microcontroller calculates the temperature using the equation or an R/T table.

🔹 Best Practices

🧩 Choose Rref ≈ 1 kΩ for a balanced bridge around 25 °C.
⚡ Keep the current ≤ 1 mA to avoid self-heating.
💧 Protect the terminals from moisture (resin or sleeve).
🔄 Calibrate at 25 °C and 150 °C to ensure optimal accuracy.
🧲 Add an RC filter to stabilize the analog reading in an industrial environment.